national defense maritime engineering journal · lcdr doug o'reilly (naval architecture) lcdr paul...

National DefenseDefence nationals

MaritimeEngineeringJournal

June 1994

Afloat Logistic SupportThe future is now for multirole ships

Also:• Greenspace: A Better OWS Mousetrap• 10th Ship Control Symposium Report

Canada

A 97-year-old sailing yacht with a familiarname is making a comeback thanks to somededicated Canadians — see page 32

MaritimeEngineeringJournal Established 1982

Director GeneralMaritime Engineering andMaintenanceCommodore Robert L. Preston

EditorCaptain(N) Sherm Embree, DMEE

Production EditorLCdr(R) Brian McCulloughTel.(819) 997-9355/FAX (819) 994-9929

Technical EditorsLCdr Jacques Lavallee (Marine Systems)LCdr Keith Dewar (Marine Systems)LCdr Doug Brown (Combat Systems)Simon Igici (Combat Systems)LCdr Doug O'Reilly (Naval Architecture)LCdr Paul Brinkhurst (Naval Architecture)

Journal RepresentativesCdr Glenn Trueman (East Coast),(902) 427-3834CPO1 Jim Dean (NCMs),(819)997-9610

Graphic DesignIvor Pontiroli, DPGS 7-2

Translation Services bySecretary of State Translation BureauMme. Josette Pelletier, Director

JUNE 1994

DEPARTMENTS

Editor's Notes 2

Letters 2

Commodore's Cornerby Commodore David G. Faulkner 3

FEATURES

Afloat Logistic Support — The future is now for multirole support vesselsby C dr S.E.King and LCdr P. J. Brinkhurst 4

Towed Array Technology — The AN/SQR-19 "Wet End"by LCdr Stephen Monkhouse 10

An AC Electric Propulsion Concept for a DDH-280-class Replacementby LCdr M. Tinney, W.A. Reinhardt, P.Eng.,J. Hensler, P.Eng. and LCdr M.J. Adams, P.Eng 15

Conference Reports:65th Commonwealth EOs Conference 1910th Ship Control Symposium 2046th CMIA Technical Conference ,...22

GREENSPACE:The membrane oil/water separator — a better mousetrap

by LCdr Keith Dewar and Lt(N) Robert de Wit

LOOKING BACK:Ontario's "Beaver" takes 1st prize in 1950 regatta!

by LCdr(R) Brian McCullough

,23

.26

NEWS BRIEFS...., 27

OUR COVERCanadian naval planners agree that the multirole support vessel is just what Canadaneeds in the wake of the Cold War. These versatile vessels even carry their own float-ing jetty and barge units along with them. (Illustration by Edwin Chan)

The Maritime Engineering Journal (ISSN 0713-0058) is an unofficial publication of the Maritime Engineersof the Canadian Forces, published three times a year by the Director General Maritime Engineering andMaintenance with the authorization of the Vice-Chief of the Defence Staff. Views expressed are those of thewriters and do not necessarily reflect official opinion or policy. Correspondence can be addressed to: TheEditor, Maritime Engineering Journal, DMEE, National Defence Headquarters, MGen George R.Pearkes Building, Ottawa, Ontario Canada K1A OK2. The editor reserves the right to reject or edit anyeditorial material, and while every effort is made to return artwork and photos in good condition the Journalcan assume no responsibility for this. Unless otherwise stated, Journal articles may be reprinted with propercredit.

MARITIME ENGINEERING JOURNAL, JUNE 1994

Editor's NotesThe navy's "can do" attitudea blessing or a curse?

By Captain(N) Sherm Embree, CD, P.Eng., CIMarEDirector of Marine and Electrical Engineering

If the Periodic Engineering Letterscoming out of the fleet are any indica-tion, it is probably safe to say that thenavy's "can do" approach to things isintact. For that matter, take a spinthrough a few back issues of the Journalsometime. You might (or might not) besurprised at the number of articles thatallude in some way to the ages-old navytradition of never saying "can't bedone."

On the face of it a "can do" attitude isa laudable virtue, especially in our lineof work where taking risk to achieve amission is generally thought (by thepublic and military alike) to be a goodthing. Throughout our navy's 84-yearhistory there have been countless in-stances where our willingness to take on

seemingly impossible odds has helped usovercome the challenges of the sea, theenemy and our own bureaucracy. Saying"can do" agrees with our natural sense ofcheerful initiative, imagination andgung-ho spirit — the true hallmarks ofany sailor. And besides, there is nothingquite like achieving the impossible forbuilding esprit de corps.

Still, if we were to rely excessively onour initiative, we might unintentionallyignore the wisdom of experience gainedover many years in the form of policiesand procedures — possibly at the ex-pense of safety; likely at the expense ofthe interests of someone else. In the finalanalysis it might be that a "can do" ap-proach is beneficial only when it is tem-pered by equal measures of co-operation

and responsibility. "Ready, aye, ready"should not mean having to abandon ourvalues and strengths under the press ofexpediency.

Can it be that the same ultrapositiveoutlook that helps us get a Gulf taskforce ready in record time is also a badthing? Is the inherent industriousness ofa "can do" attitude ever a vice? What'syour feeling? Do we show too much"can do" in the navy? Too little? Is itever okay to say "Can't do!"? Blessingor a curse — you tell us and we willpublish a selection of your views in anupcoming issue. *

Letters to the EditorArticle doesn't fit in

I received my copy of the February1994 issue of the MARE journal thisweek and was surprised to see an articleon a sailing trip across the Atlantic.Thinking that perhaps there was somemarine engineering issue discussed in thearticle I set to reading the submission. Tomy surprise, although the article wasvery interesting, it did not contain anyinformation which would render it avalid article for a technical journal.

At first I thought my concern waspetty and perhaps the MARE journal

should include articles of general inter-est, until I found the six objectives of theMARE journal on page 2. Try as I mightI could not fit this article into any ofthese objectives.

I would suggest that either the objec-tives be expanded to include a categoryfor general interest, or that the Journalobjectives be followed more closely.—Lt(N) G.F. Hallam, Directorate ofMaritime Engineering Support,NDHQ, Ottawa.

(The fact you found the article "veryinteresting" means the Journal was achievingits second objective of "providing an openforum where topics of interest...can be pre-sented...." On the other hand, the fact thatyou view the Journal strictly as a technicalpublication means our editorial messagecould probably stand being a whole lotclearer. To this end we are already workingon a readership survey to be included withour October issue. Thanks for writing.— Ed.) &


Commodore's CornerManagement options deliver theirown strengths

By Commodore David G. FaulknerAssistant Chief of Staff Materiel

We have, over the past years, spokenoften of the need for change, of the needto become more effective and efficient inthe delivery of engineering support to thefleet. The recent budget not only drives usforcibly in that direction, but it providesus with the yardstick by which we areobliged to measure progress. Of course,the currency of measurement in the bud-get is dollars.

You should know that the future, atleast in its appearance, promises to bearlittle resemblance to the world we havedefined for ourselves over the course ofour careers. Indeed, as I write this com-mentary, our professional lives are beingredefined by three major studies. Each ofthese studies seeks, with the assistance ofprivate consultants, to improve our deliv-ery of naval engineering support to itsultimate customer, the Maritime Com-mander.

The Ship Repair Unit (SRU) Manage-ment Options Study has examined threealternative management frameworks: anextension of the existing structure (withan increased authority vested in the unitcommanding officers), a single operatingagency, and a government-owned/con-tractor-operated (GO/CO) option. Mostsignificantly, the study found all threeoptions to be feasible, with substantiveimprovements in management account-ability, cost control and efficiency achiev-able more through the introduction of abusiness planning ethic than a new man-agement framework.

Not surprisingly, each option deliversits own strengths. Enhancements to theexisting structure, for example, promisemore flexibility in meeting the MaritimeCommander's operational requirements,and may offer an optimum balance ofeffectiveness and efficiency. The GO/COoption, on the other hand, tends to a nar-rower optimization on resource effi-ciency. Finally, the study suggests thatthe benefits of a single operating agency

can be secured within the enhancementsto the existing structure.

The Management Options Study willform an input to two more wide-rangingstudies — ADM(Mat)'s evaluation of theNDHQ materiel group, and the MaritimeCommander's Naval Engineering &Maintenance Functional Review. Both ofthese studies seek to reengineer existingprocesses, and both promise reductionsin the cost of doing business of at least20 percent. Both studies completed their

"Business plans are beinggenerated at the unit,formation and commandlevels, and already wehave begun to see thebenefits of a renewed costconsciousness."

initial phases in March, and will now bewell into the detailed definition of thechange requirement. We must begin torecoup savings in the immediate future.

ADM(Mat)'s study targets the overlapin three specific areas: engineering andlogistic support in NDHQ, logistic sup-port in NDHQ and the Command, andengineering support in NDHQ and theCommand (that is, between DGMEMand the NEUs).

The MARCOM functional reviewexamines the application of naval engi-neering and maintenance across theCommand — specifically, in the NEUs,SRUs, fleet maintenance groups and thethree Maritime Command headquarters.The relationship with other functionalareas such as logistic support is alsobeing defined, and the requirement forchange in these related areas will bepursued through interface discussions.

It will be apparent to you that if we areto reach our savings target we must enter-tain the need for radical change. My aim isto replicate, to the extent practicable in apublic enterprise, a business-like environ-ment. In that vein, integrated businessplans are being generated at the unit, for-mation and command levels, and alreadywe have begun to see the benefits of arenewed cost consciousness.

Underpinning the MARCOM func-tional review is a philosophy which seeksto delegate decision-making authority tothe lowest level practicable, and whichseeks to hold decision-makers accountablewithin the framework provided by theirrespective business plans. The goal is toremove the vast majority of artificial con-straints previously imposed by "the sys-tem," and to let managers manage.

The Maritime Commander has made itclear that our overriding objective must bethe protection of the navy's core capabil-ity. While this core is most frequentlyexpressed in terms of ships, we must notlose sight of the fact that it necessarilyincludes a minimum essential materielsupport infrastructure. The navy's historicsuccess in operations is attributable in nosmall measure to the support provided bythat infrastructure. Accordingly, as wedefine that which constitutes the minimumessential infrastructure, it behooves eachof us to measure the extent to which theprescribed changes will impact opera-tional capability. The second currency bywhich we must measure the consequenceof change is military effectiveness.

There is no question but that the navalengineering community has the talent torespond professionally to the challenge.Let me assure you, however, that if we failto exercise the will to respond, it will be atour peril. We have met similarly demand-ing challenges in the past, and I am fullyconfident that we will succeed equallywell in this. «*


Afloat Logistic Support — The future isnow for multirole support vesselsTake a look at the ship that naval planners agree isthe one to support Canadian Forces operations athome and abroad.Article by Cdr S.E. King and LCdr P.J. BrinkhurstIllustrations by Edwin Chan

On the face of it, it was business asusual. Two of the navy's three AORunderway replenishment ships were onceagain being dispatched to foreign shores.The missions of the two 25,000-tonnetankers involved neither battle nor, sur-prisingly, NATO exercises. Far from it.It was late 1992 and HMCS Protecteurwas on her way south to provide disaster

relief in the wake of Hurricane Andrew,while her sister ship Preserver was beingsent halfway around the world to supportpeacekeeping operations in Somalia.

Upon closer inspection the two de-ployments illustrate the new reality fac-ing military policy makers and planners— the Cold War is over and Canada canno longer afford the luxury of grooming

her navy for a few, well-defined missions.Now more than ever, Canadian navalforces must be prepared to respond to theunpredictability of a world rife withregional conflict. At the same time theymust meet new challenges in our ownback yard regarding the national fishery,environmental protection and other areasof concern to the federal government.

MRSV


HMCS Preserver

That same year, in response to thesepressures, NDHQ naval staff reexaminedthe range of missions the navy could beexpected to undertake or support duringthe next several decades. What theyfound reflects a need for flexibility in ournaval forces, rather than such Cold Warspecializations as protecting sea lines ofcommunication and conducting antisub-marine warfare. Going a step farther,they identified the equipment the navywould need to meet the new challenges.Nowhere is the emphasis on flexibilitymore clearly evident than in the currentinitiative to acquire four new multirolesupport vessels (MRSVs) to add a much-needed sealift capability and replace theAORs.

Afloat Logistic SupportLong before Preserver dropped

anchor in the roadstead off Bosasso on

Somalia's north coast in the autumn of1992, the Director of Naval Require-ments (DNR) in National Defence Head-quarters in Ottawa/Hull was respondingto the changing strategic environment.DNR development staff was studying thesubject of military sealift (or moreprecisely, afloat logistic support)comprising:

• underway support to naval units;

• sealift transport of large volumesof equipment and supplies overlong distances in support of de-ployed forces; and

• in-theatre, sea-based support tojoint forces ashore (such as wasPreserver's mission in Somalia).

Underway support is a stock-in-tradewith the Canadian fleet. As well it shouldbe — our three AORs were designedspecifically for the task. HMC ships

Preserver, Protecteur and Provider havebeen supplying fuel, food, ammunition,spare parts, fresh water, stores, essentialmedical services and second-line aircraftmaintenance support to the ships ofCanadian and allied task groups foryears. For that matter, as far as refuel-ling goes, an AOR's 13,000-tonne cargofuel capacity far exceeds the 8,000tonnes naval planners estimate anMRSV would need to maintain a taskgroup at sea for 60 days (Fig. 1).

Replenishing ships at sea is no prob-lem for the AORs. It is with the othertwo aspects of afloat logistic supportthat they fare less well. No one knowsbetter than the navy that the tankercrews have done yeoman (and innova-tive) service over the years, but theAORs simply were not designed formilitary sealift operations and sea-basedsupport to joint forces ashore.


Sealift Transport

Consider the AOR's 500 lane metresof vehicle cargo space (i.e. 500 metres ofdeck space 2.5 metres wide). Handy in apinch, maybe, but it comes nowhere nearthe 2,500-lane-metres identified by ajoint services study team as the minimumessential for Canadian Forces sealiftoperations. And what about containers?Standard cargo containers are the mostefficient means of transporting non-vehicular equipment, yet the AORsaren't fitted to carry them. At the veryminimum, the study indicated, an MRSVshould carry enough containers to trans-port vehicles and equipment for two CF-18 squadrons or a rapid response groundforce.

Naturally, the ease with which ve-hicles and stores can be loaded oroffloaded is of great importance to anysealift mission. As Preserver discoveredin Somalia, inadequate harbour facilitiescan seriously hamper loading and un-loading operations. The most efficient

way of handling vehicles is to simplydrive them onto and off the ship — aprocedure known as roll-on/roll-off (ro/ro). It's no coincidence that 42 percent ofthe 127 USN vessels activated for DesertShield/Storm were ro/ro configured!

When it comes to handling stores, themodern sealift vessel must be capable ofoffloading its own containers. A self-unloading ship is a much more versatileasset to the maritime commander as it canbe deployed to just about anywhere in theworld. No jetty? No problem. A sealiftvessel carrying its own self-propelledpontoons, such as GEC EngineeringLimited's "Mexeflote" system (see box),can easily construct a temporary landingstage and motorized ferry for personnel,vehicles, equipment and stores.

Joint-force SupportSupporting an embarked joint-force

HQ staff means more than just providingliving quarters and ops room space. Forinstance the MRSV must be fitted for, or

REQUIREMENT

Ice Capable

Underway SupportFuelJP5Ammunition

SealiftDeck Space

(incl. upper deck)Container SystemJetty Independence

Joint Force SupportNaval CommunicationsShore Comm.Command/ControlHelo CapabilityHospital

Contingency OpsTemp. AccommodationsEnvironmental Ops

Ship ParticularsCrew SizeLengthBeamDraft (Deep)DepthDisplacement (Deep)SpeedPropulsionShaftRange

MRSV

Y

8,000 tonnes533 1300 1

3,305 lane m

YY

YYY3+Full

300+Y

111 (+30 spare)193m28m8.2m21 m21, 800t20ktsDieselSingle1 0,800 nm@ 15 kt

AOR

PARTIAL

1 3,200 1510tsoot

500 lane m

NN

YNN3Limited

NN

334 (Somalia deployment)172m23.2m10.6m12.4m26,389 121 ktsSteamSingle7,[email protected]

with, a broad range of communicationand command and control equipment toensure interoperability with other ships,shore-based forces and national facilities.Such a ship should also be capable ofmaintaining national rear-link communi-cations. The AORs can provide somemeasure of this. Apart from the absenceof VHP-AM equipment needed to com-municate with troops ashore, their nor-mal communication equipment fit meetsminimum requirements. Their commandand control and ops room configurations,on the other hand, while adequate for theships themselves, fall short of the require-ments for a joint-force headquarters.

By its very nature, joint-force supportcan be a strange brew of requirementsand taskings. For instance, which joint-service mission can do without helicop-ter support these days? The MRSV mustbe capable of carrying, operating andmaintaining large helicopters suitable fortactical surveillance, personnel transport,medevac and cargo airlift operations. Amultirole support vessel must also becapable of providing full military hospi-tal facilities, including comprehensivesurgical and dental services, and fullytooled technical facilities such as metaland woodworking shops for basic con-struction work and battle damage repair.Of course, extensive hospital and shopfacilities would not have to be built intothe ship as these could be carried incontainerized modules that could tap intoship's power, water, waste and ventila-tion systems.

On the Home Front

In addition to the three main ALScategories there are some aspects ofafloat logistic support that have a morenational context. Both the 1992 defencepolicy and the government's Green Plancall for DND to be ready to respond tonational emergencies. This could wellmean having to provide:

• command and control support

• temporary communicationfacilities

• security and rescue services

• transportation and convoyassistance

• temporary accommodations

• logistic support, equipment andpersonnel

Fig. 1. MRSV/AOR Comparison Table (Courtesy of Edwin Chan)


A dedicated naval MRSV designed tomeet the stringent requirements of tacti-cal military sealift support is perfectlysuited to any and all such operations. Forexample, if Canada were to suffer anenvironmental disaster similar to thatcaused by the Exxon Valdez spill offAlaska, DND would likely be taskedwith transporting equipment and person-nel to the spill site, and possibly with co-ordinating the clean-up operation aswell. An MRSV could handle the job justas effectively as it could handle a disas-ter relief mission or a full-blown militarysealift operation anywhere in the world.

A Multirole Support Vessel

As early as mid-1992 the Director ofNaval Requirements was anticipating thegrowing importance of having a propersealift capability. Everything seemed tobe pointing to a new type of vessel, onewhich could meet the three elements ofafloat logistic support cost-efficiently. Aseries of concept studies was duly initi-ated with the Directorate of MaritimeEngineering Support (DMES) to develop

potential designs for vessels that couldfulfil the entire ALS role.

Designing a ship to cover off all threelegs of afloat logistic support is a tallorder. What the designers came up with(Fig. 2) looks rather like an ordinaryreplenishment ship, except for the largeramp openings fore and aft which hint ata roll-on/roll-off capability. At 193metres, the MRSV is 21 metres longerthan HMCS Preserver, but has a deepdisplacement of 21,800 tonnes, as op-posed to the AOR's 26,389 tonnes. Theship has a mean deep draft of 8.2 metres,and a beam of 28 metres. Ice strengthen-ing will permit the MRSV to patrol neararctic waters and transit first-year ice upto one metre thick.

Twin diesels provide 15,400 kilowattsof power to a single controllable-pitch-propeller, driving the ship at a top speedof 20 knots in sea state two. A bowthruster is provided for low-speedmanoeuvring. The MRSV carries enoughfuel and stores to give it a range of10,800 nautical miles at 15 knots, and an

endurance of 90 days. Electrical power issupplied by three 1,000-kW, and two500-kW diesel generators. The ship iscapable of providing fuel and equipmentfor portable water and power generationequipment if necessary.

A fixed ramp at the forward end ofthe upper deck leads down to theMRSV's dual vehicle decks which pro-vide nearly 2,400 lane metres of vehiclespace. Stern and bow access ramps fromthe main (lower) vehicle deck allow afull ro/ro capability, while a 20-tonnecrane gives the MRSV a considerablelift-on/lift-off capacity. The combinationof ramps, crane and a large vehicle el-evator means the vessel can land a fullload of nearly 200 vehicles — jeeps,tanks, tractor-trailers, you name it — inshort order. Attached to the ship's sidesare enough portable pontoons to estab-lish a small dock where traditional shorefacilities are unavailable.

Forward along the weatherdeck is asingle goal post, with stations to port andstarboard for transferring solids and

SEARCH RADAR MODULAR TRANSPORTABLELIGHTWEIGHT SOLID RAS SYSTEM

CANEWS

CIWS

VEHICLE RAMP(TO UPPER VEHICLE DECK)

NAVIGATION RADARS

, LOW-LIGHT TELEVISIONRAS KINGPOST(SOLIDS AND LIQUIDS)

CONTAINERCRANE/

VEHICLE RAMP(UPPER VEHICLE DECKTO WEATHER DECK)

STERN RAMP AND DOORLOWER VEHICLE DECK DOUBLE-HULL CONSTRUCTION

CARGO FUEL TANKS

SECOND HELO OPS POSITION

BOW DOORAND RAMP

BOW THRUSTER

MAIN HELO OPS POSITION PONTOONSCONTAINERS

CARGO HATCHELEVATOR (IN HANGAR) PONTOONS MODULAR TRANSPORTABLE

LIGHTWEIGHT SOLID RAS SYSTEM

Fig. 2. MRSV Side (cutaway) and Plan Views


liquids to other naval vessels. A modu-larized jackstay system can be rigged atthree locations. The MRSV has a totalcargo capacity of 11,000 tonnes, ofwhich 2,300 tonnes is dry cargo stowageand 8,000 tonnes is cargo fuel stored indouble-sided, double-bottomed tanks.The remainder is stowage for fresh waterand miscellaneous liquids.

Depending on the mission, the shipcan load a maximum of 227 standardcontainers on the vehicle decks and up-per deck. For disaster relief operationsthe containers can be packed with stores,or be specially outfitted as accommoda-tion modules below decks for up to 300relief workers or refugees. Other special-ized modules can be carried to expandthe MRSV's permanent four-bed medicalfacility into a full, 84-bed field hospitalcomplete with operating theatres. Any of

the special-purpose, containerized mod-ules can be fitted with galleys, heads andwashplaces, as required, and hooked upto ship systems for power, air condition-ing and drainage. Auxiliary systems onboard the MRSV, including all environ-mental protection measures, would besized to handle such an increase in load.

Modular, naval standard accommoda-tion is provided for 111 crew and 60contingency staff. Galley and loungecomplexes are located next to the accom-modation centre, while ship's offices,laundry and canteen spaces are locatedaround the outside of the hangar. Belowthese spaces, on the main deck, are thestore and workshop areas.

Other than adhering to naval standardsfor habitability, all aspects of the shipwould be designed and built according to

less expensive commercial practices.One consequence of this is that specialsurvivability features in the ship wouldbe limited. Apart from some relativelyinexpensive features like superstructureshaping to reduce radar cross-section,and degaussing to reduce the risk ofmine attack, no signature reduction mea-sures would be provided. Similarly, thedesign will not be shock- or blast-hard-ened, but instead will rely upon the con-siderable post-damage strength of a shipof this size and a comprehensive damagecontrol system.

Though not to full warship specifica-tions, the value of an asset such as theMRSV, especially fully loaded, has beenrecognized. A defensive combat systemhas been fitted, with room for expansionif required. Two close-in-weapon-sys-tems such as Phalanx are mounted and

Mexeflote: The Porta-JettyThe innovative Mexeflote por-table jetty system is made to be

used by sealift ships in places wheredocking facilities are limited or non-existent. Designed byGEC Engineering Lim-ited of Accrington,England, the systemconsists of a number ofmodular floats that canbe carried flat against aship's sides duringtransit, and then low-ered and assembled atthe disembarkationpoint. The floats can belowered and configuredto form a staging jettyand a separate, poweredbarge. Vehicles aredriven from the shiponto the Mexeflotejetty, then transferred toshore via the self-pro-pelled barge module.

The floats are spe-cially designed as eitherbow, stern or centresections for both jettyand barge, or as apower module. A six-cylinder Hydro-Masteroutboard diesel derated

to 83 b.h.p. at 1,800 r.p.m. drives a38-inch, three-bladed prop to movethe barge at a speed of seven knots.

An entire Mexeflote jetty and bargeassembly would be carried by theMRSV, at a cost of roughly $3 million.

Mexeflote modular pontoon system for loading/unloading


there is ample space for fitting newlydesigned deck-mounted weapons. Sen-sors include a surface/air-search radar,dual navigation radars, and a hull-mounted mine-avoidance sonar.

The MRSV does not have a tradi-tional operations room. Rather, spaceand equipment have been incorporatedfor contingency staff to set up a head-quarters situation room for controllingany of the multitude of missions theMRSV might encounter. Abaft and be-neath the situation room are the ESM/ECM and radar equipment spaces, and afully equipped military communicationscomplex.

Last, but far from least, the MRSVfeatures a serious capability for operatinglarge maritime and utility tactical trans-port helicopters such as the Sea King andChinook. The main flight-deck and han-gar are aft, and there is a second helo opsposition forward of the superstructure. Anelevator located in the hangar is capableof lifting a 15-tonne helicopter from themain vehicle deck, thus greatly increasingthe number of helicopters the ship caneffectively carry or operate. This signifi-cant helicopter capability is a primarysource of the MRSV's flexibility. Studiesby the Directorate of Maritime OperationsResearch have demonstrated that anMRSV with three helicopters would be atleast as capable as a purpose-built cor-vette for surveillance and sovereigntyenforcement missions.

CostAll of this capability carries a price

tag — roughly $1.5 billion (93/94) oversix years for a four-ship AOR replace-ment, including Mexeflote-style portablejetty systems and project costs. Admit-tedly this is a "D-class" estimate — plusor minus 25 percent — but designerswere generally able to keep costs reason-able through careful selection of com-mercial practices and equipment. (Bycomparison, building and operating theMRSV to full "mil spec" would increasethe cost by roughly 30 percent.)Sailaway cost of one fully loaded ship isabout $250 million.

Do the Canadian Forces really needfour multirole support vessels? The navycould manage with two if the vesselswere designed strictly for sealift (i.e.with no RAS capability), but that would

mean keeping two AORs in servicealong with them. On that note, plannersagree that acquiring four RAS-capableMRSVs with their smaller crews andmore efficient propulsion plants simplymakes better operational and economicsense. According to DMES, commission-ing four new support ships and retiringthe less efficient AORs early wouldincrease fleet life-cycle costs by only onepercent. Such a strategy would also yieldsignificant savings to the Crown throughreduced ship-design costs and the tan-gible benefits of a four-ship constructionlearning curve. Finally, given that twoMRSVs could be called on for sealiftduty at any time, the navy would need atleast four vessels to allow for refits andreplenishment duties in home waters.

A project entitled "Afloat LogisticsSupport Ship" has recently been ac-cepted into the Defence Services Pro-gram (DSP). Upcoming adjustments tothe DSP (based on changes in the role ofthe Canadian Forces over the past sev-eral years) are expected to provide for a$1.5-billion ship acquisition projectwhile still reducing overall DSP expendi-tures. Work on the next level of docu-mentation is already well under way, andonce that has been approved the navycan begin studying options in detail.

It's all manageable. Project costs for alogistic support ship could be signifi-cantly reduced if DND were to engage ina joint-design approach with both thedesign contractor and the shipbuilder,beginning with TSOR definition andpreliminary design. A ship specificationagreed upon and understood by all threeparties could be frozen to severely re-strict the costly change orders that typi-cally plague warship construction.Moreover, costs could be kept in eventighter rein by restricting the personneloverhead of the project managementoffice to about 20 employees, and theintegrated logistic support (ILS) require-ments to a level commensurate withthose for a commercial design. Duringconstruction the reduced PMO couldcontinue to provide guidance by havingemployees join the shipyard team. ILSactivities would continue, but the empha-sis would be on providing support notreadily available in the marketplace.Existing training and infrastructurewould be used whenever possible.

Conclusion

The potential of a multirole supportvessel is enormous. It fulfils the primaryrequirements of support to naval opera-tions and sealift and could contributesignificantly to resupply and military/humanitarian shore-support activities. Itssmall crew size, reduced operating costand significant helicopter capabilitymake it suitable for sovereignty patrolmissions. Its fuel capacity and RAScapability mean that four MRSVs alonewould resolve many of the deficienciesfacing the fleet, without a significantincrease in operating costs.

Make no mistake. The MRSV de-scribed here is not some kind of navy"dream" ship, boasting all the latest bellsand whistles. It has been designed withrestraint and with focus on function. It isin all respects a flexible vessel, as op-posed to one that is role-specific, and isthus fully in sync with Canada's immedi-ate and future needs. If ever there were asupport ship for our time, the MRSVwould be it. The multirole support vesselis, after all, an all-services requirementthat offers the Government of Canada asuitable vehicle to backstop its domesticand international maritime commitments.

\

« f/Cdr King is the acting Director of NavalRequirements at National DefenceHeadquarters.

LCdr Brinkhurst is a naval architect anddeputy project manager for Future Ships inDMES 3.


Towed Array Technology —The AN/SQR-19 "Wet End"Article and Photos by LCdr Stephen Monkhouse

Research and development workconducted by the Defence ResearchEstablishment Atlantic has put the Cana-dian navy in the forefront of passive anti-submarine warfare. In January 1987 thework headed up by Bob Trider, leader ofDREA's Advanced Digital SystemsGroup, resulted in the installation of aMk III Experimental Towed Array SonarSystem (ETASS) in HMCS Fraser, giv-ing the navy its first towed array sonarcapability. An ETASS Mk IV followedin October 1992.

towed array engineering knowledge hasresided with relatively few individualswho have served either on towed arrayfitted ships, or in a project capacity inDMCS 3, DREA or the naval engineer-ing units.

The aim of this article is to give thegeneral engineering community a synop-sis of the unclassified information that isavailable on the SQR-19 array. Specificdetails of the ETASS Mk IV signal pro-cessing "dry end" will have to wait foranother day.

NOTE: ACTUALBEAMWIDTHDEPENDS ONFREQUENCY

TOWED ARRAY

AFTENDFIRE

FORWARDENDFIRE

AFT CONICALBEAM BROADSIDE

FORWARD CONICALBEAM

Fig. 1. AN/SQR-19 Beam Shape

The technical and operational successof the ETASS project set the foundationfor the production of the CanadianTowed Array Sonar System (CANTASS)currently installed in HMCS Annapolis(and soon also to be installed in theHalifax-cla&s frigates). Both systems —ETASS and CANTASS — use theAmerican navy's AN/SQR-19 towedarray as the "wet end."

The advent of widespread usage oftowed array technology in the fleet pre-sents an interesting challenge, especiallyas training in towed array technology isjust now being introduced into the Com-bat Systems Engineering ApplicationsCourse. To date, the whole of the navy's

General

The AN/SQR-19 towed sonar arraydetects acoustic noise in the water, per-forms preliminary signal processing,digitizes the data and passes it up a towcable to the ship. Once on board, the dataenters the system "dry end" for digitalsignal processing using Fast FourierTransforms (FFT) to convert time-do-main noise into frequency domain arti-facts. Beamforming, performed at theFFT stage by applying coefficients froma complex trigonometric look-up table,results in 43 conical beams (Fig. 1).

A more powerful signal processorallows a higher sampling rate to be

processed giving finer resolution and animproved ability to extract signals ofinterest from the background noise. Theheart of the success of the ETASS lies inthe excellent processing capabilities ofthe dry end's UYS-501 teamed- architec-ture signal processor (TASP) which has asustained throughput of 320 millionfloating-point operations per second.

AN/SQR-19 Towed Array

The SQR-19 towed array is a complexelectrical and mechanical system com-prising a tow cable and a towed array.The tow cable is 2.7 centimetres (1.05")in diameter and 1,707 metres (5,600 ft)long. It weighs 3,583 kilograms (7,900Ibs) and has a breaking strength of31,752 kilograms (70,000 Ibs).

The array itself consists of 20 mod-ules and a rope drogue. It is a nominal8.58 centimetres (3.38") in diameter andweighs 1,416 kilograms (3,123 Ibs).Each module is 12.2 metres (40 ft) longand the drogue is approximately 20metres (65 ft) long, for a total length of264 metres (865 ft). The array modulesare neutrally buoyant and contain struc-tural components made up of a skeletonof wire strings which support environ-mental sensors, electronic cans (assem-blies) and hydrophones. The outside skinof the modules is a flexible hose filledwith ISOPAR M, a colourless, electri-cally non-conductive fluid.

The modules have watertight alumi-num bulkheads at each end fitted withports for filling and bleeding-offISOPAR M. Each module end has astainless steel locking ring with toothedlocking tabs. Acoustic modules have 60-pin connectors which are protected fromseawater ingress by O-rings and back-uprings (Fig. 2).

The towed array consists of 16 acous-tic modules, which include: eight verylow frequency (VLF) modules, four low-frequency (LF) modules, two medium-frequency (MF) modules and twohigh-frequency (HF) modules. Thearray's four non-acoustic modules in-clude two vibration isolation modules(VIMs), one telemetry drive module

10 MARITIME ENGINEERING IOURNAL, JUNE 1994

(TDM) and one heading-depth-tempera-ture module (HDTM). With the excep-tion of the VIMs, array modules of agiven type are functionally and mechani-cally interchangeable. However, moduletypes cannot be interchanged due to thetiming requirements for signal process-ing. The 20-metre rope drogue providesstability during towing by providingadditional drag which tends to keep thearray straight and dampen oscillations.

Electro-Mechanical Description

An array receiver provides the inter-face between the dry and wet ends. Itprovides a constant current 47.5 VDC,2.75 amp power to the array via the towcable, receives all data and transmits allcommand signals. The array receiver islocated in the ETASS compartment andis linked to the tow cable via a deckcable connected to the rotating winchdrum used for stowage and handling.The deck cable attaches at a coaxialrotary joint located within the slip-ringunit on the side of the winch drum.

A hydraulically controlled level-winder assembly, consisting of two verti-cal rollers, and a rotating fairlead on thestern of the ship guide the tow cable andarray during launch and recovery (seephotos). The AN/SQA-501 YDS hydrau-lic power unit provides power for stow-age and handling. Mechanical brakessecure the winch drum when not in useto prevent it from accidentally free-wheeling, which could lead to the loss ofthe array.

Tow Cable

The tow cable is made up of a singlecoaxial cable core wrapped in a polyeth-ylene shield surrounded by four torque-balanced layers of galvanized steelarmour with an outer jacket of high-density polyethylene. The coaxial shieldprovides array signal ground. The towcable carries three signals simulta-neously — data from the array, com-mand tones from the dry end, and thearray power.

Vibration Isolation Modules

Two of the VIMs act as shock absorb-ers for the array, isolating it acousticallyfrom the tow cable by preventing strum-ming from passing to acoustic modules.The VIMs, constructed of black rubberhosewalls which contain dual contra-helical layers of nylon cord reinforce-ment, can stretch up to 50 percent of

ITEM1

2345678

DESCRIPTION QTYTelemetry Drive Module 1Low Frequency Module 4Mid Frequency Module 2High Frequency Module 2Very Low Frequency Module 8O-RingBackup RingO-RingLocking Tab ScrewLocking TabCoupling RingLow Frequency ModuleMid Frequency ModuleHigh Frequency ModuleVery Low Frequency ModuleHeading, Depth, and Temperature Module 1

4228

Fig. 2. Typical Module Coupling

their original length under towing loads.A centre strength member made of ny-lon-Kevlar cord prevents excessivestretch of the VIM by acting as the load-bearing member if the VIM stretchesmore than 50 percent. This cord is at-tached to each end by an eye splice tiedto an aluminum clevis attached to thebulkheads. The nylon-Kevlar cord iscoated with a composite of polyetherpolyurethane. The coaxial cable iswrapped around this and is slightlylonger in length to prevent it from be-coming the load- bearing member understrain. Once the array is stretched pastthe 50-percent point it loses its ability toisolate vibration, thereby increasing self-noise. The VIMs have coaxial connectorsat each end and are not interchangeable.

Telemetry Drive ModuleThe TDM is the first electronic mod-

ule of the array. It is constructed of a

black thermoplastic hosewall with nyloncord reinforcement. The skeleton steelwire stringing assembly supports 21electronic can assemblies and sevenjunction assemblies and their nylonspacers. The first can at the forward endof the TDM is the cable line driver/isolation and tone coupler, which drivesdata signals up the tow cable anddecouples power and command signals.Other cans process acoustic and non-acoustic data for transmission.

The forward end of the TDM con-nects to the after VIM by a coaxial con-nector. The TDM contains a switchingmode regulator and linear regulatorcircuits to provide power for the array.Array power is partitioned by the TDMso that a short in one area will not dragthe power down in all areas. Voltagemonitoring circuits digitally encodestatus for transmission to the arrayreceiver.

MARITIME ENGINEERING JOURNAL, JUNE 1994 11

Heading Depth TemperatureModule

The HDTM is the last module in thearray, and contains sensors for determin-ing the array's heading and depth, and thesea temperature. The module is con-structed of black rubber hosewalls withlongitudinal and circumferential reinforce-ment. The HDTM also has a skeleton. Thelast half of the HDTM contains no compo-nents and its skeleton is made of a braidedpolyester cord in a zigzag fashion.

Heading data accurate to one degree isprovided by a magnetic compass thatuses LEDs and phototransistors to pro-vide digital output. Temperature data isprovided by a platinum resistance tem-perature detector whose voltage output isthen digitized. Digital array depth dataprovided by a pressure transducer is ac-curate to ± 1 percent.

The HDTM power supplies regulatepower received from the TDM and thendistribute it to the VLF modules and theHDTM.

Acoustic Modules

The 16 acoustic modules are con-structed in a similar manner to the TDM.The skeleton stringing assembly supportselectronic assembly cans including hy-drophones which convert sound-pressurewaves into electrical impulses. The im-pulses are sent to a preamplifier/filterwhich amplifies the analogue acousticsignal by five decibels and passes it

through a bandpass filter to eliminatefrequencies outside the range of interest.The signal is then multiplexed into atime division analogue data streamwhich is then sent via a differential linedriver, providing the first stage of ampli-fication of zero- or 24-decibel gain.

The acoustic data stream from eachmodule's line driver travels throughother acoustic modules before reachingthe differential line receiver in the TDMfor the LF, MF and HF modules, and inthe HDTM for the VLF modules. Thedifferential line drivers and receiversensure that if one line is down the ex-pected output will be down by six deci-bels. The hydrophones in the acousticmodules are grouped into 96 channels,and 24 other channels carry non-acousticdata. Figure 3 contains a functional dia-gram of this arrangement.

The HDTM forms a single chain ofVLF acoustic data using multiplexers.Both the HDTM and the TDM have gaincontrol amplifiers, as well as sample andhold circuits, which allow instantaneousdata samples to be amplified in the sec-ond stage of amplification in three-deci-bel steps from zero to 21 decibels andheld until the timing is correct for datafrom that channel to be queued into amultiplexer and analogue/digital convert-ers. Note that both stages of amplifica-tion provide a total range of zero to 45decibels that is controlled by the arrayreceiver as a variable of ambient noiselevels.

The order in which channel data ismultiplexed is fixed. The array receiver,therefore, must receive the data in theexpected order (which explains whymodule types cannot be shuffled aboutthe array). This digital chain of acousticdata is then multiplexed with digitalheading, depth and temperature data, andwith performance monitoring and faultlocation status data. This acoustic/non-acoustic data chain is amplified by a linedriver and transmitted to the TDM. TheTDM multiplexes this data chain withdigitized acoustic data from the LF, MFand HF channels from the forward half ofthe array.

The combined data chain is amplifiedthrough another line driver and sent asbiphase, encoded eight-bit digital datavia a coaxial cable up through the VIMsand the tow cable to the array receiver.Non-acoustic data is sent at 16 Hz, ex-cept for sync and parity which are sent atthe higher rate of acoustic data.

The TDM contains system timing andcontrol circuits that co-ordinate the se-quencing of multiplexers and the sampleand hold circuits. These circuits providethe timing control signals for theHDTM's timing circuits so that the TDMand HDTM are synchronized.

System control circuits also receivetest signals or calibration tones from thearray receiver and distribute test signalsof different frequencies and referencelevels to hydrophone preamps. They also

Fig. 3. General Signal Processing Diagram

12 MARITIME ENGINEERING JOURNAL, JUNE 1994

control the level of the gain control ampsin the HDTM and TDM as ordered by thearray receiver. Performance monitoring/fault location circuits monitor voltagelevels and array current as well as theintegrity of the control and multiplexeraddress lines for the gain control amps.Performance/fault data is sent as non-acoustic data and is monitored by thearray receiver.

Fault IsolationThe array has four modes of operation

— three invasive test modes and a normalmode. The invasive test modes causevarious DC levels to be transmitted byacoustic multiplexers in place of acousticdata. These DC tones should be visibleon the spectrum analyzer connected tothe digital/analogue converter output ofthe array receiver. Zeros are substitutedfor non-acoustic data. This checks out theproper operation of the multiplexers andthe gain control amplifiers.

The other method of testing is theFault Isolation Test Set (FITS) which candetect errors in the tow cable and array.Inserted at any point in the array, FITSwill simulate all functions abaft thatpoint. If the insertion of FITS at a givenpoint rectifies a fault, the fault must liesomewhere abaft the insertion point. Thiscan be used to localize the fault usingcalibration tones or by checking perfor-mance monitoring/fault location data.FITS also provides a load simulatorwhich can detect opens and shorts forfault isolation of the VIMs and the towcable right up to the array receiver.

MaintenanceThanks to the design of their stowage

and handling gear, USN ships can break adeployed array to insert FITS or to runother maintenance procedures. Fraserdoes not have this capability. The ab-sence of lay-by trays makes module-switching a somewhat risky evolution.The array is examined closely upon re-trieval for gouges or signs of obviousdamage, but a cut in a module deeperthan .018 centimetres (0.02"), or a cut inthe tow cable deeper than .16 centimetres(1/16") must be repaired by MartinMarietta in the United States. (Plans for aCanadian repair facility are well underway.)

Fraser relies on the support of ShipRepair Unit Atlantic to inspect the arraymore fully (usually during short workperiods if the array has more than 200

•

Naval Weapons Technicians land HMCS Fraser's towed array in DockyardHalifax. The cable can be seen passing from the winch drum, aft through thehorizontal and upright rolling fairleads of the level-winder, and out the stern ofthe ship through a bell fairlead.


towing hours on it). The array is in-spected for proper operation and correctISOPAR M fluid levels.

Normally, several modules normallyrequire refilling. Proper fill levels arevital to ensuring the array is towed alongthe horizontal plane. Overfilling canstretch a module's hosewalls and createpositive buoyancy, while underfillingcan create negative buoyancy. (Overfill-ing an HDTM would also affect thedepth sensor.) In either case the beams ofthe array would be skewed, making tar-get prosecution difficult. In a pinch,Fraser could refill a module with itsonboard hose-filling rig and supply ofISOPAR M, even though the procedureis not recommended at sea.

(In the category of tall fish stories,one leaking telemetry drive module wasfound to have two small punctures.Closer examination revealed eel's teethembedded in the hosewall! The USN hasreported similar experiences during op-erations in the South Pacific. Apparently,the low-frequency vibrations of thetowed arrays were attracting sharkattacks.)

ConclusionThe success of the SQR-19 and

ETASS Mk IV combination has givenFraser the most "in-contact" time onpassive sonar of any surface unit in thefleet. The range at which targets can besuccessfully tracked by ETASS IV hasprovided HMCS Fraser with a potentunderwater sensor. The ETASS Mk IVwill be transferred to HMCS Nipigonwhen the venerable Fraser is paid off inJuly.

Future developments in array technol-ogy include a passive-active array whichwould provide the current benefits ofVDS technology, such as being able toprovide range data and more accuratelocalization of targets at close ranges.The passive aspect provides bearinginformation for targets at great ranges.Target-motion analysis would continueto be used for range prediction.

Possible growth areas would be to usethe increasing power of modern digitalsignal processing computers to processmore data from longer arrays. Longerarrays would mean more hydrophonescould be carried to cover off greaterportions of the frequency spectrum.

Also, the sampling rate of acoustic datacould be increased to provide a finerfrequency resolution. The combinedeffect of these improvements would bean ability to detect smaller acoustic sig-nals, over a greater frequency range atgreater distances, m

References[1] Martin Marietta, Towing the Line,

Issues 1, 2 and 3, Norfolk, VA. Underauthority of Naval Sea CombatSystems Engineering Station,accepted by DND as a CFTO.

[2] USN Technical Manual, ANISQR 19

An AC Electric Propulsion Concept for aDDH-280-class Replacement*Article by LCdr M. Tinney, W.A. Reinhardt, P.Eng., J. Hensler, P.Eng. and LCdr M.J. Adams, P.Eng.

'This article is based on a paper originally presented at the Canadian Maritime Industries Association 45th Annual TechnicalConference held in Ottawa February 16,1993.

When electric propulsion first cameinto use, DC technology was used exclu-sively because of the difficulty in attain-ing speed control over AC motors. In thepast few decades, however, advance-ments in AC technology have resulted inAC drives challenging their DC counter-parts, particularly for high-power appli-cations. Power semiconductors can nowcontrol megawatts of power at severalkilovolts. Propulsion system designersare thus now able to incorporate many ofthe advantages of electric drive, therebyavoiding the disadvantages of DC sys-tems such as commutation limits, main-tenance requirements and size.

Until recently electric drives had thedisadvantage of being more expensive,heavier and bulkier than their mechanicalequivalents. The reason for these short-comings lay with the fact that electricdrive systems were developed for land-based industry. DND studies have shownthat AC propulsion systems developedspecifically for naval use can reach thepower density values of equivalent me-chanical systems.IK2J

The Royal Navy has already installedan electric cruise propulsion system in itsType 23 frigate. In this case an off-the-shelf DC system was used to minimizedesign/development costs. The overallpropulsion system is more reliable, morefuel efficient, and less maintenance-intensive than a comparable conventionalplant.

This paper describes a potential semi-electric propulsion system for a DDH-280-class replacement vessel(DDH-280R). The plant consists of ACelectric cruise propulsion, with gearedgas turbines for boost power — i.e. aCODLAG (combined diesel electric andgas) arrangement.

Attributes of Marine ElectricPropulsion

The benefits of a modern marine ACpropulsion system cover a wide spec-trum:

Performance• Infinite bi-directional speed control

of the propulsion train eliminatesthe need for controllable pitchpropellers and reversing gearboxes.

• Independent torque control (i.e.independent of propeller speed)permits virtually unlimited propel-ler force at zero shaft speed. Thisfeature is particularly useful whentrying to free propellers trapped inice.

• Simulation results indicate that afull electric ship can match orexceed a similar mechanical shipin terms of reversing time, stop-ping distance and acceleration.[3)

Survivability• Decreased infra-red and noise

signatures make the AC-propul-sion-equipped ship less susceptibleto detection.

• Decentralization of the propulsionprime movers lessens the vulner-ability of the system to single-pointfailure and catastrophic (i.e. fullydisabling) battle damage.

Reliability/Maintainability• Reliability of the overall system

improves due to the use of more-reliable electric components andmore (available) prime movers.Shorter shaft lengths and fewercomponents in the shaftline alsoserve to increase reliability.

• The simplicity of electric motorsand solid-state control circuitryoffers reduced maintenance re-quirements, especially comparedwith the maintenance required byCODOG/COGOG propulsionplants and ship's service generatorswhich may be operated at lowloads for prolonged periods.

LIFETIME OPERATING HOURS

8000-

7000-

6000-

5000-

4000-

3000-

2000-

1000-

0-

-^ 85% Cumulative running hours *-

iolilll

li

II,1 2 3 4 5 6 7 8 910111213141516171819202122232425262728

SPEED (KNOTS)

Fig. 1. Typical Frigate Operational Profile


Efficiency• An AC propulsion system achieves

improved fuel economy by effi-ciently matching propulsion loadrequirements with power genera-tion components, and by usingmore efficient, less expensivefixed-pitch propellers. A 1985 "fullelectric frigate" concept designstudy estimated fuel efficiency tobe 30 percent better than for anequivalent CODOG frigate.131

A CODLAG DDH-280R

It is likely that Canada's navy will, tosome extent, continue to play a role indrug interdiction, fishery and sovereigntypatrol, search and rescue, and UN andother allied operations such as blockadeenforcement. It is suggested that theserequirements could be met, at the mini-mum, by a multirole, frigate-sized ves-sel. For the purposes of this paper, then,equipment selection has been based onthe propulsion needs of a baseline 124-metre ship, displacing 4,200 tonnes andhaving a top speed of 30 knots.

An operational profile for such avessel (Fig. 1) shows that it spends 85percent of its time operating at 20 knotsand less. For this reason it is highly de-sirable to have a propulsion plant that isfuel efficient at low patrol speeds, yetcapable of the high speeds necessary forinterdiction and other requirements.

From the speed/power curve (Fig. 2) itcan be seen that to reach the 20-knotlevel requires seven megawatts (i.e. 20percent) of the total available propulsionpower needed to take the ship up to 30knots as specified.

The conceptual DDH-280R cruisepropulsion system shown in Fig. 3 con-sists of two 3.5-megawatt AC synchro-nous motors, each controlled by acycloconverter, providing power to afixed-pitch propeller. The main motorsare connected in the shaftline and thecycloconverters are powered from a4.16-kilovolt propulsion bus suppliedprimarily by three separate propulsiondiesel generators. The AC motors takethe ship up to 20 knots ahead, and areused for manoeuvring and astern move-ments. With all propulsion generators online, the ship has seven megawatts ofpower available for ahead and asternmovements in cruise mode.

In boost mode, two 15-megawatt(maximum continuous rating at ISO) gasturbines are brought on line with the ACelectric propulsion motors to supply theadditional 30 megawatts of powerneeded to take the ship from 20 knots upto 30 knots and beyond. Gear-meshingnoise is no longer a concern at thesespeeds since it will be masked by thehydrodynamic noise of the hull and pro-pellers. The gas turbines connect to theshaftline through a simple reduction

SHAFT POWER (MW)

10 15 20

SPEED (KNOTS)

Fig. 2. Speed/Power Curve for a Typical Frigate

gearbox and clutch arrangement, whichallows the GT machinery to be isolatedfor quietness during cruise operation.CODLAG power-sharing is achieved bycontrolling the load angle of the propul-sion electric motor by setting the angulardisplacement of the armature and poleflux vectors via the cycloconverter.

Between 20 and 30 knots the ship'sspeed can be controlled by adjustingthe speed of the gas turbine. Althoughoperating the gas turbines at slowerspeeds reduces efficiency, such operationwould only be required for a relativelysmall percentage of time in the DDH-280's life cycle. Any inefficiency wouldalso be mitigated by the fact that the loadwould be kept high on the turbines byreducing the contribution of the electricmotors while the turbines were operatingin that range.

Power GenerationElectrical power is provided by three

propulsion generators distributed conve-niently throughout the ship. By carefullyselecting the size of the generators at theoutset, an efficient combination of primemovers can be configured to closelymatch the vessel's speed/power require-ments. The DDH-280R requires approxi-mately seven megawatts of installedcruise propulsion power, and about oneand a half megawatts of ship's servicepower. Allowing for 100-percent standbyredundancy in ship's service power, atotal of 10 megawatts of installed gener-ating capacity is therefore required forboth cruise propulsion and ship's servicepower.

Three propulsion diesel generatorsrated at 1.5, 3.0 and 4.0 megawatts wereselected to provide the necessary powerand ensure maximum operating effi-ciency. Along with two 750-kilowattship's service generators, the electricalload can be configured to provide powerat 750-kW increments all the way up to10 megawatts. (For ease of support, allthree diesel engines would be of the sametype.)

For maximum efficiency, power forthe auxiliary 440V ship's service bus willnormally be provided by two 750-kWreversible synchronous motor-generatorsets connected to the main bus. Synchro-nous motor-generators were selected overtransformers to significantly reduce thelevel of harmonics transmitted from thepropulsion bus to the ship's service bus.With motor-generators, harmonics areeffectively attenuated as they pass


through the air gaps in the motor andgenerator. A ring main system was se-lected for improved survivability and easeof maintenance. The two motor-genera-tors and two ship's service diesel genera-tors each feed an independent section ofthe switchboard, each section beingjoined by bus tie-breakers.

Braking requirements for the vesselare met by feeding regenerated powerfrom the propeller back into the mainpropulsion bus. This option was selectedsince it involves recovering the kineticenergy of the moving ship and converting

it back into electric power to be used bythe auxiliary bus. If the regeneratedpower were too great to be absorbed bythe auxiliary bus, the excess would beabsorbed by the diesel generators (act-ing as motors) and by the diesels (actingas compressors). A power-managementsystem slows the diesels in sufficienttime to receive the regenerative power.As the regenerative power is absorbed itcauses the diesels to speed up. Proper-sized generators ensure that the slowing-down and speeding-up of the generatorsdoes not cause the bus frequency toexceed the allowable limits.

Some Important Considerations

Power Density

Using state-of-the-art technology forcycloconverter design, the overall volumeof an AC electric propulsion plant is nowonly eight percent to 10 percent largerthan that of a comparable geared propul-sion system. What is more, if the matur-ing technology of high-powered gateturn-off devices can be used in place ofsilicone-controlled rectifiers, the con-verter size could be decreased by anadditional 70 percent — enough to makethe difference between electrical and

i RING MAINPROPULSIONBUS

GEARBOX

CLUTCH

PORTPROPULSION

MOTOR

GEARBOX

CLUTCH

STARBOARDPROPULSIONMOTOR

Fig. 3. Conceptual DDH-280R Propulsion System


mechanical drives negligible. Anyweight penalty is compensated for by theabsence of large, heavy reduction gear-boxes and controllable pitch propellersystems.

NoiseA study conducted for DND showed

that cycloconverter-based AC driveshave the potential to reduce a ship'sunderwater acoustic noise by as much as20 decibels.14' This translates into a hun-dred-fold decrease when compared to ageared mechanical system with a con-trollable pitch propeller. Computer simu-lations and verification tests presentlybeing conducted in Canada and the U.K.also seem to converge on identical con-clusions.151

System VulnerabilitySeveral studies conducted for DND

used a Monte Carlo probability simulatorto prove that locating propulsion compo-nents freely in a ship's envelope canimprove a vessel's survivability.161 Re-sults from computer-simulated missilefirings against a design variant of theMCDV with generators dispersedthroughout the vessel showed that theprobability of losing all propulsionpower because of one hit was virtuallynon-existent.

Reliability I Availability

A study carried out on behalf of theMCDV project showed that the inherentflexibility of an electric propulsion sys-tem virtually rules out the likelihood of acatastrophic loss of system due to asingle-component failure at any time

during the life cycle of the vessel. In fact,the period between two catastrophicfailures for one option of the MCDV wascalculated to be in excess of 60 years!171

ConclusionsWhile a full costing study has yet to be

conducted, it is recognized that produc-tion costs for a conventional electricpropulsion plant, such as suggested inthis paper, are currently more expensivethan for geared mechanical propulsionschemes. The advantage of an electricplant is realized through savings in fuelcosts and operating and maintenancecosts throughout the life of the vessel.Despite the fact that the power train'stransmission efficiency is only 90 percentversus the 97 percent for a geared me-chanical drive, the optimum match ofdesign points over a relatively large per-centage of the ship's operational profileyields savings in operating and mainte-nance costs. For these savings to be real-ized, however, it is important that theright size and number of generators beselected to ensure efficient operation at(or very near) their optimum designpoints.

The capabilities of existing high-power AC technology now make ACmarine propulsion systems feasible. TheDDH-280R propulsion system describedhere offers the potential for reduced oper-ating costs (as seems to be borne out bythe U.K.'s experience with the Type 23)and increased survivability. Any negativeimpact of greater system size, weight andproduction cost may soon be eliminatedby advances in AC power technologysuch as gate turn-off components, m

References[1] AOR Re-engining Study, 1990

(DND document)

[2] Corvette Propulsion FeasibilityStudy, 1992 (DND document)

[3] W.A. Reinhardt and J.R. Storey:"ASW Frigate Electrical Propulsion— The Way Ahead," MaritimeEngineering Journal, September1988, p. 8.

[4] "Frigate Electric Propulsion Study,Phase II: Final Report," (DNDdocument), July 1986.

[5] Lt(N) T. Wagner and J. Hensler: "AnApproach for Determining theUnderwater Noise Characteristics ofElectric Propulsion Systems," RINANaval Submarines Symposium,London, 1991.

[6] "Propulsion System Study for aLight Frigate-Size Vessel," (DNDdocument), January 1992.

[7] "MCDV Design," (DND document),1990.

LCdr Mark Tinney is the DMEE 6 projectengineer for motor drives and electricpropulsion systems.

W.A. Reinhardt is the DMEE 6 section headfor shipborne electrical power generationand distribution systems.

J. Hensler is general manager of theIntegral Dynamics division of HensmandLimited of Gloucester, Ontario.

LCdr MJ. Adams is the DMEE 6 projectofficer for air-independent propulsion.

18 MARITIME ENGINEERING JOURNAL, J U N E 1994

Conference Reports65th Commonwealth Engineer Officers Conference

The 65th Commonwealth EngineerOfficers Conference was hosted inHalifax, Nova Scotia last Sept. 20-24 bythe Director General Maritime Engineer-ing and Maintenance (DGMEM). Seem-ingly in keeping with the conferencetheme of "Shrinking Budgets — Spend-ing Wisely," only nine of the 26 delegateshailed from foreign commonwealthnavies. They included three officers fromthe Royal Navy, one from the RoyalAustralian Navy, one from the RoyalNew Zealand Navy, two from the IndianNavy and two from the Royal BruneiNavy.

The week-long conference openedwith a Monday evening welcoming re-ception at the Stadacona wardroom.Besides giving delegates a chance tomeet one another, the informal occasionset the tone for the rest of the conference.Other social functions of the conferenceincluded a boat tour of the dockyardwaterfront, a tour of HMCS Toronto anddinner at Royal Artillery (RA) Park.

In his opening address, conferencechairman Cmdre Robert L. Preston(DGMEM) pointed up the current cli-mate of shrinking budgets and the need

to reduce costs of fleet support. His callfor innovation and imagination in meet-ing the challenge of reducing costs waswarmly received.

Keynote speaker for the conference,RAdm M.T. Saker (Assistant DeputyMinister Engineering and Maintenance),expanded on this theme by suggestingthat we face a significant challenge as weattempt to reduce costs during a periodof fleet renewal. Deficit reduction is theorder of the day, he said, but cautionedthat at best that meant no real growth inDND's budget. He pointed out that we

The 65th Commonwealth Engineer Officers Conference:

Top row: Lt(N) Curran, Cdr Duinker (Conf. Co-ordinator), Capt(N) Chiasson, Capt(IM) Embree, LCdr Findlay, Capt(N) Brown

Middle row: Capt Hussein (Brunei), Lt(IM) Garbe, Cdr Kar (India), LCdr Adams, Cmdr Ayers (United Kingdom)Capt(N) Sutherland, Capt(IM) Bailer (United Kingdom), LCdr Staples

Front row: Cdr Athalye (India), LCdr Hudson (Australia), RAdm Saker (Keynote Speaker), Cmdre Preston(Conf. Chairman), RAdm Walmsley (United Kingdom), Cdr Dudley (New Zealand), Maj Nooradin (Brunei)

Absent: Capt(IM) Marshall, Cdr Eldridge, Cdr Johnson, LCdr Brown, LCdr Munro, Capt Larouche, Tina Rumble


must strive constantly to find ways tospend wisely because, while funding cutshave so far been generally absorbed byfuture projects, further cuts will have tobe borne by current projects.

RAdm Saker highlighted the fact thatwe contract out 33 percent of our engi-neering support work and more than 60percent of our production work. He alsopointed out that the current allocation of$17.7 billion for naval acquisitions cov-ers such projects as CPF, TRUMP,MCDV and others. To make mattersworse, he said, industry is hungry and isapplying political pressure to have DNDcontract out more work than it alreadydoes. Because the operation and mainte-nance of the fleet accounts for over 77percent of the navy's budget, that iswhere most of the room exists to trimexpenses. Therefore, "devolution," or de-centralization, is being looked at to helpreduce costs. This means that the deci-sion levels for some of the fleet opera-tion and maintenance functions would belowered to a more practical, hands-onlevel, and that those who make the deci-sions would be held accountable for theirdecisions.

Admiral Saker's speech was followedby a presentation from RAdm Walmsley(RN), Director General Submarines andChief of Naval Engineering, who sum-marized the RN procurement process andcurrent difficulties. He extolled the vir-tues of the competitive process and evensuggested that portions of sole-sourcecontracts should be tendered for compe-tition to maintain a baseline from whichto compare non-competitive proposals.Another cost-cutting measure, the trans-

ference of design authority to industry,was also presented. This requires a"hands off, eyes on" approach — handsoff to reduce the cost of never-endingdesign changes, and eyes on to ensurethat what is being produced is what iswanted. In the course of his presentationRAdm Walmsley succinctly defined thecost-effectiveness of the "devolution"principle: "Once you have to pay for it,"he said, "you'll want less of it."

The remainder of the conference rein-forced the difficulties introduced by thesenior presentations, and verified that thepressures were indeed international.Over the next three days delegates pre-sented 14 papers, covering such topics ascontracting out ship-level support, thecost benefits of improved informationand personnel management, and thepotential savings associated with im-proved requirements definition — every-thing from R&D to project management.

The last afternoon of the conferenceconsisted of a free forum discussionperiod. RAdm Walmsley introduced anarticle from the June 1992 issue of theJournal of Naval Engineering, entitled"Should Engineers Wear Purple Caps —A Way Ahead for Technical Officers inthe RN." This stimulated much discus-sion among the delegates as to how theoperator-maintainer relationship, both atthe officer and NCM levels, should bestbe tackled.

The Indian Navy is apparently closeto embracing the principle of requiringofficer candidates to hold technical de-grees. This is familiar territory to Cana-dians. An RCN training scheme of the

late '50s and early '60s required navalofficers to obtain both engineeringcharge tickets and bridge watchkeepingtickets. The scheme had its advantages,but in the end it proved to be too expen-sive and was a serious impediment toofficers wishing to pursue only engineer-ing or bridge careers. Delegates agreedthe best course of action for Canadawould be to continue our streamedMARS and MARE training, with oppor-tunity for officers to cross-train if soinclined.

The remainder of the forum discus-sion covered the recognition of the cost-effectiveness of the competition process.It was agreed that the first step towarddeveloping cost-effective procedures wasto implement cost-accounting proce-dures.

In conclusion, the conference was avaluable forum for sharing ideas con-cerning the universal problem of copingwith shrinking budgets. Different ap-proaches and new ideas provided seedsfor thought as to how we might advancethe cause for cost-effectiveness withinthe navy. The fruit borne from this con-ference will assist the department insupporting the fleet with ever-diminish-ing resources, m

Papers from the 65lh CommonwealthEngineer Officers Conference are avail-able from: DGMEM/SPO, NDHQ (4LSTL), Ottawa, Ontario, Canada Kl AOK2. The 66th Commonwealth EOs Con-ference is tentatively scheduled for 1995in India.—by LCdr M.J. Adams,DMEE6.

10th Ship Control Systems SymposiumThe Tenth Ship Control Systems

Symposium was held in Ottawa duringthe last week of October 1993. The sym-posium was attended by 232 speakersand delegates from 14 countries, andmore than 100 papers were presentedduring the week-long meeting. The Ca-nadian federal election on the openingday of the symposium (and the stunningelection results) did more than a little tobreak the ice as delegates made acquain-tances and renewed friendships.

The symposium is held every threeyears to discuss advancements in marinecontrol philosophy and technology. Therole of symposium host rotates betweenCanada, the United States, the UnitedKingdom and the Netherlands. Canadalast hosted the event in 1981. This latestsymposium was sponsored by DMEE 7,under the chairmanship of Cdr PeterMacGillivray. Organizational responsi-bilities were managed by co-ordinatorLt(N) Carlos Zaidi and Jim Hayes

(administrative chair). The technicalchair was filled by Francine Portenier.

In his opening address, CmdreRobert L. Preston (DGMEM) spoke onthe role of IMCS in the Canadian navy,adding that these symposia have been "acornerstone of our machinery systemsdevelopment." Over the course of theweek a variety of topics were discussed,including intelligent damage controlsystems, intelligent health monitoringsystems, and new-generation machinerycontrol systems.


One paper of particular interest intoday's climate of fiscal restraint wastitled, "Reducing Overall Ship Costsusing Improved Techniques for Controland Monitoring." In his paper, MichaelGlover (U.K.) discussed the possibilitiesof reducing a ship's complement by

Melanie MacGillivray, SpousesProgram Co-ordinator. "It was greatfun. I loved every minute of it."

enhancing machinery automation. Earlierin the proceedings Barry Smith (U.K.)had touched upon this theme with his"Conjecture on the Continuing Develop-ment of Machinery Control." Artificialintelligence may replicate human perfor-mance, Smith said, but added, "We haveno desire to replicate human shortcom-ings!"

Capt(E) Nicolaas Osseweyer(RNLN), in his overview "PlatformControl Developments in the Nether-lands," posed several difficult questions:"How do we keep a watchkeeper keenand interested during his watch wheneverything is normal and the machine isdoing the job? What do we do with ahighly educated engineer when a consid-erable part of his working time is con-sumed with work on a rather low level— for example, cleaning, repairing de-fective toilets?"

Although the symposium timetablewas hectic, participants did have time tosocialize at a midweek banquet and end-of-symposium luncheon. (The RadissonHotel's chef was formerly a cook in the

Royal Netherlands Navy!) In his banquetspeech RAdm M.T. Saker talked aboutthe fiscal challenges facing the world'snavies, and explored future Canadianadvancements for IMCS technology.

A well-received spouses programconducted by Melanie MacGillivray,wife of symposium chairman Cdr PeterMacGillivray, included a full schedule oftours in and around Ottawa. "Peter said itwas going to be a lot of work," saidMelanie, who had to book time off fromher job as a Leader/Trainer with WeightWatchers. "But I really feel it's been aprivilege — I got to meet all thesewomen."

Language teacher Reidun Lutje-Schipholt, the Norwegian wife of seniorNetherlands delegate RAdm RuurdLutje-Schipholt (SACLANT AssistantChief of Staff, CIS in Norfolk, VA) saidshe thoroughly enjoyed the spouses pro-gram. "We saw the sights, but we werespoiled by all the lunches," she laughed."It was a mixed group (of women), andstill we got on very well. We had a lot totalk about," she said.

WHtOME TO THETENTH SHIP

CONTROL SYSTEMSSYMPOSIUM

BIENVENUE AUDIXltME COLLOQUESUR LES SYSTEMES

DE COMMANDES DESNAV1RES

Symposium Chairman Cdr PeterMacGillivray poses with internationalco-ordinators Barry Smith — U.K.(seated, chair-designate for 11thSCSS in 1996), Capt(E) TonyFlameling, RNLN (Ret.) — Neih.(standing, left) and JohnMoschopoulos — U.S.A. (chair of 9thSCSS in 1990).

Staff for the 10th Ship Control Systems Symposium received top marks fromspeakers and delegates alike.

Front: Ann Roberts, Valerie O'Callaghan, Carol Rosengren, Colleen Donis,Barb Gricken

Rack: Francine Portenier (technical chair), Keith Santo, Gerry McCauley, DanMcEachern, Carlos Zaidi (symposium co-ordinator), Paul York, Cdr PeterMacGillivray (general chair). Jack Sinclair, Jim Hayes (administrativechair). Marge Chartrand, Lt(N) Jody Curran.

Missing: David Atkins, Jeff Hill


As a humorous memento of their tripto Wakefield, Quebec on the steam train,the ladies gave Melanie (Mother Hen) awooden souvenir "train" whistle shecould use to keep her charges on sched-ule — toot, toot! They later presentedMelanie and Peter MacGillivray with arestaurant gift certificate and enoughbabysitter money to let them get out for aquiet meal.

Overall, the Tenth Ship Control Sys-tems Symposium was highly successful.It was both interesting and exciting tolearn about the advancements in controltechnology from such a diverse group. Ifany one idea captured the mood of thesymposium, it might be Cdr MacGillivray'ssentiment that, "As far as we thought wewere going (with IMCS) ten years ago —

today, it doesn't seem as if we went farenough." »

Copies of the symposium proceedingsare available by contacting DMEE 7,NDHQ, Ottawa.—by Lt(N) D.J.Curran, DMEE 7-2, with Journal files.

CMIA 46th Annual Technical Conferenceand Canadian Shipbuilding & OffshoreExhibition — CSOE'94

This year marks the 50th anniversaryof the Canadian Maritime IndustriesAssociation, and in February the Asso-ciation celebrated with a first-rate techni-cal conference and exhibition at theOttawa Congress Centre. The occasionwas also used to introduce new CMIApresident Andre Lafond who takes overfrom J.Y. Clarke.

Don Wilson's presentation, "QualityManagement for the Marine Sector,"sparked a great deal of discussion amongdelegates. Wilson, chief executive of-ficer of the Canadian General StandardsBoard, delivered a hard-line message onthe benefits of quality management andthe importance of the ISO 9000 series ingovernment/industry relations. "Mostpeople think quality costs," Wilson said."It does, up front, but before too longquality actually pays and becomes aninvestment." The key to improvement inall sectors, he said, is the unequivocalacceptance of QM principles. "Break-through thinking is needed," he empha-sized.

Brian Keefe, co-ordinator for DND'sMarine Engineering Technician TrainingPlan at St. Lawrence College in Cornwall,ON, was on hand with a number of hisMETTP students. "For one day in theircollege career they've come to be part ofthe marine business," Keefe said.

Second-year METTP student ABRichard Cenerini, 25, of Logan Lake,

BC seemed typical of the motivated,young engineering technicians who werevisiting the CMIA conference. Cenerini,who will complete a third year at St.Lawrence College and a technical coursein Halifax before moving on to the fleet,was unsuccessful in his first bid to jointhe Canadian Forces right after highschool. He was eventually accepted intothe METTP as a third-year science stu-dent from Cariboo College in Kamloops."I'm enjoying the program," he said. "Ithink it's well worthwhile." Cenerinisaid he particularly enjoyed an informaltour through HMCS Toronto last sum-mer. A great believer in computer con-trols, he said he was impressed by theabsence of hand-operated controls in thepatrol frigate.

The number of exhibitors at CSOE'94was reportedly down from previousyears, a sign some said of the desperateeconomic climate the industry finds itselfin. Steven Rapley, the Ontario MarineManager for International Paints(Canada) Limited, said his company isbetter off than many others because ofthe navy work they have been able topick up. "If it wasn't for the frigate pro-gram and a few other things," he said,"we would be hurting."

Also represented at the exhibition wasthe Transportation Safety Board ofCanada. "We try to avoid repetition ofcasualties," said Eric Asselin, a nauticalspecialist for investigations. "We are

working for the public — to make themaware of the dangers and of safety(issues)."

The conference wrapped up with asplendid banquet at the Westin Hotel.Guest speaker Industry Minister JohnManley spoke strongly about the needfor Canada's industry to sell itselfabroad. "We have to get the word out topotential customers around the world,"he said, "that Canadians are innovators,that we're capable of competing with thebest, and that we mean business."

Manley cited this summer's plannedgovernment/industry-sponsored tour ofthe Far East by HMCS Toronto to pro-mote sales of advanced technology in themarine and other sectors. Referring tothe Canadian patrol frigate as "one of thecrowning achievements of Canada'smarine industry," Manley said the poten-tial sales payoff of the Far East tourcould reach $1 billion. Still, he cau-tioned, the government can only play asupport role in initiatives such as the FarEast deployment. The lead, he said, mustcome from the private sector. "We canno longer solve all of the problems onour own," he said.

CMIA president Andre Lafond re-sponded to the minister's comments inhis closing remarks. "We need the fed-eral government as a full partner in oureffort to succeed internationally," hesaid. «


: Maritime Eiwironmentalltectio

The membrane oil/water separatora better mousetrapArticle by LCdr Keith Dewar and Lt(N) Robert de Wit

The international maritime commu-nity has long recognized the discharge ofoily wastewater as a significant threat tothe marine environment. This concernhas manifested itself in various interna-tional agreements such as MARPOL 73/78, and in legislation such as the CanadaShipping Act. In Canada, the Act's strictrequirements form the basis of the Mari-time Command discharge policy forships fitted with oil/water separators.The discharge policy is quite specific:

• discharge must contain less thanfive parts per million (ppm) of oilin water in inland waters (zerodischarge in the Great Lakes);

• less than 15 ppm in internal watersand territorial seas; and

• less than 100 ppm beyond 12nautical miles.

As many marine engineers know, itcan be a challenge to meet these stan-dards consistently with the oil/waterseparator (OWS) technology availabletoday. What is more, the standards willbecome even more stringent in the nearfuture. In July 1998, for example, theCanada Shipping Act will be amended toreduce the allowable content of oil inwastewater from 100 ppm to 15 ppm inwaters beyond 12 nautical miles.

Fortunately, it appears that the tech-nology to meet naval requirements is onthe horizon. So-called ultrafiltration oil/water separators employing semiperme-able membranes are showing great prom-ise for use at sea. Naval engineers areprobably more familiar with a derivativeof these units — the reverse osmosisdesalinator.

Like most oil/water separators theSAREX units (Fig. 1) prevalent through-out the fleet are based on the simpleprinciple (known as Stokes Law) that oiland water do not mix. When a smallamount of oil is mixed with a largeramount of water it becomes suspended inthe form of small droplets. The differ-

ence in the specific gravities of oil andwater results in a buoyant force on theoil droplets which causes them to accel-erate rapidly upward until they reach aterminal velocity. (By the same reason-ing, water suspended in oil will godownward.)

Foregoing the development of therelevant equations, the design factors fora simple separator (a vertical cylindricaltank) based on Stokes Law are: the spe-cific gravities of the fluids, the kinematicviscosity of the continuous medium(water or oil), the flow rate, tank diam-eter and droplet diameter.

For example, if it were desired tobuild a simple separator to produce aneffluent flow of 19 litres per minute withless than 15 ppm oil content (assumed tobe MIL-9000H @ 20°C), the tank wouldhave to be 4.75 metres in diameter! Evenif the fluid were heated to 90°C to reduceits viscosity, the tank diameter wouldonly drop to three metres. Clearly, such adesign would be impractical for navaluse.

All current shipboard oil/water sepa-rators use a multiplier to make largerdroplets out of smaller droplets whichcan then rise more rapidly against theflow to the primary oil/water interface.Multipliers, which can be filters (such asin the SAREX), parallel plates, or mixedmedia, create additional interfaces wheredroplets can coalesce, normally by pro-viding surfaces which are alternately oil-attractive and water-repellent.

The United States Navy has experi-mented extensively with parallel platetechnology (Fig. 2). This technology wasattractive due to the potentially smallunit size offered and the lack of movingparts. Although high hopes were placedon applying this technology in our ownnavy's Maritime Environmental Protec-tion Project, it is unlikely that it willmeet the stringent requirements placedon oil/water separator technology in thefuture.

Real World Problems withStokes Law Separators

Despite the simple physics involvedwith gravity separation, the oil-contentalarms continue to sound on conven-tional oil/water separators. It turns outthat the Achilles' heel of these systems isthat they only remove droplets down to agiven size. If the distribution of dropletsize changes so that many droplets be-come too small to be caught by the fil-ters, the oil content of the effluent willincrease. Conditions that can decreasethe size of oil droplets are all too com-mon in the real world.

Emulsions (suspensions of very smalldroplet size) are easily created throughmechanical or chemical means. Me-chanically produced emulsions can bepartially avoided through design byavoiding turbulent flow or agitation.Large pipes and slow-turning, positivedisplacement pumps such as theMOYNO pumps used with the SAREXseparator are normally employed.

Chemically produced emulsions,where the average droplet size may beless than 0.1 microns, are much moredifficult to handle. Chemicals calledsurfactants actively break the oil downinto smaller droplets — the same processused by most detergents and cleaningsolvents. Studies conducted at NETE andelsewhere have shown that even smallamounts of AFFF fire-extinguishantintroduced to an oil/water separator cancause massive oil discharge.

It is perhaps easy to issue an edict thatstates that surfactant chemicals are not tofind their way into bilges. The reality isthat there are many legitimate uses forsuch products: gas-turbine detergentwashing, removing oil from deck platesand other surfaces for safety, and (facingfacts) Admiral's inspections. But untilbetter technology comes along, we havelittle choice but to try to minimize theentry of these chemicals into the bilges,


or to switch to detergents such asGAMLEN Clean-Break that have mini-mal effect on OWS performance.

Furthermore, bilge contaminants suchas paraffins, fungus, grit and a host ofothers frequently plug the coalescer

filters, thereby increasing maintenanceloads and cost. The disposal arrange-ments alone for these oil-soaked filtersrepresents a serious environmental as-pect of the whole problem of bilgewatertreatment. Clearly, a better mousetrap isneeded.

OVERBOARD

WATEH

ELECTRICAL CONTROLSIGNAL

Fig. 1. SAREX Oil/Water Separator Schematic

BACK-UP OILSENSOR MANUAL

OIL-DISCHARGELINE

ENGINE ROOM

TIES INTO EXISTINGOVERBOARD LINE

Membrane Oil/water Separators

The answer might very well lie withseparators that employ semipermeablemembranes. Rather than relying on grav-ity separation and coalescer multipliers,the pore size of a membrane oil/waterseparator is selected to be impermeableto oil. The semipermeable membranesnow used in reverse osmosis desalina-tors, for instance, are capable of filteringout particles of very small size indeed —somet

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