alternatives and scenarios for hydrodynamic...

Alternatives and scenarios for hydrodynamic improvement on existing vessels hull, propeller and rudder

VICUS DESARROLLOS TECNOLÓGICOS S.L.

VIGO

1www.vicusdt.com

www.vicusdt.com 2

THE COMPANY

VICUSdt is specialized in research and development in the shipbuilding and energyindustries. We are especially skilled in the simulation of all kinds of fluid dynamicsprocesses and structural analysis, including fluid-structure interaction, heat transfer,structural and vibration analysis.

In the offshore engineering, VICUSdt is the best partner for hydrodynamics andsimulation related challenges, from concept to sea trials.

www.vicusdt.comwww.vicusdt.com 3

MAIN TOPICS

A. Fishing sector situation and philosophy for energy saving. Some ideas.B. The energy equation.C. Big or small? Scale effects on energy saving strategy depending on ship sizeD. Knowledge first! Getting the data.E. Hull. The resistance equationF. Propeller. The propulsion equation.G. Rudder. The unknown one.H. Conclusions


Fishing sector situation and philosophy for

energy saving. Some ideas.

CHALLENGES• Fuel price • Fishing grounds exhausted• Low profits• The owner don’t see a bright future, just tomorrow.• No clear energy efficiency policy.• Fishing effort indicators: engine power and GT.

SOME IDEAS• Quotas for more efficient ships• Best practices for ship design• Liters / Kg of fish• Investment guarantee for more efficient ships.• Efficiency certification with benefits.


Energy equation

PB = RT x Vs / ( ETAo x ETAh x ETArr x ETAm)

RT: ResistanceVs: Speed

ETAo: Propeller open water efficiencyETAh: Hull efficiency

ETArr: Propeller rotative-relative efficiencyETAm: mechanical efficiency


Big or small? Scale effects on energy saving

strategy depending on ship size

COASTAL TRAWLER

LENGTH 12 32 m

CONSUMPTION/DAY 95 3250 l

FISHING DAYS / YEAR 200 250 days

CREW 3 12

TOTAL FUEL / YEAR 19000 812500 l

Liters / crew 6333 67708 l/crew

RATIO 10,7

Other scale effects: energy audit, project, landside structure, product availability.


Knowledge first! Getting the data.

- Existing on board records.

- Engine room log books.

- Dedicated monitoring systems.

- Sea trials.

- Real performance measurements.

- Temporary installation of recording systems.


Knowledge first! Getting the data.


Hull. The resistance equation


Hull. Paint

Hull paints effect is produced in Frictional added resistance

A smoother surface will suffer less tangent stresses which are the cause of the

frictional resistance in a real fluid.

In a tuna seiner with a Fn=0.11 (for instance), Friction represents almost 40% of

total resistance whereas at higher Fn number, i.e. 0.29, Friction is reduced to

27%.

Realistic roughness values for a new ship in water is 150 microns.

The use of Fouling release coatings helps reducing the slope of the curve (Ct

increase/Years).

Friction is more important at low speeds compared to wave resistance.

0,00%

1,00%

2,00%

3,00%

4,00%

5,00%

6,00%

0 2 4 6 8 10 12

Incr

ease

Years

Ct increase


Hull. Bow

Bulbous bow Design

There are many types of bulbous Bow depending on:

- Length (Lb)

- Nose height (or distance from the free Surface) (Hb)

- Section (Ab) (Delta, Oval, Nabla types)

A good bulbous bow design comes as a result of a reduction in Wave formation

coefficient,

- The forward system of waves is modified and its interaction with the waves

generated at the aft part, too.

- Lb, Hb and Ab affect the way free Surface is modified. It starts to be

significant at Fn above 0.2.

- Maximum savings are obtained for one design condition, while averaging for

different load conditions (typical in Tuna Seiners) lead to more discrete

savings. Easily, resistance reduction for a single condition can overcome 15%.


Hull. Bow

Bulbous bow Design

Main driver for this retrofit in fishing vessels is not always fuel Consumption

reduction but performance increase for Fish catching (top speed) and ROI,

due to extra incomes is more difficult to estimate.

ROI expected, considering only high speed profile scenarios, is around 3-5

years .


Hull. Bow

Bulbous bow Production issues

Docking period for conversion need to be included in ROI estimation.

Steel Work is a bit more expensive due to complexity of shape.

Normally, bow tunnel thruster room must be rellocated.

Ballast system must be modified accordingly (as bow is a ballast tank, indeed).

Normally, authorities do not require to ship owner a change in GTs.


Hull. Lengthening

Lengthening

Froude number is basically a ship speed to length ratio and it accounts for the

relationship between gravitational and inertial effects over a fluid, it means,

free surface related issues.𝑣

𝑔𝐿𝑠ℎ𝑖𝑝

Ct as a f(Fn)

Ct

Fn

DISPLACEMENT


Hull. Lengthening

Lengthening

Increasing length means reducing Fn, and thus Ct, so Resistance is reduced. In

which amount? It will depend on each Ct-Fn curve and slope in the region of

study.

Savings from 2 to 5% are reasonable, keeping in mind that target scenario is mid

to high speed conditions.

Technical and political issues. Return of investment with increased hold

Considerable docking period.

GTs changed.

Most of ship systems affected (piping, cable trays, etc)

Holds capacity increased. For one of our customers such

conversion meant 5% extra capacity with reduced consumption.


Hull. Stern

Stern design, how it can be improved based on your mean operational speed

According to most frequent load conditions and averaged time in them, a dry

transom can be designed for minimum drag.

Nevertheless this must be done together with the bulbous bow design and best

trim selection.

In this case ROI expected is similar to a merchant vessel (2-3 years) provided that

the physics beneath this improvement is not only Froude (wave coefficient)

dependant phenomena but dependant on viscous pressure phenomena as well.


Hull. Stern wedge. Trim

Stern wedge, trim issues

Most of ships trim excessively by the aft and most of cases it is not required.

Just common thinking that the more the propeller inmersion the better the

ship performance. And that is true, but until certain extent.

Trimming by the bow, sailing evel keel or reducing aft draft helps reducing

resistance at high speeds.

In a single speed and loading condition (for high speed cases) resistance

differences between aft trim and fwd trim can be as high as 25%.

Trim

Res

ista

nce

By bow


Hull. Stern wedge. Trim

Stern wedge, trim issues

Where the savings come from?

1. Less transom inmersion means less drag.

2. Bulbous bow interacts in a more efficient wave with free surface.

3. Stern wedges helps changing trim but it also helps increasing pressure in

propeller area thus improving propeller performance.


Hull. Appendages

Bilge keels, sonar dome, tunnel thrusters

Appendages account for 10-15% of the overall ship resistance.

Aligned appendages help reducing resistance around 1-2%, which in the

overall are below 0.5%. This is not a significant saving but neither the

cost so it pays off .

MISSALIGNED

ALIGNED


Propeller. The propulsion equation.

PB = RT x Vs / ( ETAo x ETAh x ETArr x ETAm)RT: ResistanceVs: Speed

ETAo: Propeller open water efficiency. Diameter - rpm

ETAh: Hull efficiency. Wake- thrust deduction.

ETArr: Propeller rotative-relative efficiency. Wake adapted.

ETAm: mechanical efficiency. Not much to do here.

w

th

1

1


Propeller. Wake adapted design.

- Advanced CFD tools - Best technology available at reasonable prices- Old designs were ok at that time- Better knowledge of the flow- 5% improvements easily.


Propeller. Key issues.

Adapt the design to the real operational profile. Now you know it! They had no idea when the ship was built 20 years ago, now you know what your average power is and speed on each condition, so no need to guess.

41%

25%

25%

5% 4%

Perfil tipo % consumos totales propulsión

Navegación

Largando

Virando

Parado

Chicoteando

0%

10%

20%

30%

40%

50%

60%

% C

arga

MAIN ENGINE LOAD

215220225230235240245250255

Co

ns.

esp

. (g/

kWh

)

ESPECIFIC FUEL CONSUMPTION MAIN ENGINE



Don’t size for full power. Now that you know the real power use, the designer should go for a smart design avoiding conservative sizing.

EXAMPLE: tuna seiner designed for 18.5 knots top speed instead of 17 knots means

1.6% EFFICIENCY LOST. Talking about money, we can say some 20 € / h at this speed range.

0%

10%

20%

30%

40%

50%

60%

% C

arga

MAIN ENGINE LOAD



Investigate the flow. Calculate the wake so you avoid too much margin on it.

Recommended to do a complete CFD study of hull and current propeller before buying the new propeller / CP blades .



Diameter: is connected with the rotational speed of the propulsion system. If you are able to increase diameter it is needed to reduce rpm accordingly. This is only possible when you change engine or reduction gear, but is worth analyzing it connected with the CFD study, a favorable wake and a small change in diameter and speed can lead to huge savings.

A ROUGH FIGURE FOR A DIAMETER CHANGE ASSOCIATED WITH DIFFERENT RPM AND BLADE DESIGN CAN BE 3% MORE EFFICIENT PROPELLER FOR AN INCREASE OF 5 % ON

DIAMETER.



Rotational speed: the lower the better, but in strict connection with the diameter.

Thrust deduction: another player into the hull efficiency equation.- The lower the better. - Moving your propeller aftwards,

especially for ducted. - Wake effect.

T

RTt

Effy.↑ - D ↑ - N ↓

0,6 0,7 0,8 0,9 1 1,1 1,2 1,3

Prop effy 0,551 0,579 0,591 0,594 0,592 0,586 0,58 0,573

J 0,433 0,478 0,522 0,566 0,609 0,65 0,69 0,728

D 6,42 5,81 5,32 4,91 4,56 4,27 4,03 3,82

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

0,45

0,5

0,55

0,6

0,65

D (

m)

Pro

p.

eff

y

P/D

Optimal Propeller DiameterSubject: L0XXX SHIP TYPE AND SHIPYARD

CSR condition

Prop effy

J

D



Pitch: -Mean hydrodynamic pitch. Load-Pitch distribution. Optimize for effciiency / cavitation trade off.

UNLOADING THE TIP BY 30% CAN LEAD TO A EFFICIENCY DECREASE BETWEEN 2-3%.



EAR: blade area is needed to deal with the low pressure on the blade surface mainly for cavitation reasons; higher blade area means higher friction, approximately 1% efficiency lost for a 0.1 increase in blade area ratio.

TAKE CARE WITH KELLER !

Get paid for the old propeller: The old propeller / CP blades can be kept as spare, but it is recommended to agree with the supplier of the new propeller so the price can be reduced in exchange of this nice scrap bronze material, the invoice can be reduced significantly, you will be surprised. For a large propeller it can be a 35 % reduction on price.

KDPP

TZ

A

A

VoO

E

2

3.03.1


CP Propeller considerations

- Good option due to its better

maneuvering response.

- Advised only in combination with a PTO

on the reduction gear driving a shaft

generator, only when you have large

electrical power demand,

- Can increase the fuel consumption by

running at constant speed.

- Combinator mode reduces fuel

consumption dramatically

0

500

1000

1500

2000

2500

0 5 10 15

Po

ten

cia

[kW

]

Velocidad [kN]

Potencia_velocidad (media)

0

500

1000

1500

2000

2500

3000

0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0 16,0

P [

kW]

Velocidad [kn]

MOTORES PRINCIPALES

0,0

100,0

200,0

300,0

400,0

500,0

0 500 1000 1500

g/kW

h

P [kW]

CONSUMO ESPECÍFICO MOTORES PRINCIPALES


Blade replacement vs complete system exchange

- Blade foot geometry

- CP hub sizing

- Control unit adjustment

- Improve cavitation and

vibration performance

- Savings from 5% to 10%

- ROI 1-3 years


Propeller. Shafting. Practical issues

Torsional: check due to variations on propeller inertia and entrained water Alignment: Worth checking, cause many failures.Gearbox: OD box when moving from FP to CPShaft CP to FP: you can recycle a CP shaft.Stern tube: normally not modified.


Rudder. The unknown one.

- Wake adapted rudders are normally better for open propellers.

- Better high load

- Improvement on the maneuverability performance of the ship.


Rudder. The unknown one.

- New blade or modify the existing one.

- Streamlined hub cap connecting propeller and bulb

- 4-9% savings.


THANK YOU !

Vicus Desarrollos Tecnológicos S.L.Av. Beiramar 77-1º

36202 – VIGO – SPAIN

www.vicusdt.com

[email protected]

T: +34 886113547

Adrián Sarasquete

T: +34 629384214

[email protected]

alternatives and scenarios for hydrodynamic...

Documents