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Alternatives and scenarios for hydrodynamic improvement on existing vessels hull, propeller and rudder
VICUS DESARROLLOS TECNOLÓGICOS S.L.
VIGO
1www.vicusdt.com
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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.
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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
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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.
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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
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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.
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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.
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Knowledge first! Getting the data.
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Hull. The resistance equation
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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
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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%.
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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 .
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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.
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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
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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.
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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.
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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
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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.
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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
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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
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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.
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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
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Propeller. Key issues.
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
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Propeller. Key issues.
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 .
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Propeller. Key issues.
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.
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Propeller. Key issues.
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
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Propeller. Key issues.
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%.
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Propeller. Key issues.
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
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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
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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
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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.
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Rudder. The unknown one.
- Wake adapted rudders are normally better for open propellers.
- Better high load
- Improvement on the maneuverability performance of the ship.
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Rudder. The unknown one.
- New blade or modify the existing one.
- Streamlined hub cap connecting propeller and bulb
- 4-9% savings.
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THANK YOU !
Vicus Desarrollos Tecnológicos S.L.Av. Beiramar 77-1º
36202 – VIGO – SPAIN
www.vicusdt.com
T: +34 886113547
Adrián Sarasquete
T: +34 629384214