Propeller / Hull Status Report 2009

8/9/2019 Propeller / Hull Status Report 2009

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STATUS REPORTJUNE 2009STORMFGELN AB (PUBL)

REPORT AND CONCLUSIONS FROMINTERIM REPORT STORMFGELNPROPULSION SYSTEMTRANSIENT DYNAMIC ANALYSIS


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STATUS REPORT, JUNE 2009STORMFGELN AB (PUBL)

CONTENTS

Summary 3

Verification analyses that arecrucial for the Stormfgeln 5

Positive results from strengthand lifetime analyses 6

The Stormfgeln Driving UnitTransient Dynamic Analysisproject 7

Competitive efficiency 8

The CFD-analysis of propulsiveefficiency 15

Further verifications planned

in the next stage 16

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STATUS REPORT, JUNE 2009STORMFGELN AB (PUBL)

SUMMARY

Several interim reports from the ongoing verication analyses of the

Stormfgeln performance have provided the company with a clearerimage of the competitiveness of its products and the segments of themarine industry in which the products have their greatest commer-cial potential. One of the conclusions of the interim reports is that theStormfgeln concept is probably suitable for commercial marine trans-port that needs to operate at speeds that exceed 30 knots. This covers,for example, ferry trafc, paramilitary applications and goods transportthat aims to compete with road transport.

The Stormfgeln concept has several clear advantages over the main

technologies that are currently used for this type of marine trafc, suchas traditional propeller systems with straight shafts, water jet technol-ogy, and traditional surfacepiercing propellers. The advantages areeconomic, environmental and performance-related. Work will now con-tinue such that it will be possible during the autumn to conrm the ad-vantages of the Stormfgeln over conventional systems. Potential OEMpartners will be courted in parallel with this, informing them of the newand probably crucial facts that are presented in the interim reports.

The company CTD Marine, Lennart Berghult, in Switzerland (where CTD isan abbreviation for computational turbomachinery design) has determined the

eciency of the Stormfgeln propeller, under commission from Stormfgeln. The calculations have been carried out using computational uid dynamics(CFD) analysis, and they have formed the basis for ongoing strength calcula-tions for the propulsor and its propeller blades and mechanism. The latter cal-culations are being carried out by IMES, the Institute of Mechanical Systemsat the Zrich University of Applied Sciences, and consist of two parts staticand dynamic analysis. The static analysis is now complete. The static analysis,supplemented by fatigue analysis, has allowed IMES to conclude in the interimreport that the propulsion of the Stormfgeln will satisfy the demands for life-time placed on it.

CTD Marine has calculated that the eciency of the Stormfgeln propeller is62%, which agrees well with previous assumptions from eld trials of the proto-type Stormfgeln. The analyses suggest that there is a relatively large potentialfor improvement, and CTD Marine believes that the eciency of the propel-ler can be increased to over 70% by optimising the blades. This gure is in line

with that achieved by other surface-piercing propellers. An eciency of 70%will mean that the Stormfgeln is in line with water-jet technology, the optimalperformance of which is calculated to be approximately 70% at its design speed.It should be pointed out in this context that the optimised speed for water-jetboats is normally set to lie between 30 and 40 knots. There are, furthermore, in-

dications that the eciency of water-jet technology tends to decrease at speedsabove 40 knots.

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The Stormfgeln concept has major advantages over both water-jet technologyand traditional surface-piercing propellers. The water-jet suers from a low or

very low eciency at all speeds apart from just the designed optimal speed, andthis means that the fuel costs are relatively high and thus also the impact on theenvironment. Further, water-jet technology is sensitive to weight, and normallyneeds extensive and expensive maintenance. The expense arises from, amongother factors, cavitation problems, which lead to damaging erosion when theload deviates from what is suitable.

Traditional surface-piercing propellers experience problems in reaching theplaning condition, and there is a risk that they will loose the planing condition atspeeds around the planing threshold. These vessels also suer from poor reverse

thrust properties. These are the Achilles heels of conventional surface-piercingtechnology, and the principal reasons that it cannot gain territory from water-jet technology. The Stormfgeln solves all of these disadvantages. The pitchablepropeller blades of the Stormfgeln are of major signicance for its unique per-formance. They are used to obtain rear thrust during reversing, at the transi-tion to the planing condition, and when planing at dierent speeds, in order toachieve an optimal ratio of engine rate of revolution to propeller rate of revolu-tion. It is worth noting in this context that the international patent for whichStormfgeln has applied relating to an adjustable surface-piercing propeller withfully ventilating blades was published on 2 April 2009, which means that the pat-ent application has been approved.

The pulsating forces that arise naturally when the propeller blades continuouslypass from air to water and from water to air are relatively low in the Stormfgelnsystem, and thus the risks that the propeller blades are damaged or broken arealso low. This is otherwise a further weakness of the traditional surface-piercingpropeller technology.

One of the critical advantages of the Stormfgeln concept in comparison withcompeting systems is the rotation of its propeller blades. This function makesit possible to achieve the lowest possible fuel consumption in all speed regions,independently of how the vessel is loaded. The adjustment of the ratio of therate of revolution of the engine to that of the propeller can be carried out takinginto consideration the eciency of the propeller and the specic fuel consump-tion of the engine. Such an adjustment is not possible on installations that use

water-jet units or propellers with xed blades. These can be optimised solely forone optimal speed at any given load.

A number of verication analyses and calculations remain to be done, in orderto optimise the propulsion of the Stormfgeln for increased strength and e-ciency. We hope that it will be possible to complete these during the summer andautumn. At the same time, we are seeking deeper contact with potential OEM

partners and other interested parties, who initially can contribute to the nanc-ing of the remaining planned analyses.

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VERIFICATION ANALYSES THAT ARE CRUCIAL FOR THE STORMFGELN

The measurements of fuel consumption that were carried out in October 2008showed that the Stormfgeln concept is probably commercially interesting forseveral segments within the marine industry. If a system, however, is to be usedfor commercial marine transport, its strength, lifetime and maintenance require-ments are critical. To put it another way: there are many good ideas that have thepotential to provide both environmental and economic advantages, but few ofthem can prove that they are viable in the long run, and in daily commercial use.

The verication analyses that Stormfgeln started at the end of 2008, and whichwere initiated by several potential OEM partners, are thus crucial for the futureof the Stormfgeln and the possibilities for the company to place its products on

the market. The analyses consist of ve parts:1. the propulsive eciency of the Stormfgeln propeller2. static calculations of strength and lifetime of the propeller blades and

mechanism of the propulsor3. dynamic calculations of strength and lifetime of the propeller blades and

mechanism of the propulsor4. optimisation analyses of propeller blades5. comparative analyses of competing propulsions and hulls.

Of the ve parts listed above, the eciency has been determined and the staticanalyses have been carried out. The results from these were presented as an in-terim report on 26 May 2009 at IMES, the Institute of Mechanical Systems atthe Zrich University of Applied Sciences, which is responsible for the analysesof strength and lifetime. The eciency has been determined by CTD Marine,Lennart Berghult Computational Turbomachinery Design, Switzerland.

The conclusions of the interim report allow us to conclude that the propulsionof the Stormfgeln will satisfy the demands for lifetime required for commercialmarine transport. The Stormfgeln has thus passed a signicant obstacle on thepathway to commercialisation, and has been able to overcome an obstacle at

which many good ideas fall. Further, the eciency that has been determined al-

lows us to see more clearly and to conrm the segments of the marine industryin which the Stormfgeln will have the greatest competitivity.

The performance of the

Stormfgeln propulsor and its

propeller blades and mechanism

has been veried in a number

of analyses, presented on

26 May 2009.

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POSITIVE RESULTS FROM STRENGTH AND LIFETIME ANALYSES

The commission undertaken by IMES, the Institute of Mechanical Systems atthe Zrich University of Applied Sciences, is divided into several parts, as de-scribed above, all of which are included in the project Stormfgeln Driving Unit

Transient Dynamic Analysis. The rst stage carried out by IMES has been sta-tic strength and lifetime calculations for the propeller blades of the Stormfgelnand the mechanism of its propulsor.

IMES has built a 3D model of the complete Stormfgeln propulsor, includingthe propeller blades, the complete mechanism that allows the blades to rotate,and those parts of the propulsor that transfer power from the engines. ProfessorDr. Jrg Meier at IMES has led the work. His conclusion of the results from thestatic analyses includes the following:

We have carried out several analyses as a part of the project Stormfgeln Driving Unit

Transient Dynamic Analysis. Frequency and static stress analyses of the blades and mecha-nism under dynamic load show that there are no critical weaknesses that cannot be solvedby minor design and/or material improvements. Based on the facts from these analyses anda complementary fatigue analysis, our conclusion is that the Stormfgeln propulsion sys-tem will meet the lifetime requirements. With the results from our next step a dynamic

analysis we will be able to determine the exact lifetime and make suggestions concerningdetailed design and material improvements.

A complete 3D model of the

Stormfgeln propulsor has been

created within the framework

of Stormfgeln Driving Unit

Transient Dynamic Analysis,

including the propeller blades

and the complete mecha-

nism by which the

blades can be

rotated.

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The analyses are based on a 3D model of the complete Storm-fgeln propulsor, including the propeller blades, the completemechanism that allows the blades to rotate, and those parts ofthe propulsor that transfer power from the engines. Rotation ofthe blades is used in order to reach the planing condition rapidlyand remain in it, and while reversing under reverse thrust. Thelatter situation involves turning the blades such that the propul-sive force of the propeller changes direction from forwards toreverse.

CTD Marine, Computational Turbomachinery Design, has used acomputational uid dynamics calculation to determine the ef-ciency of the propeller. The thrust and the torque have been cal-culated with the aid of the calculated blade forces, and these inturn give the efciency. IMES has subjected the design to these

loads in a computer model, and examined the tensions that it

creates. Static calculations of the oscillations and the stress thatthe blades and other parts of the construction experience have

been carried out in a rst stage in order to calculate the strength

and lifetime. The calculations are based on the maximal load,which from the point of view of strength is a worstcase scena-rio, in which the force has been a maximum. In this case, thisgives the efciency of the propeller at 58 knots.

The forces applied in the analyses have been static and notvarying. The next stage in the work will involve dynamic analy-ses. To put it simply, this means that the propulsor is rotatedand subjected to varying loads, something that increases thetensions it experiences. The experience gained from the staticanalyses allows us to predict with reasonably high condence

the magnitude of the increase, and we can therefore already as-sess the strength of the Stormfgeln propulsor. The main aim ofthe dynamic analyses is to produce the information required tooptimise the design at a detailed level and to specify the values

of lifetime for all parts of the construction.

The loads have been applied as static loads in the computer model analy-ses referred to by Professor Meier above. The next stage in the work is

constituted by dynamic analyses, in which the propulsor is rotatedwhile being subjected to varying loads. In simple terms, this means

that the frequency and static stress that arise when the parts arein motion (which increases the tensions that aect the ttings)are examined. The main aim of the dynamic analyses is to ob-tain the background information required to optimise the de-

sign.

Lennart Berghult at CTD Marine has stated that it has been established thatthe Stormfgeln possesses a robust system with respect to a long lifetime.

The lifetime analyses carried out by the university are compatible with the standardfor lifetime calculations for commercial and military systems. The results are unambigu-ous, and are of major signicance in several respects. They indicate, for example, that themaintenance cycles of the Stormfgeln are more advantageous than the cycles that can beachieved by currently available water-jet applications. The Stormfgeln cycles are equiva-

lent to those used by robust conventional propeller systems used in vessels.

Stormfgeln has developed contacts with several potential OEM partners. Dis-cussions with these have come to something of a standstill while waiting for

the results of the strength and lifetime ana-lyses. A positive result from these will prob-ably determine the result of these discus-sions. Stormfgeln has previously intendedto present the results once the study has

been completed. The conclusions reached by IMESand CTD Marine, however, are so clear and unambiguous

that the company can proceed with the discussions now.

THE STORMFGELN DRIVING UNIT TRANSIENT DYNAMIC ANALYSIS

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COMPETITIVE EFFICIENCY

The propulsive eciency (the ratio between the power supplied and the powerdelivered) of the Stormfgeln has been calculated, and used as a basis for theanalyses of strength and lifetime. The eciency that the Stormfgeln currentlyhas and the potential optimisation of the blades have also given valuable infor-mation about the performance of the Stormfgeln in comparison with compet-

ing systems, and thus also concerning the segments in which the concept of thecompany will be most interesting.

CTD Marine, Lennart Berghult Computational Turbomachinery Design inZrich, has used parameters in the form of speed, rate of propeller revolution,blade design and blade angle to determine the propulsive eciency of the Storm-fgeln, by computational uid dynamics. CTD Marine has used the parametersof only one particular condition, and calculated the eciency at this condition:the loads experienced by the propulsion at maximal load, which occurs at its topspeed of 58 knots. The eciency at this speed is 62%.

This means that it is not possible to plot the graph of propulsive eciency atvarious speeds. CTD Marine, however, has drawn up a probable graph of thepropulsive eciency of the Stormfgeln, based on the values that were measuredduring the measurement of fuel consumption. An important fact on which this

graph is based is that the fuel consumption of the prototype is essentially con-stant in the range of speed from 22 to 58 knots (where it is 4.1 litres per nauticalmile).


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The CFD analysis shows that the propeller blades of the Stormfgeln have apotential for improvement (see the box on Page 15 for details). It has been cal-culated that it will be possible to improve the eciency from its current 62% toover 70%. The latter value corresponds to the eciency of traditional surface-piercing propellers. CTD Marine is of the opinion that it will be possible for theStormfgeln to reach this value, based on the optimisation potential revealed bythe CFD analysis, and based on the observation that the propeller blades of theStormfgeln are the result of assumptions made during the design process and in the

absence of appropriate design tools.

An optimal graph of the propulsive eciency of the Stormfgeln shows thatthe eciency is 58-63% at 10 knots and 72-75% at 60 knots. It is, however, veryimportant to point out that the graph is based on assumptions. The eciencybelow 15-20 knots is particularly uncertain. A CFD analysis based on optimisedblades and the eciency at several speeds are required in order to determine amore exact calculated curve. The verication calculations are included in analy-ses planned for the future (Part 4 of the analysis programme).

The optimal graph for the propulsive eciency of the Stormfgeln allows anumber of interesting comparisons to be made with competing systems. Thesein turn allow us to determine which segments are commercially interesting forthe Stormfgeln concept.

The comparisons presented below relate to the propulsive eciency of commonpropeller systems. The comparisons do not take the possibility of optimisingthe fuel consumption at dierent speeds into account. This possibility is a majorcompetitive advantage of the Stormfgeln concept.

It is possible to turn the blades of the Stormfgeln propeller to a position atwhich the best eciency is achieved at all speeds. Only limited power is with-drawn from the engines when driving at a relatively low speed, such as 30 knots.

The engines have their lowest specic fuel consumption at a specic rate ofrevolution, for this level of power. It is possible to adjust the engine rate of revo-

lution when the blades are rotated. The ideal rates of revolution of the enginesand the propeller, however, dier. It is therefore necessary to compromise be-

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Vessel Speed

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t

The graph to the right shows

the assumed propulsive co-

ecient of the Stormfgeln.

CTD Marine has based its

assumptions on the eciency

determined at 58 knots with

the current design of the

propeller blades in combination

with a probable potential for

optimisation.

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tween the ideal values for the engine and the propeller in order to obtain optimallow fuel consumption.

The Stormfgeln makes it possible to set this optimal compromise, and in thisway obtain the optimal low fuel consumption, independently of how the vesselis loaded. Such an adjustment is not possible on installations that use water-jetunits or propellers with xed blades (known as xed pitch propellers). Thesesystems force the user to accept the parameters achieved at any one speed, andthe rate of revolution is determined by the current torque developed by the

propeller. This means, in turn, that it is only possible to optimise the propellerfor one speed. It is not possible to inuence the fuel consumption at any otherspeed.

The Stormfgeln was run at

58 knots during the electronic

measurements of fuel consump-

tion in October 2008, with short

spikes at 59 knots.

The consumption lay constant

in the range of speeds 22-58 knots

at approximately 4.1 litres per

nautical mile.

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A comparison of the Stormfgeln with conventional propellers:COMMERCIALLY INTERESTING AT SPEEDS ABOVE 30 KNOTS

The graph shows that a conventional propeller has a higher eciency at speedsbelow 25 knots. The eciency drops dramatically at speeds above 30 knots. Itcan be added that the appendage drag from shafts and shaft mountings increasesdramatically at higher speeds, and it can be noted that the Stormfgeln surface-piercing propulsor does not experience appendage drag.

The comparison shows that the Stormfgeln should be interesting for segmentsthat operate above 30 knots. This is the case for passenger ferries, for example,

and for military and paramilitary applications such as Coast Guard vessels. TheStormfgeln may also be interesting for pure transport vessels such as supplyboats for merchant vessels and oilrigs. It may also be interesting for goods trans-port with a high fuel eciency that attempts to compete with road transport.

The eciency in this comparison concerns also the propulsive force producedby the propeller. Ocke Mannerfelt Design concluded in November 2008, basedon results from measurements of the fuel consumption of the prototype Storm-fgeln, that the propulsion and hull of the Stormfgeln give an eciency thatis 10% higher than the most modern drive technology in combination with a

well designed ventilated stepped hull, and 35% higher than conventional straightdrive shaft technology. The comparison shows that the Stormfgeln concept isrobust and lies in line with the latest technology. This comparison, however, israther like comparing apples and oranges. The most modern propulsion techno-logy has not been designed for large vessels, while an installation with a straightdrive shaft is not normally used for speeds above 30 knots.

It is more interesting to compare the Stormfgeln concept with the systems thatare normally used for large vessels and for vessels that operate in the speed range

above 30 knots. Thus, the interest-ing comparisons are those with other

surface-piercing propellers and withwater-jet technology.

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ofcient

The Misago boat (where

Misago is the Japanese

word for Stormfgeln) is a

high-speed motor yacht that

IF Design has drawn, with

the propulsion and hull of the

Stormfgeln.

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The diagram shows a compa-

rison between the assumed

curve of the Stormfgeln

propulsive coecient (red) and

the curve of a conventional

underwater propeller (yellow).

The latter curve has been

published by the ITTC (The

International Towing Tank

Conference), with reference to

Black et al. 2006. The ITTC

is an international association

responsible for predicting the

hydrodynamic properties of

marine installations by physi-

cal and numerical modelling.


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Stormfgeln compared with a traditional surface-piercing propeller:THE SAME OR BETTER EFFICIENCY WITHOUT ANY ACHILLES HEELS

The dierence between the expected propulsive eciency of the Stormfgelnand that of a traditional surface-piercing propeller is not dramatic. It is, however,a fact that the eciency of the Stormfgeln is higher in the speed range up to 40knots, as a result of the possibility of turning the blades of the Stormfgeln pro-peller. The largest dierence between the two systems is that the Stormfgelnsolves the Achilles heels that plague traditional surface-piercing technology. severe diculty in attaining the planing condition problems with driving the boat at a constant speed at speeds close to

the planing threshold, the boat readily falls out of the planing condition poor reversing ability.

Thus, the pitchable propeller blades are one of the strengths of the Stormfgelnconcept. They can be used: when reversing, with reverse thrust to achieve high manoeuvrability at the transition to the planing condition, by adjusting the ratio of the rate of

revolution of the engine to that of the propeller (the Stormfgeln requiresonly a few boat lengths to achieve the planing condition), and

when planing at dierent speeds, in order to adjust the ratio of the rate ofrevolution of the engine to that of the propeller.

The CFD analyses also show that the pulsating forces on the propeller blades ofthe Stormfgeln are relatively low. These forces, which arise when the propellerblades continuously pass from air to water and from water to air, can cause thepropeller blades to become damaged or broken and are a further weakness of thetraditional surface-piercing propeller technology.

The ability of the Stormfgeln to reach the planing condition, to retain the plan-ing condition at speeds that lie close to the threshold speed, the high manoeu-

vrability when reversing and the relatively low pulsating forces on the propeller

blades all ensure that the Stormfgeln concept appears very advantageous whencompared with the traditional surface-piercing propeller technology.





the curve of a conventional

surface-piercing propeller

(green).


published by ITTC (The


Conference), which is an inter-

national association responsible

for predicting the hydrody-

namic properties of marine

installations by physical and

numerical modelling.

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10 20 30 40 50 60 Vessel Speed

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ofcient

A sequence from the CFD analysis

of the propulsor of the Stormfgeln,

used to determine its propulsivecoecient.


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The Stormfgeln compared with water-jet technology:SUPERIOR EFFICIENCY IN MOST SPEED RANGESAND LOWER MAINTENANCE COSTS

The propulsive eciency of a water-jet can be optimised by dimensioning theintake for one optimised speed. The propulsive eciency is high at this optimalspeed. The eciency is lower at all other speeds both below and above the op-timising speed and this gives relatively high fuel costs in these sequences, andthus also an increased impact on the environment.

It should be pointed out in this context that the optimised speed for water-jet

boats is normally set to lie between 30 and 40 knots. There are, furthermore, in-dications that the eciency of water-jet technology tends to decrease at speedsabove 40 knots. The curve presented by the Internal Towing Tank Conferencepresented above is based on theory, allowing a water-jet to be optimised for thetop speed of the Stormfgeln, around 60 knots. This comparison between theStormfgeln concept and water-jet technology is based on this theoretical point.

The Stormfgeln has considerable advantages over water-jet technology. The ef-ciency of the Stormfgeln is higher in all speed segments, with the exception ofthe speed that is optimal for the water-jet.

A water-jet diers from traditional surface-piercing propellers and the conceptof the Stormfgeln in that it has a high eciency, and thus also a good fueleconomy, only at its optimal speed. Despite this, water-jet technology has todaya strong position within the ferry segment and as an application for military andparamilitary boats. The Achilles heels of the traditional surface-piercing propel-

ler technology (described on Page 12) area crucial factor in the general conclu-

sion that water-jet technology is abetter alternative.

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OverallPropulsiveCo

fcient

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the curve of a water-jet system(blue).


published by the ITTC (The


Conference), with reference to

Black et al. 2006. The ITTC

is an international association

responsible for predicting the

hydrodynamic properties of

marine installations by physi-cal and numerical modelling.

The original propeller blades

of the Stormfgeln have been

modied in several stages

according to a method based

on analyses of measured data,

basic calculations, and trial

and error. The propeller blades

have not yet reached their

optimal design, in their current

shape and size. CFD analyses

have indicated that there

remains potential for

improvement.


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Water-jet technology, however, also has weaknesses. The propulsor of the Stormfgeln is not sensitive to cavitation, but this can

constitute a major problem for water-jet technology, aecting its performanceand its potential need for maintenance.

The design of a water-jet is adapted during its construction to the loads thatwill inuence the system at an optimal speed, and to the need to avoid cavita -tion at this speed. Cavitation can have disastrous eects both on the ecie-cy and lifetime of the system. The eect on lifetime arises since the cavitation

in a water-jet causes harmful erosion. To put it simply: this means that the maintenance requirements of water-jet

technology are normally sensitive to speeds and loads that do not correspondto the optimal speed and calculated load. This may constitute, for example, anexpensive limitation for shipping companies, since it means that they cannotoptimise the load (made up of goods and/or passengers). The water-jet dis-turbs stones and gravel from the water bottom, and this has a negative impactnot only on the environment but also on the costs of maintenance and ofinactive periods.

Further, the hull of a water-jet vessel must be designed such that it avoids

mixing air into the water owing around the water-jet unit. Thus, for exam-ple, a modern high-eciency hull with a ventilated stepped design is highlyunsuitable for use with water-jet technology. The propulsor of the Stormfgelndoes not suer from these problems.

Thus, the Stormfgeln has considerable advantages over water-jet technology.The propulsive eciency of the Stormfgeln is higher in all speed segments,with the exception of the speed that is optimal for the water-jet. The eciencyof the Stormfgeln today at the speed for which the prototype boat has beendesigned (approximately 60 knots) is pretty much equal to that of a water-jet

vessel optimised for the same speed. CTD Marine states in its evaluation of the

strength and lifetime analyses carried out by IMES that the maintenance cyclesof the Stormfgeln are more advantageous than the cycles that can be achieved by currentlyavailable water-jet technology. The Stormfgeln cycles are equivalent to those used by ro-bust conventional propeller systems used in vessels.

A sequence from the CFD analysis

of the propulsor of the Stormfgeln,

used to determine its propulsive

coecient.


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CTD Marine in Zrich has determined the propulsive efciency

of the Stormfgeln based on values of speed, rate of revolutionof the propeller, and the shape and angle of the propeller blade.The input values have been obtained from maximal load on thepropulsor with its propeller blades and mechanism. The speed inthis case was taken to be 58 knots.

To put it simply: the propulsive efciency is constituted by the

power ratio between the power that is supplied to the propel-ler (the torque multiplied by the rate of revolution) and thepower that is delivered by the propeller (thrust multiplied byspeed). The CFD calculations have considered three media, andthis makes them very complex and advanced. Not only does thepropulsor function in the interface between water and air layers,cavitation also arises when the propeller blades move throughthe water. This gives rise to a third medium, steam, which ariseswhen the pressure becomes so low that the water boils.

The propulsive efciency of the Stormfgeln has been deter-mined to be 62% at a speed of 58 knots, which agrees well withthe assumptions that were made in association with the testsof fuel consumption carried out in October 2008. CTD Marinepoints out in its report that a number of probable optimisationpossibilities are available, which will increase the efciency if

carried out. A traditional surface-piercing propeller with well-designed blades can achieve an efciency above 70% at optimal

speed. The propeller blades of the Stormfgeln are, as CTDMarine expresses it, the result of assumptions made during thedesign process and in the absence of appropriate design tools.The Stormfgeln has had access to only a single set of blades

THE CFD ANALYSIS OF PROPULSIVE EFFICIENCY

during the development of the blade design, and this has been,obviously, a limiting factor. This has led CTD Marine to the con-clusion that the propeller of the Stormfgeln can reach a propul-sive efciency greater than 70%, given the correct optimisation.

One indication of the potential for optimisation is the pressure

that the CFD analysis discovered on the suction side of the pro-peller blade, which gives a counteracting force. To put it simply:the boat is pressed backwards by this pressure and this reducesthe propulsive efciency. It is the opinion of CFD Marine that it

is possible to transfer this negative pressure to the forward pres-sure side of the blade by a redesign of the blade, and increasethe efciency in this way.

There is probably further potential in an optimal adjustmentof the size of the blade. The surface area of the blade has beengradually changed, and the blade prole was changed on one

occasion, using a trial and error method. It is impossible todetermine whether the current size and shape are correct. Whatwe do know is that the current design is more efcient than pre-vious versions. It will only be possible to determine whether theefciency can be increased by redesigning the form and prole

of the blade in two ways: either by further CFD analyses or bycasting a series of new blade sets. The CFD analyses are prefer-able for several reasons not least economic reasons. Theseanalyses must also be carried out using trial and error, and theyhave been included in the planned programme of verication

for the Stormfgeln performance.

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FURTHER VERIFICATIONS PLANNED IN THE NEXT STAGE

The evaluation presented in this status report shows that the Stormfgeln con-cept is strong in those segments that operate in the speed range above 30 knots.It shows also that the Stormfgeln has clear advantages over the systems that arenormally chosen for these segments.

The Stormfgeln company is in a nancial situation in which it is of utmostimportance to form ties with one or several OEM partners, who together withthe company can take the Stormfgeln concept to commercial exploitation.

The company will continue with further verication tests in order to present

as strong a case as possible when discussing with potential partners. These testshave been previously planned.

Dynamic calculations of strength and lifetime of the propeller blades

and mechanism of the propulsorThe purposes of these calculations are to determine the lifetime of the pro-pulsor and its components, and to draw up detailed proposals for improve-ments in design and material choice. They will be carried out by IMES, theInstitute of Mechanical Systems at the Zrich University of Applied Sciences.

Optimisation analyses of propeller blades

The purpose of these analyses is to optimise the propulsive eciency. Theywill be based on the results from the CFD analysis that indicated that thereis a large potential for optimisation.

Comparative analyses of competing propulsions and hulls

A conrmed curve for the propulsive eciency of the Stormfgeln will bedetermined using CFD analysis, based on the optimisation of the propel-ler. This curve will be used as a starting point for an in-depth and conrmedcomparison with competing systems (traditional propellers, surface-piercingpropellers and water-jet technology). Furthermore, CFD will be used to carry

out comparative analyses of the overall eciency (propulsion and hull) of theStormfgeln with those of competing propulsions and hulls, at a model level.

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stgtagatan 93SE-116 64 StockholmPhone +46 8 717 80 70Fax +46 8 551 136 44Web www.stormfagel.se

Propeller / Hull Status Report 2009

Documents

Transcript of Propeller / Hull Status Report 2009