1. Introduction
Saving of fuel engy in the propulsion of small fishing craft can be achieved by one of a combi-nation of the five options listed below:
Develop improved energy efficient engines and/or propelling devices.
Concentrate on reduction of hull resistance in the design of new fishing vessels. Change fishing emphasis from high energy consuming fishing methods to those requiring lower energy inputs e.g. a switch from stern-trawling to mechanized longline systems for high quality bottom fish stocks.
Reduce installed HP and operating speeds. Use alternative energy sources e.g. wind
power.
Considerable attentioD is being paid in a number of FAQ fisheries projects in developing countries to this problem and it would appear that the most inmiediate results in fuel saving can be expecte4 from a combination of choices 4) and 5) with application of choice 3) where appropriate.
Probably the most significant fuel saving in small fishing craft can be achieved by a reduction in operating speed i e a reduction in utilized SHP/ ton of displacement,.(always provided that an appropriate propeller is fitted for the reduced operating HP and RPM). Recent fuel consumption trials of ap 8.7m (28'6") inshore fishing craft with a 30 BHP engine installed, indicated that a
one. knot reduction in speed from 7 to 6 knots for this craft (i.e. from ratio 1.4 to 1.2) resulted in a reduction from 6 SHP/ton ofdisplacement to 2.6 and a reduction in fuel consumption of about 30%. Actual fueUconsumption in litres/nautical mile dropping from 0.93 to 0.6. While this sort of saving can be expected in small craft operating near their maximum hull speed, such savings in fuel costs do not take account of the cost of in-creased voyage time, possible re4uction in fish prices for later arrival in port, nor the human reaction of a fisherman not wishing to see his contemporaries pass him ata knot better operating
speed.
For this particular vessel it wasssible to de-monstrate that the use of 24m2 of sail in a 15
knot true wind using 65% RPM (approximately 60% of maximum continUous BHP) gave an operating
speed of 7 knots at an apparent wind angle of 90° and 6.5 knots at. an angle of 500, see Fig.1. Similar experiments with a 27m fishing trawler
(Reference 5), with a sail area of 18Om2 and 150 BHP on lOOt, displacement in a 20 knot true wind, at a ship speed of 9 knots required a power in-put of 36 BHP at true wind angle 60°, 11 HP at 90°,. 21 HP at 120°, while at the same wind speed for a. ship speed of 10 K 103 HP was required at 60°, 62 HP at 90° and 88 HP at 120°. At the most favourable wind angle i.e. 900 this represents a saving qf 92% for a speed of 9 knots and some 59% at 10 knots.
Savings of this order, even when only the most favourable wind conditions have been taken into consideration indicate that a close look at the option of motor sailing to achieve a constant ship speed could well repay an investment in the n-cessary sailing rig. With an appreciable return on the investment possible in areas where climatic conditions are favourable to the use of sail. Apart from the practical design considerations of how to fit an efficient sailing rig to a fishing vessel without interfering with the fishing opera-tion, the determination of potential fuel savings by the use of sail power in fishing vessels must take four factors into account;
Climatic factors - the strength and direction of mean wind forces in the operational area under consideration.
The percentage of usefUl wind that can be applied to productive propulsion.
An estimation of the maximum sail area that can be carried by the hull of the vessel/ vessels under consideration.
The driving force that can be produced by a particular wind strength and direction on the sail area carried by the ship and thus pro-vide an estimation of ship speed under sail
and power.
The use of sail in fishing craft will in the fore-seeable future be as an adjunct to mechanical power and in any analysis if sail engine power combination for energy saving it can be assumed that the sail rig will not be required without power assistance except under particularly
9 FEB. 198k
Lab.
v. Scheepsbouwkune
ARCHIEF
Technische
Hogeschool
THE USE OF SAIL/ENGINE POWER COMBINATIONS FOR THE SAVING OF
DeIfi
FUEL ENERGY IN SMALL FISHING CRAFTJ.F. Fyson
Fishery Industry Officer (Vessels)
favourable conditions. Design, stability and At the other end of the scale, we would expect to performance predictions are therefore discussed find modern day purse seining and deep bottom and in the light of this basic assumption. mid-water trawling. The high tOwing power needed for a trawl or the speed for setting a seine, to-2. Vessel DesiRn Considerations gether with the considerable auxiliary power re-2.1 Hull design requirements for sail powered quirement of winches and power blocks demand
con-craft siderable alternative energy sources for the large
amounts of power needed, with a consequent reduction Before proceeding too far with the design of sail in the economic importance of the proportion of assisted fishing craft, thought must be given to energy input which can be provided by sail power. a marriage of the sail system to be adopted with
the operational conditions under which the vessel A.Hopper (Reference 6) investigated the possibi-will be working. lity of rigging present day stern trawlers with
The following list shows factors which require sail. The conclusion to be drawn is that savings consideration during the preliminary design stage: to be achieved on this specific type of fishing
fishing method (or methods) to be used; vessel are not sufficient to warrant sail fitting working, deck space required and the lo- at this time. Purpose designed sail assisted cation of the principal operating areas; vessels of this type, to provide equivalent per-amount of time spent travelling to the formance to that of a fully powered craft would fishing grounds; have tobeconsiderably longer to carry the amount climatic conditions likely to be encoun- of sail necessary and the increased building cost tered and their probable variation through could not be economically justified in terms of the yearly cycle; fuel saving. Present dày fishing vessels designed power requirements for propulsion during for powered operation in the upper rrange of speed the fishing operation; length ratios for displacement craft have hull expected catch and the method of bringing shapes which are not ideally suited tO effective
it aboard; sailing.
auxiliary sources of power necessary to: Many recent designs of fully powered craft have the fishing operation, e.g. winches, large installed horsepower powering wide beam! net and line haulers, etc. hulls on a relatively short overall length. Wide navigation and detection of fish, e.g. immersed transoths and increased bouyancy aft are radar, echo sounders, sonar, etc. designed to avoid excessive stetn time at the upper conservation of catch, e.g. power re- limit of thc s?eed rangeo This gives a poorly ba-quirement for refrigeration in one of lanced hull then heeled under sail and stability its several forms. may not always be sufficient to carry an effective (ci) life on board, e.g. cooking, lighting, sail rig.
heating or cooling of living spaces, Design Requirements for combined sail/engine pOwer
etc. operation of fishing vessels to achieve a saving
The ease with which a particular type of fishing of fuel energy Chóuld include:
can be adapted to sail power will depend on speed - a simple, reliable and durable sail rig at requirements for fish capture, and the relation- lowest cost
ship betweeü travel to the grounds and the inten- - a rig which provides a minimum of interfer-sity and duration of fishing operations. Obviously ence to the fishing operations
certain fishing methods - those requiring long - the sail area and hull form stability must periods of free running at less tharI full speed, be such that angles of heel will be small to will lend themselves most readily to an Investment permit easy operation of gear and to mini-in the gear and skill needed to operate a sailmini-ing mize crew fatigue
fishing boat, the advantages to be derived de- - the hull of the vessel must be able to re-creasing in proportion as the power output for sist the sideways force of the sailing rig gear operation and/or speed requirements for fish toa sufficient extent to avoid excessive
capture increase. amounts of leeway.
A few examples should be sufficient to emphasize - The shape shOuld be of a sufficiently balan-the point. In descending order of advantage we ced form that heeling under sail will not result
might list: in an immoderate increase in immersed volume either
trolling for surface and near surface fore or aft of the centre line.
-pelagic fish As mentioned above, beamy hard chine fishing long lining vessels with wide transoms with maximum transom pot and trap fishing beam carried well out to the immersed waterline gilinetting are not likely to produce a happy result under
sail, unless the amount of sail carried is so small as not to result in appreciable heeling moment. In this case sail could only be consi-deredasán auxiliary to a powerful engine and while some benefit in fuel economy may be derived, this will not be as significant as in a craft which is purpose designed to carry sufficient sail to operate under sail alone when the wind is most favourable, or with assistance from an engine at reduced power.
The hull should have fairly well rounded sections with a moderate deadrise and a smooth run to its longitudinals. A transom stern is not disadvan-tageous, provided its shape and that of the after body are designed so as not to immerse larger volumes aft when the craft heels.
- Fishing vessels can and often do vary their displacement and trim during a fishing trip, heavy loads of fish in the hold or gear on deck
can resuLt in an increase of centre of gravity so that less sail can be carried for a given angle of heel.
in materials such as steel, ferrocement or FRP a box keel section is useful to provide 'space low down for the ballast which will be needed for stability. Double bottom fuel tanks are also useful for this purpose provided that they can be arranged to be filled with ballastwater in the exceptional case where no fuel is carried and no fish have been caught to add the necessary weight. Any changes of weight distribution due to fuel consumption and the taking on of fish must be carefully planned to avoid trim changes to which a sailing vessel is much more sensitive than a wide beamed full powered motor vessel.
- Superstructures must be stripped of unnec-essary projections and be installed low enough to reduce the height of centre of effort of the sail rig to the minimum to maintain stability and minimize heeling.
vi) Sailing vessels travelling at low speeds require larger rudder areas that
fully
powered motor craft. Sailing vessels also rely on the rudder tO develop some hydrodynamic force and to resist leeway so that as a general rule sailing craft have larger rudders than powercraft. Even assuming that the major part of the
operation of our combined sail/power vessel will include an engine component there will still be a requirement for an increase in rudder size over powered craft.
2.2 Sail Area and Stability
A sail powered 'commercial fishing vessel has very different design criteria from those of a sailing
yacht of the same general dimensions.
A sailing yacht normally has some 30-40% of her total displacement carried as ballast in the heel to give her sufficient stability to carry her sail area effectively while an equivalent powered fishing vessel when fully loaded will be carrying up to 50 to 60% of her displacement in her fish-hold and the vertical centre of gravity of this
load will be near the waterline.
Stability to carry an effective rig must be pro-vided by a change in form and/or lower placing
of the load.
While calculation of sail area, balance and sta-bility of a sailing fishing vessel requires a complete design study, it is possible to make a preliminary estimation of the sail area
requi-red to propel suchafishingvessel at a reasonable
speed. A provisional figure can be obtained for
load carying fishing vessels in the size range 12-22 m LOA from the equation:
Sail Area,in m2 Loaded displacement
in tons (ms)
This calcultion which gives a reasonably close result when compared with actual designed sail areas, does not take into account the hull sta-bility required to carry this amount of sail. It is however possible to make some basic assump-tions which for preliminary design calculaassump-tions will indicate whether a particular sail area and sail plan are acceptable on a properly designed
hull. The stability of a sailing craft can be
shOwn to be dependent on the sail area SA, the heeling arm H (which is approximately the height of the centre of effort of the sail area above ti'ie mid draught Of the hull) and the wind pressure
P to which the sails are subjected. The forces generated by these three components tending to heel the vessel to an angle of X degrees will be opposed by the 'righting arm GZ of the hull mul-tiplied by the displacement. For small angles of heel the righting arm GZ can be taken as equal to GM sin Q where GM is the transverse metaceñ-tric height and the angle of heel.
The windforce acting on sails can 'be generally calculated as: FSA = p12. A . V2. CL, where:
p - mass density of air (0,125kg/rn3) A - sail area /m2/
V - wind speed /m/sec/
CL - nondirnensional lift force coefficient
The windforce acting approximately at the centre of' gravity of the sail area together with the hydrodynamic force acting approximately at the tentre of gravity of the lateral plan of the immersed body produces a heeling couple: F. H. When the vessel is heeled under a certain angle this heeling moment becomes: FSA. H. COS2 0 see
Fig. 2.
-Coefficient of 1.5
The heeling moment is equalized by the stability moment. GZ
= Lx..
GM .. sin0:
So that FSA . H. COS2
0 =
.GM. SIN 0 orp12. A. v2., CL. H. c0S2 0
=A'.
GM. SIN 0This equation can be applied to calculate the sail area if for example the heeling angle is lithited to an acceptable figure (say : 200 at
a wind Force 5 for sailing fishing vessels).
ThenA
=. GM. SINO
p/2 . V2. CL . H. COS2 0
or to calculate the heeling angle:
sinO
A/2.v2.CL.H
COS2O.
1.GM
As for, small angles COS2 0 1 we obtain:
sinø=A/2..v2. CL. H
.GM
For example in a small 8.7m fishing craft for a heeling angle 0 of 10° and where GM = 0.67m,
V = 15 knots 7.71rn/sec, i = 3.300kg, p12=
0.6250 kg/rn3, CL = 1.02, H =4.4m, COS
0 =
9.968A = 3 300.0,67. 0,173.. 9,81 =
.0,6250.. 7,712.1,02.4, 4.0,968
Using an average value of CL a variety of sail areas and centres of effort of the sail plan can be examined to find which will provide acceptable heeling angles.
It should be emphasized that the preliminary cal-culatioris given above are intended to provide a first approximation of likely sail areas. For example while the use of the stability formula suggested above will tell us approximately what, is possible, a complete design calculation must also take into account the full range of
stabili-ty and what value of wind pressure e.g. strong gust will cause the vessel to heel to an angle at which it will capsize.. Factors such as the freeboardand the vertical position of the centre
of gravity of the boat in relation to its centre of buoyancy at different heel angles must be ta-ken into account and a full stability calcula-tion made.
Small modern combination trawlers/purse seiners, for example, have increased superstructure height to retain maximum deck length for working
purpo-ses. Attempts to put adequate amounts of sail
on this type of vessel will result in a large heeling arm due to the centre of effort of the sails being very high over the centre of lateral plane and stability will suffer. Acceptable hee-ling arms for saihee-ling fishing craft of' 50-100 t displacement range from 7.8rn for 50 t.
displace-ment to 10.5m at 100 t and superstructure heights
24m2
must be modif-ied to remain close to these values if a reasonable amount of sail is to be carried.
2..3 Engine Power
A modest amount of engine power will improve the motion of a sailing craft especially in winds.
forward of the beam in a seaway. The other ad-vantage, an increase, in speed froma motor sai-ling combination can be explained by examining the equation for driving force from the sails FR.= 1/2p/g . CR. A. VA2 where .'R = driving force from the sails, CR = coefficient of dri-ving force, VA = apparent wind speed, A = sail area,. p = weight density of air, g = force due to gravity
from which it can be seen that the effect of in-creased apparent wind speed on the propulsive forces on the rig varies as the square of the wind speed.
As had been noted 'in 1977 by C. Mudie (Ref.7), from the same equation it can be seen that if the hull speed is maintained constant by a power in-put from the main engine then the driving force from the sails becomes proportional to the sail
area.
If we accept that, except in most favourable con-ditions' of wind strength and direction, there will be a proportion of the power input provided
from the. main engine then the sail area can be kept lower than that required for pure sailing ability. Yacht standards of windward performance under sail will not be required and angles of heel and leeway and the increased resistance
pro-duced can be kept to the minimum.
In the discussions of performance prediction in section 3, to maintain a fixed service speed varying amounts of' engine power are proposed according to the driving force provided by the sail power component. In order that the thrust required can be provided with the engine working at economical RPM a controllable pitch propellr should be fitted. Ideally this should be the fully feathering variety to reduce drag especial-ly if wind conditions are such as to justify an appreciable' amount of pure sailing at favourable wind angles.
Controllable pitch propellers have as their main advantage the possibility of operating at opti-mum efficiency for a given diameter through a wide range of speed and loading conditions of
a vessel. Controllable pitch propellers do not guarantee fuel savings throughout the operating speed range. If the major part of the fishing vessels operation is free running at maximum speed and power the controllable pitch propeller will be detrimental to fuel savings due to losses in propeller efficiency associated with larger!
boss diameter and a certain restriction on pitch distribution. However, in the case of a vessel using sail and reduced engine power this loss at
the top of the range can be offset by improved efficiency at partial load operation.
If a fully feathering propeller is not provided then the engine should be run at minimum RPM while sailing and the reduction in propeller drag and consequent increased performance compared with the fuel costs incurred.
For larger vessels an effective solution to the requirement for widely varying amounts of power at the most efficient engine 'operation levels could be in the fitting of a two engine installa-tion, of the "father and son" type with engines of different power driving a single shaft thrOugh a multiple gear box and fitted with a controll-able pitch propeller.
In this way full power could be obtained for per-formance in head winds and in fishing operations requiring maximum thrust or with one or other of the engines working at its optimum according to main engine power demand anci the needs for auxi-liary poer for winch operation, refrigeration requirements etc.
Economic justification for the higher capital costs of such an installation should be veryfied-by an economic evaluation as suggested in
sec-tion 4.
2.4 Sail systems
References 2 and 7 discuss the aspect ratios of sails in relation to lift and drag coefficients and the derived driving force. In reference 2 driving force coeffIcients have'been plotted for Bermüdan and gaff rigs of contrasting aspect ratio and it can be seen that the higher aspect ratio Bermudan sail produces' higher driving for-cès up to 700 beyond this angle a lover aspect ratio sail is advantageous (see Fig. 3 for CL and CD values at different aspect ratios). In ra-cing yachts the disadvantages àf the bermudan rig off the wind are made up by a variety of light weight downwind sails, spinnakeres, large rea-ching genoas etc. The working fishing vessel is unlikely to want or be able to carry such gear as the rigging requirements and Sail handling are likely to interfere with fishing operations.
As has already been mentioned, as vessels speed increases, apparent wind speed also increases and driving forces increase as the square of the apparent wind. At the same time increases in vessel and apparent wind speeds for a given true wind force and direction will result in the
appa-rent wind drawing ahead reducing the angle of apparent wind to course sailed. While this is of lesser importance to smaller craft' operating
at low speeds for larger 'crAft where combinatiOn of engine and sAil power provides a fixed vessel speed at or neAr the displacement hull limit', the higher proportion of close hauled conditions
suggest a higher aspect' ratio sail for maximum driving force from the sAil pOwer component.
While the usual solution is a modern bermu'dan rig see Fig. 4,another very reAl possibility is the Chinese Lug sail, which in its higher aspect ratio, fully batteted versions can produce good driving qualities when sheeted in hard at low wind angles, see Fig. 5.
Additional advantages of this rig are in the possibility of fitting free standing masts with-out rigging at the ships 'sides to interfere with fishing opetation. Figures at the end of this paper illus'trate some sailing rigs which have been fitted to small fishing craft in FAQ pro-jects in developing countries.
3. Performance Prediction'
3.1 Performance ünder'saii
The detailed performance prediction of a vessel under sail at all headings is a complex process, as it involves the 'tesolUtion of the total aero-dynamic force of wind pressure on the sails into a driving force acting along the course direction and a heeling force actiüg perpendicular to the couse in combination with the hydrodynamic resi-stance of the hull which in itself varies with the heeling angle caused by the wind force. The matter is further complicated by the amount of side force exerted y 'the wind pressure on the hull and particularly when sailing close hauled,
the action of the aerodynamic drag component which varies as the angle of incidence of the
sail to the apparent wind. Propulsion efficiency of a sailing rig to windward is further affected by its aspect ratio and the interaction Of the various sails of the rig.
Fortunately in the cOnsideration of the use- of sail power for the propulsiOn of fishing vessels, the determination of fdrce 'and thus speed pre-diction can be simplied as 'pure windward perfor-mance is not 'a mAjor requirement.
For all except the smallest inshore fishing ves-sels the use of sail will, 'in the foreseeable future be as 'an adj'unct to mechanical power and in 'any analysis of sail power for energy saving it can be assumed that the sail rig will not be required at least without pOwer assistance for close hauled performance to windward.
This means that in all considerations of percen-tage of useful winds and performance prediction,
Given a fixed vessel speed VS and any particular wind speed VT it is possible to calculate the apparent wind speed VA and thus from the driving
force equation derived above the thrust due to the sails at the most favourable apparent wind angles. From this result follows the percentage
of the total thrust for a given VS which can be provided by the sails, the percentage of engine power required to maintain VS and the % fuel
saving.
This result will provide a first estimation of the fuel saving to be expected under the most favourable conditions. A fuller investigation of the percentage savings in fuel over a wider range of course angles will require a more de-tailed investigation of lift .and drag forces in order to calculate driving and heeling forces. From Reference .2 it can be shown that for a par-ticular aspect ratio and camber of sail from wind tunnel tests we can plot a polar diagram of lift and drag coefficients CL and CD for different angles of incidence see Fig. 3.
These can be resolved into actual lift and drag forces for a particular sail and apparent wind strength using the standard force equations FL = 1/2 pIg VA2 SA CL
FD = 1/2 PIg VA2 SA CD
From Fig. 8 we can see that the driving and hee-ling forces are related to the lift and drag forces by the equations FR = L x
si/3-
D x cos$= L x cos/3x D x sin For a fixed vessel speed it is therefore possible
to calculate the driving and heeling forces on a sail rig provided we make the following
appro-xiinations:
The lift/drag coefficient curve can be applie4 to the total area. of sail.. Leeway angles and hence increased
resi-stance will be assumed to be small for moderate windspeeds due to the percentage
of forward motion provided by the engine power component.
Resistance due to heel will be increased by about 0.5% per degree of heel up to 20 degrees.
Thrusts due to the sail component at a fixed vessel speed for various wind strengths can then be calculated for a range of course angles to true wind. Given the component of engine power required to maintain fixed vessel speed and power required to achieve the same speed without sails it is possible to calculate the percentage of fuel saving due to the use of the sail rig. Calculation of performance and the simplifying assumptions made are based on acceptance of the fact that very close winded performance is not going to be demanded. of a sailing fishing boat. With angles of the apparent wind tocourseof the
vessel less 45° it is assumed that the sails will be taken down and the vessel will proceed under power alone.' In this case air resistance of masts, booms and rigging will cause a loss of speed when compared with performance of an equi-valent vessel without sailing rig. The force causing this resistance can be derived from F = q . A. C
where q = wind velocity pressure
A = the shadOw area of the' rigging per-pendicular to the wind
C = a non-dimensional coefficient dic-tated primarily by body shape. The force F can alsO be calculated from the
formula F = 1/2
pIg.
A. V2. CDwhere CD is a non-dimensional drag force coeff i-cient.
Assuming that the masts are cylindrical, drag force coefficients for circular cyclinders of 5:1 ratio and of infinite length are given in re-ference 2 as 0.8 and around 1.2 respectively. The wind resistance of the rig at the vessel
speeds under consideration can then be estimated by calculating the "shadow11 area of the mast(s) and rigging and multiplying this by the values q. CD. ' To this value is added the additional
resistances at the wind forces being considered to obtain the total resistance 'of the rig. From the resistance curve it is then possible to cal-culate the additional thrust required to maintain the desired vessel speed. For wind angles other then dead ahead the component of resistance is the total rig resistance multiplied by the cosine of the apparent wind angle.
Curves of fuel saving for the various course angles at different wind strengths can then be plotted. See Fig. 9.
An examination of charts of wind strength and direction for the area under consideration will then enable a prediction to be made of possible overall fuel saving either for each seasonal period or on 'an annual basis.
Another approach to this problem is under process of preparation (personal cotmninication from A. Boswell of Sharp Allied Consultants), in which a computer program has been written to anlyse the
percentage of wind forces and directions accor-ding to wind distribution charts and calculate
the mean thrust in lbs/lOOsq. feet of sail for a given course and ship speed. These are then re-lated to a specific hull by plotting the thrust due to sail power on the resistance curve. The resultant figures for fuel saved are plotted as percentages of fuel used under power alone against ship speed for different wind strengths and can then be applied directly to current fuel costs for a vessel operating under power.
Either method given will enable cost saving data to be prepared for use in an economic analysis
winds equal to or less than 50 degrees on either side of course direction can be neglected for pure sail power performance.
For a prelIminary estimation of the thrust to be derived from a sailing rig at the most favour-able wind angles, the driving force can be cal-culated from the equation FR = 1/2 Pig . CR
VA2 . A and where close hauled performance is
not being considered the driving force coeffi-cient CR can be considered as proportional to the total wind force coefficient CT
In displacement sailing craft variations in apparent wind speed as the apparent wind angle increases reduce the magnitude of the total aerodynamic force, but at least initially this reduction tends to be compensated for by the increase in driving force.
From references 2 and 7 CR can be showri,in the range of apparent course angles from 65_1800 to be within the range 1.1.3 for aspect ratios of 4-6 and from 800 to 1800 an average value of CR is approximately 1.2.
As the apparent course angle increases beyond about 1200 the decrease in apparent wind strength reduces the total driving force but at apparent wind angles of about 85° - 120° the total dri-ving force remains at a fairly constant maximum for ship speeds less than 10 K.
Assuming that where necessary a component of en-gine power will be used to maintain a constant vessel speed and that heeling and leeway angles will be at a minimum we can use this expression
fr total driving foce to derive the thrust corn-ponent due to the sails at the most favourable apparent wind angles.
3.2 Combination of engine power with sail
In its simplest form, speed estimation under po-wer can be related to displacement which in the
lower speed ranges most affects the resistance to forward motion. Where the speed/length ratios is tb be kept to one approximately 1 SHP per ton
of displacement is sufficient whereas to achieve a
v/Ti
of 1.3 where wave making resistance be-comes more important,, requires 3-4 SHP/t. A V/V' of unity will give speeds of 5.5 knots for 30 ft LWL, 5.9 for 35, 6.35 for 40. 6.7 for 45, 7.1 for 50, 7.5 for 56 ft.Therefore the combination of enough hp to achieve
a
'i//T
ratio of 1 plus sailpower can result ina significant increase in speed while utilizing power from diesel fuel at
a
most economicalle-vel.
Let us look at the istarce curve of a sail powered fishing vessel of 19th LOA and 17m (56ft) LWL as seen in Fig. 6. If with lhp/t of dis
-7-placement we can obtain a speed length ratio of unity this would be approximately 7.5 knots for
a 17 rn (56ft) LWL. At a displacement of 60 t
from the curve of Fig. 6 we can see that the thrust required to achieve this speed is 533kg. If the total sail area of the vessel is 150m2 in a true beam wind of 15 knots we may achieve a drive- component of around 2.9kg/rn2 of sail, this means that with 150m2 ( 1 400ft2 ) we can
obtain 435 kg (840 ib) of thrust.
If we sum the thrusts from engine and sail, di-vide by the displacement and compare the resul-ting figure with the resistance curve, we will find that with sail and economical engine power we can achieve a speed of 8.9 knots or a speed length ratio of 1.21 which under power alone would require more than twice the horsepower.
This is a simplified view of speed prediction and does not take account of the fact that the prediction of performance while motor sailing is not a matter of a simple algebraic sum of the speeds obtainable from sail and engine power. According to wind direction the resultant speed nay be more or less than the algebraic sum of
the two. The application of engine power to a vessel operating under sail will result
in a
speed increase which in itself further increases the speed of the apparent wind resulting -in in-creased thiust and in favourable circumstances a further increase in speed. However as boat
speed increases the angle of apparent wind draws forward as an exathination of Fig. 7 will show.
Sails must then be trimmed to the optimum angle of incidence.
At some point of true wind angle and boat speed either the heeling component of thrust and hence resistance increases to the point where forward motion will decrease or the sails are trimmed in to the point wha decrease in the angle of in-cidence will result in a stall and speed will decrease to below that obtainable under power
alone.
Where the angle of incidence can be kept close to the optimum the increase of apparent wind speed due to engine power will increase thrust from the sails to the point where performance will exceed the algebraic sum of the separate speeds over a wide range of course angles. If a given vessel speed V5is chosen then for full powered operation the thrust due to the propeller can be calculated from Bp -8curves where thrust T = 148 x DHP
Va
where ' B = propeller efficiency behind the hull
Va = speed of advance of the propeller DHP HP delivered to the propeller.
as discussed in Section 4.
4. Economical Evaluation of Sail/Engine Performance
The economic viability of substituting a renew-able energy source, wind, for non renewrenew-able fossil fuels in the powering of fishing vessels rests on an analysis of the costs of investing capital in the proposed energy source, compared
to the monetary worth of the fossil fuel saved.
As has already been suggested, a return to sail as a sole energy provider is unlikely at least
in the present and immediate future of fossil fuel availability and price. Sail power will therefore be considered as an auxiliary power source which can, under favourable operational conditions of fishing method, wind force and
direction, also be used as the sole driving force for a fixed period of time.
From the performance prediction methods of sec-tion 3 and a analysis of local climatic data it is established that for a 17m WL sailing fishing vessel with 150m2 of sail and a displacement of
60t an average thrust equivalent to 2.0K vessel speed can be provided for a constant vessel speed of 9.5K. From the resistance curve of Fig. 6 an estimated 50 HP is required to drive the vessel at a speed of 7.5 K in calm water. Assuming that at an average 10K wind speed an additional 12% resistance is created by the ac-tion of wind and waves and wind resistance of the sail rig some 60 HP will be required. For full power operation from the resistance curve, with the same weather allowances, 160 HP will be re-quired to achieve 9.5 K. To reach 10K under full power a total of 230HP will be required.
Fuel consumption in litres/hour can be derived from a typical consumption curve which might give a consumption at operating RPM of 180 g/hp/
hr.
For 60 hp this would give an average consump-tion of 10.8 kg/hr, for 160 hp 28.8 kg/hr and for 230 hp 41.4 kg/hr
or 13 l/hr, 35 l/hr, 50 1/hr respectively (roun-ded to nearest litre). With a knowledge of trip times, distances to the grounds, time spent on actual fishing operations and typical power re-quirements during fishing it is possible to make an estimate of average fuel consumption per trip.
With longer trips with considerable free running to and from the grounds the extra trip time to achieve equal fishing time must also be taken.
into account as crew costs will be higher in this
case.
Let us now examine a hypothetical operational case in order to see how an estimation of
poten-tial saving can be made using a sail/engine po-wer combination.
A breakdown of costs for a 19m (62ft) sailing fishing vessel could be of the following Order of magnitude.
Uss
Hull cost 180,000
Machinery and Installa- 40,000 tion
Hull Fittings and Equip- 34,000 ment
Sub total (1) - Hull,Equipment
& Machinery 254,000
Fishing Gear 15,000
Sub total (ii) Complete
vessel ex sail:ing rig 269,000 Masts andrigging 10,500
Sail 6,000
Steel ballast 8,500
Sub total (iii)
-Sailing rig 25,OQO
TOTAL INVESTMENT 294,000
As we can see from this breakdown the cost of the sailing rig is of the order of 8 % of the total investment although this cost may be off-set to some extent by a reduced cost of the en-gine installation if a lower HP enen-gine f:itted than the 250 HP which is commonly installed in this type of vessel.
Assuming that the vessel has been equipped for trolling and deep reel handlining the total annual mileage covered in travelling to the fi-shing grounds and in the fifi-shing operation could be of the order of 24.000 miles or a daily average of 120 miles for 200 days/year.
If annual operatiOnal mileage is 24,000 nautical miles and average daily mileage 120 miles for 200 days, the use of sail and engine input of 60 HP for a speed of 9.5 K will give an average daily operational time of 12.6 hours while the use of engine power only of 230 HP to give 10 knots will require 12.0 hours. Time difference costs can therefore be neglected.
Daily fuel consumption for an input of 60 HP will be 164 1 while 160 HP will require 363 1 and 230 HP 6001. At an average fuel price of ($0.35! 1 ($350 per ton) daily fuel costs will be $57.40, $127.05 and $210.00 with annual fuel bills of $11.480, $25.410 and $42000 respectively. Annual fuel saving for operation at 9.5 K would be $13.930 and accepting a half knot reduction
in overall speed for the sailing version compa-red to the full powecompa-red version at 10K will re-sult in a savingof $30. 520 less any time costs which must first be subtracted.
Note: (Fuel Costs for auxiliary operation have not been included as these are assumed to be
For 9.5 K operation the payback period for the initial investment in the sail rig would be 1.79 years which is acceptable as the operatio-nal life of sails and running rigging,which would account for some 1/3 of the total rig cost
is estimated as 4 years.
While this simple payback estimate will give some idea of viability of the investment this should be expanded to allow for fuel escalation costs as well as for the time value of money. In order to show whether the investment in a sail rig will be profitable over the life span of the vessel a complete cash flow analysis must be prepared balancing the yearly cash inflows from fish sales against all cash outflows for operating expenses, major repairs, re-rigging, re-enginirig, etc. and taking account of residual values at the end of the estimated service life. Discounting these cash flows to present value of future earnings will permit an economic eva-luation of the profitability of the investment as a whole.
Further details of economic analysis by net pre-sent value and benefit cost ratio can be found in references 8, 9 and 10.
5. Conclusions
The use of a combination of. sail and engine power to operate a fishing vessel at a fixed operational speed varying the power input from the main engine according to the wind strength encountered provi-des a viable solution to the problem of increasing operational fuel costs and the reduced profitabi-lity of small fishing vessels. A number of sim-plifying assumptions can be made to assist in per-formance prediction and preliminary design analy-ses can be carried Out using the methods sugges-ted to assist in deciding whether the fitting of a sail rig is justified in individual cases.
REFERENCE S
FYSON, J.F. 'The use of Sail Power in Fishing Vessels' South Pacific Commission Thirteenth Regional Technical Meeting on Fisheries
August 1981
MARCHAJ, C.A. 'Sailing Theory and Practice'
Adlard Coles Ltd. 1964
MARCHAJ, C.A. 'Aero-Hydrodynamics of Sailing'
Adlard Coles Ltd. 1979
BARNABY, K.C., 'Basic Naval Architecture'
Hutchinson 5th Ed. 1967
LANGE, K. and SHENZLE, P. 'Full Scale Trials with Wind Propulsion on a Small Fishing Ves-sel' International Council for the
Explora-tion of the Sea 1981
-9-HOPPER, A.G. 'Energy Efficiency in Fishing Vessels' Fishing Industry Energy Conservation
Conference Seattle 1981
MUDIE, C. 'Reducing the Running Costs at Sea' The Journal of Navigation Vol. 30
No. 2 May 1977
FYSON, J.F. ' Fishing Boat Designs:3 Small
Trawlers' FAO Technical Paper No.188- 1980
SWARTZ, A.N. 'Economic Analysis of Fishing Industry Energy Conservation Technology' Fishing Industry Energy Conservation
Con-ference Seattle 1981
BENFORD, H. 'A Method for Deriving the Annual Cost of Capital Recovery for
Commer-cial Sailing Ships'
MAIN PARTICULARS
Length over all 8.70 m (28ft 6 In)
Length water line 75Cm (24ff 7in)
Beam maximum 2.65 m ( 8 ft 8 in)
Depth )opprox.) I. 10 rn (3 ft 7.in)
Displacement light (oppiox) 3,000kg (6,600 lb)
Engine 30hp
Sail area (total) 24.54m2 (264ff2)
I. Wooden sprit length 7. 80m, maximum diameter 120mm
Sprit topping lift Spritsal peak halyard Spritsoil, area 9.50 m2 (210 ff2) Spritsail throat halyard
Mast length from deck 5 50m,greatest diameter 120mm 7 Jib halyard
Jib area 5.04 m2 (54 ff2)
Pipe bowsprit
IC. Strop for raising and lowering the sprit
II. Jib sheets .
(2. Side stay in 6mm stainless steel wire
Broiling lines for hail reduction Main sheet
Rape main sheet traveller
6. Aft.guy for sprit control
o o5 0 in 2,0 25 Me??., 0 I 2 5 4 5 6 1 8 Feel
87OmFRP Fishing Bodt (Sri Lanka) EXPERIMENTAL SPRIT SAIL RIG
Rig d,s,gn SA/JF
Ro,ne. Mn 1962 sokiii-i
F±g. 1
Experimental sprit sail rig on an 8.7 in fihing boat,
Drxa, No scale on shown I Protect No
SAIL FORCE
FSA
HEELING
H
ARM
