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APRIL 1960 MODEL SHIPS – CARS « YACHTS « ENGINEERING Special / A miniature model of the new P. & O. liner CANBERRA APRIL, 1960 Yacht Design Part One of a new series by John Lewis Left, a planimeter in use; this instrument is valuable to the regular designer but methods of doing the same work in simpler ways GFnas on the technicalities of yacht designing have been the subject of many articles in the past, but I hope to show in this series that the model designer can get along very well by following a few simple rules. Provided the basic choice of dimension for a yacht is reasonable, differences in hull form and keel shape between two good designs will only account for a few feet in terms of speed through the water on the average racing course. The factors which combine to outweigh refinement in design are :— (a) Ability of skipper. (b) Quality of sails and gear. {c) Luck. Extravagant claims are sometimes made but investigation usually discloses that the particular model is blessed with a consistentenly good skipper, is fitted out to the nth degree and has on occasions been well beaten by some old wreck. If the basic lines I hope to make clear are followed, it should be possible to go ahead with confidence and produce a satisfactory racing model. With practice the designer will develop his own characteristics and can then embark on more original work. The big joy in yacht designing, apart from pro- ducing something intrinsically beautiful, is the incorporation of one’s own pet ideas and innovations. Serious experimental work is very tedious with sailing models as it is impossible to measure the forces acting on the hull. It takes years for the lone hand to get anywhere by a series of trial and error designs, and even with the most careful observation on the water results can be misleading. It is necessary to look to the Model Testing Tanks at the National Physical Laboratories and Messrs. Saunders Roe Ltd., for more rapid advance in yacht design in this country. We live in hope, however, that one day a model designer will stumble on some new approach which will revolutionise design and also be applicable to manned-up craft in a worthwhile way. It can happen. (3) will be explained To combine beauty in this series. of line with superlative performance under a given set of conditions _ is. the art and science of the experienced. It is with 1 and 2 that these articles are mostly concerned. Equipment. Preparing a design without proper equipment is tedious, but it is not necessary to go to great expense however. The following “items are very desirable and I would recommend that they are all obtained if more than the occasional design is going to be prepared. (1) A drawing board 54in.x32in. is the most useful size but as they are very expensive look around for a secondhand one. It is not necessary to have a straight edge down one side for a T square so that a piece of block ‘board can be used as an alternative. The drawing board should be covered with a sheet of good quality cartridge paper and I recommend the use of Terry clips rather than drawing pins. (2) A really good ebony edged straight edge 48 in. long is a necessity and a good one is an investment. The whole accuracy of the drawing depends on this instrument as waterlines have to be quite straight and parallel. It is better to plot these lines rather than use a T square. (3) One 10 in. celluloid 45° set square. (4) One set of Dixon Kemp pear shaped curves. They are made specially for the Naval Architect and with them the job of fairing up a set of cross sections becomes quite easy. It is also easier to ensure that the body plan is harmonious from end to end. Ordinary French curves are useless. (5) A set of splines and spline weights are essential if much work is going to be done. The splines are usually made of lancewood, but celluloid ones are also available. The most useful sizes are :— 4×3/16 in. tapering to 3/16×3/16 in. by 60 in. long. 3/16x} in. tapering to 4x 4 in. by 48 in. long. 3/16x} in. tapering to +4 x1/16 in. by 48 in. long. + xtin.taperingto +4 x1/32 in. by 36 in. long. Designing can be divided into three stages :— (1) To produce a design of good all-round performance being relatively easy. (2) To combine the above with good looks requires the guidance of an experienced hand. 173 JAHOGANY SCREWED for you The most useful ones’are listed below :— Yachting Designing and Planning by Howard Chappelle. Sailing Yacht Design by Douglas H C. Birt. Cruising Yachts by T. Harrison Butler. Thoughts on Yachts and BASE TO LEAD WEIGHT SPLINE WEIGHT Yachting. TERRY SPRING 5 REQUIRED 7 Racing, Cruising and Design. CLIP | Sailing Seamanship and Yacht r by Uffa Fox. Construction. Sail and Power. They are all obtainable from Messrs. Stanleys of London. The spline weights are very expensive and a simple design is shown so that they may be cast at fiome. J Uffa Fox’s Second Book. Yacht Architecture by Dixon Kemp. All the above books describe in detail the actual process of drawing a set of lines, except those of Uffa Fox whose books show a collection of drawings together with enough information to make them really valuable to the student. Next month we will deal with some design features in more detail and in the meantime here is a new 10-rater to study. They should be covered in some soft material such as leatherette and at least five are required. It is possible to manage with strips of 4+ x +} in. balsa wood held down with pins Great care must be taken, however, to see that the curves are nice and fair The use of splines requires practice and “patience. (6) A planimeter is an instrument used for measuring the areas of figures bounded by curves and with its use it is possible to calculate quickly the displacement of a hull. They are expensive to buy new, ranging from £14 15s. Od. to £25 but it is well worthwhile looking in pawnbrokers’ shops for a secondhand one. {| have on two occasions purchased perfectly good instruments for 50s. Alternatively it is possible to use squared paper and I will describe the method in a later article. ~ (7) There are many different types of drawing paper to choose from and one soon develops a preference for a particular grade. Personally I like Gateway medium weight tracing paper. Using a transparent paper enables one to compare sets of lines by superimposing the drawings This is a great Fae when SET developing a new design. (8) The only other instruments not normally found at home are an accurate scale rule and a good 12in. steel engineer’s rule. WHIRLWIND Aves new design is a development of what is now quite a large family of designs. The well-known Sirocco has so far been the most successful in competition, having won the 10 rater championships twice. If that design has a fault it is that she is rather slow in getting away downwind and subsequent efforts have been aimed at overcoming that defect without sacrificing too much windward ability. Whirlwind represents my latest thoughts on 10 raters—other than those designed for twin keels, which still require quite a lot of experimental work. It will be seen that there is quite a resemblance to the No. 19 design already published, but this resem- Study and Research. Before actually putting pencil to paper and starting off with a design have a really good look at all the drawings you can lay your hands on. It does not matter whether they are of the correct class of yacht or not as fhey will, if carefully studied, show how different designers lay out their drawings and solve problems by different methods. To learn anything from a design it is mecessary to know for what purpose the design was prepared. There is very little difference between designing full-sized yachts and models There are many practical considerations to be considered in the mannedup boat, but the process of thought and actual work entailed in drawing the hull lines is very similar. There are some very good books on designing which are well worth asking your library to procure 1960 ——_ SSE OF FIVE DIXON KEMP CURVES ae April May June August September September 174 CHAMPIONSHIPS 23/24 21/22 4-6 14-21 36in.R 6M 10R A 17,18 Q(R/C) 3/4 M Bournville Bournville Fleetwood Gosport Harwich Witton Lake (Birmingham) Entries by March April May July 26 23 7 16 August 20 August 6 Other regattas on page 172 The Little Portugal Cup (A Class) will be held at the Rick Pond, Of SPLINE WEIGHTS M.Y.A. Surbiton, on April 17th. Compared with No. 19 the new boat \ sae is slightly lighter, has Ny more L.W.L. beam as try, and possibly with ° The keel has been XN BODY PLAN. FULL SIZE. throughout the coun- performance. y ral ( | | i 38 Wat- 10892 “3 ’50: 4TH. 50’50° 7-75. 2ND. 64:50: Ist. 3RD. ~ LWL. BEAM ON 31’55LBS. DISPLACEMENT LEAD BALLAST 21:25 LBS. ie IN. HERTS. WATFORD, OF COPYRIGHT RO. Pk Road, ford, Herts 3B, CLARENDON Service, Clarendon MODEL MAKER PLANS SERVICE Plans ) Full size copies of the drawing on right, which includes full size body plan and half size sheer and water lines can be obtained price 10/6 post free from MODEL MAKER John Lewis Ww. pe A ss LW.L. j . performance. 1o SAIL AREA ss WATERLINES | cessful for windward SECTIONS SPACED to be the most suc- 12:0″ W.Lé. Ne es This plan has proved 55:0 ” high aspect ratio with a medium sized jib. 72-32″ : % DRAUGHT difficult to handle. I personally don’t think the angle of leading edge matters very much, so have bowed to popular opinion for once. The sail plan is of LW. edge makes a_ boat Lo. . PTT » owt thinned down and given more rake aft. The thinning is the result of information on tank testing and more rake has been given because many people believe that too steep a leading | vis a | a better all round 9 WL6 z compensation, has a shallower canoe body and is 1in. shorter on the L.W.L. The sections forward are finer and the bow is not snubbed. These alterations should produce a boat with wide appeal Io Lew ; X ie new. all Hm — Whirlwind is quite ss : Sas likeness only and Lo 4 x DECK LINE. blance is more superficial than first glance leads one to suppose. There is the family WHIRLWIND | APRIL, 1960 Loe Ce ea MODE MAKER Do-it-Yourself SAILMAKING for racing and cruising craft Part Five—Conclusion TS), woe =oe Ne Waterproofing Union Silk Wo is pretty easy, though a trifle messy. Complete the sail first, and then use MESOW AX, as used for tents, etc., following the instructions on the tin, and remember jtwo thin coats are always better than one thick. Allow plenty of time to dry. It is always a good idea to treat flax cordage with this wax, for so impregnated it will last for years. Doping is done by spraying with banana oil thinned with good (not cleaning) quality cellulos e thinners, and applied with a Celspray or with a cheap scent spray. Watch the materials for celluloid or plastic are dissolved by Cellulose. Be warned by Clotson who did not! Thin at least two parts thinners to one part b. oil; a little experiment will be needed to suit the spray. Use two thin coats each side, on the “blank” as roughed out from the paper pattern and before final cutting, the rough being hung up by the clew and tack, with a small weight. about 20z., at the upside down head to keep from curling, and when finished a final spray over the tape and stitching to seal everything off. Two important don’ts. Don’t treat the tape of a cloth sail without the bulk, or it will go all shapes, don’t ever smoke when using cellulose thinners mixes, or have fires on in room, and do always keep window open, Marking. Name, etc., on tape, for all cloth except doped where it is alright as it is, rub a spot of Durofix into the tape to prevent ink running. To mark sail numbers cut a stencil from hard, thin cardboar d, such as a dress box; the diagram shows how to leave “middles in”. Tape firmly to sail with masking tape and mark with a boot brush and black Cherry Blossom. For all cloth, doped, waxed or plain. Not ———— too much on brush at once. For prototype craft an excellent tanned or coloured sail can be obtained with coloured boot polishes over all the sail; this has a natural “weathered” look, imparts nearly as good a waterproofing as Mesowax , and dries in about 2 to 4 hours. Numbers can be in black as before, or by masking off the numbers with reverse stencils of masking tape left unmarked to simulate “white marking”. Don’t forget you MUST MASK OFF BOTH SIDES each time. This is also a better method for galleons and similar decorative sails, avoiding the heavy effect so often seen. Little rust patches, stains, etc., are all possible. An old trick here, but still a good one, if the model ship, with all sails set up on false masting and sparring, and the hull covered, is set in the stream make a second suit, or a luff, especially in Terylene, that has gone hollow, and a leach can be tackled also, provided you first remove battens, and, by testing sail as for flow and blow, ensure that you are far enough in to clear the stretch in the leach. Excellent jibs can almost always be made from otherwise scrap mainsails, and where the luff has gone hollow, well, that is what you want for a jib. All that may be needed there is to remove the sail hooks, re-eyelet and fit luff rings, the spacing used, 6 in. from tack, being the same in both cases. Generally with a leach it will be O.K. if you can clear inside the roach and another 2in., but always check first. If you can unpick the tape for using again so much the better as it has stretche d to the sail material, if not, you will be well advised to condition it as follows. Cloth, Tinen tape, soak in cold, clean water for 4 hours, get wife to iron gently, soak again for an hour and hang up to dry with a weight of about 3 Ib. (regardless of length, 2 to 6ft. of tape) for 24 hours before use. For Terylene, hang up with same weight for same time, but a few minutes after hanging up, and again after about 12 hours, warm the tape with an electric fire, or hair-drier is even better, going slowly up and down about three times. Get it warm, but not hot, oe your hand alongside the tape, you soon know then! Or if you can get torn strips off the old sail instead, so much the better. “Tapes” of Terylene must always be torn, to ensure they are truly parallel with the weave of the material. Just one word, do please always keep selvedge s parallel with the leaches, and while stitching keep the needle off eyelets and suchlike, or you will cuss! You can rub out old markings off Terylene with a little turps and care, but old cloth ones must be blacked out with a boot polish cross and remarked. It is permissible. Never wash a cloth sail, you will ALWAYS spoil it. If it gets dirty or stained, let it Stay, or in severe cases carefully bleach with a very weak solution of oxalic acid, and rinse well. But best let it stay dirty. Spinnakers. There are literally dozens of sorts of these, as would fill a series of articles, and even then leave you without the sort that the perisher who took those critical two points out of you, removed from his pocket at the last moment before rigging. Mostly they are either one piece or 3-panelled, but I must admit that there are some weird multipanel efforts about now, my own included. of an electric fan and each sail sprayed with banana Cloth provides no problems, the luff (boom to oil from near the sail, between this and the fan, the head hook) is taped and other edges are hemmed sails will dry into the bellied shape with all the life- \ and panels best overlapped and stitched over on like flow you need. Obviously, here you must mark second line of stitch. crosses, etc., on sail first. Now back to the Class boat for a while. It is a pity to throw away old sails and any sail can be recut to use the material. There should be no prob- lems now to retaping a foot that has been cut up to 194 Polythene is best joined by heat. Cut two hardboard plates about 19 in. long, curved one side and straight the other, and by placing the panels between them so that about 1/16in. of each panel is proud (Concluded on page 199) APRIL, Stalled, current consumption was approximately amps. then be shunted across the supply, as shown in Fig. 3, to provide a shunt-series or compound circuit. 7 This reduces the speed and current consumption, but Power and speed characteristics appeared typical of a series wound motor, torque and current tending to fall rapidly from the stall condition and then at the same time tends to give a motor with more nearly “constant speed” characteristics—i.e. it can accommodate a certain amount of loading without loss of speed, or relatively little loss of speed. It was not possible to investigate the compound connection performance in any detail because the motor was damaged in disassembly (necessary to settling down into substantially linear curves. The ‘run-away” -characteristics of a series motor are limited by the fact that the anmature is always driving the gearbox and is thus never unloaded. Stall torque is very high—as much as one could hold by grasping a screwdriver inserted in the slot in the output shaft. check the wiring), and also the brush gear was in pretty bad shape. It had obviously had a lot of running time and was overdue for a brush replacement. Construction-wise the motor embodies two separate field coils mounted on pole pieces formed integral with the main casing, a twelve-pole armature mounted on a 5/16in. steel spindle (not hardened) running in ball races press-fitted into the cast ends. The armature was balanced and wound with heavy At the upper end of the speed range, speed decreases almost proportionately with load. A normal waterscrew load should pull the output r.p.m. down to about 800 r.p.m. on a 12 volt supply, when current consumption should representing a power horsepower. be around output of the 2 amp something mark, like .025 gauge wire. Brush gear is mounted at the terminal end, the square section carbon brushes being spring- This is definitely a motor which must be used with accumulator-type batteries — lead-acid cells for preference with a capacity of the order of 5 ampere- hours for a full afternoon’s running time. loaded and held by a split pin. Brushes are readily removed after detaching the aluminium end cover but disassembly of the motor any further is not ; recommended. Essentially, it appears, this is a high current consumption motor which, if used as a series wound motor, could flatten batteries readily if heavily It is a motor for a large displacement hull on account of its limited shaft output speed—and it must be a reasonably large hull to accommodate the motor weight plus attendant battery supply. 54 lb. Rela- tively thick stranded wiring is also recommended as this will be called upon to take 2 amps current or more continuously. loaded or stalled. from about 24 in. l.o.a. upwards, but that current demand can represent a real headache. (Continued from page 194) SAILMAKING and passing a lighted taper along the join, a heat seal is made. terminal shown in the diagram. strip which is wired spoil the panel. It is rather prone to do this. The edges are best done with a line of cellotape as Treating the centre terminal as a standard battery connection, connecting the other battery lead to one side terminal energises one field coil only to give a Standard series connection with rotation in the same direction irrespective of the polarity of the battery. Leaving the centre connection as before and connecting the other side of the battery to the other end terminal utilises the second field coil (first coil now out of circuit) for a series wound motor which runs in the opposite direction. Performance in either direction, as a series wound motor, is identical. Operated as a series motor, it will be appreciated, only one field coil is used at a time (depending on the direction of rotation required). The motor then has the normal series characteristics of a dipping current—r.p.m. curve, rising sharply towards the stall. Speed is variable with load, being pulled down (with corresponding increase in current consumption) with increasing load. The arrangement of the windings also allows the motor to be connected as a compound type. If one of the normal series set-ups is used (depending on the direction of rotation required), the other coil can ; . This is quite sound, and quite easy with a few trial goes, but always keep the plates of hardboard on the job, so that it can’t flare into a hole and ends of long bolts holding the whole motor together (and the cover plate in position). Removal of this a in series. field coil is more : F Efficiency of the motor appears to be quite high and the size and weight make it adaptable to models see Fig. 2 — which reached a stable free-running speed of 9,000 r.pm. on 12 volts, drawing nearly 3 amps at this speed. Stall current was well over 10 amps. Connections are a little obscure without removing the aluminium end cover. The two screws on this cover are not connections but are merely the exposes Direction of rotation can be selected by connecting the appropriate coil As a compound motor, bringing the unused into circuit across the supply, running economical. ; Type No. 17330 is a much more compact unit with a straight drive and 5/16in. diameter output shaft. This shaft is threaded at the end }in. B.S.F. but it is intended that the drive be keyed on, the spindle being cut with a keyway and a key fitted. Casing length is Sin. and overall diameter 23 in. The spindle protrudes 1 in. Motor weight is 23 Ib. This also proved to be a series wound motor— cover 1960 stuck on and then stitched along both edges with a very wide thread spacing and very easy tension, and keeping needle moist with white spirit. Corners, surgeons’ adhesive tape, stitched across, and eyeleted. Marking. Cloth and white _nylon as cloth, Polythene, as Terylene, but it doesn’t stay on very well. Anyone found owt better, please? Holes in spinnakers, cloth or nylon, varnish patch about 4in. diameter bigger than hole, allow to dry and cut out. It will never “go”. The same method is i excellent for “hemming” flags. For Polythene, just press a hot pipe of the required size (not that sort of pipe, Clotson, a bit of metal Hers tube) through, and it will seal itself. Now I know that there is a lot unsaid in these articles, and I know some experts will find them elementary, and needlessly full of detailed explanation of the obvious, but to them I can only apologise, and say, yes, but most things are easy when you know how and why. Excepting of course those hidden reasons which we would all like to know, the real reasons why a boat is faster than another so similar, and sometimes theoretically better. ; But that is the charm of model sailing boats. 199 APRIL, nterested in any aspect of model yachting, including radio control and the new “Q’’ Class, or who own any of the classes recog- nised by the M.Y.A. In addition, an entirely new junior section will be formed in which juniors, under 18, will be able to enjoy all the privileges of the club on payment of a very reasonable annual subscription. Details of this will, however, have to be agreed at the Thus, by changing the future policy of the club, a complete break will be made with the past, and all the traditions of the club, but it is felt that we must move with the times if we wish to increase our membership. Support for the “A’’ Class is not so good as it was a few years ago, but it is hoped that, by broadening our scope, we may be able to attract a few more people to the class. The chief object in writing this letter is to bring to the notice of your readers the fact that enquiries about membership will be welcomed, and should be addressed to the Hon. Secretary either at The Clubhouse, Home Park, Hampton Court, or to the address given in the M.Y.A. Fixture List. The Club’s sailing water is the Rick Pond, which is situated in delightful surroundings near the end of the Long Water, Hampton Court, and can easily be reached by road through the Kingston Gate. Nearest stations are Hampton Wick or Surbiton. From Surbiton station, it is necessary to cross the river by Hart’s Ferry. Westcliff-on-Sea, Essex. N. D. HATFIELD Hon. Secretary. WHAT YACHT? DEar Sir, Apparently my previous letter has received the wrath of the gods; however, I am obliged to Messrs. Andrews and Shackleton for their replies and would like to add my congratulations to the M.Y.A. on their recent secretarial appointment. Please note, gentlemen, the skilful way in which Mr. Andrews has introduced into his reply propaganda for M.Y-A. membership . . . more power to his Whilst I am delighted to learn of the M.Y.A.’s attitude and future plans for R:C. yachting (not previously published), I am dismayed to note Mr. Andrews’ comments regarding the unsuitability of existing classes for radio and the proposed introduction of a future class. Judging from his new design and article in another publication, I assume he refers to the 5.5 metre; if so my previous ‘comments regarding ‘“‘A’’ ‘class equally apply. Perhaps Mr. Andrews would give his sound technical reasons for the rejection of the 10-Rater as, whilst I admire his designs, I would with all respect point out the average R.C. enthusiast has neither the knowledge or time to build boats to a complicated formula and it is perhaps significant that after seven years of R/C yachting a National event for the majority class resulted in an entry of six, with one exception, all ancient boats. May I therefore reiterate my previous suggestion for a Nationals for any yacht which qualifies for an existing class rating prior to the installation of radio equipment (including 5.5 metre) as such a contest would eventually provide valuable information relating to the efficiency of each class. I would add that another well-known designer, having recovered from the initial shock of watching a mixed class race, has since sent me a highly unorthodox design for an R/C 10-Rater, which is now in process of construction. Naturally I would like to compare the efficiency of this against Mr. Andrews’ 5.5 metre, so if he cares to bring his boat to the I.R.C.M.S. contest next year, I feel sure we shall both have a most enjoyable day or so making comparisons—unless, of course, the Marbleheads tan both our hides. Mr. Shackleton’s difficulty in acquiring information regarding suitable radio equipment is understandable, as we all have our own pet ideas. However, if he commences with the system recently given in MODEL 1960 MAKER by Mr. N. F. Armstrong, I think he will be satisfied with the initial results. In conclusion may I assure Mr. Andrews that these suggestions are offered with the best of intentions and he will no doubt be very pleased to learn that I fully acknowledge the valuable assistance and technical knowhow which has been given to me by his many colleagues in the N.M.Y.C. Gosforth, OVERLAP ESTABLISHED Newcastle-upon-Tyne 3. HOUNDED DEaR SIR, I have read with interest the recent letters regarding R/C yachts and as I propose shortly to build such a craft, I am of course, interested in acquiring a suitable design for a class which is, or will be, recognised. “Overlap Established’? appears to think that 10-Raters are the answer and as I have recently seen the two local R/C 10-Rater Sharpies on the water, I must say I am very impressed. However, having read elsewhere Mr. Andrews further observations on this subject, he appears to favour the 5.5 Metre. ay I therefore, having recently been converted from power boats, declare my support for the views put forward by “‘O.E.’’ as I am appalled to be confronted with the task of building an A Class or 5.5 Metre (I anticipated getting the ?! ?) boat on the water this year!). Please, Mr, Andrews, give your “‘sound technical reasons’’ for by-passing the 10-Raters, as I feel that many other would-be R/C yachtsmen, such as myself, would receive more encouragement if this class was recognised for a Nationals event by the M.Y.A. Sharpies are comparatively cheap and easy to build and the 10-Rater formula allows this type of hull. To conclude, I would remind Mr. Andrews that “‘baying at the foot of the tree’’ is better than barking up the wrong one. Northumberland. WATER. (See below; more next month—Eb.). Some Thoughts on an “Exclusive Class” of R/C Yachts H.E. Andrews replies to ‘‘Water’’ and ‘‘Overlap Established’’ proportions | Lrohag jhe the pages of the Mopet MAKER the past few months I am delighted to see the interest which the possibility of an exclusive class for radio-control model yacht racing has evoked. I think it is clear that had the M.Y.A. not taken the step of recognising an interim “Conversion” Class this discussion would not have burst into print in the excellent way it has. This public discussion is all to the good and all those concerned with the government of the sport of model yachting welcome it. Many ideas have been expressed, but on balance most R/C men want a simple rule producing a portable boat which is easy to build. This desire, laudable in itself, stems, I feel, from the average R/C man’s unfamiliarity, and, as Mr. Armstrong of the Newcastle M.Y.C. put it to me, the “fear” of yachts. This “fear” is, in a sense, justified, for the art of yacht design is at least as complex as that of radio design and it is asking a lot of a chap to master both arts. However, to understand the “exclusive R/C class” discussion certain basic facts concerning model yacht design must be grasped if sound conclusions are to be arrived at. I think it is true to say that most R/C men, and, notwithstanding the popularity of the “M” Class, most “free sailing’ model yachtsmen want, first of all, a “pretty” yacht, because such a boat increases their pleasure and pride of ownership. This means that the boat must have overhangs and that all its must bear relationship to each other. The classic yacht shape was settled way back in 1893 by G. L. Watson when he designed those two masterpieces Britannia and Valkyrie IJ for the then Prince of Wales and Lord Dunraven respectively. This classic shape has continued unchanged in essentials to the present day, as witness Jimmie McGruer’s 8 metre Cruiser/Racer Orana in the February, 1960, “Yachting World” and C. E. Nicholson’s 25 ft. L.W.L. cruiser in the 1960 Boat Show, to quote only two recent examples. I think this inherent desire for a yacht “which looks like a yacht” is something which the proponents of the “M” Class type of hull and the sharple have failed to take into account. The correspondent “Water” in this issue asks me to expound the “sound technical reasons” governing the selection of a hull type for R/C use and at the risk of sounding like a schoolmaster I will try to do so as far as I see them. The first thing to be emphasised is that, in the past, model yachts have been designed to sail EMPTY (except for the 13 6 metres). This means that the designer’s main datum line, the L.W.L. (on which the whole hull form mainly depends and on which all his calculations rest) has been what it says, the yacht’s loaded water line, i.e., the line on which she floats when at rest. The fact that these boats have sailed empty has enabled the designers to establish a displacement/ballast ratio of something in the region of 70% to 75% which has given the yachts their (comparatively) terrific stability. Having 203 MODE MAKER established this excessive stability designers have been able to “slack off” their boats’ section lines, thus giving less wetted surface and sleeker, and therefore, faster lines. When it comes to designing yachts for radio-control the designers are up against the inescapable fact that the radio and ancillary gear to be installed in the boat has weight. (I have heard of some super-het equipments, including batteries, weighing as much as 161b.). This weight has got to be put into a boat, ideally of moderate displacement, without spoiling her lines or sailing ability. In my 5.5 metre design Debonnaire, to which “Water” makes reference, the loaded displacement ballast ratio is only 45%, a very different figure from the 70% of the free sailing model. This low ratio figure necessitates a very different hull form from the free sailing model, for hull form now must play its part in giving stability. Those who have seen Debonnaire’s lines will have noted her very firm mid-section which adds considerably to the stability given by her lead ballast. In this connection a further point for consideration is the fact that the centre of gravity of the radio gear is placed high, thus contributing to the tendency to instability which has to be rectified by the adjustment of hull shape. If my argument is right, and I believe it is, it means that the “conversion” of a boat from the M.Y.A, fleet, of whatever class, can never be anything more than a very inefficient radiocontrolled yacht. This is why we of the M.Y.A. deprecate the use of free-sailing class boats for R/C racing. The main purpose of a Rating Rule is to produce the type and size of yacht the originators of the tule consider desirable for the use to which the yacht is to be put. Designers and owners, being what they are, it is hopeless to have a “simple” rule if it is not to be shot to pieces in the quest for extra speed, or (in full size) a demand for extra accommodation on a given length. The 10-Rater is a simple rule, but when Dixon Kemp invented it in 1887 he never envisaged the abortions which it would eventually produce. Britannia, earlier quoted, was built to the L. and S.A. Rule, but by 1897 raters like Kismet were being produced with a L.O.A. 24 times their L.W.L.! (Readers who live near Surbiton can see this type in the Thames Raters moored at Hart’s Ferry). Similarly, the originators of the “M” Class Rule could never have foreseen the diabolically clever abortions the rule now produces (and I have been as guilty as other designers in the class). to their rudders in order to make them sufficiently manoeuvrable; 2. the only two fin and skeg full-size 6 metres, Josephine by Bill Daniels and Maida by Uffa Fox, were both doubtful successes despite repeated alterations, Some correspondents have made the claims of the sharpie type of hull for radio control under the impression that sharpies, or hard chine hulls, are easier to build than round bilge hulls. I can only say that from a good many years’ experience of model yacht building this is a fallacy, unless, like the kit-set dinghy, all the parts are prefabricated. In any case, if a hard chine 10-Rater conversion is used for R/C as “Water” would like, she would, with the weight of the radio gear, be sailing 4 in. lower in the water than her designer intended and she would be a perfect “sow” to sail! (The depth of a chine’s immersion and the length of chine immersed are critical design factors). To sum up then, the following points can be made:— 1. 2. 3. Owners and builders have no need to fear a complex Rating Rule. Designers should remember the essential differences required in planning a R/C model both as to hull form and rudder form and position. In my view the type of model best suited to R/C operation is a firm bilged full keeler with good reserve buoyancy in the form of overhangs and good freeboard and of such displacement that the total weight of radio gear is not more than about 1/S5th the yacht’s total weight. The foregoing are my own personal views on these problems, but I would like to conclude by saying a few words to all R/C model yachtsmen as the Hon. Secretary of the Model Yachting Association. A survey recently carried out by Mopet MAKER revealed that there are some 400 unattached R/C model yachtsmen. I appeal to all of them to join their appropriate M.Y.A. clubs in order that their voices and opinions may be heeded when it comes to making decisions on R/C policy. I have already addressed an appeal in the March issue of the M.Y.A. News asking all clubs to welcome R/C yachtsmen and to give them all the advice and assistance that lies in their power and I have no doubt that radio chaps will be welcome in the clubs. Three major items of R/C policy fall for consideration and probable decision this year. Thus, to get a healthy type. of yacht, the simple 1. Recognition of an exclusive R/C Class (or tule is OUT. However, owners and builders needn’t ° Classes). worry about this. The measurement of a yacht is 2. The revision of the Racing Rules to conform the designer’s and measurer’s worry. All the builder to the 1959 I.Y.R.U. Rules. has to do is to follow implicitly the designer’s 3. The international status of the R/C side of the instructions. If he does so, the boat will be in rating. sport. Another cardinal difference between free-sailing M.Y.A. policy is, in the long run, decided by the models and R/C models is the function of the rudder. individual members of the clubs, so I say “join in” In a free-sailing model the rudder is used solely to and make vour opinions heard in time for the next maintain a course pre-determined by the vane setting. M.Y.A, A.G.M. If you don’t, the decisions of the In a R/C yacht the rudder must perform its main M.Y.A.. will be unrepresentative and all the poorer function of altering the yacht’s course, either for for that, and a great chance of setting off the sport avoiding action or to round buoys. This calls for a of R/C model yachting on the right foot will be different size, position and type of rudder. This missed. Tequirement, in my view, brings us back to the type “Water”, in nis letter, chides me for using the favoured by the full-size designers, i.e., the full keel expression “baying at the foot of the tree”, but I yacht. Two pointers guide us to this view: am unrepentant. If you want organised R/C yachting 1. of all the fin and skeg “conversions” I have seen it is no use criticising the M.Y.A. from the outside. the majority have had to have additions affixed Come in and lend a hand. 204
