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| | 7 Wraith ay ve _ r ~ *3 > Ris a 00 gs 3 OR some months now the mention of radio control and yachts has brought a faraway look to our eyes, and we have spent a lot of time, in conversation and correspondence, in eliciting views on the subject. Some of our conclusions were mentioned in our January editorial, where we said that the most frequent request was for a yacht about Marblehead size, but prettier, i.e. with overhangs. Since that date we have had ample confirmation that such a boat would be acceptable to the majority. A couple of years ago, in a conversation, D. A. Macdonald made the off-the-cuff suggestion that a 5 or 6 rater might be an interesting possibility for a smallish R/C yacht class, and this recent repeated request for “M size and nice looks” brought the conversation back to mind. A few calculations and sketches showed that either a 5 or 6 would be possible, but a 6 would have advantages which we will come to later. First thoughts were to limit size—there is no point in a rule which allows boats to get bigger and bigger, and if certain maximums were laid down in the first place, designers would work to these and we would not have the unhappy state of models now being outdated in a year or two. Portability is obviously a key factor—people will want to be able to take their boats home to tinker with the radio, and travelling between clubs should be as easy as possible, since, initially at least, competitive sailing will involve more travel than may be the case in a strong club of “free” sailers, so that a maximum length and weight are desirable. The basic equation would be:— SA x WL = 6, where SA is total sail area in sq. in. 6000 and WL the load waterline length in inches. There are a tremendous number of Marblehead sails about, and if we take 800 sq. in. as a probable sail area we get a 45 in. waterline, which seems a happy arrangement. Adding 20% to this for overhangs gives an overall length of 54 in., which we suggest is a reasonable maximum. Now a 54 in. waterline would allow 666 sq. in. of sail, which some might consider offers possibilities, so it would be necessary to make some form of mandatory maximum for the WL, say that WL must not exceed 85% of L.O.A. This would ensure that the spirit of the rule, ie. to produce a nice-looking craft, would be met at the upper end; no designer is likely to decrease his waterline to below 40-42 in., but even at 36 in. and 1,000 sq. in. of sail the model need not look too freakish—or would it be safer to have a limit? As far as displacement goes, it would seem reasonable to allow for the radio equipment to occupy about 10% of the total all-up weight. Entirely suitable radio and intergear can be built for well under 24 Ib. —Jack Gascoigne described his equipment installed i ea haa eran ees yeset|2es8 FErEA abe: WEE, tH] ee ay eT = in a Marblehead, in our May, 1958, issue, and gave the weight, including mounting box, as 2 lb. 6 oz., while radio wizard Dave McQue has a powerful closed-servo loop system which, complete with super- 226 het receiver, weighs less than 2 lb.—so that a maximum displacement of 24 lb. should be quite adequate. There is nothing to prevent anyone using four or five pounds of gear if he wishes, but the trend is towards Our own idea of a nice-looking, handy size R/C yacht is Wraith, illustrated at left. Note that this is an interim drawing and slight corrections have been made since, notably in softening the dip in the buttock lines between stations 5 and 6. We do not propose to include this design in our Plans Service at this stage, but should any experimenter be genuinely tempted we could no doubt arrange to supply full-size lines MAY,1960 More thoughts on a Radio Controlled Yacht Class I sere See | ae ee J Bn are making themselves more FF a SCENE Se \ VI [combined 6 The idea of an unlimited weight but some other restriction, such as beam x draught not to exceed Length of righting lever onc’ WL — — : AUWL. — 5 pf = Ly La T | onc’ WL. Length of nghtinglever \_ at @ ongie of heel if | \\ \\ D rd Ae \ “pores lever \ \\ £ Estimated CG.cflead free soiling Estimated GG .of leod a expressed to us, and it is hoped that they may stimulate some thought, bringing the basic points which we have outlined, as well as those we may have — \ Combined C.G. 130, or even beam x displacement not to exceed 230, did occur, but a simple limit seems best. No particular restriction of rig appears desirable— the method of measuring a M’s sail area should suffice. Several people have brought up the question of a one-design class. We are against this, since who can say that one particular hull is the best for the purpose at this stage? Besides, a fixed class would remove much of the pleasure for those who like to design, and might prevent some from participating if they didn’t fancy the particular design used; everyone has his own ideas of a decent boat, which is why we feel that the freedom of a rater rule is best. These are purely our own ideas, based on opinions ee a feat oak a ot 0 | ont soilng) rig ( free CG of hullond ares, oa \ and more overlooked, into focus. To demonstrate our suggestions, we are reproducing our Wraith design, which we have under construction. This has a 54 in. L.O.A., 45 in. L.W.L., max. beam 11 in., L.W.L. beam 10.75, draught 11.2, displacement 21 lb., S.A. 800 sq. in. Note that by cutting off the stern at the waterline ending and snubbing the bow by 3 in., quite a respectable Marblehead emerges. As an M she would carry 16 Ib. of lead and use a conventional skeg and rudder; the fully-floating rudder shown is designed for quicker If A is L.W.L. with R/C fitted, B is D.W.L. Estimated weight of radio gear 2 Led Average weight of hull, rig, paint, etc. … ot 438 au Free-Sailing hull, Weight of hull, rig, etc. Weight of lead oi os 6 ces ; ves Pee If A is D.L.W., C is L.W.L. Weight of hull and rig Weight of radio gear Weight of lead ay response under radio by eliminating any fixed sideways resistance aft. Copies of the initial rough design sketch were sent to various kindly and eminent yachtsmen, with a favourable reaction all round. John Lewis suggested some detail modifications for which we express our thanks; these have been incorporated, with consequent improvement. Harry Andrews went to the trouble of carrying out a stability analysis, and with his permission we reproduce his diagram and part of his letter, since it illustrates very well his last month’s notes on the subject of conversions. Harry writes: “As a design I like your draft very much… (but)… from the viewpoint of my theories | as expressed in the article (last month) … it falls down AS AN R/C YACHT. If the drawn W.L. is her sailing W.L. her stability will be insufficient to carry her sail … if drawn without reference to radio gear her sailing W.L. will be about ~ in. above the drawn W.L. and she would in consequence be very Muti Bar } bined pale me ot 9: CBhedes(CWL) VE \ | estmatedce \ smaller and lighter sets and batteries, especially since transistors felt. oe Ren sluggish. As a vane steered boat she would be excellent and I only wish the Ms had developed on your lines…” In reply, we pointed out that Harry was working on a 5 lb. boat, 6 lb. of radio, and 10 lb. of lead. We had in mind (and should have said so) 5 lb. of boat, 2 lb. of radio, and 14 lb. of lead, which was a much different picture. In answer, Harry hadn’t realised Se 6 lb. 5 Ib. 21 Ib. has ag bas ne, ee Ye ee oee oe des = 5 Ib. 16 Ib. 21 Ib. i 5 Ib. 6 lb. 16 lb. 27 Ib. This is Harry Andrews’ empirical stability analysis of Wraith under three conditions as noted. It illustrates well the points made in his last month’s article, taking no account of desirable changes of hull form for a R/C yacht. A boat with a firmer bilge would move the heeled CB further out, thus increasing the height of M and length of righting lever. Analysis allows 6 lb. of radio gear, whereas design envisages only 2 lb.; result would therefore be more favourable. that 2 lb. was a possible total weight for radio, intergear, and batteries, but adds “. .. We are getting down to something like the scale crew weight… and almost the last snag to future development is removed, The last snag seems to be the cost” (see later). Further comment from Harry Andrews is: “I don’t know why everyone seems to think that there is room for only one exclusive Radio Control Class. Provided ve rope them all in I visualise developments on three ines:— 1. A fairly small one-design Class, probably fibreglassed or kitted bread and butter. 2. A “simple rule” class, about the size of your design, which would be the happy hunting ground of the hull and rig experimenters. 3. A pukka Open Class producing a large boat. preferably the 5.5m. This, I think, would attract the same type of enthusiast as the A Class in vane sailing, i.e. the man who is prepared really to ‘go to 227 MODEL MAKER) town’ both on the yacht and equipment.” From Bourneville, Jack Drury makes an urgent plea as secretary of one of the few clubs with really close ties with both the M.Y.A. and the I.R.C.MLS. “Don’t let’s have any new class,” he says, “which will not make provision for either the existing 10r/6M or the M, not too much altered except for radio, to fit into it. The job of converting an already complete boat should be fairly small,” he goes on “Just some alterations to lead and/or rigging, plus building and fitting radio—not too bad, and there are plenty – of all three classes available complete bar the Radio Control. The job of building a complete new boat and radio is almost impossible except for a few retired folk, or a man wealthy enough to buy most gear, and of these there are, interested, very few. If you accept conversions, and why not, it’s a reasonable compromise, things should flourish, the new class can allow for the old, but if the ideal is insisted on— new. class, new boats, new radio—most of the children will be killed off before birth, and the class will be hoist 67 in. from deck, fore triangle less 15%. (Would prevent more than one top suit.) All M’s would fit such a rule, and nearly all 6M, any a shade long might need an inch off the counter. The normal S.A. (about 1030) would rate, or need only slight reduction. The few modern 6M of 28-30 ib. and 45 in. W.L. would need more modification, but their numbers are very small. As a point of interest, Wraith would meet this rule and could go up to about 850 sq. in. of sail. There, for the moment, we will leave the yacht side of things, in the hope that something among these suggestions will provoke discussion and even act as a catalyst to harden off a proposition which can be submitted for official consideration. The M.Y.A. secretary, Harry Andrews, has expressed approval of this public discussion and everyone has an equal chance to air his views; if you have something constructive to say, please write in. Radio In yet another conversation, this time with pioneer radio-controller Tommy Ives, the germ of an idea emerged and is worthy of study. Briefly recapping stillborn.” This question has been borne in mind in our suggestions, We put forward a maximum length of 54 in.; M’s are 50 in. Similarly, most M’s come inside the 24 lb. limit. The only snag is the overhang and W.L. problem, and it should not be impossible to stretch the rule in some way to include M’s. We suggested a maximum W.L. of 85% of the L.O.A., which in a 54 in. hull would be 45.9 in., barely enough to take in many present M’s. A sail area penalty may be the answer—if we subtract the W.L. from 50 and the position, we wish to control, at the minimum, two yachts independently, and for reliability we need four channels in each. To avoid any possibility of interference, crystal control is desirable, but a crystal can only be conveniently fitted to a superhet receiver. Cost of a commercially-built transmitter and receiver for 4-channel simultaneous control, with crystals, would be in the order of £50 at present prices. If a club bought an 8-channel simultaneous transmitter (not necessarily crystal controlled) for £30-£35, and plugged in two control boxes with four coutrols each, each skipper need only buy a 4-channel receiver which would plug into his intergear. It needs no crystal and need not be a superhet; price would be around £14. The transmitter reeds could be tuned to each pair of receivers in a few seconds, so that one transmitter could be used for a complete race between a dozen boats. If one receiver gave trouble, rather than waste time fiddling, someone else’s receiver could be plugged in in the boat instead. Tommy stresses that he has not personally tried this, but we know at least three experts who have, and multiply the result by 10, we would have a figure which, as square inches, could be subtracted from the sail area allowable under the rating rule (ignoring maximums) which would even out M performance thus: WL 47 in. rated 766 minus penalty of 30 = 736. 48 49 50 750 735 720 20 = 730. 10 = 725. wane = pak The idea of this is that a converted M will be quite eligible for competition, but at a slight disadvantage on S.A. It may be that the overhangs of a boat built to the rule and the normal reduction of sail arising from the M waterline length would provide a sufficient differential—this is a hot chestnut tossed in for argument, and this acceptance of the M in the class is the chief reason for suggesting a 6 rater rather than a 5. Jack Drury has also produced a suggested rule which would rate either a 6 M or an M, as well as some of the older small IOR and many of the Continental classes—quite a wide net, which would no doubt lead to a gradual development of a particular type which people would change te*over the years. This suggestion is for a 7 rater, thus: Total of exceed 100. L.O.A. and L.W.L. in inches not to Total of maximum beam and draught not to exceed 21 in., any excess multiplied by 4 and added to L.W.L. before measuring. Weight with radio, not to exceed 25 lb. 1 be added to measured L.W.L. part thereof in excess. in. to for each pound or Rating L.W.L. inc. any excess as above x S.A. two models can definitely be operated side by side in the water. The snag is that an 8-channel simultaneous transmitter can only in fact send two signals simultaneously (we have checked this with V. Rigby, E.D.’s radio designer) so that if one skipper held on rudder while adjusting his sheets, he would prevent his opponent from operating until he released one key. However, since signals would normally be of only 3-4 seconds maximum duration, this may not be so bad as it sounds. The alternative is to provide two simultaneous 4-channel transmitters. To avoid retuning, it should be possible to con‘ struct the transmitter(s) so that each skipper plugged in his own set of transmitter reeds, matched to his boat; this could be done with crystals, incidentally, to allow a club to use two transmitters for any number of crystal-equipped boats. By having the whole cost of the equipment lifted from the individual’s shoulders in this way, many more would be tempted to have a go, and no doubt in due course would purchase their own transmitters. There is no doubt 6000 not to exceed 7. Limits, same mast and main boom all suits. S.A. measurement as 6M, i.e. limit to jib hoist 53.5, main that even the most sceptical traditionalist yachtsman gets quickly absorbed in manoeuvring a model if someone passes him a control box, so much so that S = ey with reluctance that he hands control ac 228 – = mn Typical sheer for normal 10 roter nae | ie 3 4 3 = —LWL rm rg 2 Fug 7 Ses Se ore here ae e I Profile fuller th a i. fairly consistent. It is decision to take and on unlikely that any radical yachts as they have the easiest rules. The Marblehead class, although a very simple rule, is beyond: even the experts. Hideous contrivances have won races but the number of M class boats which combine efficiency and aesthetic beauty are few. If the yacht falls within the dimensions given below a satisfactory boat should be the result, 10 Raters LEW acy 54/55 in. LOA; oss 68/72 in. L.W.L. Beam … ire elUPN tein Draét ** sc. see Boe Wp PASEie Displacement … … 30/34 Ib. A Class POW. 54/55 in. E.OAS. L.W.L. Beam 78/82 in. 134/144 in. Draft Displacement in. 55/60 Ib. Very few modern, successful yachts lie outside these limits. In the 10-Rater class, it would be advisable to keep the displacement nearer 30 lb., if the lake generally used has light winds, and 34 Ib. if sailing on an exposed coastal lake. . With the A class, the choice is not at all critical and provided no penalties are incurred by the rule, it is probably the easiest class in which to produce a successful design. The rule is so well drawn up that departure from well established design traditions will inevitably lead to disappointment. There is scope, however, for detail technical development and the artist in the designer can have full rein. Having made the choice, the design can now be started and it is a convenience if the positioning of the profile, plan and body plan is kept constant for all designs. This enables drawings to be superim° ay | | ESE 2 5 4 line shows true arc : BY JOHN LEWIS Yacht Design change in hull design will render existing designs obsolete until further studies are made in sails and rigging. That will inevitably take a long time. These notes will be confined to 10 raters and A class Mina ees. ae \ = which all positive success of the yacht depends, is the choice of the principal dimensions. It is not wise in a first design to depart from figures that have proved successful and it is now fortunate for the ‘beginner that waterline lengths and displacements are Dotted aes X important ae profile @ visihe here \ NG PART TWO Chae most \ —\ SS i” posed and comparisons easily made. I find it advisable to draw the profile and plan at half full- size and the body plan full size. The waterlines should be spaced either 1 in. or + in. apart. The latter dimension is convenient for bread and butter constructors, as it is the finished thickness of 1 in. nominal thick planks. It is usual to divide the waterline length into ten equal parts and numbering them 0-10, starting from the bow, helps with the calculation. Three buttock lines are adequate and it is usual to space them equally, dividing the L.W.L. beam into four. Absolute accuracy in setting out these basic lines is essential. Professional naval architects nearly always draw their yachts with the bow facing to the right, but most amateurs face theirs the opposite way. instinctive to do this, so let us obey instinct. It is possible to draw in a profile. This curve does not need to be. symmetrical, and, in fact, it is better if itis not so. Fig. 1 shows an arc drawn through these three points to make more clear the form of the profile curve. The length of the overhangs is determined by the freeboard, but it helps in later stages of the design if the bow overhang is kept longer that the stern by 2 to 3 in. Freeboard forward on a 10-rater should not be less than 34 in., and 53 in. for an A boat will be usually adequate, but do not forget that the average freeboard on an A boat is determined by the rule and no penalty for lack of this can be tolerated. One should say, at this point, that no design ought to be started without 5 6 7 8 9 ile} __ EE LWL = V |v 2 Fig ‘Sheer very canoe 232 is The profile is attacked first, and so far the only things fixed are the endings of the L.W.L. With model designing it is easier to separate the keel from the hull and consider them apart. It is now obvious that the position of maximum hull depth and the actual amount of the depth must be established. At this point we skirt around the lot of learned counsel involving taking midship sections and deep chested profiles etc. and say straight away, let the maximum depth and maximum beam be midships. For the A class the depth will be about 54 in. and for the 10-Rater about 34 in. These dimensions are, of course, closely related to the L.W.L. beam and displacement, so that for a given displacement with narrow beam the hull depth will tend to increase. With 3 points now established on the sheet plan, it pronounced stern type for MAY, 1960 a proper study of the rules, and a silly mistake at this stage could lead to untold waste of time. Freeboards aft should not be less than 2} in. for the 10 rater and 41 in. for the A class. Extreme Bow _ The shape of the sheer curve is the most aesthetically important line of the yacht and much can be learned by studying the work of well-known designers. For example, William Fife was noted for his beautiful sheer lines. It is interesting to see how the characteristics of each designer shows itself in the sheer. Laurent Giles—sweeping well up to the bow: Robert Clark’s smooth and graceful, but rather weak aft; Charles Nicolson, almost straight; 3 rg for scow type 10 rater / i Moderate form of Bow 1 for short overhang boot. ‘ ‘ ‘ and from the model fraternity, Daniels, the most grace- ful of them all. The guiding principle can be set down, but like all things artistic, it is mot possible to provide a formula, and experience and an eye to see, are the final criterion. If the hull is narrow as in the 10 rater, the spring to the sheer can be relatively flat, whilst with the A class, which carries more beam, Bow for’A’ class of normal form Dotted lines show continuction of AS == ————s—“SOSTMOCOCOCOCOCOCOCOCOCOC the sheer can be more pronounced. If the deckline plan aft terminates in a point, then the sheer aft should have a distinct lift, whereas a wide transom The position of minimum will need less curve. freeboard is important and should be well aft. There Reverse Transom stern suitable for all types 4 3a is nothing uglier than a sagging symmetrical line making the hull look like a distorted banana. A few years ago, it was the fashion to have flat or even reverse curve sheers and Laurent Giles was of the very few designers who could handle this The idea behind this difficult line satisfactorily. fashion was to get the maximum accommodation into a hull, but the tide has turned and traditional shapes are coming back again. In a model there is no , Dixon Kemp curve of yocht keel will be dealt with later in more detail, but as a guide; let the leading edge start sweeping from the hull at about section 3 and let it reach maximum draught 14 in. in front of section 5. The after edge can be drawn to satisfy a eye for the time rN, . eing. | We should now con- ‘54 sider the midship reason for having a straight or reverse sheer from a performance point of view, so one may as well make it as beautiful as possible. Don’t tell me that I have designed with a flat sheer—Il know—and I must confess that I was influenced by fashion. Further experience has taught me that the slight reduction obtained in windage and ease of using plywood for decking, are not sufficient to offset the section. In some respects | this should have been done before the profile, but it is natural to want to tackle the profile later due to a slight maximum change in Until the eye is trained, the sheer curve should be more pronounced than you think is correct and depth. even then it will probably be inadequate. With the sheer line established the exact shape of the bow and stern profiles can be drawn in.. The modern reverse transom fits any form of hull very well and it is much easier to deal with than the old-fashioned counter or the canoe stern. Beware of canoe sterns, they are difficult to develop. My very first design had a pointed stern, and it taught The depth of the midship section has been wile i by the proe and we must select It is now possible to draw an infinite number of shapes through me a lot about the effect of curves when seen in 3 dimensions. The bow profile should in some measure reflect It the general character of the midship section. would be unwise to try and marry a long slender bow to a hull of the scow form. Examples of bows are shown in the sketches. The actual change in curvature of the bow can be quite subtle but for all practical purposes the Dixon Kemp type of curve produces a very satisfactory shape. All the sketches those two points. The fundamental fact to be satisfed is that the cubic contents of the hull shall provide the desired disolacement and the area of the midship section under water deter- the necessarv area by the use of a formula but one may just as well ap- slight refinements do not repay the effort. in, so that the whole elevation is there to see. The the mining influence. It is possible to appropriate are so drawn. The purist would say that there should be quite a chin in the bow profile in order to strengthen its character. This is quite true but in a model one very rarely sees this curve. so that very At this stage a tentative keel profile can be put is proximate by having a (continued on page 249) 233 a\ \ | \ : i ; —7–4 7 : ii ecommended cwi == a suitable L.W.L. beam. A ; ! first, even if it does have to be modified loss of appearance. / / \ as Midship = sections Z c ar “Tumblehome’ \ iai LW.L [ See 1a oN te a N es
