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MOOEL MAKER Hull Balance… in SLIGHTLY FINER SECTIONS FORWARD SECTIONED TO SHOW Model & Fullsize Yachts WATERLINE OF “SWALLOW” — WELL BEHAVED WITH GOOD BALANCE ON HELM BY Parc I LT.-COL. C. E. BOWDEN is model average 1 (a) The “symwith beam narrow metrical” sections fore and aft. Both ends almost the same, to give buoyancy as hull heels. BOLDER SECTIONS AFT SECTIONS FORE & AFT VERY SIMILAR OR SYMMETRICAL A full-scale average 1 (4) The modern yacht—greater beam— | underwater lines filling out bolder aft—narrower in foresections and yet still well balanced on helm as yacht heels. MODEL NOTES: es LIGHTL : AFT OF AMIDSHIPS “symmetrical” lines for balance. 1 (6) The modern beamier fullscale racing yacht sails more upright with better windward keel action. Slight “unbalance” of buoyancy fore and aft helps 7 SLIGHTLY FINER FORWARD windward performance. Bolder aft sections fit into water flow at speed, gaining support on quarter wave to help stiffness to carry sail. Rig usually lower than model. Cleaner water delivery with fatter buttocks akin to dinghy stern. \ SLIGHTLY BOULDER SECTIONS AFT B 1 (2) The narrow model heels more because of lack of beam and a taller rig than fullsize craft. Therefore emphasis is on FULL SCALE OT long ago a Mopet MAKER editorial called for a controversial discussion. There are all the ingredients in the interesting difference between the model and the full-scale yacht, where there is a marked divergence between the model “symmetrical” hull and the full-scale hull. This occurs in the method of achieving good “balance” on the helm as the craft heels, Both model and full-scale yachts are what is termed well-balanced, but the different outlook in achieving the object should interest the student of design. A well-known authority in model design stated in a recent article in MODEL MAKER on the question of “balance”: “It is surprising that the designers of full-size yachts have not taken more interest in the work and research that has taken place for many years among the model yachtsmen of this country.” He then went on to describe what is usually termed in the full-scale world, “symmetrical balanced. hull design,” in which the model hull usually has the forebody sections almost, if not entirely, identical in volumetric balance with the aft sections as it heels which, in theory at any rate, should mean that neither the bows nor stern rise or fall as the heel increases. In fact, this is only partly true, as I will endeavour to explain. The full-scale designer to-day seldom, if ever, produces a hull in this form. He certainly attends to the same approximate volumetric balance fore and aft, but in almost every fullsize design, he departs from this, by finer entry sections, the maximum beam a little aft of centre, and slightly bolder sections aft. See Fig. 1, which I have purposely exaggerated to clarify the situation for the uninitiated. In some cases the sections aft are considerably bolder to suit certain specific requirements, and yet the modern hull, if sailed reasonably upright, is very well-balanced on _ the 378 helm. Modern sailing technique to win races regularly requires “upright sailing,’ even on a keel boat hull that gains its initial stability by heeling. There must be a trace of “weatherhelm,” or a- slight tendency to eat up to the windgusts, as the racing helmsman of to-day “feathers” up to the gusts. The old method of “sailing off” free and by, to windward, is virtually finished. As both types of hull are balanced in their own way, why is there this divergence in design, with both admitting that volumetric similarity is neces- sary? What can we learn from it? I have, so to speak, a foot in either camp, model and full-scale, for I regularly race full-scale keel boats and I also carry out experimental work on sails, hulls and keels, and first in conjunction with friendly financial support from America, using in the instance models, and later full-scale craft: At one time I wondered if full-scale designers might be unaware of model developments in hull design and balance. I wondered if they might be missing something. Therefore I made it my business in the course of my work, to tackle several wellknown full-scale designer friends that my racing and experimental work brought me into contact with, including “towing tank” experts. I soon discovered, as might be expected, that they were all well aware of model “symmetrical” hull developments. All recognised the fundamental desirability of good volumetric balance fore and aft as the boat heeled. In fact they practiced it, but with a difference, based on practical racing results and tank towing tests. Full recognition was given to the work by the model men some years ago in emphasis on the importance of balance. plained why they appreciably diverged standard modern model “symmetrical” | a laying the They exfrom the hull. See —_—— AUGUST, _ Apart from sailing in hundreds of full-scale races but more easily handled than an “A” class boat. This | propsse to do in the fairly near future. Radio racing has developed, rightly, along the full scale Royal Yachting Association racing rules that introduce all the fun and excitement of racing tactics. This means the emphasis must be on quick in keel boats and dinghies, I have built many model hulls of glves poor large size, for comparative I find results the smaller when model produced full- scale after sailing a model free. These models have been of widely diverging types and shapes, from the purely “symmetrical” hull to the light planing wide transome keel boat hull. I have tried long manoeuvre, is true to say, that the very closely every ‘‘sym- be the best to windward, or the fastest off the wind, either in a helmsman’s hand or in the tank. In order to emphasise that this is not my personal quate Mr. Douglas Birt, that well- known yacht designer and writer of articles and books expressing modern design trends, who said “The completely symmetrical hull, in which the fore and aft bodies are identical, as opposed to being merely similar, is to-day uncommon—but yachts that we know. There seem it, and other considerations mitigate against exact I submit, it is these “other considerations” that we must consider, if we are to understand why there is this difference in outlook in practical application of the well-balanced model and the well-balanced fullscale yacht of to-day, Nowadays, quite unlike the days of long ago, it is obvious to all that very widely diverging buoyancy sections fore and aft, as the hull heels, cannot be tolerated. Thus, if the stern cocks up and the bows drop very appreciably as the hull heels, as happened in the old narrow vertical stemmed, and wide aftersectioned cutters of many years ago, the boat became hard mouthed in a blow. On the other hand, if through uneven buoyancy shifts the bows rise and the stern drops as heeling takes place there will be a lee helm, dangersus and bad to windward, as well as slow because of stern drag. The whole matter of balance is now particularly important to the model yachtsman interested in radio controlled racing, which has definitely “arrived” in spite of the gloomy forecasts of some of the model “experts” a few years ago. Radio racing is increasing rapidly as more taste its fun and sport: as radio gear becomes lighter due to the transistor, and now that it is s) much more reliable. Waterproofing has been solved, and a One Design hull can be made so much more cheaply in fibreglass. In the latter respect I recently made several light displacement semi-planning type hulls strictly one design from the same mould in fibreglass, for comparative radio controlled sailing trials of detachable rigs. I find that once. a form is decided upon, and a female mould made, the cost per hull is far lighter than building individual boats in wood which can never all be exactly the same. It will, therefore, be possible to make a real One Design radio racing class with adequate buoyancy for radio, and a weatherly hull, that will fit into reasonable portability, the combined cost of hull and radio being reasonable, the hull to be somewhere a little larger than a Ten Rater just like the by keel and hull. We should therefore was found that to When radio control arrived, make them amenable for stunting and competitive manoeuvres, some of this grooved stability and the wingsections had to be modified, A full scale designer friend of mine described a well known One Design keel boat in the following words, which I think sum up the modern full scale outlook very well. He said “The waterline endings, to be little justification, theoretical or practical , for such a shape, since balance may be achieved without symmetry.” gust on “grooved” stability. it Harrison would holding, slavishly. It is a fact that when model aircraft were originally power driven only, they concentrated Butler’s Trutina design is the only modern example amongst course study the full scale designer’s ideas, for radio racing yachts. It is perfectly true, and I am the last to deny it, that the Vane controlled model has produced what may well be the best shaped hull for its job of holding a “grooved” course without vice, from one end of the sailing point to the other, but the radio yacht should not necessarily follow this concept model designers) with forebody and aft sections almost identical, has not been found in Practice to let me good the “hands of the helmsman”. The latter means the full scale yacht’s eagerness to eat to windward in metrical” full scale hull (as most frequently used by opinion, and modern full scale racing yacht, with the vital ability to “feather” up to the gusts by the radio tiller in narrow hulls, medium beam models with heavy displacement, light displacement, hardchine and round bilge, and the modern American beamy hull in model form. It 1958 fine forward, and bold aft, accord with modern con- ception imported from America”. This is, of course, not the model “symmetrical” conception which has both ends virtually the same. In the full scale world I sail this craft, which is beautifully balanced with two fingers on the helm, whilst in the model world I often radio control a nine-foot long model hull designed by that most successful of the American designers, Mr. Phil Rhodes, whose famous yacht Carina has won so much over here and surprised our less beamy yachts. The model was designed for my American partner in experiment. We built her fifth scale, to test the hull, my twin “wingsail” rigs, and hydrofoil bilge keels, on Poole water under radio control, before the full scale yacht is built. George ‘’Honnest Redlich produced the radio gear. Mr. Rhodes came over here last season on his way round Burope on a business trip, and watched his hull in model form perform under radio control. During his stay for several days, we discussed the reasons for his design and her exceptionally fine helm balance at all speeds on all points of sailing, which we could observe by a pointer on the helm as I sailed the model past our operating launch in open seawater. We found this very wide beamed hull, by British standards, fine forward, bold aft, maximum beam a little aft of centre, a most weatherly boat in really rough conditions. In fact a sight for sore eyes in a blow as regard to speed and balance, and she is no sluggard in light airs. (To be continued) 379 PVN NANPA PNSPAAG PASEPAS AGES REMINDER: 1. R.C.M.S. REGATTA August 3rd/4th at Model Yacht Kingston-upon-Hull, Yorks. ¢ Details from: A. S. Wilson, 14 Washington, Co. Durham. Pond, Bidick East Lane, Park, Fatfield, Nl MAKER C Spe FIV A NEW 10-RATER DESIGN BY 53 WAP EY 4 incorporates most ofextent the IX-FIVE to a large lessons learnt in recent years with this class of yacht and as she apart, has no perhaps, design from tricks, the in- oie board rudder, the use of which is showing signs of becoming standard practice, she can be said to be a typical ten-rater. A great deal of work has gone into the development of her lines and the result is so pleasing that I am constructing ‘her myself, being at the time of writing just completing the job of planking her up. Although I myself am using a form of double – diagonal planking of one- sixteenth birch her form is such that any of the accepted methods of building can be used with- out difficulty. : Dan, 13 HO: Unlike some contemporary designs she is not particularly long or heavy as I feel that the continued increase in size and 7 <4 AN Ne oe oa7_t of ee L wold meme waTromp "0, ro epaskuoss responsible to d 4 0 MODEL MAKER PLANS SERVICE is no sub- a large extent for the increase, first by the alteration in the rules by which only 85 per cent. was ir) hy ® rapt lg displacement stitute for improvement in design technique. Admittedly the improvement in sailplan efficiency, etc., has been 386 the fore measured triangle area instead of | AUGUST, the actual foresail area, then the continual valuable water-line length. By this I do not imply that the maximum nominal hull draught should occur on or behind the mid-section, but only the peak of the displacement curve. The sail plan of Six-Five is of medium height with a top suit L. to F. ratio of approx. 3.25. I have given her a moderate A.R., (or L.F.) not merely to give an all round performance in top suit, but because I feel that such a sail gives a greater thrust per sq. in. of area in almost any weather, than higher or lower sails of the same area. It seems to me that the very tall sail plans which can, after all, only be used in fair or moderate breezes just do not pull as well as those with an aspect ratio of nearer three. This is particularly noticeable in ultra-light “ghosting” conditions where the stiffer material now used has difficulty in assuming the high camber more suitable for such winds. Also it is naturally better to have increase in aspect ratio plus the introduction of the mainsail kicking strap, rigging simplification, wire stays, Terylene sails and more recently the foresail strap. The vane gear also tends to make for a larger hull as with this device the long skeg extension formerly used is no longer necessary, thus reducing the wetted area, but at the same time lowering the centre of lateral resistance of the appendages with a consequent reduction of stability. This again requires a compensating increase in the weight of the keel. As Six-Five may represent something near the ultimate development of the present rather stereotyped form of ten-rater, I feel it is probable that any real future progress can only be made by a reversion to the all metal bulb keel. It may surprise some people to learn that what have come to be generally known as flying fins are not in principle a recent innovation. In fact several yachts of the late eighteenhundreds were so designed and an excellent example is contained in an Uffa Fox book, “On Yachts and Yachting” in which is shown "" ee the plan of a one-rater by Charlie a low top suit in the stronger ment in performance with the lower mainsail which is not surprising as in this direction the theoretical A.R. is unity. Incidentally I remember seeing the best theoretical A.R. for performance to windward quoted as five to one. Although I by no means agree with these figures they make an interesting comparison with those which practical experience has shown to be more realistic. Sibbick ass) COMING The skeg and rudder are also of the 2k eee EVENTS M.P.B.A. INTERNATIONAL AND ST. ALBANS REGATTA Venue: Verulamium Park, St. Albans. usual design, although it may be remembered that a year or two ago any sort of rudder without a bite out near the hull was likely to be criticised in certain quarters. A feature of this design is the way the moderately veed bow sections merge into the planing type mid-sections without any noticeable degree of unbalance or asymmetry of the submerged lee sections. Also the combination of dynamic and metacentric hull balance inherent in the design should give directional stability of a very high order enabling her to hold course even in the hardest wind slam. The bow and stern sections run into overhangs of moderate length and the hull form is such that they can be used to the full extent. If the hull design is faulty and the maximum depth of the wave hollow forms ahead of the mid-section then the aft “overhang” is, to all intents, below the waterline, and not only creates more wetted area, but also squanders reasonably breezes. Downwind also there is some improve- called Unorna with this type of fin. Incidentally for anyone really interested in design, this book and others similar in scope are probably available at your reference library. The fin on the accompanying design is of the more normal type allowing the root to be fully centralised in a more or less neutral position, thus permitting the formation of an uninterrupted wave hollow without any pressure wave boil out to windward from the after edge. 1958 Saturday, August 2nd.—2.30-6.00 p.m. Speed and straight running practice. Sunday, August 3rd.—1!2.30-6.00 p.m. Nomination, steering, pole events (all classes). Monday, August 4th.—!1!.00-6.00 p.m. International Speed—all hydroplane classes. French, Belgian and Italian clubs have promised support, and regatta should be largest ever held in this country. SCALEXTRIC DRIVERS’ CHAMPIONSHIP Venue: Gamage’s Model Dept., High Holborn. London, E.C.1. Wednesday and Thursday, August 20th-2Ist.— Junior 3-5 p.m. 20th; senior 5-7 2lst. Demonstrations throughout the week This is second event in Junior and Senior Model Car Racing Champion ships, first being held at Goodwood Easter Meeting. All Scalextric Owners’ Club members eligible. Further particulars from: Minimodels Ltd., New Lane, Havant, Hants. RADIO CONTROL YACHTING Birkenhead M.Y. and P.B.C. advise us that they will endeavour to arrange r/c fixtures at Birkenhead, or any other water, and that enquiries connected with r/c yachting are. welcomed, and should be addressed to: R. Snell, 27 Thistleton Avenue, Birkenhead. If interest justifies a Northern R/C Yachting Section will be formed. 387 MODEL MAHER) FORESTAY FITTING An ingenious tripod fitting fully adjustable for all suits of sails BY P. J. BUSSEY strap. On the boat aboard which the prototype is shipped, the jib tack is 34in. off the deck. No dimensions have been shown on the sketch, since individual fittings will vary to suit different deck to jib tack heights, but can be proportionately the same. In practice the fitting has worked perfectly, and no modifications have been found necessary. The kick strap holds the jib quite firmly, and the forestay can be tightened to the HE fitting shown has been developed from three previous similar fittings, all of which have had the same aims of: (1) Allowing the forestay direct fixing to the deck. (2) An effective jib kick strap independent of the forestay. (3) Fore and aft movement, together with the ability to take up a position in line with the forestay. (4) All components to be simple, light and accessible on deck. Although this fitting can be used as a radial jib boom fitting, it is intended for use with the normal pattern jib booms and it must be said at the start that as such, it is more suitable to boats of the Marblehead Class than others, since in this class sail area is restricted and many modern designs tend to lift the jib foot up, in order to allow the use of a firm kick desired tautness without pulling down on the jib boom as with the orthodox offset hook pattern. One disadvantage which does not crop up on my boat, is that with jibs of varying size on the foot, the whole fitting must be moved fore and aft when changing suits, entailing the removal and refitting of all four deck rack bolts. A small enough job on paper, but a bind when sailing, and a skipper with this problem would be well advised to consider how best the whole fitting can be mounted on some form of sliding rack, or similar. With jibs of the same size on the foot, all that is required is the realignment of the back leg with the new forestay line, and on such a boat, once the correct jib tack point has been found, the deck racks can be dispensed with and single eye plates fitted in lieu, thereby effecting a reduction in weight. As can be seen from a glance at the sketch, A. Forward compression legs made up from { in. dia. brass tubing with end plates for bolting to back leg and’deck racks. B. } in. thick brass plate; C. Bent plate, silver soldered to[back flat of tee section brass, with attachment hole in line with centre line of tube"above; ye FULL SIZE D. } in. dia. brass tube with brass plug TtoJ[bot- tom. Silver solder tube to back flat of T; E. Forestay F. Jib tack hooks on to forestay hook; G. Jib boom; H. Kick strap. Kick strap can be either turnbuclke or bowsie adjusted J. T section brass back leg; K. Battery terminal nut as clamp nut; L. 4 B.A. screw soldered to tee; M. |. PORT VIEW Brass rod with pointed end; N.B. Dimensions to + +P suit boat and rig. 388 AUGUST, the fitting is built up as a tripod, with a variable pitch back leg in the centre. The tripod feet are bolted, with the exception of the back leg which is done via a brass plate, to three deck racks which are firmly screwed down and allow for fore and aft movement. Now for constructional details. The deck racks are made from tee section brass, and drilled 3/32 in. holes at 4 in. centres to provide anchorage for the tripod by means of 8 B.A. bolts. Great care must be taken to ensure that all racks are lined up with one another, and that all holes are equally spaced. The front legs of the tripod are made of light gauge 4 in. overall diameter brass tubing, with riveted and soldered end plates protruding out as shown for fixing purposes. The back leg is made from wee section brass with the flat face aft. At the top the back face is cut away and the centre spine of the section carries up, drilled to clear an 8 B.A. bolt which clamps the two front legs either side of the spine, and around which the back leg pivots. Above this point is the forestay hook attachment hole. Silver soldered to the back face, also at the top, is a short length of 4 in. overall diameter brass tubing, open at the top but plugged at the bottom. Lower down on the back face is the kick strap attachment eye, simply a piece of bent sheet brass riveted and soldered into position. Make sure that the attachment hole is centred directly under the tube centre, otherwise the kick strap will never NATIONAL SIX 1958 maintain a steady hold on the jib and will either tighten or slacken as the boom is paid out. At the bottom of the back leg, one side of the back face is cut away to allow the centre spine of the tee section to bed nicely against the slotted } in. brass plate bolted to the centre rear deck rack. The slot to the plate is curved, and the radius originates from the top centre pivot point. This is very important otherwise the tripod will alter its shape as soon as the back leg pitch is adjusted. Running in the slot is a 4 B.A. bolt fitted through the back leg centre spine and soldered to prevent its turning. A 4 B.A. knurled nut is used to clamp the back leg against the brass plate, together with a leather or rubber washer in the appropriate position. A battery terminal nut is ideal for this, since it is easily gripped by the fingers and is not too heavy. The slot in the brass plate must be of sufficient length to allow the back leg to take up the top and smallest suit forestay slopes. The use of thinner brass for this component is inadvisable, since it has to take the rather considerable pull exerted by the forestay. A brass rod with the lower end coned pletes the fitting, and this fits into the top whilst being connected to the jib boom similar manner to the gooseneck on a boom. METRE comtube, in a main CHAMPIONSHIPS Bournville, 31 May—lI June With a day and a half scheduled, only eight entries, and, except for an hour or so on the Saturday, moderate to strong winds, it was possible to sail three complete rounds for the 6M Championship, despite rainy periods which at times were quite heavy. J. Drury and mate A. Cole maintained consistent top- line sailing for a well-deserved win, having clear leads at the end of each round of 9, 18 and 24 points. RESULTS Gey | Wacken) | Lapwing 2 Oberon 3 Psyche 4 Heather 5 Dare 6 Chance Again Seafarer 8 Just It Nes
