- Description of contents
MODEL YACHTS WY) Li] S) a \O S = © Zz APRIL 1961 SHIPS * CARS ENGINEERING MODEL WANED minimum. wh An unusual 10-rater designed by S. Witty status the rules still produce the fastest and most attractive designs of all. In no other class is the designer quite so free to develop something out of of performance in certain respects, and because of 9. get a bigger yacht this way, but the process can are guided (or misguided) by tank test reports, as such conditions can never be simulated artificially. Looking over the lines of the Flying Fifteen upon which Triplane was based I came to the conclusion that the balance and all round performance could be much improved while still retaining the advantages of The hull form and a shallow, easily driven hull. sections of the original F15 are unacceptable to the majority of yachtsmen and rightly I think, since Uffa Fox designed her to be driven more or less upright, whereas in unmanned craft the angle of hull is often around 25 degrees. The first requirement is for better balance and less wetted area and this can only be achieved by reverting to a hull of more normal dimensions. The design shown in the half scale drawings has a beam of 11.55 ins. and a displacement of 21 lbs. but in case some may wish to build a more powerful version, sections are provided for a hull with 12.0 ins. beam and 21 lbs. displacement. The former will have stability equal to a normal 10R of approx. 28 Ibs., 12 ins. draught, and the same beam, while the latter will compare with a yacht of 30 lb. and similar beam. This amounts to a saving of 7 lbs. deadweight in each case and the gain should be even greater in practice since, in the figures given, no account is taken of the elimination of the stability-reducing deadwood in the fin. While any mention of a flying fin is enough to arouse the ire of some more conservative yachtsmen, there are undoubtedly great advantages with this compared The weight of the fin is forward of the C. of B., therefore the lead can be lower (or heavier for a given position, angle, etc.). The fin is highly efficient due to the sharp sections and high A.R. a point where the power is the same as it was. You liveliness. Anyway this spectacle was enough to provide the original basis and incentive for the design shown. Certainly it provided a lesson for those who small 5. 8. greater power and then to increase the sail A.R. to wild conditions, surfing to windward in a series of short bursts, with her rudder visibly over at an angle of 25 or 30°, but going fast, with great verve and is There is no wood to reduce the stability when 7. this we are sometimes treated to the spectacle of some old hulk nobody gave a dog’s chance, walking away with the prize or, at least, giving the leaders a fright. Modern practice is to develop a heavy hull to give pretty manner with her nose down and transom stern well out of the water, moving, or rather, due to the displacement 4. 6. the ordinary. As in the other classes, the 10R has much increased in size and weight, to the detriment I remember seeing Triplane perform in the 1952 Championships and was most impressed by her action in the gale which “brewed up” halfway through the meeting. She went to windward in an effective if not Volumetric with an orthodox fin. (This becomes increasingly important as the speed rises, there being no congestion at the fin root.) T the present time there is a considerable revival of interest in the 10R Class. This seems largely due to the fact that although without international become something of a snare. Wetted area is much reduced. heeled. Spill and end losses are minimised as both ends are blocked. Interference losses (proximity) normal due to the small chord. Being metal the edges can be made The way power EXCALIBUR sharper and less prone to damage. economical most to of improve a yacht th e with- are less than BY OESIGHEOD SWitty castanwiior MODEL MAKER PLANS SERVICE 36, CLARENOON RO. WATFORD. HEARTS nm Excalibur configuration. Looking at it from another angle, I do not believe Triplane would have enjoyed her initial success had she been fitted with a normal fin. To summarise the advantages of this arrangement: 1, Frontal area of the fin is reduced to a out materially affecting the light weather performance, etc., is to increase the draught of the fin, thereby lowering the position of the lead keel. Unfortunately this must not be overdone as by so doing the centre of paras ag oat is also | —oe wile reached where more is being lost than gained. will ae | area and form resistance LWL owered, until a point is The increase in wetted must also be considered. Another factor affecting the stability is that when a hull with a long fin hard really is root pressed, the pressure to leeward of the fin tends to slide downwards due to the inclination and may lead to a complete This flow breakdown. does not happen to a narrow chord fin with anything like the same severity. In the original full-size F15 the draught of the keel was so low that to get the necessary lateral area the fin had to ex- tend to the aft tip of the bulb-keel. This was continued in Triplane, but with a draught in excess of fifteen inches this is 186 Le) \ \ SO WL# N me N IN ss) MN] baA iY. Ss : ~ a BS or ~SY a L—-|_ y A le peer ce ENTIRE APPENDAGE i 0-25″ DATA LENGTH QA. 74-23″ 74:23″ BEAM 155° 15-094 12-05 15-156 455° 4°55″ LENGTH WL. SAIL AREA SECTIONS WEIGHT OF FIN EXCLUDING ING HULL & BULB ASSEMBLY KEEL II’55″BEAM VERSION. ROS BEAM VERSION. 10 LBS. & 12 LBS. B 187 7 | eee =———————— r} S| : | a? 2 = ee hp, eel over windward performances have been considered. As the designer does not consider himself particularly gifted it is more than possible that others have considered a project similar in concept to that shown but are barred from further progress by a lack of draughting experience, since the development of a really fair round bilge is a difficult proposition for anyone unskilled in the art. If this is the case I hope this article may prove of value and encouragement. without upsetting the balance over the usual range of heel. * experimental. the several designs adapted from full size craft in being designed to the 10R Rule from the very start. With her small wetted area, shallow body and long, smooth curve of waterline, either version will be able to outrun an orthodox 10R, so only factors affecting energy conservation at normal speeds, the sections of the fore and after body should appear to be spaced approximately equally. This is impossible with the deep-chested Fox designs and may be partly responsible for their poor showing in light weather. 54-6″ 1092-20″ 21 LBS. 546° 1092:2. = 23 LBS.
