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Novemb (LR. £1.06, U:S,A- [> wncazne pAPoVGwelarbssouanHReelSOl,reDea’si.gneTMe ~ . An International | ‘A’ Class S | mentioned in my recent article “’A’ lass Design Parameters,’’ October Mode! Boats, it is one thing to deduce parameters for a yacht design, and quite a separate one to design a successful boat. With no previous experience in the ‘A’ Class, and none sailing locally for comparison, |am probably sticking my neck way out to design one, but here goes. My design philosophy for the Orca was a rather simple one. | used the already proven techniques developed for the WNerka, Kisutch, and Keta series of boats, and simply changed the dimensions to provide me with an ‘A’ boat which fitted into the rather narrow range which | concluded in the design article should result in the best all-around boats. More specifically, | chose the 55in. LWL in order to maximise the SA/Ib, and likewise chose the ‘’72 per cent of the minimum displacement,” or 381Ib for the same reason. With the hull shape already chosen, and the above dimensions set, it was a relatively simple matter to arrive at the actual dimensions. | decided to give the boat what | hope to be 10 per cent working overhangs, and these are tangent to the rocker at the waterline. The spoon bow was developed to give as natural as possible lines to the forward sections, avoiding the distortions and hollows you get with many shapes of bows. The result was an overall length of 69in. and a beam of 14%,in. The long bow overhang increased the prismatic somewhat over the Keta, and | ended up with a displacement of 38.7Ib including the displacement of the appendages. These have considerable volume in an ‘A’ boat, making up about 12 per cent of the total. You will note that other than the displacement penalty (which from my previous article is shown to actually be an asset), the yacht carries no other penalties. The quarter-beam length, draught, and freeboard, are all within allowed limits. | should mention at this point that the accuracy of most drawings and building techniques are at best plus or minus one per cent each, leading to a two per cent possible error even with great care being taken at all stages. An error of only Vg9in. over the surface of the hull will produce this much variation in volume, an error which for an ‘A’ boat of this size works out to about ¥,lb. Since the hull will displace an extra 1.7lb for every 0.1in. that is pushed into the water, and this will change the waterline by approximately %,in. with even the small two per cent tolerance, the hull may have a waterline plus or minus ‘,in. at the original displacement of 38.7Ib. This, of course, will affect the rating somewhat, and may require a slight change in sail area. It is, of course, possible to go even further afield, 594 — Designed by R. B. Sterne by simply adding or subtracting weight, although | would not recommend varying from the designed LWL by more than an inch either way. For example, at a LWL of 56in., the displacement would be 41.0lb, and the sail area 1130sq.in. approximately, while at a LWL of 54in., the displacement would be 36.5lb, and the sail area about 1165sq.in. You will note that although neither of these boats fall within the narrow range determined in my article on design parameters, they would both have distinct advantages in different weather conditions, with the shorter boat being better in light airs, of course, while the longer LWL, carrying more lead, would have the advantage in heavier winds. | still feel, however, that the 55in. LWL offers the best compromise. The plans show 29lb for the amount of ballast, as | feel that with any reasonably light construction, a ballast ratio of 75 per cent is easily possible for an “A” boat. You should, of course, carry as much ballast as possible without exceeding the LWL and displacement desired. When! was considering the shape of the ballast, | looked at triangular, rectangular, and elliptical sections, as well as circular. | discarded the triangular and rectangular sections because of likely changes in drag due to the pitching motion which is always present in waves. This left me with the ellipse and the circle. An ellipse measuring 2’in. x 3%, in. was considered vs. the 3/,in. circular section, and the elliptical ballast would have increased the righting moment by two per cent, but would have increased the wetted surface about about one per cent. As | was still faced with the possibility of increased drag when heeled, or when pitching, | opted for the conventional circular sections. The profile of the lead, incidentally, was taken from plans of one of the fastest American nuclear attack submarines, with the parallel midbody removed. | figured | certainly couldn’t argue with their shape! The rig was designed at the maximum allowable height, as is current practice. The dimensions were chosen to give about 40 per cent of the total area in the jib, a figure which | favour for radio control yachts. | chose to have no roach on the jib, as it would have to overlap the mast to add any area, and this would obviously present problems when tacking in light airs. If you want more sail area in light conditions, then | suggest that you build yourself a Genoa. | have shown a 180 per cent Genoa on the sailplan. This is certainly possible by radio control, as has been demonstrated For Radio Control quite successfully on the Vortex 60 from Vortex Model Engineering in California, USA. They even produce a winch, called a ‘sheet eater’ | believe, for this purpose. | have not seen the unit, and do not know its weight, but another possibility would be one or two of the Whirlwind, or Jackson winches. It seems to me to exploit this area of the rule makes a great deal of sense, particularly if you have a lot of light winds in your area. If the experience of full size yachts applies, the difference in light conditions could be devastating. | suspect that the lack of a suitable material for the sail has been one of the reasons that this has not been done more, but one of the new Y,oz mylars should be admirably suited for the job. If anyone succeeds (or has succeeded) in perfecting this system, why not write an article about it for Mode/ Boats magazine? Probably the biggest chance | had to take in offering a design without actually building a boat, was the mast position. | have really just made a ‘‘best guess” based on a few calculations, information from other designs, and previous experience. It would not surprise me to find that the final position is several inches from the one shown on the drawing. If this upsets you, let me relate to you a short story about this. When | first started designing model yachts, | asked a naval architect friend of mine about the amount of ‘lead’ required between the centre of effort and the centre of lateral resistance. His initial answer was “depending on the type of the boat, any- where between plus 30 per cent and minus 10 per cent of the length of the waterline.” After the initial shock, | supplied him with more information, and he then narrowed the range somewhat, although the range still amounted to about 10 per cent of the LWL. From that point on, it becomes a matter of adapting previous experience. When someone out there actually builds an Orca, and gets it sorted out, p/ease write to me and give the mast position you found, measured from the bow. When | have received enough replies to obtain a con- census of opinion, | will make sure that the correct position is announced and the drawing changed, if necessary. Any comments about the boat’s performance would likewise be appreciated, including a brief summary of the skipper’s experience, wind conditions, and level of competition in the area. It really is a shame that there is no interest in the ‘A’ Class locally, so that | could offer a more proven design, although | am quite confident that properly tuned and sailed, it should prove to be a competitive boat. As far as construction techniques are Model Boats LY masT POSITION APPROX. ON 3x | 24th of beam camber | fu} Bees $2.3 uaF poruse cuca! SO”) Tr ueAcn Fito sorwrr lB ee net oe wmaoarizroacn) Male ; er LEA 17 FOOT Se 180% GE wok WW LIGHT fi nae ~ WHAT USE USE OF uses Sak. AREA $2& =10:d23″YBte connec 1179 «4.978: ae 12’ HER RIGHTS retained BY R. Te (39-37″max! B STERNE E39 E mu & AL OM + concerned, my personal choice would be two layers of 50z Kevlar for the hull, and a fabric covered deck. Whilst most of the traditional ‘A’ boat types are recovering from shock, let me remind the rest of you that every ounce you save gives you more ballast and a more powerful boat. | would also use a carbon fibre mast, again in the interest of less weight aloft, with the additional benefits of less mast turbulence, due to the smaller diameter possible, and the increase in stiffness over aluminium. | estimate that it should be possible to keep the weight of the complete boat, less ballast, to about 6lb, and therefore increase [_wwri997_| D z a2 R: 9:06″ ; °F + 4 Plans for Orca, plan and elevation half full size, body plan full size, and sail rig 1/10th full size are available from Model Boats Plans Service, P.O. Box 35, Bridge Street, Hemel Hempstead, Herts, HP7 1EE. Please quote Plan MM1337 when ordering, Price Code Lee £2.95 plus 45p postage and packing. both sides of the balsa, the planks do not have to be spiled with the same accuracy as look after the fore and aft loads. Another in an all wood hull, simplifying this rather fibre reinforced spar, tedious task. from lead to deck. Obviously, it should be | won’t keep harping on the advantages of building light, as | feel that in this day and located at the centre of gravity of the lead, to minimise the twisting strain when the method would involve building a carbon- which again runs age it is a well proven fact. Be careful, how- boat is heeled. The fin can then be built up ever, that in your quest for lightness you do not compromise strength. Build light where around this tube or spar, from thin ply or a you can, and strong where you should. In glassfibre. The same construction techniques can be used for the rudder. particular, if you fit a fabric deck, make sure that you have sufficient beams to resist dis- solid balsa core, covered with 20z Kevlar or | would like to summarise the design of tortion, and to withstand reasonable collisions. The lack of diagonal bracing that | the Orca by comparing it to the criteria fora have seen in some ultralight decks concerns me. Once the deck is not rigid, sufficient diagonal bracing must be used to vious article on prevent twisting of the hull, particularly for the Orca. easy lines of the Orca should lend themselves readily to this technique. My advice here would be to keep everything as light as between the fin and rudder locations. For the deck material itself, use a good quality Parameter Recommended Orca fabric LWL above 55in. 55in. SA/Ib above 28.8sq.in./lb 29.7 SA/WS above 1.3 1.32 possible, especially the frames. You will not likely approach the weight of a Kevlar hull, Pay particular attention to the fin installation. Engineer this properly, paying particular attention to spreading the load over DF/WS above 1.5 1.57 Disp/Length below 150 130 Disp. below 45lb 38.7 the ballast, and therefore the power to windward by about 10 per cent to 15 per cent over the 29lb ballast shown on the drawing. Most people, however, will builda ‘one-off’ boat by plank on frame, and the with a wood boat, with one possible exception. The entire boat could be planked up in balsa, and then covered in 20z Kevlar or fibreglass on both sides. Don’t make the mistake of only doing the outside, as the balsa is not strong enough to withstand much of an impact unless it is used as a ‘sandwich’ material. You can even remove the frames after glassing the outside, and before glassing the inside, in fact this is recommended. Since you will be covering November 1982 type of model aircraft covering material, not one of the films. The films do not have the tear resistance of the fabric. as large an area as possible. With the shortness of the ‘A’ Class fin, it would seem practical to me to have an aluminium tube from (inside) the lead all the way to the deck, where it is fastened to a deck beam to provide the support needed athwartships. If it is pinned into a wooden block where it passes through the hull, and pinned into the lead, then the downward load should be taken care of. The fin itself will probably successful ‘A’ design presented in my premeters. ‘A’ Class Design In the table below, Para- | show the recommended values, and then the value SA above 1100sq. in. 1149 WS below 1000sq. in. 870 Prismatic Coeff above 0.54 0.545 As you can see, | have managed to come up with a yacht which meets all the criteria previously laid down for top ‘A’ class boat. | can only hope that the Orca lives up to my expectations. | may be contacted by writing to: R. B. Sterne, 3785 Edinburgh Street, Burnaby, BC, V5C 1R4, Canada. 595 George Leeds Older model yachtsmen will be sorry to learn of the death in his late 80s of George Bournville MYC, whoemigrated oferly Leeds, form to join his daughter in Australia some 15 years or so ago. George was for many years MYA Publica- tions Secretary and will be especially remem- bered as the regular Starter at the A Class Championships in the 1950s and 60s. Mickey Fun — reported by Mike Kemp On Sunday August 22, 1982 a small group of model yachtsmen gathered to contest the Mickey Finn National Championships. The venue was a delightful puddle deep in the heart of chocolate country — the Bournville club’s water in Birmingto ham. The weather varied from bright and sunny an amazing simulation of a water cannon. Meanwhile the wind blew, gusted, swirled and disappeared — all on one leg of the course! Now the course: suffice to say it used all of the lake, wound its way around six marks and went up and down the lake five times for each race; it went across ita few times as well. Officer of the Day, Dave Hollom explained that the map drawn in the clubhouse should be viewed on its side (just to add to the amusement). He also explained that, as only 12 boats would be sailing, everyone would sail in every race. a is General Meeting of the IMRYU at Armbouts-Cappel, France, during the World RM and R10R Championships in July, was without doubt the best-attended ever, with six of the seven-member Executive Board (plus the secretary/treasurer’s wife, Joyce Roberts, who does most of the Union’s typing etc.) and national representatives from Australia, Belgium, Brazil, Denmark, England, France, Holland, Italy, New Zealand, Norway, South Africa, Sweden and USA. In matters arising from the last GM minutes, action had been taken on all questions requiring it and Neil Bennell (Australia) reported his discussions with an Olympic Committee member re- garding possible recognition of model yachting; this seems unlikely in the immediate future but Neil is pursuing enquiries in connection with the World Games as an alternative. The chairman’s Report summarised matters over the last two years, most of which have been touched on or discussed in this column. From the accounts discussion emerged a decision that the IMYRU would pay freightage by surface mail if necessary for the return of trophies in time for the next event, but only if they were despatched at least four months prior to the date arranged for the event. Otherwise the National Authority concerned would be obliged to pay the full cost of return by whatever means was neces- sary to ensure the arrival of a trophy in time for the event. There was some discussion on finance, but eventually the motion proposing an increase in the boat levy to 10p sterling per currently registered yacht (in the international classes) was unanimously agreed. Amendments to radio racing rules put forward by the Racing Rules Officer (as required by Constitution Rule 6.7) to bring them into line with the 1981-4 IYRU rules were held over to be referred back to National Authorities for postal voting. A proposal that the IMYRU adopt the IYRU racing rules in their entirety, with a list of necessary amendments for R/C racing, was adopted, the main advantage being that IYRU rules are available in all common languages and only the short the hope that, despite the many views and amendments submitted to him, it should be possible to meet the original time schedule for postal votes. A proposal from Sweden, seconded by Holland, that YRU measurement instructions be followed as closely as possible in the future was agreed. (As a comment, one wonders how many present understood the implications of this?). Mr. Neil Bennell, OBE, was elected President in place of Byron Sansom (USA) who wished to retire after a four-year stint and who was appointed a Vice-President in recognition of his services. The remaining officers were re-elected. Also elected, to serve on the Rating Rules Standing Committee, were Alan Fish (Australia), JeanPierre Dole Robbe (France), Alexander Verheus (Holland), Jan Dejmo (Sweden) and Standley Goodwin (USA), and, for a new Racing Rules Committee, Hein ten Harmsen van der Beck (Holland), Des Fairbank (South Africa) and a nominee from New Zealand. Another new com- mittee, for International Events, will comprise nominees from Brazil, France and South Africa, reporting to the IMYRU Chairman. Ratification of recent Executive Board decisions included acceptance of new members Brazil, Hong Kong, Portugal and Switzerland, and recognition of the Royal MYC Antwerp, Dansk Modelbads Union, Nederlands Model Zeil Organisatie, and Svenska Modellseglarforbundet as the representative bodies of Belgium, Denmark, Holland and Sweden respectively. The Italian situation has been amicably resolved internally, the approved authority now being Modelvela Italia. In USA, the confused position there were no protests and very few penalty turns necessary: even the hailing for right of way developed into lighthearted banter. The target starting time of 10.00am was missed by only a few minutes. The fleet amassed behind the start line with mutterings of “‘where do we go from here?” and “who’s going to navigate?” Off we set on the first of many treks up and down the lakeside; surely a comical sight to the uninitiated, as the skippers struggled to guide their craft around the buoys and themselves past each other and the luckless spectators. Much to everyone’s surprise no-one managed to walk into, or on, the water — quite a feat considering that nobody appeared to be looking where they were walking. There was a short break after the first race whilst what appeared to be half the fleet was rebuilt. This may be an exaggeration but it did show one advantage of the strict one design rules — there is a strong element of interchangeability of components and gear. The only early permanent retirement was Mike Alton who then spent the rest of the day coaching father Roger, who has more than a passing interest in the Mickey Finn! Racing continued when repairs were complete and a pattern began to emerge. Andrew Hollom and Barry Jackson were the two to beat; only one person managed to beat both in one race during the rest of the day and that was Derek Priestley in the second race. With the exception of races, four and seven, when Jack Lee edged into second place, Messrs Jackson and Hollom monopolised the first two places. Part way has been handed back to the EB to sort out. through the morning’s racing there was some that the Olympic scoring system should be used at all future World Championships was referred continued briefly during the lunchtime Annual General Meeting of the Mickey Finn Association. Neither discussion was conclusive and the arguments for and against OOD action, and its constitutional standing, remain to be settled. The The minor wording alterations to the A and present M rules were carried, but the proposal back for postal voting. This concluded the business of the meeting, list of modifications for radio sailing would there- which had been in progress for not quite three hours. Although business was transacted, the main value was to allow people from various national organisations to meet (many for the first The Rating Rules Officer mentioned progress detail has to be discussed and decided in order to fore need to be translated. time) and to realise how much apparently small on the revision of the M Class rules and expressed keep the Union running smoothly. 602 Skippers were put on their honour to recognise their own infringements of the racing rules and self penalise accordingly. It is worth noting that discussion about the possibility of the OOD order- ing a change in suits of sails. This discussion was only conclusion that can be drawn, from personal experience, is that on a lake such as Bournville to change down a suit when nobody else does isa tactical bloomer of the highest order. The difference in boat speed in the more moderate wind has to be experienced to be believed: hang on to Model Boats top suit for as long as possible. | was lapped by the whole fleet! The OOD and skippers thanked the Bournville Club for the water, tea, coffee and hospitality. After the lunchtime AGM and some lunch, minor AGM must be like to be a spider being chased around The results of the AGM were as follows: There being no other opposing nominations, Dave Hollom, the OOD, continued to officiate the elected officials remain: even though appearing as if he had fallen in, Chairman Conclusions Secretary Ken Shaw Jack Lee Registrar Chris Dicks After a short period of cooking the figures; ten under some conditions, it can not difficult for a beginner to become a Mickey Finner so let us see a few more at Mickey Fun Amongst the AOB discussed was the apparent shipped from Rojair and the number appearing at sailing meetings, i.e. around 800 having left the factory and a good proportion of them somewhere in the British Isles. There is no doubt that sailing can but, perform successfully against Marbleheads. It is events. mismatch between the number of Mickey Finns MF’s to The latter come with practice and the application, opinion ville. Date to be decided, but clear of the holiday humoured only due The purists will say, as they did of the 575, that period. follows: with it is not a real boat. They are entitled to their races, ¥g point for winning and position points competition order as that, behaviour not of money, but of powers of observation re- thereafter, with one worst score discarded; the beauty boat garding wind strength and direction. Venue for the 1983 Championship — Bourn- bedraggled OOD presented the prizes in inverse showed in mined almost exclusively by racing tactical skills. Derek Priestley Treasurer races differences tuning, the race finishing positions are deter- the bath by a shower unit turned full on! Brave which he hadn’t. his/her toes in the big time sailing rules. The championship racing resumed and the rains came; and How! For a short while skippers got an impression of what it gression for the model sailor to have fun and dip be fun, bunch sailing as with appeared such at a good Bournville Allin all the day provided a very pleasant period of generally very close racing, despite the weather. Even those of us lower in the ultimate order were able at one time or another to ‘mix it’ with the obvious experts. They, in turn, were quite willing to chat about the particular features of their boat relative to the others. The whole makes it even more enjoyable. Even the lettering session was a remarkable contrast to the image supplied in the kit can be manipulated to produce that a beginner might have gained, from recent anagrammatical discussion in the modelling press, of a model boat names: the current champion’s is Muckey Fun! yacht ‘Class’ meeting. As a beginner in this class | The Duplex 575 has achieved a reputation for being a ‘fun’ class for racing especially suited to can thoroughly recommend it; | shall be back for more! the beginner. The Mickey Finn is a logical pro- Mike Kemp The MYA Amendment to ‘M’ rules proposals by IMYRU (Continued from last month). 10. RESTRICTIONS ON THE EDGES OF SAILS (a) The width of the roach shall not exceed two inches (5.1cm) measured from the after edge of the sail to the leech. (b) The area between foot and bottom edge of sail shall not exceed one inch (2.5cm) in depth. (c) Any area forward of the measured triangle at the Luff shall be measured as a bow and added to the sail area except if the extent of the bow is within the following restriction. If the half width measurement of a triangular mainsail does not exceed /, DIAGONAL B + the above area shall one inch (2.5cm) then not be included in the measured area. Distorting the shape of the front edge of the sail to avoid measurement is not permitted. 11. CALCULATION OF SAIL AREA (a) Triangular mainsail: multiply A by B and divide by 2. (b) Jib: Multiply Q by R and divide by 2. If shapes other than triangles are to (c) be measured then the shape is to be divided up into triangles and curved edges for the calculation of the measured area: the restrictions on the edges of the sails are to be applied as for triangular sails. (d) Curved front edge measurement: multiply 7 Luff by the PERPENDICULAR P. 12. BATTEN LIMITS (a) Battens in mainsail shall not exceed four in number and shall divide the leech into approximately equal parts. Battens not to exceed four inches in length (10.2cm). (b) Battens in headsail shall not exceed three in number and shall divide the leech into approximately equal parts. Battens not to exceed two inches in length (5.1cm). 13. HEADBOARDS AND EYELETS (a) Headboards shall not extend more than one inch (2.5cm) above the HEAD and shall not be more than three quarters of aninch(1.9cm) wide. (b) Eyelets or attachment points must be fixed to the sail within the measured area with the exception of headboards and the front edge bow. 14. SPINNAKER AND SPINNAKER BOOM (a) The maximum spinnaker hoist for any rig shall be sixty eight inches (172.7cm). (b) Spinnaker boom not to exceed fifteen inches in length (38.1cm), measured from centre of mast to outer end of boom. 15. DISTINGUISHING MARKS (a) The class mark is to be approximately one inch (2.5cm) high and one quarter of and inch (0.6cm) in thickness. (b) The registered numbers are to be a minimum of three inches (7.6cm) high, two inches (5.1cm) wide (except for the number one) and half aninch (1.3cm) thickness. (c) The national letter shall be the same size as the numbers and shall be placed at a different height to both class mark and numbers. 16. RADIO CONTROLLED MARBLEHEADS These rating rules apply to all Marbleheads but radio controlled yachts must comply with the following rules. (a) Spinnakers are prohibited. (b) All radio equipment shall be fixed in position during a race or series of races but items of equipment may be replaced by similar parts. November 1982 603
