- Description of contents
209 April 1978 Woodspring Model Sailing Club Member JIM EDWARDS describes his Schooner Rigged ‘Kubernetes’ Aro three years ago two of our members, Jack and Steve Wadman, built a fine model of the wishbone schooner Argus twice the size of the original MAP plan version. When I saw how well it looked and sailed on the water I decided that one day I would build something similar. The opportunity to do so came when another of our members, Bob Underwood, added Kubernetes to the range of glass fibre hulls he has produced. Kubernetes is the 79:36lbs. heavyweight designed by John Lewis and the shape of the hull suggested a schooner rig to me, and so I set about designing a sail plan. As I liked the look of the wishbone spars on Argus it was decided to incorporate them on both the fore and mainsails. When it came to determining the sail area I decided not to use the original sail area of Kubernetes which, of course, has to comply with the A class rating rules, but instead to use a sail area calculated from an equation I had developed. This equation relates sail area to displacement as this seems a realistic approach to producing more correctly ‘canvased’ yachts. Just as nobody would use the same size engines in boats displacing say, 50lbs. and 75lbs. and expect the same performance, so the sail area should increase with displacement to produce the extra force necessary to drive the greater weight. The equation is: D?2 25D + -A50, ose 110 —D Total sail area Left in light airs the enlarged sail area shows its value. Above, details of the attractive rig. when D is the displacement in Ibs. As with most equations of this type it has its limitations. For example if it was true for all displacements then a non-existent boat weighing Olbs. would need to carry 450 sq. ins. of sail! Also the equation produces a curve (Fig. 1) with a maximum point at 88-4lbs., beyond which the sail area decreases as the displacement increases. 2300 2100 1900 1700 ; The sails are operated from a single winch drum which is possible provided the points of attachment on all three booms are the same distance from their individual pivot points. An 84in. x 34in. spade rudder is fitted 2in. forward of the position shown on the MAP plan and has proved to be extremely effective giving the boat a high degree of manoeuvrability. On the water the schooner rig looks very well and attracts favourable comments. It would be nice if this type of sailing boat became popular as races between schooners would be a fine sight, as well as testing the racing skills of their skippers. TOP SUIT SHOWN. 2ND SUIT DIMENSIONS IN BRACKETS. 1500 + 1300 1100 10 20 30 40 50 60 70 80 90 100 iO Fig 1. Calculating the sail area for 79-36lbs. produces a figure of 2,230 sq. ins. which may seem excessive but in practice has turned out to be about right, and the final sail plan is shown in Figure 2. With the top suit fitted the boat sails well in winds up to about 15 mph, and is still manageable beyond _ that, although it is advisable to change to the second suit. Model Boats 226 T= month, I will cover the remaining method of utilising the modified sectional area curve to produce a hull lines plan from the existing basis hull half breadths. This technique offers the least scope from departing from the original basic design. (2) Procedure for Drawing a Body Plan from Existing Basic Hull Half-Breadths It is possible to draw a body plan, correct for Cp and LCB from a basis form, by lifting sections for the new design from the basis hull lines plan at a revised spacing MODEL YACHT DESI G B.Sc. Al~~<. y( SA.CURVE / [ans 1 Le WA from the ends. The sections are derived without the need of fairing. Fig. 1. below, shows part of a sectional area curve, which has been corrected for the new design, superimposed upon the original S.A. curve. Part Four by CHARLES ROBERTSON, D 7ba_ he VA 7 me TM EyLS if NAV. ARCH. LWL b4=by ° Basis. spacing: Original eer oe T * D. Basis, ss T+ SN EAS x 8Design. esign.Basis B Design. D: Design Draught. 2/ BASIS WL. PLAN. | ae ee HALF BREADTHS LIFTED AT A MODIFIED POSITION (4°). | If we now consider any station (4 say) on the new design, it will be seen that if we drawa line at A horizontal to meet the basis sectional area curve at B, then the sectional area of both curves at 4A and 4B will be the same. We now draw a vertical at B. As the reader will recall, the S.A. curve is plotted on the same scale as the basis half-breadth plan, either on the same base, or directly above or below it. If the vertical at B is extended, it will therefore cut the waterlines at that corresponding position, (the revised section spacing 4’), where we now lift the waterline offsets. These offsets are correct for the basis design, but will require a correction for the new design beam and draught. The following relationships apply: 4 Breadth (design) = 4 Breadth (basis) « b(design) where; b (basis) 4+ Breadth (design) = maximum half breadth of 4 Breadth (basis) b (design) b (basis) load waterline. = maximum half breadth of load basis waterline. = half breadth of station under consideration (unknown). = half breadth basis at the modified station position. therefore, (b,) design = (b,’) basis « (4 Breadth) design and (4 Breadth) basis waterline spacing (design) = Original spacing x Draught (design) Draught (basis) We repeat this process for the other sections, dealing up to the LWL only (we could continue above, but the sections would probably require redrawing anyway in order to obtain a good hull balance — so that we may as well choose the type of body which we wish to achieve above the LWL in the first place and balance this). It will be noticed from this description, that we again require a tentative sheer plan and also maximum load water line half-breadth for our new design. I feel that even though this procedure is rigid, it provides the most elegant method of quickly modifying and producing a hull lines plan up to the LWL. This lends itself to a designer who isn’t a ‘one off’ type, but develops his ideas systematically through a series of designs. If we now move away from the sectional area curve approach, another modification method springs to mind, although I feel that it lends itself more to the 10R and A class type of design than to the Marblehead class which has no overhangs. (3) Procedure for Drawing a Body Plan for a Specified Block Coefficient from a Basis Form by Proportional Means A required volume displacement is produced, which retains the same coefficients of form as the basis hull. The proportions and coeff. of form of the basis hull must be fairly close to those of the design. A draught from the basis ship must be chosen to give the same block coefficient as required in the design. The waterline halfbreadths from the basis sections are expanded or contracted in the ratio of design LWL max breadth/basis LWL max breadth, and set off on waterlines spaced at intervals on the design plan in the ratio of design draught/ basis draught chosen (This approach is the same as method 2, except that a basis draught is chosen for the required block coeff. and the sectional area curve is not required). LWL. ra Bll? AB. LWL. : faye) ba Pilgitbo. DB BASIS fe) PESIGN _| 227 Spacing of waterlines (design) hp = hp = Tp/Ts Half breadths for the design for a particular section [iiye— on Bp/Bs By this method, a bodyplan to give the required displacement, without the need of fairing is obtained, but there is no control, however, over the position of the LCB. (For similar designs it will not alter very much). My personal views upon this method, are that too much work is entailed to find the correct draught of the basis hull for the required block coefficient. In practice, we require a set of hydrostatic curves for this basis hull, from which it is easy to read the required draught, but the work entailed in the formulation of these curves is outweighed if we forget about the required block coeff. and leave the normal basis draught as the one which we use in our equations, it is a simple matter to choose values for the draught and waterline (LWL) beam for our new design, and apply the ratios to produce a very quick lines plan. I hope I have covered in these articles all the usual methods which can be employed when developing a hull design (except the trial, error and frustration method), and I hope that the reader will have been given some insight into, and be able to utilise these techniques to produce any type of hull design which he requires. A systemmatic method is the basis of these techniques, and I hope stage by stage development will be rendered possible. I would now like to diversify, and cover my method of hull design: a novel and very easy design tecnnique, which produces from first principles, a ready faired underwater body plan of required parameters, with the minimum of effort (Lazy!). It is based upon the mathematics of a parabola, so I suppose a good name for it would be the ‘Parabolic Arc Method’. (I know of no April 1978 I checked this by drawing out a series of parabolas on permatrace be glad to try to answer them. Parabolic Are Method Let us first consider what we will require for a new design. The main items are: 1. Displacement. This is decided upon at the beginning, which will enable us to arrive at the required under- drawing film) and ellipse, hyperbola and the circle. A few years ago, a circular arc theory of yacht design was popular (promulgated by a Mr G. Blogg if I can remember correctly), which utilised arcs of circles to form the body plan. It never gained in popularity, due to the fact that the yachts produced by this method in spite of always sailing well, were never quite competitive against the top competition models of the day. If the reader can remember back to his days at school, he may recall that the parabola, ellipse, hyperbola and the circle are all basically similar; the locus of a point which moves so that its distance from a fixed point called the focus divided by its distance from a fixed line called the directrix, is equal to a constant e, where e varies between <1 for the ellipse, = 1 for the parabola, >1 in the case of the hyperbola, and = 0 for a circle. It follows then, that if a body plan can be generated using a circle as basis, surely it is possible to do the same with the other curves? It is, but in the case of the ellipse, the curve produced is very flat with a harsh turn of bilge when its major axis is horizontal (not quite suitable for a yacht hull, but if the major axis is vertical, a good catamaran type body is produced). MAJOR MINOR AXYS. AXIS. HARSH BILGE. MAJOR AXIS. ee MINOR AXE. water midship section area by use of the prismatic 2. coefficient (described earlier in these articles), the value of which is also selected. Sheer plan, showing the deck line, and the under- water body profile. 3. Load waterline plan (see last month). Having determined these, we will be able to commence with our design. If the reader examines the bodyplans of several different designs, it will be apparent that all the sections appear to increase or decrease in their fullness by some varying proportion. It is also true that the midship section of any hull is part of a parabola with its axis inclined towards the vertical. \4 ; sf ANGLE |OF INCLINAWON TOWARDS VERTICAL. y PARABOLIC AXIS HORIZONTAL PARABOLA Or » Lp ee SE Jo | – (to be continued) ‘SWISH’ SPLINES. SECTION OF ‘SWISH’ PLASTIC. RAIL. —USE FOR LINK ONLY AGAINST RADIOSED EDGE | i ea es aes icl STIFF | SECTIONS. PART HERE*USING SHARP eit oe deere: MED: STIFF FOR FAIRING STRON CURVES. USED FLAT. : ie superimposing way out designs, and I doubt that even then. There are 4 different types of curves which are generally available from mathematical formula; the parabola, literature pertaining to this technique at the moment, and would be interested to know if any reader has encountered it elsewhere?). I will explain the reasoning, and should be glad of any constructive (or otherwise) comments. Should the reader encounter problems, I will (plastic them in turn upon the midship section until I found one that fitted exactly (only up to point 0, the origin of the parabola). This will always happen, except possibly in | ( ! l Any reader contemplating draughting his own designs will need a set of splines which are very expensive and virtually impossible to get hold of. Satisfactory ones, however, may be made from plastic curtain rail, (Swish section), by splitting the original section as above. 229 insisted upon by the French Admiralty to comply with maritime regulations. Additional air trapped inside the ‘bell’ shape of the hull assisted air supplies already in the timber, and the pressure kept out the sea allowing the craft to have an open bottom for easy marching, the men just standing up inside. The Admiralty realised that their men could row and sail better than they could march. Rowing was the obvious choice, underwater, and a five-man ‘Underwater Rowing Craft’ was cunningly designed with the use of French self-feathering oars by which a speed of 15 knots was attained. By carefully arranging the neutralising effect/weight ratio, full control of depth and direction was achieved by a rudder and fore-and-aft stabilizing fins operated at the bow by the helmsman through fine-linked chains and pulleys. Underwater duration was two hours, compensated by the greater speed of the self-feathe ring oars. Underwater Lanterns were dispensed with by the Admiralty, who conveniently did not inform the Army of changed regulations owing to difficulties with the Paris Pigeon Post. All tests were highly successful, and the French furniture industry was mobilised for mass production, which would have happened but for a disaster to supplies. But, first, the Admiralty design was to be duplicated by the Left Bank and Right Bank Polytechnics whose students held the first underwater boat race ever to take place in the Seine. This was a success but was never repeated, because the many thousands of spectators lining the route never had any indication who was in the lead, April 1978 or who had won, or even when it was that the crews passed them by upriver. A serious set-back occurred for the French when the famous 1815 Paris timber fire swept through the Park Forest, destroying all’the N.S.B. trees. Napoleon was furious at this and ordered another forest to be planted or found. The only other forest of N.S.B. trees known was some way outside Brussels and was called the Waterloo Forest, from which the near-by village gained its name. As history relates, Napoleon advanced on Waterloo, but was defeated by the Duke of Wellington who had no idea why Napoleon should ever want the locality captured. Only after the battle did a hint come to light regarding the value of the trees, and another war nearly occurred between the Allies about who should have the timber for its navy. This was resolved by a British compromise. All trees were cut down (there is no trace of the Waterloo Forest today), and were heaped together to forma huge mound. Covered with earth, it had a British Lion placed at its peak to show that it was their idea. They didn’t think underwater craft ‘cricket’, anyway. Thus ended the intrigues of the N.S.B. tree, the mound still being evident even today at Waterloo in Belgium. A working model of these illustrated craft, if any N.S.B. timber can be found, would be of value at the pondside for recovery of sunken models. Particularly at the Round Pond, Kensington, where unfortunately the Royal Park Regulations do not allow this since A.b. 1066. SELF —-FEATHERING OARS HINGED STABILIZER FIN RUDDER CHAIN STEERING FIN FRENCH ADMIRALTY UNDERWATER ROWING I9t%. bei. of SCALE CENTURY CRAFT OAR FT. SECTION Unenlightened readers should kindly note, this /s the APRIL issue. ‘LOG BOOK’ From our MYA Correspondent Cy cen invitations have now gone out to all member Federations for what is billed as the ‘First Naviga World Championship for Yacht Models”, to be held in Milan 29th July to 6th August 1978. Classes are DM, DX, and D10 (vane Ms, 10 raters, and X class) and F5M. FSX, and F510 (same classes with R/C) and every member country can enter four competitors in each D class and three in each F%S, Sailing will be under Naviga rules. Since there are still people who are puzzled by Naviga, perhaps it should be explained once more. It was originally formed in the 1950s as a body to bring together national European organisations; one national body was recognised per country, since most countries possibly interested had a single national authority covering both sail and power. It is not unfair to say that there was a bias towards power boats, simply because only a very small number of Europeans sailed model yachts competitively, so that when a national authority was approached, it tended to be the power side if separate power and sail bodies existed. Thus the MPBA was invited to join for Britain, but declined. A result of this was that German and French were adopted as official languages. Another was that in countries with an IMYRU ~— affiliated yachting body, something of a schism was created domestically. Model Boats 230 A very small group of British enthusiasts wished to visit major European regattas — basically the late Col. Taplin, his sons John and the late Michael, a clubmate, George Goodfellow, and Vic Smeed — and for a time Col. Taplin paid the affiliation fee for Britain. Ultimately an MPBA team was persuaded to visit one of the biannual Championships (Amiens, 1967) and returned pronounced Euro-fans. Since then teams have visited Bulgaria, Belgium, Czechoslovakia, and Russia, while the 1975 Championships were held at Welwyn Garden City. Next year’s host is West Germany. Originally, the sailing events were held with the power classifications but were then split to separate water and, after 1967, with growing entries, to total separation, being run in interleaving years, odd years for power, even for sail. As many as 200 competitors have participated. In 1976 Naviga agreed to open membership to countries outside Europe (hence 1978 is classed as the ‘First Naviga World Championship’) and in 1977 adopted IMYRU (i.e. MYA) radio sailing rules. At the moment, free-sailing rules differ quite considerably as far as sailing is concerned, but there has been a definite if slow movement towards rapprochement with the IMYRU. We are, after all, all interested in the same thing. We are left with the situation in Britain where only the MPBA is officially recognised, but nominal membership of an affiliated club is no obstacle to anyone wishing to sail at Milan; many clubs have affiliation both to the MYA and the MPBA anyway. Full rules and details are expected at any time, and the MYA International Secretary should be in the picture before long. All of this will also help to explain the significance of the Naviga/MYA R/C Regatta planned for Fleetwood in July 1979. It is to be hoped that some of the Eastern European skippers will be able to come along; by all accounts they’re pretty hot — as indeed are others — and it would be interesting to see how they got on at Fleet- wood. – Now that the New Forest club has permanently moved from Setley Lake at Boldre, a new club has been formed to cater for those living in the area who prefer to sail at Setley. This is the Solent RCMYC, and membership was 12 even before the inaugural meeting. Tragically, one of the steering committee, Jack Gascoigne, died suddenly a few days after the first meeting; an appreciation appears elsewhere. Commodore of the new club is Bob Jeffries, and membership applications should be made to Eric Shaw, 21 Leelands, Lymington, Hants. (Lymington 76623). Membership is £3 p.a., the club is basically for RMs, and MYA affiliation has been applied for. Change of sec. for Tameside (Carrbrook) RMYC — now Jack Lee, 58 Urwick Road, Romiley, Stockport SK6 3JP. Alas, notification of their open meeting on 26th March (Festival Cup) did not arrive in time for the last issue, but the Ciba-Geigy Cup, which counts towards the new league, will be on 8th October. For over two years a small group has regularly sailed RMs at Pittville Park in Cheltenham, and is now officially Cheltenham MYC, already MYA-— affiliated. Use of the lake is officially limited to the winter months, when the municipal rowing boats are locked away, and buoys have to be placed and retrieved for every session, but this does not stop an almost continual series of informal races. A form of ‘racing ladder’, to carry results forward from week to week, is currently the subject of some thought. A major priority is finding a permanent site where open events might be held; Parks Dept. permission at Pittville is to named individuals, so visitors are asked to get in touch with the hon. sec., Cyril Adams, 173 Hatherley Road, Cheltenham (Chelt. 57613) before turning up at the pondside with a boat. Mike Hopkins of this club obviously thinks about rules and sailing, and has offered the following for pondering: The time limit rule in R/C racing. An inexperienced newcomer to both full size and model yacht racing has a number of substantial barriers to his enjoyment. There are some things we cannot change, some experienced competitors are always on the lookout for a pawn to use in a complex protest or a butt for a gamesmanship play. We can, however, take a close look at some of the rules which may be more harsh than they pa One such rule would seem to be the “time limit rule”’. Rule 3.10 recommends that a time limit of 3 minutes be allowed for all other yachts to cross the line after the winner has finished. This rule is essential for the proper management of the 20 or 30 race schedules which are commonplace these days and there cannot be many OODs who would be prepared to do without it. However, the same rule has a sting in its tail which gives zero points to any competitor who is out of time. Furthermore, rule 9 implies the theoretical situation where the winner could collect 12 points in a given race while the remaining 5 competitors receive zero for the same race. This nearly happened in a recent competition. An analysis of the scores of the 1977 Nylet Trophy for R1ORs raises some interesting points. 1. Of the 17 competitors who started, no less than 9 picked up at least one zero score through being out of time. 2. The winner of the wooden spoon scored non-zero in all but one race. 3. In two races all but the second place boat were out of time. If one postulates a new rule 3.10 which says: Sratendkess A yacht not finishing within the time allowed will score as if it had finished (last). Two or more yachts not finishing within the time allowed will score as if they had finished in dead heat (for the remaining positions),” and recalculates the scores of that particular meeting, the following happens: 1. 2. The first five scores and positions are unchanged. Most of the other competitors have small revisions to their scores but nobody moves up or down more than two places. 3. The three bottom competitors go home with double figure instead of single figure scores. What has been gained then by this change? I believe that rule 3.10 as it stands selectively discriminates against low scoring competitors and further reduces their scores. This can only discourage such competitors and such discouragement cannot be in the long term best interests of our hobby and sport. JACK GASCOIGNE We regret to announce the death of Jack Gascoigne, who passed suddenly away on 28th January. Old-time modellers will remember Jack as a cable-racing enthusiast in the immediate post-war years, and later as a power boater who was one of the very first “fast electric” devotees, in the days when silver-zinc was the only source of high power. Later still he turned to yachts and was a pioneer in R/C yacht development. He moved from western London to Bournemouth on his retirement, and was Commodore of Poole MYC for ten years. Recently he became interested in the smaller RM class, and only days before his death helped to launch the new Solent club. His models were invariably beautifully built and fitted, as became a man who will long be remembered for his sportsmanship, courtesy, and unfailing gentle good humour. Our sympathy is extended to Susan, his widow.
