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MAY 1974 TURI An 181 lb M which sailed off for first place in the 1972 Australian Championship. By D. V. Billing Full-size M.M.1182. lines Price drawing 75p inc. available fat from M.M. Plans, EN 1 | ref. i i i —<—<—<———} j After designing the ‘A’ class yacht Kia Kia, and before building it, I wanted to try out the same principle of hull shape on something smaller; quite naturally the step down was to an M class yacht. This class itself has changed from the heavier displacement type yacht to the medium and lighter planing dinghy type. Naturally everyone wants a boat that will point high to windward with good boat speed and go like the devil when eased to reaching or running. In Sydney our sailing water could be classified as basically sheltered conditions with average wind speed of six to nine m.p.h., and a maximum average of 20 to 22 m.p.h. With these thoughts in mind it was decided not to design a real lightweight but to work towards a medium weight of 18 to 19 lb. on a beam of around 104 in. The same system of design was carried out as in the ‘A’ class Kia Kia, with basic profiles of maximum hull draft at section 44 and maximum waterline beam at section 6 being maintained. The L.W.L. was kept at 48.5 in., as under light conditions of beating or close reaching, when all resistance has to be kept to a minimum, if a short overhang is kept at transom, as the boat heels to 10 deg. there will be less resistance or drag from the only partly immersed transom. A lot of ideas and thoughts have gone into the requirements of forward sections when considering planing. I agree with the principle that the underwater bow sections have everything to do with the action of the hull downwind. The bows must lift before planing can commence. If the bow digs in no amount of freeboard will prevent this tendency, also a slowing down of planing speed will occur. The garboard radius has been kept in this design as the hull shape experimentation could not be tried without it. Wetted area is reduced by using a garboard radius; for example, say a keel has a length at hull of 10 in. and a garboard radius of 1 in., then reduction in wetted area is approximately 8.5 sq. in. A wedge-shaped keel of fairly short length is used to give effective lateral area in the lead profile to help directional stability in light weather. The short length of lead allows some rake to the leading edge of the (continued opposite) 163 ee ee eee STRESS ee R/C Yachting in the U.S.A. In Part Three Laurence V. Goodrich con- cludes his review of the experiences of the Eastern Division of the Model Yacht Racing Association of America in R/C. However, if the servos do hold up, then we will have a real breakthrough in the cost and ease of getting into R/C quickly. Instead of $50 to $75 for a conventional SCU and battery, the cost of adapting a servo should be less than $5 and most of our R/C sets are sold in a package with two servos. We are for the most part using synchronous sheeting for the jib and main to one drum because the weight and bulk of our conventional winches are too great to permit the use of separate winches for jib and main. But adding a second modified servo adds only about three ounces of weight, although many will question whether the $45 additional cost for separate sheet control is worth it, at least for starters. Using one each for jib and main will spread the load and give more pull on each sheet. The amount of labour and skill required to modify a servo (once the technique SAIL CONTROL UNITS continued The other approach is theoretically much more promising, but we are not sure that it will hold up under hard use. A commercial rotary servo is modified to act as the SCU, eliminating the need for (i) has been worked out by a club’s electronics experts) is very much less than trying to build a conventional winch like mine. I hope the servo manufacturers will take note of this and begin developing stronger servos, or perhaps even fully modified servos, to fill what I believe would be an enormous demand from model yachtsmen. As I have tried to indicate, conversion to R/C is very simple and well within the capabilities of the average club member, but the winch remains a sticky problem for most. the extra motor (ii) the battery for the extra motor and (iii) the reversing servo and the two_ limit switches — all resulting in an enormous saving in weight and bulk. The rotary servo is modified by disconnecting its own potentiometer (which limits rotor travel to a quarter turn) and by substituting a 15 to 25 turn pot and then mounting a plastic sewing machine bobbin on top of the rotor to act as a drum. Ted Kuron from our Prospect Park MYC has done this successfully on a Kraft servo, for which replacement gears are available, by attaching the substituted pot to the outside of the servo casing, mounting the extra gear on the shaft of the pot, and connecting the extra gear back into the servo gear system through a slot cut in the servo casing. (There are many brands of servo and so you will have to experiment to see which can be modified this way. We have not been able to figure out an easy way to modify the MRC servo which does not have the all important 360° drive gear). Vane and R/C. Contrary to our earlier fears, we have found that vane sailing and R/C sailing are not incompatible but are in fact complementary. Some of our new members who came to us from R/C powerboating are now our most enthusiastic vane sailors. The trick is for the club to schedule races thoughtfully so that there is a good balance between the two, based on member interest. We have had great fun this last season experimenting with open racing — any class and any control — in which case we sail pond style instead of triangular courses to keep the vane boats more competitive. In a steady wind, the R/C skippers find the vane boats quite hard to beat and it gives them a good control against which to gauge the performance of their R/C conversions. The vane sailors, of course, delight in beating the R/C skippers on occasion. When a club has enough members with R/C, some races should The modified servo system does produce a fully proportional winch (not much of an advantage in my view) and on the Kraft with the sewing machine bobbin gives a 4 to 5 lb. pull, which is certainly adequate for an M, probably enough for a 10R but may be not enough for an A, although Ted Kuron used two all last season on an A. The speed from full out to full in is somewhat too slow, perhaps 25 seconds, but it does allow for very fine adjustments which are very difficult on my faster conventional winch. We have not had enough experience to know whether the rather tender plastic Kraft gears will hold up under hard use, and so this method is not recommended for general use yet. If we ruin the servo, that is about $40 down the drain. Top picture, Ted Kuron’s experimental on-board R/C gear mounted on his converted M. Through the plexiglass cover can be seen in the foreground his modified servo main sheet winch with a plastic sewing machine bobbin drum. At the back right is his modified servo jib trim winch, At the back left is a conventional rudder servo hook-up. While still experimental, this modified servo winch system may be a real breakthrough in developing lightweight sail control because the servos weigh only several ounces and they operate off the same battery as the receiver. 166 MAY 1974 Left, a glass-fibre March Hare converted to R/C by Central Park’s Noel Mcintosh. Note the deep wave pattern caused by considerable overloading, though despite the weight the conversion has proved a good performer. Lighter sail control under development should go a long way to restoring the designed waterline. ends of the pond and that this adds up to days in the large regattas. At Central Park last year the OD would try to set each race to last from 20 to 30 minutes with a five minute break between races and a two minute warn- ing gun for the running starts. We found that several laps of a short triangular course were more fun than one lap of a long course. If races must be run in two or more fleets because of frequency conflicts, it is probably best to alternate the races by fleets since skippers who have just finished 30 minutes of racing can use the time, while the other fleet is racing, to change batteries or make other adjustments. Our cautious and deliberate move into R/C has been a great success so far. Our clubs are growing in activity and membership and our supply of unused boats for sale or charter to new members is virtually austed so we are planning to make some moulds fibreglass hulls which can be produced in quantity. be scheduled for them separately so that they can learn and enjoy the new challenges of triangular courses and racing tactics. It may be that in time R/C will displace the vane as the vane displaced the Braine, but for now we are having great fun with vane and R/C and with occasional mixtures of both. Most of the really active skippers in the ED have converted their models to R/C so that they can sail either way, depending on the race schedule. We expect many more conversions for next season and to see more retired members come back with R/C since it is a lot less demanding physically than vane sailing. On the other hand, I find R/C racing more demanding mentally and emotionally than vane racing and that an hour or two of continuous R/C racing is as tiring as a long day of vane racing. Unlike vane racing, in R/C racing you are sailing against a fleet of up to 11 other boats around a triangular course using rights-of-way rules with constant control of the boat and sails. A corollary thought is that R/C racing is much more efficient than vane racing in the sense that a club can provide more actual racing time to more skippers in a given time period. While I enjoy vane racing, I have to admit that the tradition of racing in pairs means a lot of waiting around at both READERS WRITE Sir, accordance the R.P.M. long traditions of masking tip Featherston [n Model Boat statement your ‘Five by March Paddle | paddle a what it is, and then take it to the lakeside and compare the exhaust recorder! Benfleet, Essex note with the L. FLAGGING tape Hodgson from the newspape of Mr. Baister’s retirement: ‘He started tugs then late— Wellington to Liverpodl took and the €E. in tug returned paint line, my son a brush) iva at aw theulstick Bde none a door sane or y g suitable P corner until it: goesF a ait With No tea GE ial weather it overturned jand sank. Mr. Gillin ies g E. City of Manduring gusty Baister was picked/up by the tug milky cats Sachin ae vn arnt g. In February towing the Sunderlan is of you ee + th vive cood si ie Poe with the screw tug 1950 while chester to etc., a (after hav- y first, say from putting the W.L. on) that yachts if you in pull off from the roll Sellotape (not masking tape if are using recites and comparing it at home, it be quicker to record the note off for a learned Tugs named Stag’. he last tug named Stag was a screw tug. | quote and designing, ae pulled the fresh paint off one of Column by M. Law (August, M.B.) | would suggest that instead of recording it would of racing rules from scratch, but R/C does not mean t we can forget all we have learned about designing, ilding and racing with vane. The author would be pleased to receive comments and suggestions concerning this article, or inquiries ca@ncerning MYRAA, addressed as follows: L. V. odrich, MYRAA Secretary, 295 Henry Street, Brooklyn, New York 11201, U.S.A.) Sic Mr. W. issue of have thod of steering and sail control. It will add many dimensions to the sport and is fun to experiment h. We will have to learn some new things about | wish to correct i with We STAGGERED Dear TAPE ; IT AT HOME Dear In RAA. ilding and racing model yachts and of experimen- ane F it nario b * k soca As i rie : mo Xa jets earn tna ae at g ‘ Kent c : fa. Gould : Gentlemen, Fulwell’. the kit. The caption identifies the ship as ‘late 18th century’ — she must have had a very long life, since the White Ensign was not adopted in its present form until 1864. She wouldn't So |! think the /T Wellington which Mr. Featherston!) mentions was not the tug that was Idst in Feb. 1950 and was not renamed Stag. East Boldon, Co. Durh@m J. Shanks garding Endurance’ Racing in_ the thought that all Radio/Control Gear should have changeable crystals. | use a 5-channel propo set (saved up for and worked hard for), and to UNMASKING another | have just received the December issue of Model Boats and congratulate the builder of the cover model (H.M.S. Serapis — built from a kit). | wonder if the flags were part of mere eeecce the Union so Flag long shown a at life the to it wasn't adopted until 1801. The builder sible for one Union Flag at must be held wear main — respon- goof, however: the the main is upside | also have a newspaper photo of the screw tug Stag towing the barque Olivebank into the rivet Wear in 1935. | have also been several times aboard the screw tug Stag. Dear Sir, models hobby, are rather | am _ very fascinated and appreciate any model, and the workmanship jnvolved. Read- Ontario, re Canada Ss Arthur B. Harris ing Mr. his J. B. lifeboat a Dear Sir, | feel | must take exception to a statement by the M.P.B.A. Sec. Jim King in ‘The Secretary Writes’ re- apleam only Although scale not my particular down. | thought only barbarians from this side of the Atlantic made that mistake! OH! King’s and @xcellent article the 167 ee fear he had competitors set is have one moment. Multi to most pey unfair, frequency racing at the costs a fortune to remain tive, without being involved expense. In due to an also. Barking, my case | interest in Essex if fot at. they the present competiin extra use 5-channel aeromodelling R. J. Riches i ae a MODEL BOATS GENIE Part 5 of Vic Smeed’s ultra-simple Marblehead class yacht for vane or radio- control sailing. Drawings for this 50 in. model are all full-size (except sail plan) and show all construction detail and _ fittings. Full-size copies (two sheets) available, MM1175, price £1.10 including V.A.T. and post, from Model Maker Plans Service, P.O. Box 35, Bridge Street, Hemel Hempstead, Herts HP1 1EE. PSHE use of synchronous sheeting for vane-steered - yachts has become quite common over the past five or six years. All it means is that the main and jib booms are synchronised so that moving one control adjusts both booms the same amount. In a race, if the boat comes into the bank and a retrim is required to ease or harden the sail sheets, one large bowsie is moved and that is all. If an independent adjustment is needed for either sail, provision is made for this. To make both booms move the same amount in the simplest possible way, all that is needed is to have the sheet attachment points on the booms exactly the same distance from the pivot point in each case. The sheets are led through eyes on the centre line (to give equal setting on either tack) to the main bowsie, which must be aft of the mainsheet eye at all times if the sheets lead straight to it. Otherwise, if it was between the centre-line sheet eyes, movement tightening one sheet would be easing the other until the bowsie was past the easing eye. The amount of sheet feed needed to move the booms from full out (90 deg. to hull) to full in is rather more than can comfortably be accommodated in the deck space aft of the mainsheet eye, and to shorten the distance from boom pivots to sheet attach- ment points would mean accepting coarser adjustment. The simple answer is to lead the sheets well aft and turn them through an eye (or pulley block) and then to make them off to the main bowsie, which can now be moved almost the entire length of the boat if necessary. It means that the action of the bowsie is reversed, i.e. when it is moved towards the bow the booms are pulled in, but this is a simple mental adjustment. Our final deck fittings, then, are the eye to turn the sheets and two eyes to take the adjustable jackline on which slides the main bowsie, positions for which are shown on the plan. The Mast Most people can obtain aluminium or dural tube without too much difficulty, but if in trouble, Nylet Ltd., 118-122 Station Road, Fordingbridge, Hants can help. The main length of mast is 56 in. but if you wish to simplify and have room for the extra length, 172 it can be made 684 in., which then means only a ‘loose’ 2} in. piece for the masthead /jumper strut but also involves carrying unwanted mast if you have a second and third sail suit. It is still possible to add an extension if you wish to use a high aspect ratio rig for light winds. A length of 56 in. will fit in many car boots, which can simplify transport. Find some beech dowel or carve a hardwood plug to fit in the bottom end (the heel) and epoxy it in place. Mark carefully and accurately saw a slit to receive a slip of brass or s/s across the diameter and epoxy this in; the slip should fit in the slots of the mast step in the bottom of the hull. If desired, a shallow slot can be sawn at right angles to the first one before fitting the slip, and the slip filed after fitting until the fore and aft slot engages over the top of the mast step. This means that the slip locates the mast heel fore and aft, and the slot ensures that the heel is central on the step and cannot slip sideways. Clean up the exterior so that the mast passes easily through the mast slide. If a Tufnol gooseneck and wire eye for the kicking strap are to be used, as drawing, mark their positions and check, by stepping the mast in place, that they are at the height shown before fitting. If a commercial fitting is to be used, slide in place and again make sure all is clear before tightening the pinch screws. In either event, ensure that the fittings are correctly aligned dead fore and aft. Mark an accurately-placed line up the centre of the afterside of the mast and measure off for the jackstay securing holes, spacing them in pairs about 4in. apart and at 7-8 in. centres. Make a light pop mark at each: use a nail as a centre-pop if you don’t own a sharp one. Also mark the holes for the upper shroud hooks and jibstay hook and centre-pop. Drill them all 1/16 in., then use a round needle file in the jackstay holes, angling it to clean up the holes and allow a fair run for the stay. How the jackstay is fitted baffles some people, but it takes about two minutes. All you need is a needle threader, one of those fine wire diamond shapes. This is pushed into the second hole of each pair, inclined towards the first hole, and the cord is poked into the first hole for an inch or so. Withdraw the needle MAY strength required, and } in. is for Genie, though 4 in. can be boom. If you use a Roberts jib totype model, it comes with a threader and with it the end of the cord; it really is as simple as that. All rigging cord on the original model is 55 lb. breaking strain Sea Ranger braided nylon fishing line, which will wear for years and doesn’t shrink. It is absolutely ideal for the job and can be obtained from virtually all shops selling fishing tackle. There is, alas, one snag — it comes in 150-yard reels and costs somewhere around £2.75 a reel. One reel will fit out a dozen or more yachts, but it is a lot to pay out for just one. However, good rigging cord can be obtained in smaller quantities from the fittings suppliers previously mentioned. The jackstay should be hauled up as taut as possible and can either be knotted through the mast as drawn or tied in a loop through two holes close to each other. It is not difficult to get it tight but if flax cord, etc., is used it might be necessary to retighten it after an hour or two of sailing. To complete this part of the mast, bend one side of the shroud attachment to shape, cut off to length, slide through and bend the other side. It is not possible to avoid a slight amount of sideways movement, which is unimportant and not worth securing washers, etc., and it is extremely difficult to get absolute symmetry when bending quite heavy wire under these circumstances. We put a dab of paint on one side and a similar dab on the top loop of the shroud wire fitted to that side, so that the same shroud is always rigged on the same side. The short mast head length comes next, and while doing this it is convenient to make the mast joiner, since both require plugs. The plugs can be made from tubing, hardwood dowel, or turned from aluminium rod, but in any case it is essential that they (especially the mast joiner) fit very snugly inside the mast tube. Any sloppiness in the joiner will cause a kink in the mast and make it difficult to get the mainsail to set properly. If metal is used, after careful fitting, a touch of grease is desirable; if wood, shellac it and rub a little wax over it. As drawn, the masthead is plugged into the main mast direct for 2nd or 3rd suits. For the working top suit, the 12} in. topmast is plugged into the mast and the masthead fitted in the top of that. If a high aspect sailplan is used, the longer topmast is fitted in place 1974 an adequate diameter used for the mainsail fitting, as on the prodowel boom and all fittings attached; wood can be used for the mainboom too, epoxying and binding on metal or Tufnol plates for the gooseneck end. For the booms drawn, cut the tube to length and epoxy a hardwood plug in the fore end of each. The vertical sail pullis not transmitted to the boom pivot pins, so these can be simple lengths of brass or stainless steel rod cut to length and cross-drilled for the horizontal pivot wire. If 18 s.w.g. wire is used, this means a 3/64th hole, and 3/32 in. rod would be thick enough. A 3/32 in. slot thus has to be sawn in the plugged end of each boom and the resulting ‘jaws’ drilled for the horizontal wire. Slip a dress pin through the holes, with the pivot pin in place, and check that the pivot pin has freedom of movement; if we think of the boom end lifting, say, 20 deg. when the pivot is held in its fitting, that will be plenty of movement. The cross-wire can be a short length clipped off and epoxied (in the boom jaws only) but is best made off into a loop at each end; one of these loops will then serve as an attachment point for the sheet bowsie jackline. A simple way of dealing with the other ends of the booms is to flatten them in a vice, using smooth jaws or packing, and making sure that the flattened part is vertical. A touch of epoxy inside before flattening is a refinement but not essential. A line is then scribed lightly and stepped off into equal spaces, the steps centre-punched and drilled to produce a neat row of holes, These holes accept the clew hook of the sail, and by varying the hook position the flow of the sail can be altered. Light winds require maximum flow, i.e. the hook in the most forward hole, stepping back as the wind increases until in a limit breeze the aftermost hole is being used. Two holes are also drilled in the flattened part of the underside of the boom, one of these taking the other end of the bowsie jackline. The second is normally used for the sheet itself, but for synchronous sheeting the one in the mainboom is left spare. of the 124 in. one. Note that both topmasts carry a short length of jackstay to keep the sail luff hooked in close. To complete the masthead, add the jumper strut, which is epoxied in a slot sawn in the top of the tube. A commercial strut clamping on the tube can be used if preferred. Booms The function of a boom is basically to spread and set the sail; it needs to be stiff and strong enough to do this, but excess weight should be avoided since in light airs heavy booms can reduce performance. As an example, when the boat is hardly heeled a heavy jib boom may well tend to swing to centre so that a puff has first to move the sail to its working position before any useful drive is felt, and by the time the boom has swung, the puff is past. Sometimes the weight of the breeze is not enough to move the sail but enough to move the boat’s head round; the lighter the boom the more chance there is of getting drive in the desired direction. On the other hand, the booms have to be strong enough to withstand the sail forces, and the restraint by the sheets, in a blow. Aluminium tube combines the light weight and 173 A Te TCP MODEL BOATS If a high aspect ratio suit is to be used, the mainboom needs an attachment eye for the narrow-footed sail clew hook, a single eye being enough since flow alteration on a high rig is less necessary — the rig is only likely to be carried in light airs when maximum flow will be used. To complete the booms, provision for kicking strap anchorages are needed, and these can be a single hole beneath, to take a hook as shown on the plan, or a V hook with its ends turned in and squeezed into holes drilled each side of the boom. Fordingbridge, Hampshire) and G. Bantock (26 Alan Road, Witham, Essex) on our last three or four boats and all are completely satisfactory. The cost of a working suit would be in the region of £4 and, if treated with reasonable care, will last two or three seasons at least. Whether you also have additional suits of sails depends on your intentions. If you propose to compete you can’t back out of a race because the wind is stronger than you like, nor can you sail efficiently if your boat is over-canvassed, so at least one smaller suit of sails is a must. A keen competitor would have a high aspect, working, second, and third suit, to get the best out of his boat under any conditions. Conversely, a chap who will only have a sail for fun when the weather’s nice will only bother with a working Sails It is strongly recommended that, if this is your first yacht, you give it the maximum possible chance by buying a working suit of sails from one of the expert sailmakers. Each maker tends to cut his sails differently, but until you are pretty expert the degree of fullness and the position of the max. camber line will not mean a great deal; you learn about these things from racing experience and different skippers have different preferences. We have used ‘professionally made’ sails from W. Jones (57 Forest Road, Birkenhead, Cheshire), Nylet Ltd. (118-122 Station Road, suit. Those who wish to make sails are advised to refer to the notes on the subject in the M.A.P. book Model Racing Yacht Construction which they can request at their nearest public library if they haven’t already bought a copy. This book also includes spinnakers, which won't concern radio skippers (yet, anyway) but would be required for vane racing. PM P.B.A. NATIONAL R/C RECORDS | JANUARY, 1974 ro YARDS SPEED. CLASS RECORDS Clas Time (secs.) Speed (mph) Holder No. 17 June 73 2-5KG Electric 14-83 9-765 15-70 23-04 R. Burman ML52 25 February '73 0-2-5cc 9-96 22-84 22-59 R. Burman S. Read ML52 17 June ’73 18 June ’72 21 October ’73 27 Sept. '70 17 June ’73 18 June ’72 IKG Electric Unlimited Electric 2-51-3-5cc 9-85 9-46 3°51-5cec 8-85 5-01-I5cc 110 YARDS SPEED Unrestricted 7, 5KG Electric 21 October ’73 2-51-3-5cc 17 June '73 12 October '69 27 Sept. ‘70 17 June ’73 Unlimited Electric 0-2-5cc 3-51-5cc 5-01-I5cc 6-98 32:23 L. Norris 14:70 61-2 | July '73 17 June ’73 30 Sept. ’73 17 June '73 5-01-15cec 2:51-3-5cec 17 June ’73 5-01-I5cc 17 June '73 3-51-5- One 17 June ’73 17 June ’73 17 June ’73 17 June ’73 FIV-2-5 FIV-3-5 FIV-5-0 FIV-15 2:5KG Electric F3-V Opus Coventry ML52 Witton Bluestreak Mirage Witton Witton P. Connolly 25-20 22:00 gests 13-30 M. Law Seawasp O/D Seawasp Rossi S/T O/D Kali O/D Batley Maidstone ML52 NL44 OS30 o/D o/D L. Senior P. Connolly HDII cols S/T Kroker O/D o/D Manchester Bradford W. Isard J. Fagan CMI16 KF28 OPS Taipan Nova O/D Keighley Keighley 16-90 P. Palmer ML65 Oliver Johnson Witton 30-40 C. Wilson NB30 KB 40 Mirage Witton E.D. Apollo Rossi Wells Witton 13-84 16°63 22°16 P. Palmer R. Palmer M. Lister P. Palmer T. Cann 18-60 T. Cann LC48 Kroker Witton T. Cann 39-80 ML52 cols LC48 WTI8 Wells 22:00 31-00 30-80 Coventry Rossi 3-91 65-0. Hopalong Gannet O/R 57-50 40-60 Veco WU4 MCI4 20-36 54:10 Cols Witton R. Don J. Faux 11-05 7:4 R. Burman R. Burman ML65 ML66 LC8| ML65 LC48 LC48 / Seawasp S/T Rossi Cobra Nippy Cobra Kali Manchester Manchester Witton Witton Witton Witton Batley M. Lister P. Palmer LC8| ML65 E.D. S/T Appolo Cobra Witton Witton D. Sims COI7 Seawasp o/D Witton ML65 Oliver NAVIGA 30M TRIANGLE STEERING 28 May ’73 OPS S/T KB 40 NAVIGA 30M TRIANGLE SPEED CLASS RECORDS 3 June '73 CM131 Coventry SLI2 cols 440 YARDS SPEED CLASS RECORDS 17 June ’73 Coventry Opus M. Long P. Connolly 17:98 17 miles, 1705 yards 14 miles, 798 yards Unlimited Electric Tornado OPS 18-07 23-80 T. Cann 3-51-5-Occ O.D. Os 49-80 37-80 18-60 110 YARDS SPEED CLASS ss 17 June ’73 2:51-3-5cc S/T BVI6 Witton Witton FIV-15 JUNIOR RECORDS Coventry Phantom Mayfly P. Connolly T. Cann D. Harvey 10cc 3-5cec Hopalong Searam S/T 26-20 ONE-HOUR RECORDS Coventry Veco ML52 12 July ’70 |5cc petrol 33-90 N/N 35cc petrol 34:20 NAVIGA 30M TRIANGLE STEERING CLASS RECORDS 24 June '73 F3-V 142 points in 40 seconds 15 July ’73 F3-E 141-2 points in 43-6 seconds 26 August ’72 26 August '73 Witton cols WU24 23-00 22-00 23-10 FIV-5-0 Witton Mayfly P. Connolly S. Read IKG Electric 6 May '73 Witton Kosmic R. Burman Unlimited Electric FIV-2-5 FIV-3-5 2:5KG Electric 17 June ’73 R. Burman Witton 17-32 16-27 50:2 9-15 SL3 Venue 51-96 55-00 NAVIGA 30M TRIANGLE SPEED CLASS RECORDS 6 May '73 20 August ’71 3 June ’73 6 Sept. ’70 CM131 D. Hughes 440 YARDS Srere CLASS RECORDS 17 June ’73 G Electric 98-3 17 June '73 L. Norris W. Pollit 24:86 32:23 NB88 cols 26°55 Hull ML52 P. Connolly 9-05 6:98 I5cc 23-78 R. Burman Engine 138-20 points in 59-00 seconds P. Palmer 174 LC48 Rossi Wells Johnson Witton MAY 1974 History series of 1/1200 scale waterline warships. The first two are Hood and Bismarck, with 67 and 49 parts respectively. They go together well, though a little cement avoids one or two gaps springing open and reduces the force needed to insert some of the tinier parts. Excellent value at 30p each. A glass fibre M hull of modern Witty’s Typhoon, is being moulded are included; only glue and paint are additional. Price is £6.95, which with the amount of ply, degree of pre-cutting etc. seems reasonable these days. From Airfix comes a new range of clip-together Naval Sail Aerodynamics Graham Bantock ciarifies one or two woolly bits in design, the late Stan by Wavecrest Models, 18 Alexandra Road, Hemel Hempstead, Herts., at, we understand, about £8.00, delivery in rotation. Wavecrest tell us that their earlier production problems have now been overcome. The Typhoon has proved a good design for vane or radio, and the moulding is very accurate to the drawing. Cotan >, =L/D eS ae —_ previous aerodynamic articles It was nice to see articles on sail aerodynamics in December and January Model Boats, though the December one was based on tests done well before the war and much of the theory expressed in the original paper has since been discounted. In fact, a recent article in another journal described a long series of tests using computerised fluid flow mapping and came to the conclusion that the long-standing slot theory did not really work. There are one or two points in the January article which could mislead others looking into aerodynamics. The first revolves around Fig. 1 which shows a resultant force vector having a component directly into wind. This can never be, or yachts would indeed be able to sail directly into wind! Fig. 1 here shows a correct arrangement of forces where the vector parallel to the wind represents drag D; the resultant R, the total force on the airfoil, cannot be less than 90 deg. and is only 90 deg. for no drag. Lift (L) is always shown at 90 deg. to the freestream direction and since the other force component, drag, is in the direction of the wind it is drawn pointing away from the wind. The angle 6 is known as the drag angle, and it is because the resultant R is away from the wind that most people find it difficult to grasp why a boat moves to windward. From the January Fig. 1 the fallacy that most of the sail force is translated into forward motion is easy to fall into, but basically only one-third of the total force is useful in propelling a yacht to windward. In fact tank tests are done on the basis that for windward sailing the hull has to be given enough yaw to produce three times as much side force as drag at any given speed (Fig 2). The greater efficiency of a jib (or indeed a monosail) as opposed to a sloop rig is basically due to the fact that the jib bends the airflow on to the main, hence the main is operating in a flow of air more from the bow. The resultant force it thus produces is bound to be more to the side of the boat and hence the main is less efficient square inch for square inch at producing forward force. A small point, but a fact which is often used to give a mast a bad name. Some confusion arises between turbulent flow and separation. Flow over a sail can be laminar or turbulent, but this is taken to mean the flow within the boundary layer, which is very thin, probably only 7s in. or so thick over most of a model sail. January’s Fig. 6 does not therefore really refer to laminar and turbulent flow; the second sketch is one of separation, which means that because of the adverse pressure distribution the boundary layer has become detached from the foil surface, and because its velocity is less it rolls up into vortices. Separation can occur with both laminar and turbulent boundary layers, and normally occurs at the leading edge of foils when in a stalled condition, or as in the sketch mentioned when, say, the after edge of the foil is overcambered. Generally, turbulent separation has lower increased drag than laminar separation and for this reason studs are put on 12-metre masts and some modern masts are triangular so that the sharp edges create turbulent separation. Turbulent boundary layers tend to stick to the surface and also tend to reattach to the surface quicker; if separation is going to occur, the idea is to get the boundary layer reattached to the sail surface as quickly as possible by promoting early turbulent separation. One therefore cannot really compare the effect of a thread on the leading edge of a wing and a mast on a sail, as the former induces turbulence within the boundary layer and the latter separation of the boundary layer. A further small point is the suggestion that the round shape of a mast inside a double luff sail leaves something to be desired for an efficient aerofoil. This is not necessarily true, as the rig used on Lady Helmsman, after extensive windtunnel-testing at Southampton used a round leading edge as opposed to elliptical or parabolic leading edges often stated as being the shape to have for a leading edge to keels etc. One must be careful in comparing wings and mast/ sail arrangements for yachts, as they really fulfil different purposes. The wing is designed to produce a known lift, the weight of the plane plus a bit for climbing, for the minimum drag. Hence wings operate at only a few degrees of incidence with only a few per cent of camber and thickness, and perhaps with a lift/ drag ratio in excess of 10:1. Mast and sail combinaL R_ Forward force=F L, MODEL BOATS tions can accept a high drag and, indeed, for reaching conditions a high total force is necessary, regardless of lift or drag. Hence sails operate at 10-20 degrees angle of attack, are relatively heavily cambered, and have working lift/drag ratios of around 5:1 for windward sailing and 2-3:1 for reaching. For this reason wing masts are likely to be a good deal thicker than January’s Fig. 12, as well as because thick foils are less sensitive to trim, i.e. when the boat rolls, pitches, luffs, or bears away. To those interested in sail aerodynamics Marchaj’s book ‘Sailing Theory and Practice’ should be extremely helpful; it presents a lot of data and theory on rigs (and some on hulls) and although over ten years old is still the best book at explaining some of the harder topics of fluid dynamics as applied to yacht rigs. the The Secretary writes… M.P.B.A. International Secretary Jim King keeps it short this month due to pressure of Naviga 75 we welcome the coming months. of the show and so make it the best as I have several time-consuming jobs that I have promised to do in connection with Naviga 75 and at the present time they take priority, So I will close down now and here’s to a happy season This is the time of the year when the winter is ending and the new season is ahead of us (remember that these words are being put on paper in the last days of March) and it is with anticipation of the pleasures before us that running European Championships yet. If you can help, let me have your name as soon as possible. It is not my intention to write too much this month, ahead. Jim King Inspec- tion of the regatta lists of the two national model boating bodies shows that every weekend holds attractive meetings for everyone and the only difficulty is deciding where one’s journey is to be on a Sunday. With the possibility that the petrol shortage will not be affecting us too much, regatta organisers will no doubt be anticipating increased attendances this year. We will all share the disappointments of the hydroplane followers that at the present time the loss of suitable waters for If it’s a model it’s good THE SIGN has meant that meetings are at the a long time. This does not mean that action is not being taken to overcome this problem and at the present time efforts are being made to obtain suitable waters; more about this when firm news is available. Whether you are a hydro enthusiast or not ! am sure that you will wish those looking for some place where this part of our hobby can be practised every success, for it is the variety of interest that keeps the model power boating hobby alive. By now the names of people interested in taking part in competition in the Naviga 75 events will have been tabulated by Frank Bradbury. There is some lack of numbers in the ‘E’ classes due, I suspect, to the uncertainty caused by the lack of an English translation of the rules. After much hard work by several people we now have a translation of the rules as was proposed in Berlin in 1972, and duplicated copies of these should be available by the time you read this. Since this delay in getting a copy translated has affected the possible entry it may be politic for someone to suggest to the committee a new date for closing the list, and if such a course of action does take place then quick publicity will be given to such a move. Talking of Naviga 75, much work has been done on the project and we are now approaching the time OF QUALITY their activities lowest ebb for NO CATALOGUES AT PRESENT AVAILABLE but, we are the Makers of the finest Model Fittings in the world for Yachts, Sailing Ships, Launch, Liner, Naval or Marine, and they will give you entire satis- when many of the details of the organisation will be worked out. One of these items will be the need to know who is going to come to Welwyn Garden City for the week in August 1975 so that we can make a more up-to-date assessment of the accommodation required for people in the home country. If you intend to come, don’t just come to watch, come and give a hand in CEANIC SHIP scale detailed MODELS, 1/1250th metal kits for col- faction. YOUR ENQUIRIES WILL BE ANSWER IF YOU ENCLOSE S.A.E. OTHERWISE THEY WILL NOT BE ANSWERED. THE WEB MODEL FITTING CO. Telephone: 01-888 4683 204(R/C) HIGH ROAD, WOOD GREEN, LONDON N22 4HH, ENGLAND crash tender — no mechanics, £10. Both models beautifully finished. Tel: WorkK‘ sop 3929. } for radio, Racing hulls 34 modified Balu and Mistrale, in. a 26 in. lectors and wargamers. Historic models 1200 B.C. onwards. W.W.II and modern REMCON 6-channel transmitter-receiver version. Coming soon, scale tug and more yacht hulls. Send stamp for il- over o.n.o. ings, 47 warships 100 and auxiliaries, types available. ferries. Prices Now from 10p. S.A.E. for lists. G. Skinner, 126 Westhill Road, Torquay/ TQ1 4NS. I/J. FoR SALE. Rossi engines, new, never used, 2 Rossi, 15 speed marine, £20 each. 1 Rossi 15 speed C/L, £22, 1 Rossi 60 marine R/C ring, £40. Write to Ph. Tiberghien, 13 Galerie B.6000 Charleroi, Belgium. 34 for Bernard, K/L. IN. Wave Princess, 0.S. 20 powered, Mini Waltron R/C. Ready sailing, £45. Also 34 in, R.A.F. for sale. Tel: Excellent 023 374 533. condition, = DVERTISER would be interested ie the the purchase Berkshire or of a model Southern shop area, in or would consider a joint expansion with an existing shop, ring in confidence to Northwood 6117 Road, Newbury. or write to 15 Friars K/L. GLASSFIBRE model boat hulls. 36 in. Vosper M.T.B. plan also available. 30 in. fast cruiser and speedboat. 30 in. yacht with plan and 182 instructions, ideal lustrated leaflets Kingston to Kingston Road, Poole, Mould- Dorset. K. glassfibre hull -H.G. 37 in. ‘Surfury’ fitted with shaft, prop, and rudder, unused, £6. Womack, 2 Hall Goreges: Ingham, Norwich NOR 33Z : POSTAGE free on glassfibre boat hulls. Cigarette, £4.50, 36 in. Contester, £4. State colour required, white, orange, also metal flake at 50p extra. F. Knight & Son, 44 Bath Street, js don, Berks. Phone: 1927.
