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© —- h U.S.A. & CANADA Boats A. HOBBY MAGAZINE THE ONLY FULLY APPROVED MODEL | OF SIR FRANCIS CHICHESTERS GIPSY MOTH IV A 26} in. Francis semi-scale Chichester, working the model gallant of lone the famous navigator, boat fought in which Sir beat the plastic Hull and treacherous oceans of the world. Hobbies easy-to-assemble Kit contains: pre-cut parts, moulded and Cockpit, ready cut Sails, basic Fittings and cast Keel. Complete with log . features from ‘““THE SUNDAY TIMES’’. Designed with a view to simple adaptation to Radio Control. Catalogue No. 2MB 230 From Kit price 97/6 carriage 6/0 your nearest Hobbies Limited Shop or stockist, or direct by post. EXCLUSIVE WORLD RIGHTS FOR PRODUCTION 2193 DEREHAM Comprehensive Stocks of Model Boat Kits and RUS PLA N S SH | ° Fittings FOR Mersey Marine and RipMax Fittings O.S. renee my Trident Trawler LE A UNDERHILT AM By HAROLD Ev Goce DENA.M.I.E.S. ice From leading dealers or direct from ‘ oo arabia 23/7 Sea Scout 179/40 | cc. Viking £3/11/2 Hei i 120/2 34” Crash Tender eunniy a ay ALL . dwes ater coole yf 40/2 alas ea Hunter 75/6 ea/2/10 £8 RUSS, 101 BATTERSEA RISE, LONDON, S.W.11 BASSETT-LOWKE LTD. ST. Servos Sea Urchin 11/2 can the executors ILLUSTRATED LIST OF 35 POWER CRAFT 1/- KINGSWELL Unimite Aquamite Servos £7/11/9 each BS Ouse ee Lg acetal eSiO7! Titan Tug ILLUSTRATED LIST OF 70 SAILING SHIP DESIGNS 2/10 ourtesy of RADIO CONTROL £17 McGregor — all ce in stock Crystal Tx THE ENTIRE SAILING SHIP & POWER CRAFT Y Pixie Ariel 6-channel £40/3/9 WORK MODEL NORTHAMPTON Tel. BAT 6319 TAYCOL HIGH POWER — HIGH EFFICIENCY ELECTRIC BOAT MOTORS Powers range from 6 to 64 milli. H.P. Consumption from | to 5} amps. Ask your retailer for Price installation of the most List with complete data for suitable motor for your boat. A TAYCOL LIMITED 74 COVENA ROAD, SOUTHBOURNE, BOURNEMOUTH KINDLY MENTION 36” RADIO CONTROLLED “DOUBLE SPECIAL”. “MODEL BOATS” VERON MARLIN — TAYCOL 12 Venner Cells, Taplin 2} x 24 Prop. —_—T#7<2!_ motors ca be revarsee by. single spate, c/o Switch, as WHEN REPLYING TO ADVERTISEMENTS es MODEL BOATS HIGH OR LOW PRISMATIC COEFFICIENT? A five per cent increase makes a surprising difference in hull shape, as shown by these two new Marblehead designs By S. Witty (THE term may sound a little technical but the basic * idea is very straightforward. Imagine a block of wood, the same waterline length as the hull in question and of similar cross section throughout as the shape of the submerged mid-section of the hull proper. This constitutes the prism, the coefficient being the proportion of this taken up by the under- water canoe-body. A relatively full ended yacht would tend to fill a larger part of this prism and so has a higher coeff. Taking the prism as unity a normal shape of hull usually fills 0.5 to 0.6 of this. The finer ended yacht with the low coeff. will tend to be more easily driven over the lower speed range than the hull with a high P.C. due to phenomena connected with wave formations. This is a_ vast over-simplification of the problem as there are many factors which affect resistance, both heeled and upright, and indeed one could fill a book on this subject alone. Full size powered ships can, to a large extent, be designed to the particular coeff. which gives minimum resistance over the particular speed range required. Low coefficient or conventional hull is typified by ‘Typhoon’? below; ‘Sprint’? has a higher coeff. and is altogether flatter and fuller-ended, a remarkably different appearance considering the similarity of the hull midship cross-sections. Full size copies of either drawing are available from Model Maker Plans Service, 13-35 Bridge Street, Hemel Hempstead, Herts., price 6/6 inc. post. ‘“‘Typhoon’’ reference is MM.932, ‘Sprint’? MM.931. Note that in the drawingsthe body plan and fin are shown full size but sheer and waterlines are half size. ——— TYPHOON My) s-witty ii: Sin 6/- | THE MODEL MAKER PLANS SERVICE 1 | ee “Ne -\ Ne \ Ne 280 + JULY 1967 ] | —— | | MARBLEHEAD LENGTH MAX 50-25" SAIL AREA 798 so" DSPLACEMENT «21.5 LBS SECTIONS 4 e7s* 50/800 th || Ir Yachts, on the other hand, have no source of power parison being similar in beam, draught and displacement. The respective prismatic coeffs are 0.536 for the conventional hull and 0.586 for the other, so it will be seen that quite a small difference in this figure means a considerable change in hull shape. Bulb keel other than the wind and so hull shapes must be found which give a good performance over a whole range of conditions of wind and water, varying angles of heel etc. boats are now well established, and being second generation types, the two hulls shown can be considered well balanced in every respect. In fact I feel that the appendage configuration shown is more or Model yachts are required to perform over an even wider speed range, proportional to size, for the ability of these small displacement hulls to plane can be a considerable advantage. It has been found that a hull with a fairly high P.C. and relatively full ends allows flatter, easier lines around the midsection resulting in improved planing ability. As will be clear, this must inevitably be at the cost of light weather performance to some extent. The pros and cons of both types are many less standard for a moderate draught boat. Indeed, for the past few years I have realised it to be point- less to design other than bulb-keel boats in either 1OR or M, and feel that soon, anything else will not be regarded as top flight boats by the leading skippers. and varied and by no means fully resolved. In the recent M Championships both types did well, and though the first two were high P.C. boats, my impression was that on the whole the lower P.C. designs were at an advantage, being able to sit up more, allowing the stem to ride over the broken water. I believe that in future I shall concentrate on the latter as being less restrictive over the performance as a whole. In the strong March wind the Golden Archer bulb-keeler proved quite invincible to windward. Downwind she was less outstanding but well able to hold her own due to her ability to carry sail. The two types shown make an interesting com- Both the bulb-keels in the designs shown weigh 14.5 lbs. giving the usual 30 per cent increase in power over fin keels. This weight may prove about the optimum for M craft, as above this figure the bulb tends to look chubby. The canoe-body of the more conventional design shown is developed from the Wasp/Hustler series, the dynamics of which are well known. The high P.C. hull derives from the G.A. design and chine Toboggan. Beam is moderate in both designs, since this greatly reduces resistance and wetted area, any reduction in stability being more than compensated for by the bulb and the high C.L.R. of the fin. 281 Mi eee | BOATING FOR BEGINNERS STARLET & - INCE a yacht derives its motion solely from its sails, the better the sails the better the perfor- mance. For this reason we recommend the purchase of expertly cut and made sails from a professional; considered against the purchase of an engine and fuel, the thirty-five bob or so for a first-class suit of sails for Starlet is not expensive. However, there are those who like to make everything possible, so some brief notes follow. The first essential is materials matched as closely as possible. If terylene cloth is used, terylene tape and terylene thread must be used too. If cotton cloth, cotton tape and cotton thread. It is perhaps not quite so important with synthetics, but cotton shrinks (sails get wet) and shrinkage must be near enough equal or puckers develop. Cotton thread on terylene cloth will produce puckers when the thread shrinks. Second, and most important, is the leach (after edge of the sail) must be parallel with the selvedge of the material. As it is curved, perhaps it would be better to say that the selvedge should be tangential see Fig J. First lay out the sail shapes on brown paper, using the dimensions given on the plan to draw two triangles. The leach of each sail incorporates a little roach (curve providing unmeasured area) and the maximum curvature should be between 50 and 66 per cent up the mainsail and down the jib. For cotton, 1 in. or less on the main and ¢ in. on the jib is reasonable; in terylene 14 in. and 3 in. can be allowed. Mark the point of max. curve and draw the curve in with a thin strip of wood or ¢ in. wire or some similar improvised spline. Lightweight hot-rolled terylene dinghy cloth possibly the simplest material to use, since it is is 298 SUEY 1967 FIG 3 \ Photos opposite show model nearly complete, general shot of centre area including shroud plate, hounds fitting, and gooseneck with kicking strap. Above sketches are mentioned in text; dimensions between arrows in 2 is minute in fact (see text). Below, head board and mainsail uphaul, hounds and jib uphaul, close-up of gooseneck showing split pin through mast, main tack hook, and bottom of jackstay. stable enough to be cut with a sharp razor and need only be hemmed on luff (front edge) and foot, the leach being finished by slightly melting the fibres with a soldering iron passed gently along—practise first on scraps, though! Hem with a fairly coarse needle, stitches at least x's in. Jong, hems about } in.; again, practise first. Nurses’ veiling, or tarantulle, is a cotton material sufficient for sails of this size; it needs as tiny a hem as possible on the leach and the luff and foot must be folded into cotton tape. The tape needs to be sewn on a trifle slack, ie. not stretched as much as the cloth while sewing, since when the sails are broken in the cloth will stretch slightly more than the tape. A finer needle and smaller stitches can be used. Either material will need triangular reinforcement patches in each corner, sewn into the hems (Fig. 3) and either will need a mainsail headboard, eyelets in the corners, luffhooks, and batten pockets, When marking out, allow for hems and also for the shaping which gives the sail a slight belly. This is where some of the art comes in—we have to cut 299 a faint ‘S’ shape yet sew it to form a straight line by a bit of judicious tension on the cloth as it is sewn. The ‘S’ is slight—only a shade over 7s in. for terylene, and still under + in. for cotton—but it is one reason for amateur-imade sails often proving inferior. Fig. 2, grossly exaggerated, shows the form of the ‘S’. It simplifies work if the sail cloth is pinned out flat but unstretched for marking and cutting, and subsequently if a trace of adhesive is used to tack down hems, reinforcement patches, etc. The suggestion of photo mounting tissue in our last issue is excellent for cloth; otherwise use a faint smear of. Copydex or similar, or, for terylene, Bostik 1, Holdtite, or other very tacky adhesive. Pages could be written on the actual sewing, and readers would still have to find out by experience; with what has been said, a discussion with a sewing machine expert (at least someone who’s used one!) should provide a sound having a try will do the rest. starting point and only The head of the mainsail should finish abut # in. wide, in a hem, and a small headboard, cut from MODEL BOATS Jib tack with fishing swivel, and clews of both sails. Jib (top) could have done with slightly shorter foot or longer boom. in at intervals of just over 6 turned ins., the vertical, slots and the wire soldered into these, thus holding it against Again, right nutted Perspex, Paxolin, ply, or even thin metal, should be sewn in place. It can be riveted with +s in. sail eyelets. The tack and clew corners should be eyeletted with eyelets of + in. bore or slightly larger; in the case of the jib, the head needs one of these. The eyelets pass through both hems/tapes, which overlap in the corners. Battens stiffen a sail and belp prevent flutter and collapse of the roach; for this reason they are usually covered in the rules. Normally four are allowed in the mainsail, approximately equally dis- posed, and three in the jib. With a terylene jib this size, their advantages are hardly worth their weight. The battens should be of thickish celluloid, about + in. x 3} in. main and (if fitted) 4 x 23 in. jib, They are slipped into pockets made by stitching pieces of terylene (tape for cotton sails) at right-angles to the sail leach, the pockets being sewn closed after insertion of the battens. It is possible to “sew” the mainsail luff to the mast by means of a slightly slack spiral of thread; the jib luff can be secured to its stay in the same way. Alternatively, wire rings can be used; neither system allows the sails to be removed conveniently and neither is really efficient. The luff of each sail must always be taut and there should be no gap between main luff and mast. Luff-hooks are the normal practice, and these are simply # in. dressmakers’ hooks opened to a V and sewn or eyeletted to the sail. The eyes, which have to be bought with the hooks, are useful for small sheet hooks etc. later, at least on a model this size. The jib luff hooks simply ezigage on a cord stay, but those on the main require a jack stay fitted to the mast. We drilled through, fore and aft, at the top of the gooseneck strap, and fitted a split pin. The eye of this carries a hook which engages the tack eyelet of the sail (see photo) and the shank supplies an anchorage for the lower end of the jackstay. Light Laystrate stranded control-line wire, which is corrosion-resistant, forms the stay, the lower end being twisted back on itself and touched with solder. At the top (opposite the headboard) a 10 B.A. bolt was screwed in (it could go right through, with a nut) and the wire passed through the: screw slot, wound round the shank, and twisted off on itself, again with a touch of solder. Further bolts are screwed 300 the bolts through would mast. passed and do, or split pins could be used. A further _ method is simply to bind the stay in place with a loop of wire, | with a _ touch of solder to prevent slip. In any method, ensure that the luff-hooks do not coincide with the stay clips. To rig the model, fit the jib boom with a smallish fishing swivel, the lower end of which has been converted from an eye to a jib rack. hook to engage in the Slip the mast in mid-position and make- off to each eye of the hounds fitting a shroud; this can be stranded wire, in which case a turnbuckle or bottle screw should be fitted at the bottom (these can be bought) or rigging cord, which should be passed through the eye of a hook and made off with a flat bowsie. The turnbuckle or hook engages in the shroud plate either side, Rigging cord is usually flax, and can be braided; where supplies are difficult good quality fishing twine can be used. Cord will always stretch or shrink a little, depend- ing on how wet it is, so that adjustments need to be checked frequently while sailing. Make off a cord to the top tack eye of the jib boom, pass through a hook to engage in the hounds- plate, and finish in a flat bowsie. Hook in the boom swivel and tighten up. Sight the mast from side and front for vertical alignment; these three stays are the only support for the mast. Now bolt the jib tack eyelet to its screweye, uSing a short brass 8 or 10 B.A. bolt and washers if necessary. Fit a line made off through a hook and bowsie to the head eyelet, hook into one of the holes in the hounds plate, and tighten up. There will be very little adjust- ment possible or needed. Hook the luff-hooks round the forestay, hook in the clew outhaul previously discussed, and the sail is bent. An alternative is to hook the forestay to the head eyelet of the jib, pass it up to a hook on the hounds, down to the tack eye on the boom, and back up a couple of inches to make off in a bowsie, Thus tightening the stay draws the jib-luff taut, but a change of jib means removing stay and boom as well as sail. The mainsail hooks on to the tack hook near the gooseneck and its clew is attached to the outhaul— assuming the boom has been fitted previously, of course. A line is made off or hooked to the headboard, passed up, then through a fore and aft hole drilled in the wood topmast, down to the hounds plate, made off in a bowsie, and drawn taut. The luffhooks are engaged and the model needs only its sheets and rudder pintle to be sailable.
