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MAY 1969 TWO SHILLINGS AND SIXPENCE U.S.A. & CANADA SIXTY CENTS © ; © © Nl MODELS BOATS the stern waterlines when upright is less relevant, since the run is so flat that the stern wave has to rise very little to reach the transom. At speeds too low to cause any wave formation, what resistance there is will be due almost entirely to skin friction. In any case quick acceleration and a sparkling planing performance will more than compensate for any lack of ability to carry way. The long forward sections should be a great asset in this respect, and the above waterlines are even sharper, so that waves of any appreciable height will arrive pre-sliced. The long forward overhang is unusual in a planing hull and reminiscent of the very early raters. An indirect benefit is that one can have a certain length of overhang at the stern to balance the profile, and give a larger hull. Just how relevant sailing length is, in what is essentially a planing type, is hard to say, but even the most ardent lightweight enthusiast can’t expect planing to occur all the time. It looks nice anyway and a shorter stern over- GLIPPER The first 10-rater design published since the change of rules last autumn By STAN WITTY ITH the introduction of the new rule it seems certain that the latest ten raters will be considerably lighter thanin recent years. Under the old rule, a large amount of hang tends to look chopped off. To obtain the full potential from a hull of this type and to get the maximum lift from the sections it follows that free area could be obtained by using sails of fairly high aspect ratio. The width of the mainsail roach was not limited, and whereas in former years the restrictions on the sailplan should be of moderate aspect ratio. Acceleration under pressure from the spinnaker is another factor which must also be considered, so here too the hoist height isn’t too greedy. Alternative sailplans are shown, the respective areas being similar, though requiring different mast positions. batten length kept this within reasonable limits, the newer, stiffer sail materials now used can support a much larger area. In addition, there was the triangle under the headstick, and also the 85 per cent fore triangle allowance tended to be on the generous side. The actual spinnaker area also increased with the height of the hoist, partly due to the extra four inches added on to the width. The fact that the foot of any sail could not exceed that of the tallest suit discouraged extreme aspect ratios as have developed in the ‘M’ class, since it meant losing too much area on the lower suits. All these factors combined to encourage the heavier designs with plenty of stability to windward. It is surprisng, though, that bulb keel types did not emerge more rapidly, particularly as the designs adapted from Flying 15s and 25s proved so successful. Attempts to gain the advantages of these designs without the drawbacks tended to fail, partly because they were less extreme, whereas in some. respects they should have been more so. The conflict between outdated balance theories and present trends was undoubtedly a major factor in this. With the extra stability of the bulb, it has become clear that since the fin no longer has to be shaped to contain the keel, the profile can be drawn to achieve a high C.L.R. whichin turn alsoimproves stability. As will be seen, the draughtis quite moderate, for if a deep keel designed to sailin waters where thereis plenty of depth does well, then invariably the owner will want to enter competitions where the depth is less. In this concept the C. of B. is well aft, and this allows the fin to be placed centrally without need of a prognathous keel. To take full advantage of the rule it would seem that future designs must plane not only downwind or on the reach, but also to windward. It follows that to achieve this and to obtain the maximum stability, the hull sections should be fairly flat floored. Not so long ago it was felt that any yacht with such sections would be dead in light winds but thisis no longer true. The reasons for this are complex, but briefly, for good dynamic Hul/ balance the Welch Axis should be more or less straight at a reasonable sailing angle, say 23 deg. With canoe stern sections giving good static balance, the resistance is less, but the W.A. is curved. With wide flat sections at the stern the converse holds true and at the usual 10-15 deg. heel to windward in light conditions, the shape of the heeled waterline tends to be a bit thick aft. With Clipper, only the rims of the sections are immersed when heeled, and this gives a better shape of stern waterline. The shape of 202 CLIPPER \ DESIGNED = 6Y fame THE MODEL MAKER PLANS SERVICE (S35, BRIOGE STREET, HEMEL HEMPSTEAD, HERTS MAINBAIL 5 MAST (romney aan 2nd MAIN USED wiTH NOTE I (iat Shee 2) Nal TOP FORESAN MAINSAR * S60 5 + 42:6 Ve 167-96 053 \ “, — j= – jis + che 62s” FORESAIL ; ). aur (3206) +/2sare)e(r5e03 | z } 2 i J NV RATING \ Te om – MAX. AREA * |247.6′ a . . atid — > SPINNAKER 770 a Hoi a7) ALLOWED 1250°° ell al)+ = FORESAN B as TOTAL 3438 * 6604+ 41) ee ease .\ * 544 + 76-27 620-77 TOTAL \ a9 AREA (243-61°” va SPINNAKER = + (2uT) + 622 S6+)-401 250 * at © 840)-44 1250 70-5″ (HOIST? + Ti” ( wOIST) 41 1250)7) J* 13-8″ (800M) 770-56 MAST + 622-04 we so —fh— oe * 52:8 485544 875+ 66-04″ * 477-04″* & 60n 12476 “jo -3 38 + 432 + 426+ 148-24 Sar| { / ‘ J» ()401250)— $ 7/2 75 + 19-9″ (800m) 622-84 MAY 1969 probably, the sailplan of more normal proportions will The first type has what is probably the better arrangement of the lateral areas, while the other is designed to obtain the maximum size of spinnaker. Under the new rule only the length of boom and hoist height are calculated, but the effect is the same. In some respects there is some similarity with the ‘M’ rule in that there is no fixed maximum width of spinnaker. Other factors combine to limit the width and fullness for any particular set of conditions. For maximum spinnaker boom and hoist (J x1), the area of the foresail must equal that of the mainsail, plus most of the mast. This seems not to be an ideal arrangement perhaps, but as it happens the winning yachtin the last championship to be held under the old rule carried a sailplan of similar proportions, allowing a very large spinnaker to be used to good effect in the light conditions which prevailed. One curious phenomenon was that the masthead-flown balloon backwinded the mainsail into a neutral fore and aft position, so that without the foresail, no drive at all was obtained from the lateral give all the spinnaker area which can be handled, and for this reason I favour this type. At the time of writing there is some speculation on what ultimate form of rig and sail will be evolved. Gaff rigs and fully battened sails are standard topics for discussion, but with the relatively stiff dinghy cloth at least, I feel that full length battens are worth while only where the roach is widest. Double-luff sails can be used, skippers swearing by or at them, mostly because a bend in the mast alters the set of the mainsail so much. Since lightweight designs depend on their ability to accelerate out of trouble, and ease pressure on the sails, light construction and a smooth finish are even more essential thanin a displacement type. Though the concept is designed to reach maximum speed sailed cat-style, the high inherent stability, good dynamic balance and long easy entry should make the design well suited to the U.S. ‘X’ class with minor modifications at the fin. These are simply the addition of a | in. garboard radius as in the ‘M’ class, and an extra 1/16 in. on the fin thickness. Different sails would be needed as the rule has specific restrictions on the maximum roach etc., but the actual sail area allowed works out about the same as a 60 in. L.W.L. ten rater. The surfaces, yet the arrangement undoubtedly paid off. With such a large foresail the aerodynamic balance is excellent for windward work. Tests carried out on a Marblehead with a similar proportion of areas show no noticeable loss of speed, though gyeing is more difficult It may be that this kind of sailplan allows more spinnaker area than can be usefully employed. No doubt a season or two under the new rule will clarify matters. Quite newer ‘X’ class yachts are of similar length on the water line, so designs to these rules have much in common. CLIPPER © RATER Lwi, 60° BEAM | LOA Osp. 21-5 LOS SA 7a” |-4* ORAUGHT [3-8° 1250″ wu 203 joss
