- Description of contents
MAY 1970 THREE SHILLINGS U.S.A. & CANADA SEVENTY CENTS HOBBY MAGAZINE T the end of 1968, I was fortunate enough to have the offer of a new ‘A’ class yacht, which would be built by a very good model yacht builder, to my design. The only stipulations were that the boat should be capable of winning the ‘A’ class National Championships, and should have no resemblance to the boat I was then sailing! The second of these stipulations was quite simple to meet, but the first required rather more thought, as this would be my first serious attempt to design a boat to this class. After toying with ideas of super-lightweight and superheavyweight designs, I came to the conclusion that the best approach would be to adopt average dimensions for the class and try to achieve something extra by use of several ideas which had been successfully tried in the other classes. The dimensions decided upon were a waterline of 55 in. and a displacement of about 554 lb., giving a sail area of just over 1,500 sq. in. Having decided upon the main dimensions of the boat, the only other basic factor to be decided upon was the shape of the mid-section. I could see no logical alternative to making this of a U-shape, which not only keeps the wetted surface area low, but also keeps the resistance due to wave-making to a minimum. This type of section also a EMPEROR Gesigned by | My) CAE Dicks. copyrignt of The Model Maker Plans Service 13-35 Bridge Street, Heme! Hempstead, Herts. = – s | 1 ——_4+_. 8 £9 9_ ——_-_£ | t tl : aS = Sea a ~s DECK UNE, Ene ce Ee ACTUAL LINL. ON ORIGINAL BOAT* =A | =e pe 2) See > Spel ~ SCALE ~ 1/2 FULL SIZE iS > oe \ a 2st Sra LEAD LINE. FU sve peta -9 <—————} aN mm ___ OBL = 478" | eet. eee| SAL PLAN. 1/8 FULL SIZE 198 L BZ MAY 1970 EMPEROR One of of the finest recent years, 1969 British A Class equal Open boats first in the Championships DESIGNED BY CHRIS DICKS CLASS “n YACHT ‘EMPEROR LOA LWL SEAM = 73.25" enables the boat to lift and plane downwind when pressed hard, which can be quite an important factor in the ‘A’ class, which are basically displacement type yachts. At both Fleetwood and Gosport lakes, the waves produced by the wind can become quite large, and the ability to sail fast through these must be one of the main objects in any design produced with these lakes in mind. The sight and sound of one of the full-sectioned A boats smashing its way to windward in a good breeze can be quite exciting, but the resultant pitching can slow the boat to an alarming degree as well as completely upsetting the trim of the sails. In order to enable the boat to slice cleanly through the waves, the bow waterlines were kept as fine as possible, giving the boat a distinct wedge shape, with the bow being drawn out to the longest practical to prevent it being driven underwater when running in a strong breeze. The large amount of tumble-home aft is a direct result of combining fine forward sections with a full mid-section while still retaining good volumetric balance. One inevitable result of using fine forward sections is that the quarter beam length is reduced. This reduction, however, is at the forward end, and I think it far more practical to push the quarter beam buttock as far as aft as possible, as any gains in sailing length are mostly attained at the stern of the boat, the increase at the bow being minimal. In addition to this, any increase in sailing length is only of use in stronger conditions, when the ability to sail through waves is more important. Although the present tendency in the Marblehead and 10-Rater classes is to fit fin and bulb keels, it was thought that the application of this to the A-Class would not be very effective as, due to the high percentage of ballast involved, coupled with the restricted draught, it would tend to give a very jerky heeling action. Therefore a more conventional type of fin was fitted, as small as possible while still incorporating sufficient volume of lead, in order to keep the wetted surface area to a minimum. One of the faults of a large number of A class yachts is a certain lack of directional stability due to a combination of the high waterline/beam ratio and the large sail area. In view of the shortness of the fin on this boat, some trouble was expected in this respect, and so a deep skeg 55-00" 1435" DRAUGHT 12-25" OBL 47:80" DISPLACEMENT. 56°50 LBS. u 45°00 LBS. SECTIONS SPACED, Photographs show Emperor competing at Fleetwood in 1969, where the boat proved outstanding. (Pictures by courtesy of Joyce Roberts ) 5:50" MMI060 Full-size copies of this drawing are available, reference MM 1060, price 15/-. post free from Model Maker Plans Service, 13-35 Bridge Street, Hemel Hempstead, Herts. Sheer and waterline plans are half-size, body plan and fin full-size. (continued on page 201) 199 MAY 1970 STARBOARD ONLY J iJN.S. KATORI skipper rather than the boat. EMPEROR (continued from page 199) and rudder was fitted, and the garboard was continued through to the back of the skeg. In fact, the boat has quite good directional stability, but whether this is due to the above features, or to something else entirely, is a matter for conjecture. The sail plan is entirely normal for present-day practice, as it was felt that this was as good a compromise as can be obtained under the rule. The completed boat has so far performed even better than was hoped, finishing equal first in last year’s National Championship with very little time being available for tuning the boat before this event. The majority of points lost in this race were due to deficiencies in the 201 I would give one word of warning to any potential builders. In view of the fine forward sections, the diagonals are very straight towards the bow, and extreme care should be taken to prevent reverse curves from forming in this area. When completed the waterline of the finished boat may be allowed to vary between 55 in. and 56 in. (the original was 55.8 in.), but should not be outside these limits. Any adjustment to sail area necessary due to variations in building should be made by amending the foot of the mainsail. I would like very much to hear from someone who decides to build to this design, and will be only too glad to give any assistance or advice which may be required.
