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Seecial Chr Wed MODEL SHIPS – YACHTS – 1/C. ENGINES LOCOMOTIVES: CARS- RADIO CONTROL MODEL MAKER which is high for a 10 rater, and in fact, her maximum beam was 12 in. It seemed remarkable that a boat like this should be able to hold a good class “A” Boat of 14.5 in. maximum beam, 54 in. L.W.L., 53 Ib. displacement, which was sailing in a Ia suit of about 1,350 sq. in. Sirocco proved this was no flash in the pan by winning practically every 10 rater race she was entered for in 1956, including the British Championship. Her to watch remarkable PART i TWO By B. H. PRIEST, M.I.Mar.E. blowing at Birkenhead, and Commando was tuning up in a la suit of sails, but Sirocco was sailing level with her in a top suit. Sirocco is 34.51b. displacement on 54 in. L.W.L., and carries her 1,110sq.in. on a high aspect sail plan. She was not a beamy boat for her weight, yee he } S } \ Fig. IV.—Mid sections and water line end sec- ae tions fe: er tae eg | 10 : 4 COMMANDO. 10.300″ HIGHLANDER Xn 11-400″ gah SE eel sal z COMMANDO OUT WENGE 70% cr IN WEOGE « WGHLANDER OUT WEDGE 80-5 % OF IN WEDGE John successful Lewis’s 10-rater, Sirocco Highlander with mid section of Commando superimposed for com- RATER parison \ *10-rater enthusiasts N TYPE of Fig. V.—Mid section of LEWIS “SIROCCO’ was to her a faster boat than the same Why Pandora had been the fastest boat to windward in a heavy blow new John Lewis designed 10 rater Sirocco. It so happened there was a fresh nose ender | was designer’s Staghound. HAD observed one day last summer, the i. work due needed for the penny to drop. Thing s started to drop into place. Why the American Flying Cloud Covieapl although weight her running was slightly suspec t. Her designer agrees with me that she is so powerful that she could be redesigned at about 31.5 to 321b. with an even better all round performance.* In September last year the writer had just completed Saxon’s line with a view to buildi ng her for the 1957 Championships, and had visited John Lewis for a friendly debate over her lines. During the evening Sirocco’s lines were produced. One glance at them was all the writer aE aL. = windward who Zin weoce ‘ ie —S Site J Lewis’ mer, HIGHLANDER———__ till features yet 19, be Fohn latest Number ‘¥ 3 7” COMMANDO==-~ not { leased to learn that MANDAL it Ef have seen MODEL MAKER 10R, a slim- 32.8 1b. de- velopment of Sirocco.Plans are aucilablé; MM/486, Pr. ce 8/6. 596 at Fleetwood in 1953. And Pandora was 50 Ib. displacement, 14 in. beam, 54 in. L.W.L. , but with only 1,450 sq. in. of sail area. Pandora had carried sail better than the heavies under strong conditions, but her designer, Mr. Andrews, has discar ded her because of her very poor light weather performance. Fig. IV shows, by kind permission of John Lewis, the mid sections and water line end sections of a typical 10 rater of the Sirocco concept. There may be those who have seen the lines of Pandora and will see the same concept applied to an “A” boat, for according to her designer he scaled up the mid section of a very old and famous Daniels 10 rater, and then dropped it downwards in the water, so that the turn of the bilge was below water line. The writer went away and designed his experimental Highlander. How the idea was applied to this “A” boat is shown in the lines, and in Fig. V where her mid section is super- imposed over that of Commando. The differ- ence between the In and Out wedge s of the two designs gives the key at once, and High- lander must carry sail far better than Commando. The danger was, having no data except. Pandora and the beam sail area graph go upon, that a boat might be produc ed to which was a flop in lighter winds. A calcul ated DECEMBER, gamble was taken and she was given half an inch less beam than Commando on the L.W.L. and her body depth decreased. Her displacement was made slightly less than Commando. Lastly it was thought that if she was given about the same sail area as Commando she should, due to less beam, manage to look after herself in light winds. The hull was, of course, balanced on the Turner metacentric shelf system. If the designer’s ideas were correct, she should take an easy 5° heel in light airs, but the more she was pressed the more she should settle in the water. She should be as good as Commando in light airs and far better in stronger winds. Also she should plane on the run faster than Commando owing to the extra life she would get from her flat floors. Her bilge was designed easier that that of Pandora in an extra endeavour to make her not quite so powerful in light weather. Her top sides were given half an inch of tumblehome so that the “in wedge” would be further reduced and she would lean on a long level bearing when rail down. It would appear that the experiment was successful for Highlander performs exactly as was predicted. She won the Coronation Cup at Birkenhead in a light nose end wind from Commando, and the following day the Nor- thern Districts Championship in a fresh nose ender. This was not all, for the boat displayed other virtues which had not been allowed for in the design. Firstly she pointed higher, and kept sailing, than any other boat the writer had owned. Those who saw her lee bow Tango Fill, a “classic” design by the doyen of all designers, W. J. Daniels, which finished 7} points behind Highlander in the hands of Arthur Levison 1957 and Cumbria from leeward berth before the first turn in an 8-10 m.p.h. nose ender on the Thursday at Fleetwood (and both boats are no mean opponents under those conditions) will understand what is meant. On that afternoon she was 20 feet higher up in the lake on the third turn than any other boat in the fleet. Another virtue she displayed, which is a valuable one in championship sailing, was that the trim of main and jib and the vane angle were the same for all windward trims in all suits of sails for any wind strength between 5 m.p.h. to 40 m.p.h. Suits of sails could be changed up or down with no fear of losing trim. The writer feels that she could go slightly larger and still be slightly better. It is his intention to scale her up up to Highlander Mark II and Mark III and of the three it is suspected that the latter might be too powerful and that Mark II would be the best all round boat of the three, but only experiment in racing conditions will prove it. Highlander Mark I L.W.L. 54 in. L.W.L. beam 13.6in. Displacement 521b. Sail 1,540. Highlander Mark II L.W.L. 54.5in. L.W.L. beam 13.85in. Displacement 55 1b. Sail 1,560. Highlander Mark Ill L.W.L. 55in. L.W.L. beam 14.3in. Displacement 58 lb. Sail 1,570. The scale factor for Mark II being X 1.025. The scale factor for Mark III being X 1.05. Both mark II and Mark III would display exactly the same action, etc., as the original. Finally for all who might build Highlander it is essential that the final weight of 52 1b. is not exceeded by more than half a pound. Highlander’s elegant lines out of the water just ask to be copied, and we are sure she will prove a winner for many enterprising skippers in the future Os a *° SS eae ih 597 EO Another Daniels design, N. D. Hatfield’s Serica, third at Fleetwood. N.D.H. got her a place higher this year and will get that top bracket yet! DECEMBER, es Yacht Designer remains a student from the inception of his first plan until the completion of his last set of lines. Yet nearly all of us at some phase of our careers think we have discovered the secret of the perfect racing yacht, only to find our bright new ideas are hoary fallacies, discarded by our predecessors long ago. UCKER’S TOPICAL TALKS In reality, yacht design is such a complex business that it remains an art rather than an exact science, since, when one tries to analyse the factors that make for good performance, one finds these. cannot be translated into figures and formulae because of constantly changing conditions of wind and water. Hence our most reliable guides are certain broad principles based on experience, and plain rule-of-thumb. In fact almost the only incontrovertible axiom is that perfect hull balance is ‘essential, and that this results from volumetric balance. One may well wonder why the dynamic balance of a hull is affected by its static volumetric balance, especially as the latter is ascertained by rough-andready methods of approximation. The probable explanation is that when we balance the hull volumetrically, we balance the entry and delivery rates to which the water must conform as it flows round the hull. We are not meticulously calculating the displacement. Now in checking the fore-and-aft position of the C.B. of the heeled hull, we draw the so-called “inwedge” and “out-wedge” of the hull by taking an imaginary heeled L.W.L. through the intersection of the upright L.W.L. and centre-line. The usual angle of heel taken for this purpose is 20-25 degrees. It is obvious that in any normal hull, the in-wedge ascertained in this fashion exceeds the out-wedge by an appreciable amount, but even if this method is not entirely accurate, it gives us sufficiently reliable data to ascertain the fore-and-aft position of the heeled C.B. On the other hand, comparisons of in- and out-wedges ascertained in this fashion are unreliable and useless for ascertaining the probable behaviour of yachts having different types of section, or the comparison of one boat with another. By way of illustration, let us examine two designs of 36-inch Restricted Class models, having midship sections of vastly different characteristics. olf Fig. 1. EUDORA, designed by the author and published in Marive Models, August, 1934. This was inspired ty Iris, published in March of the same year The first of these, Eudora (Fig. 1), in “Marine Models”, August, 1934, was directly inspired by the M-Class design, /ris, published in’ March of the same year. Both: these designs were canoe-sterned with a midships section in which the in-wedge and the out-wedge were almost equal in area. I claim no originality for this idea as it was borrowed from the lines of Haze, a sailing canoe designed by Linton Hope and raced by him with tremendous success in the 1890’s. As a matter of fact, Eudora was a nice little boat and proved very successful in her day. However, in her design I did not take advantage of toa WHAT EFFECT HAS MIDSHIP SECTION DESIGN ON SPEED ? = er4 the full 12 in. depth permitted by the rule, and with a beam of 7.85in. she was a long way inside the 9in. allowed. Hence, in due course, she gave way to bigger and more powerful craft. The relevant details of Eudora are: Displacement 11; 1b., Area Mid-Section (Upright) 20.54 sq. in., In-wedge at 20 degrees Heel 2.82, Out-wedge 2.68 (= 95 p.c. of In-wedge), Area Mid-Section (Heeled) 20.54 + 2.82 — 2.68 = 20.68; difference between Inand QOut-wedges 0.14 (= 0.7 p.c. of Heeled MidSection Area). Fi g. 2 (right) WATER SPRITE, aesigned by the auther in sane spring of OUT Fig. 3 (below, centre). SPRITE’S flared bows aes Fig. 4 (above) SPRITE’S tumblehome transom The second yacht, Water-Sprite (Fig. 2), was designed by me in the Spring of 1955, and was deliberately made a very powerful boat. One difficulty in boats without overhangs is to provide sufficient reserve buoyancy forward to enable them to be driven hard down-wind without burying their noses or broaching. To attain this, I gave her heavily flared bows, almost like those of a motor launch (Fig. 3), and balanced her appearance by pinching the deckline in aft to an appreciable tumble-home on the transom Fig. 4). Actually, this also made for dryness aft, especially when combined with the flared bow. About the same time, I made a similar design in the M-Class. Both the 36 and the M-Class have been built to, and I have had good reports of each of them, particularly the latter. Details of Water-Sprite are: Displacement 114 lb., Area Mid-Section (Upright) 19.70 sq. in., In-wedge at 20 degrees Heel 3.44, Out-wedge 2.64 (= 77 p.c. of In-wedge), Area Mid-Section (Heeled) 19.70 + 3.44 — 2.64 = 20.50, difference between In- and Out-wedges 0.80 (= 3.4 p.c. of Heeled Mid-Section Area). Now the L:W.L. Plane of Water-Sprite has an area of 194.4 sq. in., and it takes an additional 4 lb. weight to depress her 1/14in. in the water. Hence our assumed heeled L.W.L. will be approximately 1/16 in. too high. In the case of Eudora the difference between In- and Out-wedges is so small that it will be only about 1/80in. too high. The difference in the heeled trim of the two boats will then be 1/16in. — 1/80 in. = 1/20in. But in taking these comparisons of In- and Outwedges we have assumed that the yachts are arti- ficially heeled by moving a weight already aboard, and totally ignored the fact that when boats are heeled by wind-pressure during sailing, their dis- 615 IM ty nN MODEL MAHER) placement is very considerably increased by the downthrust of the wind on the sails. The force of this down-thrust is altered by the strength of the wind, angle of heel, etc., and each of these factors varies continuously. Hence it serves no practical purpose to try to calculate it exactly. We do know, however, that it is many times greater than any small up-lift arising from differences between In- and Out-wedges. Hence we see that these differences have no practical influence on a boat’s behaviour, and can be ignored with impunity. Some model yachtsmen have the erroneous notion that a big difference in volume between In- and OutWedges is liable to make a boat rise on her bilge when close-hauled in heavy weather, but the above will show this is nothing to do with this fault. The factors that have to be considered in this connection are (a) Proportion of Beam to Body Depth; (b) Angle of Rise of Floor; (c) Proportion of Lead Ballast to total Displacement; (d) Design of Garboard Angle. Probably more than one of these things can be blamed, but it depends on the boat and the design. As a matter of fact, tumble-home is a legacy of the old “Wooden Walls”, and in these vessels it served as a gun-platform when firing broadsides, and also proved a distinct advantage when the order was “Repel Boarders!”’. In a yacht tumble-home is of very little practical use. A slight tumble-home can be used to obviate an appearance of wall-sideness in a yacht with generous freeboard, as called for under the A-Class Rule. It can also be used in the after part of the yacht to keep the decks comparatively dry. It has this effect in Water-Sprite, with the additional advantage that in conjunction with her flared bow, it is decidedly decorative. In view of the above, readers may question my use of a rounded deck-edge in the “Ducks”. Actually this is not a true tumble-home, but simply a roundingoff of the angle made by the topsides and deck along the gunwale. It serves a double purpose when the yacht is sailing close-hauled, rail down. On the lee side the rounded edge mitigates water disturbance along the gunwale, and on the weather side it relieves wind pressure on the lifted weather side of the hull, particularly forward. This rounded deck-edge is shown in the mid-section of the original Donald Duck (Fig. 5). I incorporated this feature in her lines Lowe ee veal | produce the most powerful hull possible under the restrictions on displacement and body dimensions in order to carry the largest S.A. possible. How well I succeeded is shown by the fact that Donald Duck proved a real sail-carrier under her first suit of 846 sq. in., and her extra large suit for use in light winds had an area of no less than 1,062! It must not be forgotten, however, that this boat was designed long before vane steering came into use. When vane steering came into vogue, the length available as a base for the sail plan was shortened by several inches, and the SA had to be decreased by about 200 sq. in. As a result, the original Donald Duck was rather too powerful, and was slowed in light weather by being under-canvassed. Hence in later “Ducks” the section was eased and the bilge turn lifted somewhat. This had the desired effect of making the yachts easier to drive, and they proved considerably faster under all conditions than the original design. Further, though they had decidedly less sail, they could carry their first suits just as long. Their record from 1947, when the first “Duck” was built, to date speaks for itself As a matter of fact, no single design in the whole history of organised model yacht racing ever scored as many successes in M.Y.A. National Championships as the 36-inch “Ducks”. The majority of the credit for this must, of course, go to the clever skippers who have sailed them to victory—in particular, D. A. MacDonald, who has done so no less than four times. Much of the credit for these various wins must also° be ascribed to Arthur Levison, who has built so many nice hulls to “‘Duck” Lines for various skippers. Of course, I am proud of my own minor share in the “Ducks” successes, but I do wish people would realise that I have designed as good as or better boats to other classes, even if these other craft have not been as lucky in their skippers. I guess this will about fill the space our Editor can spare this time. I will, therefore, take the opportunity of wishing all my readers A VERY AND GOOD when it began an amazing series of contest sucesses in the hands of D. A. Macdonald SAILING DURING 1958. eee OBITUARY Fig. 5.DONALD DUCK, designed Spring, 1939, but not built until 1947, HAPPY CHRISTMAS MR. MARK FAIRBROTHER., Model yachtsmen the world over will learn with regret of the death on November Ist of Mark Fairbrother, for many years one of the leading figures in the national and international thrombosis. scene. Cause of death was coronary A top-flight skipper in his sailing days, Mark had for the last few years devoted his time to the organisation because of the abnormally powerful shoulders due to the “Duck” bow. As it seemed to work well, | retained the rounded deck-edge in later “Ducks”. Donald Duck was actually designed in the Spring of 1939, but due to the war, remained unbuilt until 1947. It will be noted that Donald Duck has the turn of her bilge lower than the more normal section of Water-Sprite, though it is not as low as on Eudora. She is, however, beamier than the latter boat and has less body depth. As S.A. is unrestricted unde the 36-inch Rule, my objective in the design was to 616 and administration of the sport, and was at the time of his death Racing Secretary to the Model Yachting Association and the Midland District, Editor of the M.Y.A. News, and Secretary of Bournville M.Y.P.B.C., his home club and one which owes its present excellent position to his boundless enthusiasm and drive. Always a forceful personality despite his small stature, and never afraid to express his opinion or stick to a fair ruling, Mark will perhaps best be remembered by yachtsmin as the O.0.D., starter, umpire, or other official at ianumerable regattas up and down the country. The model yachting movement as a whole will sadly miss so tireless a worker and so keen an enthusiast.
