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FEBRUARY 1962 TWO SHILLINGS _US.A.& CANADA ~~ FORTY CENTS. a | MIGIDEM ARE Experiments with John Lewis describes Twin-keeled the thoughts behind 10-raters CANNOT remember exactly why I had the urge to design a 10-rater with twin fins, perhaps it was the desire to break into new ground and produce something different, perhaps it was an impish wish to hear tongues wagging at the sight of such a monstrosity, or perhaps seeing the designs of various twin keeled cruising yachts sowed the necessary seeds. |—+—_+—t~ However, I do remember quite well that I had no expectations that such excursions into the relatively unknown would produce a world beating yacht—and I was quite right. There is nothing new in the idea. Over the years several cruising yachts have been so fitted and just lately there is quite an epidemic of twin finned boats, they can hardly be called yachts, sitting primly upright on the mud in very many estuaries around our coast. This, of course, is their great advantage: gone is the fear of swamping the yacht before it lifts again on a rising tide, and it is so much more convenient to wait for the water in an upright attitude. Then there are the bilge board scows but with these racing machines the windward board would be retracted. With the model, however, there is no problem in running aground and it is hardly practicable to make the fins retract. We had to have two fixed ballasted keels, or more correctly fins, and it was thought worthwhile to investigate the pure hydrodynamic proportions of such a configuration. I was very fortunate in having the co-operation of Ken Jones of the Birkenhead club, who built and raced the two experimental models Moonstone and Herald. It is quite tempting to make an experimental model somewhat quickly and below general standards of workmanship, but in this case Mr. Jones built both models with the utmost care and fitted them out to the highest possible standard. Many people will have seen Herald at the Inter- {|_| CI mei \ X Tilt and the results obtained with his two intriguing and now famous twin keelers national Boat Show last winter where it won the Championship Cup. The first design was Moonstone and the object was to see what happened to a normal hull when fitted with twin fins and to this end no other experimental features were incorporated. The canoe body was almost identical to the No. 19 10-rater published in Model Maker Manual and the wetted surface of the model was kept the same as a conventional 10rater. The aspect ratio of the fins was chosen arbitrarily as was the actual position about the midsection and their splay angle. There was no available data on which to base this design. One of the limiting factors on aspect ratio was the need to get some 11 lbs. of lead into each fin and in order to avoid a cross-section that was too thick the keels were probably a little lower in aspect ratio than I would have chosen. Even so the fins were rather thick in proportion to their chord. At this stage I did not think it wise to introduce asymmetric sections or angles of toe-in, so the fins were located parallel to the centreline. A general arrangement drawing of this yacht appears below and is I think self-explanatory. The very first race that Moonstone entered was the National 10-Rater Championship held at Birkenhead. I was somewhat nervous about this for I do not believe that untried yachts should enter for National competitions. They can so often waste a lot of time both on the bank and in the water which is very irritating to other competitors. I need not have worried, as Moonstone appeared to handle in a perfectly normal manner. There were no characteristics in steering or trimming to cause any difficulty, and when the boat was afloat no-one would suspect that she was in any way unusual. She did not win the Championship—I did not expect her to—but she showed herself capable of very high speeds both on and off the wind, given a good blow. During this race her mast position was too . FEBRUARY There was the added advantage that the reduced weight would make it possible to design high aspect ratio fins and thus improve their efficiency, and so Herald was born complete with twin The following rules rudders for good measure. summarise the observation of one year’s tests :— 1. Twin rudders were a wash-out, and were immediately removed. They were probably badly far forward and she had to be sailed with quite a lot of lee helm and this always slows a boat down. Over a couple of years’ racing, including one or two first prizes, we were able to summarise the ex- twin fins. periment in the following terms :— 1. Twin fins parallel to the centre-line need not induce any peculiar steering effects on the hull and the boat handled in a normal way. . Compared with a similar single fin 10-rater Moonstone seemed to have excessive stability. . The windward performance in a good breeze WN designed. Lh WY . In strong winds Herald sails with one fin completely out of the water which is most entertaining. was superb. . We succeeded in making a light displacement boat weatherly in heavy weather—this is the most significant feature of the experiment. Even so she could not better the 10-rater Sirocco in strong conditions for sheer speed. 4. The light weather ability is probably worse than vA . The windward performance in light air was poor. NH . Under all wind strengths the boat made very little leeway when sailing on the wind. . Off the wind she could be driven very hard without fear of broaching. The two things which interested me particularly were the apparent stability and the poor light weather performance. The fins were shortened by Moonstone. 3. The stability expected. 6. about 1 in. and the performance was somewhat improved, and Mr. Jones is now going to shorten We also tried a 3° toe in and no apparent difference in performance was noticeable, but tests on this feature were not carried out to any really satisperformance was was not nearly as great as I Off the wind her ability is outstanding in any- thing other than light airs. The disappointing results were (4) and (5) and reflection on these has, I think, shown the errors in them still further. factory conclusion. Moonstone’s general 1962 the design. The fact that the wetted surface of Herald is less than Moonstone indicates that it is not simply skin friction that is causing the high resistance at slow speeds. It can, therefore, be due to the aspect ratio of the fins and I made a mistake in designing Herald’s fins to a high aspect. ratio. I have since learned from another source that high aspect ratio fins do have a higher resistance at low speeds than those of lower ratio given the same wetted surface. This fact seems more important than the improved encoura- ging enough to consider a completely new design and for a long time I had been playing with a design incorporating all the gadgets and features tried out individually over many years. It was natural therefore that twin fins should also be a feature. The original intention was that I should build this creation for myself, but as Mr. Ken Jones was quite willing to risk a complete failure he took the job on. The result was a most beautifully built craft lift/drag ratio of the high aspect. When Moonstone’s fins were shortened we were moving in the right direction, but for a different and a championship cup at the Boat Show. reason! I will not deal with the design features in Herald other than the twin fins. For a long time 60 in. L.W.L. and 1,000 sq. ins. of sail had been magic figures to me, but so far no long waterline 10-rater The stability question is interesting as it brings in a dynamic effect in model yacht design. Here is another reason for high aspect ratios being a mistake. The actual centre of lateral resistance is lower than usual and therefore there is a greater capsizing moment reducing the stability. My experience with centre board dinghies certainly confirms that a dinghy with a shallow board is much easier to keep upright than one with a deep board. Of course the lower aspect ratio fin will be able to carry the lead proportionally lower due to the has been consistently successful. They are very good under their particular conditions, but due to the small S.A. it has, up to now, been necessary to keep the displacement light. The result is that in heavy winds and rough water they are just not powerful enough to cope with the 34 Ib. boat. With Moonstone’s exceptionally good heavy weather performance at 32 lbs. I thought that 60 in. L.W.L. 26/27 Ibs. might be acceptable with [Continued on page 92] 71 FEBRUARY Racing Tactics 2. Was the boat we sail next one of the \ Fis! TRUE WIND \ DIRECTION \ \ \ \\ CSUy, YACHT that has been correctly tuned is only now ready for racing. A very very large percentage of model yachtsmen believe this depends more on just having the faster boat on the run or the luck of the draw than on the boat. The reason for this is that nobody has ever put down on paper the racing tactics which should be employed under all conditions. The correct usage of these tactics can turn a race which might seem lost at the start into a win. Before the tactics can be decided certain items must be given attention. These can be put down under what one often hears talked about as “Attention to detail”. For every race skipper and mate must train themselves to check the following: 1. Is all adjusted correctly on boat and vane? The mate should take off spinnaker, hook up jib and main, bail out, set up backstays and inform skipper that the boat is now ready for him to set the vane. This should always be the skipper’s job. At the same time he and the mate should now double check all that the mate has done. This clears up any chance of losing three points by a stupid omission. 1962 Z Part Two of a two- part article ‘Yacht Tuning on Racing Tactics’ and by B. H. Priest, M.1.Mar.E. feet in an A Class yacht. Next there is the effect This extends of the disturbed air from the sails. over the weather quarter of the yacht as shown in Fig. 1. The effect is equally as important as the wind shadow as the wind passing over the sails loses speed due to friction and eddies and also has been curved around so that the wind stream flowing off the sails is no longer the true wind direction of 40° off the weather bow, but is now on an axis of about 15° off the lee bow. This effect does not extend as far as the wind shadow does and of course varies according to the heel of the boat and the strength of the wind. Its effect, however, can be noticed quite strongly for one mast length astern. The deflected wind is a powerful force both in defence and attack. In the latter case, if one is ahead, a boat close astern endeavouring to burst top line or a poor one? How was she pointing and sailing on her last beat? A good skipper and mate know the name of the boat they sail on the following board whilst they are sailing the present and always keep an eye on how that boat is sailing during the board before they sail it. 3. Has the wind changed in either speed or direction? At no time is the wind ever constant in speed or direction for more than a few minutes through at a time as any who have sailed a manned up craft will know only too well. Further, various winds have their own special oddities in various parts of the country. Usually it will be found that winds between South West, West and North West are the truest and in the North of England a North West wind is probably the best as it usually comes in after a depression and its cold front have passed over and can also, if one lives on the North West coast, come in as a sea breeze. Both these winds are fairly true. A South to South West wind can be true in direction but can alter a great deal in speed. The worst winds are from the East. These are never constant either in speed and direction and can swing 20° either way and back again in the course of a minute. The good skipper is watching and checking this at least to weather at once meets this slowed deflected wind stream from dead ahead and her bow falls off at once to conform with the now true wind direction, thus she drops astern and to leeward of the leading yacht and promptly gets into her wind shadow to leeward. In Fig. 2 it will be noted how this effect is used in attack. Boat A is just ahead and to leeward of boat B. Now if boat A pinches slightly the deflected wind will soon begin to affect the sails of B when she gets close enough. As soon as this happens B’s bow will fall to at least 15° to conform with the new wind direction and will drop down to leeward of A’s stern. It is just as hard to attack a leading boat’s lee as the yacht has to burst right through the large sector of wind shadow to a position when she is fully abeam before she is clear and, of course, up to a two mast lengths distance, the further away she is the more chance she has because the shadow every ten minutes. We will take tactics on the windward leg first. If Fig. 1 is examined and studied it will be found helpful for, because of what it shows, we have to adopt various tactics. It will be noted that a wind shadow extends to leeward of a boat which is beating. This wind shadow’s axis is in the direction of the apparent wind which is about 30° off the centre line of the yacht. It has been stated that this shadow extends to leeward for about seven mast lengths, although in practice in model yacht racing the writer believes the effect is only effective for the length of two mast lengths, but this is nearly fifteen narrows. All tactics to windward in model yacht- ing are built to use or overcome these two effects to one’s advantage. In Fig. No. 3 if A and B set off on a beat and both boats sail on the dotted line course at the same speed, and provided the starting positions are twelve feet or over apart, then as B is not affected by A’s deflected wind they will arrive at the bank in the same relative positions which will preclude A being able to turn in front of B. She will hold and turn off astern and to leeward of B and we have already 93 miGiDE MIANRIEIR slipped and A can now sail the port tack normally seen that this is a hopeless position and the race, if but in a clear wind and so has at least an equal chance with B, which she would never have had both are correctly turned for the next leg, is lost as far as A is concerned. before. Fortunately for A the ideal facts as stated above B he must leave his normal trim alone as he will be far enough ahead at the turn to cross ahead of B. If he can point higher it will pay to nip his The tactics of boat B are simpler. Firstly, if she thinks she is slightly faster than A, then her obvious course is to sail her normal course, but secondly, if she suspects A is equally as fast or even slightly faster, she can ease off her vane one degree on the starboard tack. By doing this she will travel slightly faster, and should be able to keep out of A’s de- B into the deflected wind from his sails and cause B to drop astern and to leeward of trim. A’s main problem comes when he knows B is equally as fast and equally close winded. A has a choice of two tactics if he is to have any choice of winning. on A so that at the turn A is completely hemmed in and has to hold until B has been turned before she can attempt to commence her turn. The writer has used this tactic many a time with great success. do not always apply. A can-be faster than B, A can point higher than B or B can make more leeway. A from his study of B in the previous race must now decide his tactics. If he feels he is faster than flected wind because her speed will take her to an abeam position, but at the same time will fall down vane up one degree on starboard tack and thus bring The start shown in Fig. 4 crops up now and then. The wind which was a true beat swings slightly and heats are started before the O.0.D. notices what has happened. If one is lucky enough to have choice of berth then one must take the leeward one. As can be seen, B now is in the gravest danger of being in A’s deflected wind and in any case will be in it enough to be slowed up sufficiently so that A can always turn ahead of her. The writer can see no hope of B ever winning from this start providing A is well trimmed. It is a different matter entirely Firstly, to ease his vane two degrees on the starboard tack and arrive at point X in Fig. No. 3, at which point he will be in a position to turn under B’s stern and get ahead, although to leeward, in a clean wind and there is a faint chance that B may not point quite so high on the next leg and fall down into the deflected wind from A’s sails. His other chance, which the writer has only seen employed now and then, is to start normally, but with a hard gye set on the port tack. Now when the boats arrive at Al and Bl, A holds and then does a short gye. When she come in again the gye is’ st d Fi A A ve / (a) WIND ‘ FIG.3 a 47 POSITION if the wind is as shown in Fig. No. 5 and tactics 1 : !| NH < ‘\ | ey TRUE Me: | \ 4 4p WIND “Sate: ES. FIG. 6 | WIND S | AB LEEWARD Ea ACCORDING TO SAIL TRIM i sb (b) ! | i),| yw FIG.2 | | a | B fy” yi x A WEATHER ACCORDING TO SAIL TRIM 4 Se s POSITION 8 | } TRUE WIND (a) Bh LEEWARD ee 8 WEATHER ACCORDING TO SAIL TRIM SB \ \ \ \ \ \ \ ‘ \ \ \ 8B WIND \ | nA \ \ \ \ bf TRUE \ \ ae FIG.8 8 bake per, Vy \ A ok bk bok Figs , Vi A. ACCORDING TO SAIL TRIM SS i b) / em,/ | ' ene eee oe position ¢ ull // / / SS | LaFIG.7 ftind ! b) / " ae FIG.4 4 TRUE (a) a = LEEWARD \ \ \ amt WEATHER FEBRUARY his vane feather slightly to weather, then the leeward boat will fetch up on the weather bank well ahead of the weather boat. She must now gybe and a win is certain. Note that the vane is not touched in the retrim, as on the other gybe it is just about will vary depending on how far A and B can get up the lake without touching. On starts of this type B has a definite advantage. It will be noted that in this case B is clear of the danger of A’s deflected wind; on the other hand B has only to draw ahead very slightly to get A affected by her leeward the correct angle for the wind. It is when the wind swings or is blowing as Fig. No. 8 that the fun starts. Under these conditions it always pays to take weather berth. Usually both yachts will carry large spinnakers and trim for the leeward end of the finishing line, making certain that they do not broach to. In cases like this it is not improbable that both yachts will strike the lee bank. Usually the boat which had lee berth will touch first. The mistake many make is to do a fairly drastic retrim, which, if it is blowing fresh, will always result in a broach. The writer believes that if the angle to the bank at which the yacht is approaching is mentally calculated and the result divided by half then that is the maximum retrim which should be put on the vane. Should the boat come in again the vane should not be retrimmed, but the main sheet should be very slightly brought in. A maximum of half an inch on the main sheet should be aimed at. Far more races are lost through shadow. In racing yachts, both big and small, one of the most important rules is, when ahead, to always keep between your opponent and the finishing line and always to do exactly the same as he does. So when A and B arrive at the bank A should be to leeward and astern and as such touch the side first. He must now make up his mind if he is going to sail across or do a gye. B’s skipper must watch care- fully and copy whatever A does, because if A is right or wrong in his decision it makes no difference because B is doing the same thing. If A elects to gye B must endeavour to gye slightly further out as he must at all times guard against A gying on his weather quarter, and put- ting him in his leeward shadow. If A can do this B will fall off back towards the bank and A should sail through to establish a commanding lead. Tactics on the run are just as important but somewhat easier overdoing a retrim than underdoing one. to apply. It is often the case that both ming on the bank at the same boat that is astern is not too far the shore first the leading boat If the wind is dead down the middle of the lake as in Fig. No. 6 both A and B have an equal chance. The writer will usually trim to hit the leeward finishing flag because it is always easier to retrim off the lee shore rather than the weather one. Should the boat, however, hit the weather shore it It is quite hopeless to try to retrim off by vane adjustment as so many endeavour to do. Should the wind alter just before the start as shown in Fig. No. 7 and both boats as a result have their spinnakers on the wrong side, then the correct tactics are to take lee berth, if one has choice. If this is done, and at the same time the prudent skipper eases his kicking strap and moves Qeaders Write ULM BREAK-DOWN DEAR SIR, It was interesting to see L. Weed’s letter in your January issue. I have entered many regattas on the Continent and several in England, and there is a big difference between the Ulm and, say, Poole regattas. The normal meeting in England is for power boats, some electric, and average entry seems to be about 50. There were in fact more than 208 entries at Ulm, the 208 being the number who actually ran. There were 101 electric R/C boats and 78 i.c. R/C boats, broken down as follows: Elec- carry through into a winning position. tric R/C speed 25, i.c. R/C speed 35, Scale R/C steering 28, Non-Scale electric R/C steering 30, Non-scale i.c. In addition, R/C R/C steering 24. sailing had two entries, novelty 15, the Blue Ribbon 14, and the Red Ribbon 4, a total of 177 starters from 179 Cable racers totalled 29, and entries. ‘‘non-working’’) models (i.e. ‘*shelf’’? 25, a grand total of 231. Everything was well organised, with duplicate courses, etc. and everyone The average German had a chance. modeller is no millionaire, and that chap with 70 hand-made props spent more of his spare time than anything There are plenty of people with else. skill enough to produce a home-made motor from scrap—not at all an exMost of the fast pensive proposition. boats had stock motors, as did the doesn’t motor special A winners. make a fast model—it is the skill of is and this that counts, operation big his makes Weed Mr. where mistake. ALTFRIED KLEINESPEL. Dusseldorf. FAST STEERING DEAR yachts are retrimtime. When the behind and leaves must not put off because the one behind will take her wind, catch her and touch, in which case the leading yacht will be disqualified. Whilst it is a great temptation, when leading boat, under these conditions to put off still ahead to maintain one’s lead, the prudent skipper holds until the boat astern has just passed. He then lets go aiming just to weather of the new leader’s counter. It will be found that when she gets to about this spot she will bear away on her proper course. In passing the deflected wind will shadow the leader and this always appears to throw her back to the bank whilst the other will usually can only mean that the wind has moved as shown dotted, in which case the only retrim to make is to gybe the main and leave the spinnaker to look after itself. 1962 SIR, We were intrigued by the letter in Readers Write by Mr. L. Weed of Taunton, because we feel that in the 95 last part there is a good deal of sense. In the last two seasons the emphasis in contests seems to be on _ speed; steering courses are now commonly run against the clock and markers get wider and wider so that boats can get through at speed. The result is that the models with larger engines figure prominently in the honours. As for speed courses, the only skill that is needed is to hold the model on a circuit while at speed, though the new rules and classifications will help here. Let’s hope that this season steering courses will be tough, without being unreasonable, so that at least in a steering event the high and low powered boats will be on an even footing. L. R. TANSWELL. Eastbourne. WEIGHTY DEAR SIR, On reading through the Ulm regatta report in December Model Maker, I notice that emphasis is given to the comparative weights of competing speed boats entered. I would like to point out as a matter of interest that the Gannet powered Chris-Craft entered by us which came second in the speed event weighs 28 lbs.! N.W.6. G. A. NURTHEN.
