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MODEL BOATS Larry and Niel Goodrich, Central Park MYC and Mill Pond MYC, USA, provide some views on a subject ————~ which isalmost guaranteed to cause argument! RM DESIGN: LIGHT IS RIGHT | BP etic the 1976 racing season, the best skippers in 4tin. (4) Draft is 15in to 17in with an 8lb lead bulb. (5) Rudder post is 10in forward of the transom. (6) Most popular sail plan is 40/60 jib to main ratio with a 68in luff on the main, but a lower suit is advisable in winds above 15 mph. Compared with our best heavyweight, the performance characteristics of Wind II can be summarised as follows: (a) In fluky air — it will move out on puffs too light to get the heavyweight going at all. (b) In steady ‘light’ air (4 to 7 mph) — it performs about on a par with our best heavyweight on all points of sailing but it has the special advantages noted in para (e) below. (c) In ‘gentle’ air (8 to 12 mph) — it is on a par with the heavyweight to windward but begins to outperform the heavyweight off the wind and will plane early in the gusts. (d) In ‘moderate’ and ‘fresh’ air (13 to 24 mph) — its off-wind performance is astounding, planing easily for long distances with little tendency to dive or broach out. Upwind a low rig may be necessary as you get into Force 5. (e) In all these wind speeds, Wind IJ has the double advantage of marvellous acceleration and extreme manoeuvrability. (f) We have not experienced winds above Force 5 or very heavy chop so we do not know how Wind IT would fare in those conditions. We suspect that the principal problem would be in keeping reasonable control over the boat off the wind, since at high planing speeds the rudder gets so efficient an extremely delicate touch on the transmitter stick is required. Since Wind IT develops superior speed only off the wind and only in ‘gentle’ air and above, the consistency of its racing success, particularly in lighter air, must in large part be attributable to its superior acceleration and manoeuvrability. At first thought these seem like very minor advantages, hardly worth designing for. But a — the United States, almost without exception, chose to campaign RMs with displacements in the area of 184lbs all up. Reports from abroad indicate a generally similar pattern. From this evidence, one might think only a fool would depart from the conventional displacement. Fools we may be, but after a season of racing a new 14lb design, we have concluded simply: lightweight is right for RMs, no doubt about it. Wind II, designed by CPMYC member Forest Godby, is without question the most exciting new boat to appear here since we converted to R/C several years ago. At least eight CPMYC members have switched to it in midseason and for good reason — the stock version from the outset consistently placed high in the early races and Niel, with his modified version, has beaten virtually all comers in the Northeast, taking first place in the MYRAA nationals, the Campbel Cup and the Sytoff trophy. Larry did almost as well with his less modified version. Our purpose here is not to tout any particular light design. The hull is nor for sale and there are no plans. We hope nobody will be foolish enough to try to duplicate Wind II from the photos and the few details we give here. Our reason is simply that it is still very experimental and we are not sure that any particular aspect of the design is right except its light weight. The significance of Wind II is not that it is super-boat but that it has disproved the widely held conviction that a lightweight could not perform as well as a heavyweight in a broad range of conditions and especially in light air. By describing the characteristics of, and the theory behind, this light design, we hope to encourage the more adventurous skippers around the world to develop their own light designs. Our hunch is that development of that kind will produce boats far superior to anything currently being raced and will end the current vogue of the heavyweights. Even if we are wrong about that, we can assure anyone with enough guts to ‘go light’ that he is in for an entirely new experience in R/C racing. Taking control of a lightweight for the first time is like switching to a sports car after racing a truck — the extra acceleration and manoeuvrability are exciting as well as a challenge to keep under control. My photos of Wind II may give a pretty good idea of its basic shape but some specifications may help: (1) All up D is 14lbs. (An 184lb RM is almost one third heavier.) (2) Maximum beam is about 9#in, beginning about an inch aft of the midsection. (3) Transom width is about typical R/C course involves a great many tacks and quite a few changes in wind speeds. To windward, Wind IT can frequently gain a yard or two over our best heavyweight on every tack because it can tack and accelerate to hull speed more quickly. That ability puts enormous pressure on the skipper of a heavyweight in the lead. He knows that if he tacks to cover, he must give up some of his lead, and that if he does not cover, he risks allowing the lightweight to accelerate out on a fresh puff or a new lift of its own. 86 FEBRUARY 1977 Wind II gives the skipper an extraordinary sense of confidence. A veteran CPMYC skipper commented: “TI may not win every race, but with this boat I know I am always in contention. It is so forgiving, even when I make a bad mistake, I know I can recover.”’ Whether or not completely justified or not, that confidence makes him a very tough competitor, never willing to concede at any point, in a sport where a little indecision or inattention can mean the difference between winning and losing. The lightweight reacts very quickly to any change in conditions. This is a distinct advantage to the skipper on the shore who gets quick and distinct signals from the boat’s behaviour as to what is happening out there. Wind II is Forest Godby’s redesign of a heavier and beamier boat with which he was placed fifth in the 1975 AMYA nationals. After that race, he decided his boat did not have quite the speed of those he lost to. So he proceeded on an elegantly simple theory: Hull speed is the difference between the power of the sails and the drag of the hull. Since all RMs are limited by the rule as to the maximum sail area, the best way to increase speed is to reduce hull drag. The easiest way to reduce hull drag is to lower displacement. Lower displacement means less inertia and quicker acceleration (always and advantage) and quicker deceleration (usually a disadvantage). That is Godby’s basic theory — simple, easy to understand and based on sound physics. It also works! An unusual feature of this design is the placement of a large rudder 10in forward of the transom. The theory behind the forward placement is that you get quicker turning action as you get closer to the turning axis and the rudder is more efficient deep under the hull. The theory behind the use of a relatively large rudder is that there is less drag involved in diverting a large amount of water a few degrees than in diverting a smaller amount of water to a much larger angle. In normal conditions, we use a maximum rudder throw of 10 to 15° and during most of a race we use transmitter trim alone for slight course corrections. Whatever the validity of Forest’s rudder theory, it does produce a remarkably manoeuvrable boat with a lot of reserve steering capacity when you need it. So much for the good news. Lightweights have some vices along with their virtues, and those interested in designing a lightweight might pay particular attention to these three: (1) One virtue of the lightweight is that it reacts so quickly to wind changes it is easy to ‘read’ from the shore, but as wind speeds increase this virtue can become a vice in that the reaction time of the boat may severely tax the ability of the skipper to decide what control changes are necessary and to send out the R/C signals before the boat goes out of control. Experienced skippers of heavyweights will have to develop better anticipation, reflexes and concentration to exploit the full potential of the lightweight. Some novices may have more difficulty learning with a lightweight. Those designing for Fleetwood conditions might well decide that a slightly heavier boat would be more stable and a slower rudder system would be easier to manage. (2) The superior acceleration from the lower inertia is a distinct advantage but the concomitant quicker deceleration is normally a disadvantage. True, in jockeying for position at the start it is convenient to be able to stall the boat quickly if you are early. But it is much harder to get out of a stall in a model than in a dinghy because you cannot backwind your sails. For the same reason, if you unintentionally stall your model it may take an agonizingly long time to get it out of irons. If allowed to point a fraction too high, Wind IT, at least, is very prone to stalling out with very little warning to the skipper. Relatively blunt leading edges on the keel and the rudder should reduce Heading, the tan bottom of Larry’s boat highlights the underwater lines of the stock Wind ||. Note the carefully cambered high efficiency keel and the unusual rudder placement, the theory of which is explained in the text. The 50/50 rig shown has been abandoned in favour of a 40/60 rig which seems to help the boat point higher. Below left, Wind || is very ‘slippery’ off the wind and leaves very little wake even at full planing speeds. As the wind and boat speed increase the hull lifts gradually to a semi-plane and then to a full plane without the sharp break noticeable on some heavyweights when they finally pop out onto a plane. Centre, Niel’s Wind || with its silverware in a shot posed for another purpose. (He really does not set his boat up like this every night!) Note the modifications in the keel and rudder. Right, here is what competitors fear the most in Wind II = its ability to accelerate out on the slightest puff in virtually windless conditions and its speed on the reach. The beautiful double luff sails on Frank Soto’s boat, shown here, exploit this ability in Central Park conditions, but Larry and Niel, who campaign in more varied conditions, prefer the better luff control possible with single luff sails. Scales are essential for building light. Here they show only I lbs. for the authors’ entire on-board R/C system including the two hatches. Key to the system is the Dumas-Probar SCU (80z and 4 sec cycle) which, although strong enough for an ‘A’ boat, draws so little power that it can be operated, along with the Futaba receiver, off a single 4.8 volt 375 ma NiCad battery for a full day of racing. The Futaba servos are waterproof. the abruptness of the stall and give the skipper a little more time to take corrective action. (3) If Wind ITis typical, the lightweight may be devilishly hard to balance out and trim correctly. Wind II did not begin to show its speed until we moved its bulb back two full inches. After a full season of racing, we are still not sure of the best sail plan, where the keel should be and whether the bow lines could be improved. Sometimes we are simply unable to duplicate settings which in similar conditions had produced superior performance. Of course, all new boats present such problems, but in the lightweight they seem to take longer to resolve. It does not surprise us in the least that a landlocked skipper like Forest Godby, with no vane or full sized yacht experience, could produce this unique RM design on his second try. He simply does not suffer from the preconceptions of the vane skipper or of the full sized yacht sailor and can concentrate directly on the problem of designing for the performance characteristics required for a successful RM. Let us face the problem squarely. In the early days we could simply convert our vane boats to R/C and be pretty competitive. But converted vane boats cannot cut the mustard against the newer R/C-only designs. We may not be able to shuck the vane influence entirely; but we should be able to, in fact we must, analyse our vane designs to eliminate the vane-only concepts which are hindrances in R/C racing. For example, to make room for the vane gear to swing on the stern, the vane sailplan had to be moved forward, which in turn meant the keel had to be moved forward and more buoyancy had to be provided up forward to balance. Freed of that contraption on the stern, in R/C we can now put the sailplan, the keel and the buoyancy where they work best, farther back. (In fact, we are not sure these vane distortions were ever necessary in the first place. Could not the vane gear be hung out, perhaps on aluminium struts, back of the transom? Is it possible that some of the R/C only Ms could be made into marvellous vane Ms with a skeg and rudder and a vane mounted like that?) Another example of the vane influence problem: Some yacht sailors and vane skippers cling with an almost religious conviction to the notion that an RM must have a skeg. A skeg is necessary to give stability and to prevent broaching, they insist, but experience has proved them wrong. What they fail to see is that a large spade rudder, when locked on centre by the servo, is in fact the equivalent of a fixed skeg. And the marvellous thing about that skeg equivalent is that with the servo we can cock it slightly to get a little extra lift on the beat or to counterbalance a downwind tendency to broach. Once freed of 88 the skeg fixation, in R/C we can saw off the skeg, substitute a balanced spade rudder and thereby reduce drag and greatly improve manoeuvrability. We are also freed to put the rudder wherever it seems to work best, 10in forward as on Wind IJ or even, as one skipper plans to try, on the back of the keel! Some have the same sort of fascination with full sized yacht design and their naval architects. We study the literature and to some extent share that fascination, but we have long since concluded that full size yacht design has very little to offer RM design. The design parameters are so far apart, the yacht and the model operate in very different conditions and there is overwhelming evidence that full scale yachts developed from carefully tank tested models do not perform in the same way as their own models. In any event, our hunch is that the current crop of good RMs are faster in scale (i.e. relative hull speed) than any of the best racing yachts in the world. Far fetched? Not really when you try to think of a full sized monohull anywhere in the world which has exploited the high aspect rig and the high aspect keel as much as we already have. If our hunch is right, trying to emulate full sized yacht design is likely to slow us down. We have had a lot of fun with Wind II and we are particularly enthusiastic about the prospects for better lightweights; but, before anyone burns his conventional RM as hopelessly outdated, here are some thoughts by way of balance: (1) Wind ITis a competitive boat by any standards and Niel has beaten a few (but not all) of our best heavyweights in some extremely close races; and we assume that there are heavyweights here and abroad which are marginally faster. (2) The characteristics of the lightweight are exciting, but you cannot win races with one unless you can exploit its advantages to the maximum and compensate successfully for its vices. (3) While we have for this article contrasted 14lbs with 184lbs, we have no reason to believe there is some sort of danger area between those two weights which would produce a mediocre boat, as some have suggested. To the contrary, we believe that progressively lighter designs will produce a steady progress toward the characteristics we have described of Wind II. At 163lbs Tom Protheroe’s Epic, the 1976 AMYA Nationals winner, is very ‘slippery’ downwind. and is probably the fastest US RMin light air. (4) Our own efforts to improve our heavyweights, a Ballantyne Arrow VI and a Stollery March Hare, both classic vane designs, resulted in remarkably improved performance which made them really competitive. (5) The development of the super lightweight is probably years away so it is much too early to give up on the good heavyweights, some of which can be significantly improved by working the vane hindrances out of them. Since we write with so much conviction, we may give the impression that we think we know a lot about R/C design; but actually the more we get into it, the more we realise how much a mystery it remains for us. Sad to say, but we cannot think of one innovative R/C idea suggested by our famous British designers on whom we used to depend so much in vane racing. So unless and until they do their homework and get their acts together, the amateurs like us will simply have to muddle through as best we can and keep a sharp eye out for the kind of creative thinking that produced Wind II. (The authors would be pleased to receive correspondence addressed to them at: 295 Henry Street, Brooklyn Heights, New York 11201, USA; but they cannot commit to acknowledge every letter.) FEBRUARY weight, the electric could hardly be expected to give as lively a performance. Finally on the subject of electric multi-boat, my com- 1977 even when travelling through the wake of other boats. The lap size at the championships was relatively small and Murray Hunter’s Webra WR/Pascotope combination which won the 10cc multi class was averaging 15 secs consistently. Against this, Andrew Young’s 2nd placed Avenger averaged 16secsandmy own Webra ‘WR’/Avenger recorded 13-5 secs whilst on the water. Compare with this David’s measured time of 11 secs on one lap and you will get some idea of just how quick the model was. As David would be the first to admit, steering well at such speeds for the length of a multi boat race is almost impossible and the tremendous speed variation between different modelsin the same race aggravates this. Perhaps it should be regarded as an exercise which could only be tried out under the relatively leisurely conditions experienced in Australia, since other drivers would otherwise get a bit upset at the risks involved. Nevertheless it did provide an interesting foretaste of things to come in future years. The third model described is Murray Hunter’s remarkable petrol model shown in one of the photographs in the December issue. Murray was kind enough to supply a lot of technical information on his model, most of which ments on starting of races. Since all models are bound to start almost exactly at the same time, it would seem unfair to penalise any model by even the odd yard. The way we have tried to overcome this is to have a Le Mans start perpendicular to the bank instead of along it. This makes it easier for drivers to judge the separation between models during the critical first ten seconds of the race. Having said that, we have still found some problems since boats are so evenly matched and it is quite possible to have five of six boats all approaching the first turn simultaneously. The solution to this would appear to be the placement of the first turn buoy as far as possible from the bank even if it is not a part of the normal lap (Figure 2). Now on to i.c. power topics. Victorian Championships As promised, three of the more prominent models seen at the October Victorian Championships will now be featured. One of the most admired was the Super Tigre X-40 powered multi boat by Tony Gray. Not knowing the real name for the model, which is moulded and sold by J.B. Models in Victoria it will have to be known for the moment by its nickname Pascotope which describes both the designer (Jim Pascoe) and the basic hull bottom idea (Isotope 40). As with other designs popular ‘down under’, hull sides are preferred by many to minimise chances of submarining and to increase space inside the hull. The X-40 has had a lot of expert hours put into it, many of which were necessary for watercooling and to convert it to rear exhaust. From the performance it is clear that there is a good deal of power driving the Gale G-22 prop, with 18 second Naviga times possible. Whilst not exceptional for a FIV15 Naviga time, this is achieved with good stability, characteristic of all of the ‘40’ powered examples seen running. Having now started to use a K&B40 SR3 myself, it was interesting to see another Pascotope similarly equipped. Both K&Bs seem to produce more noise than power and it is clear that much time needs to be spent on these motors before they are ready for multi boat racing. More on this subject in later articles. If Tony’s model took the prize for most admired, then David Leigh’s OPS 60 Naviga model took the one for the most thrilling. Despite having done more work on silencing than anyone else I can think of, difficulty in keeping below the limit was experienced during Naviga speed. Thus it wasn’t until the multi event that the model’s true speed became apparent. The hull design is the latest in a long line of development of multi-rail models with power coming from an OPS 60 modified, I believe, to bring it into line with the very latest of these motors. Speed on the straight was estimated, perhaps even conservatively, at 45 mph and yet somehow, the model remained upright is included here. The hull is a modified Pascoe designed glass-fibre moulding measuring 42in by 14in transom width. The deck is from 2mm ply using Araldite for glueing. All up weight of the model is 16lbs. The motor started off life in a chain saw and is a 32cc STIHL rated at around 3hp at 10,000rpm on 24:1 petrol/oil mix (1-525inx 1-12in bore and stroke). The standard cowling and starter were removed and a water cooling jacket was heat shrunk and Loctite bonded in place. The STIHL is now started by means of an electric Honda starter motor with a belt and pulley. The spark plug is a Champion J4J and the silencer is fabricated from a Full Ahead front cone, welded to an expansion box with a 4ini.d. tail pipe. Moving on to the drive line, the prop shaft is sin diameter running in bronze bushes and is fitted with a 70mm by 98mm pitch alloy bronze cast prop, equivalent in size to an X70. As previously reported, Murray now holds the Austra- lian petrol Naviga’s speed record at 20-5 secs with this model — a time achieved below 90 dB and with very little fuss. I am sure that petrol enthusiasts will join me in thanking you for all this information, Murray. It is very noticeable that petrol engined boats are en- countering a major revival of interest both here and abroad. Apart from the older, lower powered models which used to be the backbone of racing in the Sydney club only three or four years ago, there are now three 4bhp Husqvarna 35cc powered models which should be running by Christmas. Added to similar interest in other States, the forthcoming Australian Nationals should see unprecedented petrol competition. KRISPIE (continued from page 106) epoxied in a hole drilled down into the rudder at about 30 per cent of its chord. filed in the after edge of the exposed part of the skeg and the rudder is epoxied to a in. od brass rod or tube; when the rudder is inserted the rod or tube should lie snugly in the groove in the skeg and the top should project about 4in. or so above the deck level. If the model is intended for radio control use, some alterations will be necessary. For example, a spade rudder may be preferred, in which case the skeg should be omitted and a tube fitted through the keel and centre stringer, supported by a wood strut, say tin. x din. glued between those two members. The tube can be bound to it with thread or with a glue-soaked bandage. Securing it in this way rather than just at the ends will help to prevent it working loose. This tube should be a mating fit to the rudder tube or rod; the latter should be rod for preference, The drawing (December issue) shows modifications needed to house radio equipment in a fairly typical installation, using a plastic food box or a box made up from Perspex etc. First obtain or make the box, then position an 4 x 3 or 4 x 4in stringer each side at the appropriate width. Saw away the centre of deck beam 4; it would be advisable to replace it with a short beam between the side stringers at the fore end of the box, which would give a nice solid framework in which to glue the box, after the deck has been added. Once all the deck beams etc are in place, the hull must be thoroughly checked and sanded to ensure that the deck will seat neatly down. The deck can be cut to approximate shape at this point, and used to check its seating. 91 MODEL BOATS KRISPIE Part Three of a short series on an inexpensive 36in yacht featured as our free Christmas plan VW SENBER to fit a handle to a 36in. yacht is really a matter of choice, since the yacht is small enough to pick out of the water without a handle. On the other hand, it is very convenient to be able to lift out with one (dry) hand and it is noticeable that a majority of experts seem to prefer a handle. Points to watch are that it should be strong enough to support 12lbs in gusty weather and that it should be big enough to allow a good and comfortable grip with the fingers without being so big that it gets in the way of the main boom kicking strap. The sawn one shown on the drawing should suit most people, but for a little more fiddling it would be possible to bury two brass bolts in slots cut in the top of the fin so that the bolt ends protrude about tin. through the deck. A piece of #in. dural tube can then have one end flattened in a vice and drilled to fit over the bolts, the unflattened part being kinked to make an easily-grasped handle pointing aft. Such a handle will be slightly to the rear of the CG, so the boat will want to hang bow-down, but not to a dangerous extent. If the sawn handle is used, it will be necessary to make a slot in the fin to accept deck beam no. 4, and to slot the centre deck stringer to pass the handle through. Otherwise the fin can butt to the underside of the deck stringer (it will still need a notch for the deck beam) and can be located by a scrap of say fin. square hardwood glued each side. Having decided the handle question, then, it is as well to prepare all the remaining deck beams, especially no. 4, and the centre stringer. Try a dry assembly of the fin and associated bits, using the occasion to mark with a pencil the line of the hull on the fin, as mentioned last time. Trace the lead line on the bottom of the fin and carve, file, and sand the ‘exposed’ part of the fin to a fairly sharp leading edge and as thin and sharp a trailing edge as you can manage. Which brings us to a point where the lead should be mentioned. That shown is a circular section torpedo bulb, which needs a pattern to be turned (or skilfully carved) and a sand or plaster mould made in which to cast the lead. If preferred, it would be possible to trace the shape on to #in. blockboard or sound dry timber and cut out the shape with vertical sides. A second tracing should follow, allowing for the fin, on the same material, and cut out. The two shapes could then be screwed together and used as a mould to produce a lead flat on top and bottom (see photos on page 645, Nov ’76 issue). This is in effect an extension of the method used to produce the lead for the Gosling design, several hundred of which have been built without snags. If this method is followed, the lead line on the fin will be slightly different, which is why it is mentioned at this point. 106 Such a lead appears to carry no noticeable penalty in sailing performance and is certainly simpler to make. The hot lead tends to burn the wood mould but the casting requires very little cleaning up. An additional advantage is that it can be planed (use turps as a lubricant and an ordinary sharp wood plane) or filed on the top or bottom to reduce weight if it has cast a little overweight. It would be quite feasible to build up a ‘cold’ lead by cutting laminations from clean sheet lead and building up a block by epoxying the sheets together, finishing with a couple of vertical pins or screws as additional security. Back to fixing the fin. We need some reinforcement in the bottom of the hull each side of the fin once it is in place, and if you have some glass mat and resin left from some other job, this is excellent for it. Alternatively glue some slips of wood to the inside of the hull bottom next to the fin to spread the strains, and drape in a couple of lengths of bandage soaked in glue, or glue the bandage in fairly dry and subsequently soak it with varnish or thinned paint. When hard this will give a good solid area of hull around the fin root. With everything standing by, then, the order of assembly could be fit remaining deck beams, centre stringer, fin, fin root reinforcement, and fin top fillets (if the sawn handle is omitted). Check and check again that the fin is true fore and aft and absolutely vertical; the only way it can be far out is if the centre deck stringer is out of true. An alternative would be to fit the fin, no. 4 beam, and the root reinforcement, which leaves a little more room to work but requires extra care to ensure that the fin is aligned accurately. Another decision is required before going much further, and relates to the mast. The drawing shows a deckstepped mast, but some skippers prefer a deck slide with the mast step in the hull bottom. The latter gives better control of the mast ‘straightness’ — it is surprising how much bend can be put into a 4in. diameter tube by adjusting various tensions, and how considerable an effect even a slight bend can have on the set of the mainsail. Having the bottom four inches or so of the mast rigidly secured at two points rather than pivoting on a deck step increases the number and subtlety of shapes that the mast can be induced to adopt. This view does not meet with universal agreement among R/C skippers, many of whom consider a deck-mounted mast as capable of providing all that they require while avoiding a large means of water getting into the hull. On balance, the simplicity of the deck step is an advantage which will sway beginners towards it. If an internal step is required, however, now is the time to instal it, and the best method would be to cut a section out of the keel and glue in a 4in. square block of hardwood about 3in. long, reinforcing with a scrap of bandage etc. A brass of stainless step can then be screwed to this. It can be flat, thickish strip with drilled holes into which a peg in the mast heel fits or, more commonly, an inverted T section with slots sawn into the vertical part to receive a metal tongue secured in the mast heel. If a deck step is to be used, a strut between the keel and the centre stringer, beneath the approximate mast position, should be glued in; the download imposed by the shrouds and stays is quite considerable. A cut-out is now required through the keel to receive the skeg, which lodges against the underside of the centre deck stringer, with a pair of short fillet strips. This must be carefully aligned with the fin, vertically and fore and aft; a pair of straight strips of timber can be used to help check. A short length of tube, at least tin. id, abuts the internal after edge of the skeg, finishing flush with the hull bottom and long enough to protrude slightly above the deck when this is fitted later. A groove should be cut and (please turn to page 91)
