WHICH IS THE FASTEST TEN FOOTER by Paolo Lodigiani

The recently concluded 2006 sailing season has been generous in satisfactions, as I won 6 of the 8 races I competed in, got 2 second places, and naturally triumphed in the class championship. Were I not innately modest, I would be getting above myself and thinking of me as a champion! But first of all, I shouldn’t be saying “I won”, instead, as Valentino Rossi always says referring to his team, “we won”. Being my own team, I could easily speak in the singular; in my case, though, “us” is my boat and I. Secondly, my pride is forcedly crushed by the recognition that my control over the championship has been far from undisputed: never as this season, races had been so uncertain up to the last track, with marginal gaps and many competitors for the final victory. Boats too were levelled out upwards, and many of them now contend on equal terms. This is why I think it is time, on my 15 years-long experience as a ten-footer racer, to try and answer to the question: which is the fastest ten footer? The qualities of a boat cannot be estimated in absolute terms, only relatively to its use and crew. In this respect the Ten Footer Class differs from other sailing classes for two relevant peculiarities. Firstly, competitiveness is tempered by a general tendency to relax: helmsmen, by age or nature, are not inclined to strain, discomfort, let alone acrobatics. The second peculiar feature, partly related to the first one, is that when it’s cold, or too windy, or, even worse, there’s a chance to get wet, racers easily agree to replace the regatta with activities more suitable to the weather… usually a lunch in good company around the table of a restaurant. It means that races can take place in very variable wind conditions, largely between 0 and 10 knots. It is some times inevitable that they may suddenly get worse, and one obviously has to cope with the changed situation. All this makes it for a fascinating design topic. It is relatively easy to design, for instance, a winning Moth (Moths are 11 foot-long boats, with a 8 m² sail area, and open rating rules and limitations, fundamentally not too different from a ten footer): build a ridiculously narrow hull, fit it with two sophisticated supporting winglets, entrust a fit, overtrained, young champion with it, one able to lift the hull and keep a precarious balance on the winglets, and you’ll see that, driven by the usually constant wind, your boat will glide over the water, flying towards victory. And if it doesn’t win, it will be because another, nearly identical boat, differing only in marginal details, undetectable to the human eye, has beaten it. In the Ten Footer Class, the designer’s job is a much harder one: many factors need to be taken into account, and drastic decisions need to be taken. This makes it difficult to say which kind of craft can be the fastest. Some observations can still be made, though: it is possible to say which boats are slower, which ones can’t run for victory. In this reversed classification I believe the catamaran would be first. It seems established that a catamaran has only a suitable condition, strong wind, for competing with trimarans and monohulls, and even then it can’t be certain of winning. It would be if it could sail on one hull, but as far as my memory goes, this has hardly ever happened. On a light wind condition, its large wet surface irremediably handicaps the catamaran. Between trimarans and monohulls the struggle is more open: as a general rule, monohulls are predominant in light wind, while trimarans in strong wind, hardly a surprise for anyone with a knowledge of hull resistance. As it is not surprising that in very strong wind, when the monohull starts skimming, it becomes competitive again, and, if well-sailed, can overtake the trimaran. Monohulls need to be narrow to be fast: the problem is how narrow can one make it without losing its stability. Certainly a monohull as narrow as a Moth (30 cm at the waterline) would be incredibly fast, but in a ten foot racer’s hands, it wouldn’t be likely to reach the starting line. Therefore, the designer’s problem is how narrow can a ten-footer be to be sailed by a ten foot racer. Nero Cirla’s Piccolo is a good example of a not too narrow, but well-performing (regardless of the Nero’s abilities) monohull, largely thanks to an excellent finishing and efficient equipment as well as to its reliability that makes it easy to master in any circumstance. Prina’s Emc3 is another interesting example: flat-bottomed, rectangular section, narrow, though not extremely narrow, it proved itself faster than its looks suggested. Conversely the Scheggia fell short of the theoretical expectations: the designer’s aim (of which I can confidently speak, as I was him) was to build a craft narrow at the waterline, with reamed flanks above the waterline so as to ensure both performance and stability. Unfortunately keeping a boat straight is not always an easy task, and my Scheggia, though capable of good spurts, doesn’t allow the necessary continuity to win regattas. Next year, two new ten foot monohulls, narrower than any other built in the past, fitted with terraces, should appear on the regattas fields. Unless they capsize, they will be rough customers for trimarans. It is easier to design a good trimaran, although theory doesn’t always combine with practice. One would think that a round hull should work better, and that an chine hull, similar to the round one, such as Guido Ratti’s Tripessit would be the ideal solution, only slightly inferior to the round hull. Whereas the trimarans Farò and Paci, with square section hulls, built by Marco Casavecchia seem to be faster. I had epic struggles with both of them, and more than once it was them who got the victory. I doubt though one would trace the causes to the shape of the hull: suffice it to say that Ratti “drives” his boat sitting in the middle of it on a comfortable cushioned chair, with a truck-like steering-wheel and an electric pump brought into action as soon as some water enters the boat (what next, Guido? A car radio?). Winning is not really the point here. Apart from this, Casavecchia’s trimarans have hulls slightly higher on the surface, giving them an unquestionable advantage, as only two hulls are normally in contact with water. As for myself, I have chosen what I think to be the best solution (I wouldn’t have chosen it otherwise), a compromise: the monotrimaran, a craft made for navigating on a single hull, though often needing two floats for avoiding capsizing. My Gerovital proved to be very versatile, as, even with a very light wind, it can be kept on the central hull with amas touching the water all but rarely. It can still be improved, and I did improve it designing Fulvio Cocchi’s Slim: much narrower, thus more difficult to sail on a single hull. It is slightly less fast than the Gerovital on a very light wind condition, but has a considerably faster pace on stronger wind, and a better hydrodynamics in the lateral hulls prevent it from slowing down too much when they enter in contact with water. Personally, I am convinced that it is the craft most likely to win in the class, as much as I am convinced that it can still be remarkably improved, getting rid of some small practical shortcoming and mostly continuing the search for a perfect compromise between the smallest possible resistance (obtainable mainly reducing the beam at waterline) and the maximum stability (increasing the beam). I believe there is still much more to say about this topic, and the forthcoming winter will give us the chance to study and discuss solutions, waiting for the tests that will substantiate or disprove them. I have only dealt with hulls, leaving sails aside, fearing this disquisition would lengthen too much. The topic is too wide to be dealt with rapidly: I shall leave it for another occasion. WILL TEN FOOTERS TAKE UP WINGS? by Paolo Lodigiani Last year, B.C.A. - Demco Kit launched the trophy “World Speed Record for Ten Footers” (the rules of participation are published on this page). Unfortunately, only few ten foot racers undertook the challenge and maybe the rules need to be changed and simplified to foster a wider involvement. The ruling champion is Fulvio Cocchi who reached 9,6 knots on his Slim, on a beautiful windy day at Cernobbio, almost ideal, save for a small detail: the GPS supplied by the organisation defaulted at the crucial point, thwarting some brilliant-looking runs. I believe that this record can be beaten easily (maybe just by remembering to put batteries in the GPS). Let us not forget that a ten footer has its critical speed at 4,15 knots, thus the recorded speed is 2.3 times the critical speed. Considering that it starts planning on average at 1.8 times the critical speed and can reach up to 3 times as much, we are still well within limits that can be broken. The problem is that a boat can’t plan without the features that allow it to do it, and needs enough power to thrust the necessary propulsion. The planing ability, given by the displacement (in kg) divided by the product between the flotation plane (in m²) and the hull length at the waterline (in m) (see page 132 of “Introduzione al capire e progettare le barche” by Paolo Lodigiani), shows that ten footers won’t easily plan, as for an 80 kg crew index values range between 20 and 35 according to the type of boat, whereas the ideal value should be less than 15. It is indeed a crude index, as almost all indexes are, and a more accurate study would require appropriate formulas. I don’t want to specify all the passages here (it would be long and tedious and would force me to a complex explanation of the Savitski formula and other amenities), and I shall jump to the conclusion: for a full planing, meaning a hull almost totally sustained by the hydrodynamic upthrust on its bottom, a boat like the Gerovital needs to reach a speed of 11 knots (about 2.6 times its critical speed); the resistance at this speed would be slightly less than 160 N (about 16 kg). To obtain a corresponding driving force from sails, in ideal conditions (sailing at 110° from the real wind, flat boat, efficient sail), a 25-30 knots real wind would be needed. Naturally these calculations are based on unverified hypothesis. In many respects, these estimates are easier for a ten footer hydrofoil: the boat conducts itself more or less like an airplane, and it is common knowledge that the aerodynamic calculation of airplanes are far simpler than the aero-hydrodynamic of boats. In an hydrofoil that navigates at high speed sustained by its foils, most of its hydrodynamic resistance is made up by the component of resistance of the force acting on the foils, the same force the lift coefficient of which sustains the hull. This force is proportional to the foils area, while their efficiency (the ratio between lift and resistance) is related to their shape, their aspect ratio, to the angle of incidence and the relative velocity of the fluid. At 11 knots, efficiency would be very high and resistance possibly lesser, though not much, than the resistance of the planing boat: thus, with an equal driving force, the boat would accelerate, reaching a higher speed. The problem is the take-off: in order to lift off, a boat fitted with foils must exceed a higher resistance wall than the one a planing boat encounters to exceed its critical speed. For the Gerovital, this barrier would range between 5 and 6 knots, and could be in the vicinity of 170/200 N (17/20 Kg), requiring a wind speed superior to 30 knots. Here are, in brief, the conclusions of this disquisition that, although rather complicated, is far more elementary than the calculations it required, and also tremendously oversimplified against reality: - It is possible to reach and exceed 11 knots, though not an easy job with planing hulls, let alone hydrofoils. Probably, a very narrow multihull is still the best, or easiest, mean to break the speed record. - Hydrofoils offer a more difficult solution compared to planning hulls, but once problems are overcome they may be potentially faster. - In any case, an aspiring recordman must sail with strong winds: guaranteed baths (for him/her) and guaranteed fun (for observers). - A Moth on foils reached the astonishing speed of 24.6 knots. It is clear that with the same sail area a ten footer could also in theory reach it, but I think we’re on different planets. - There’s plenty of food for winter thoughts and discussions of very technical contents: mine are but hypothesis and preliminary rough calculations; I’m putting forward the talk challenge, waiting for the real ones to come.