IN SEARCH OF SPEED 2nd edition A collection of “Go Fast” theory By Peter Galloway I get a lot of questions about boat speed or, more accurately, how to obtain it. Questions that range from sail shape and trim, minimum weight to rig tune to hull shape, keel shape, crew weight, etc. It seems to touch on about everything that might affect how fast a boat gets around the course. I’ve undoubtedly postulated on all of these specifics over the years, but never compiled a brief dissertation on all of them at one time. This is an attempt to do just that. These are merely personal observations or theory, and may not be subscribed to by all knowledgeable racing sailors. They are the product of years of trying different things, analyzing the results, and coming to some sort of conclusion. Some of them, I am not even entirely sure are correct! After all, I’ve known a number of talented sailors who seem to be ignorant of, or merely do not worry about the details, but have enough natural talent to win anyway. I’ve seen times when what is ordinarily a mediocre boat is instead wickedly fast in certain conditions. An explanation might be that any given combination of keel shape, hull preparation, crew weight, sail shape, trim and steering happens to be ideal for that set of conditions and that same boat might demonstrate its mediocrity when faced with a different set of conditions. Before I begin, consider that maximizing a boat’s speed through the water is only one ingredient necessary for winning. Strategy, tactics, execution, crew work, observation, a keen mind, mastering the conditions, etc. are but a few of the other ingredients needed to be successful. These don’t come from spending an inordinate time on your keel or mast or polishing your bottom. They come from skill and experience and practice and these are things you cannot find in print. But when combined with a well prepared boat, all of these contribute to a winning advantage. I dare you to name an Olympic sailor who has not agonized over his or her equipment. You just don’t leave stones unturned if you want to win at a top level of the sport. Speed boiled down to the essentials Consider that the winning boat in any given race is the one with the greatest average speed around the course. You can achieve the greatest average speed in one of three ways: 1. Be slow, but sail by far the shortest distance, i.e., start well, stay in the pressure and hit every shift perfectly. 2. Have superior speed through the water in enough abundance to make up for strategic or tactical mistakes. 3. Have a combination of both (A winning combination). This document will focus on the item two only. Page 1 of 16 1. HULL It stands to reason that you would like to start with a good hull. By that, I mean that you sail a boat that is constructed by a leading, proven builder and that the hull is both stiff and fair. Ask around and/or research which builder is building the fastest boats. What are the consistent winners using? Look for construction methods and materials. Look for attention to detail. Look for shape and finish. Look for the best hardware and layout. And look for durability. If you are not buying new or are not having it constructed to your individual tastes, then look for a used boat with a good record. It’s no surprise that the fastest boats with the best records are worth more, many times because these boats have already been optimized saving you much pain and expense later on. The lesson here is to start with a proven piece of equipment. If you are having your boat built to order, try to stay away from unusual color combinations. An all white hull simply works best. White fades less when exposed to the sun, is easiest to cosmetically repair when damaged and looks great for years to come. It is also the stealthiest, especially if most of the other boats are all white. I remember a sailor I once knew who came from another class that sailed in fleets with a rainbow of hull colors. He ordered a custom boat with a bright red hull. Imagine his surprise when he showed up for his first big regatta to discover that the rest of the fleet was all white! He stuck out like a sore thumb and had to refrain from being aggressive on the starting line for fear of being noticed too easily. As for the deck, consider an off white color such as light gray or beige. These colors reduce the reflection on bright days and as such are easier on the retinas. 2. BLADES There is not a subject that elicits more opinion than the shape of blades. By blades, I mean keels, centerboards and rudders. Being a keelboat sailor most of my life, my observations are based on that type of boat, so I will not delve into the theory of centerboards here though much of it may be applicable. Keel We all recognize that you cannot change the overall design of a keel in a one design class. But all things are made to a tolerance, and boats typically have a fairly loose tolerance to account for the hand made nature of the construction. Within any given set of tolerances there may exist fat keels, skinny keels, long keels, short keels, deep and shallow keels. Keels with their location of the greatest chord thickness varying fore and aft, and differing leading edge radii and varying keel location. With so much to take into consideration, what works the best? The answer is…nothing all of the time. Optimum keel shape is very much a function of the conditions and the sailing angle. Clearly very thin keels exhibit the least drag at zero angle of attack as would be the case while running (no leeway). But thin keels may also provide less lift at some given angle of attack (as in sailing upwind) resulting in more leeway. Generally a thin keel would be superior in flat water conditions or when sailing downwind and it would be inferior in breezier or choppy upwind conditions because a thin keel loses its lift more readily than a fat one. Page 2 of 16 Which would I choose? I would choose a compromise that is good in most conditions and sailing angles. A lot to do with my choice would have to do with the conditions I generally sail in. If I mostly sail on a lakes with primarily flat water, I might choose a thinner shape. On an ocean with rough water or a typically breezier location, I would opt for a fetter keel. More lift is more valuable than less drag most of the time. Consider that a boat sails a greater distance on upwind legs than downwind legs, and that assumes an equal number of upwind and downwind legs. Factor in that many courses have an additional upwind leg, and you can see that 75 % of distance sailed might be upwind. Also, I would rather be faster upwind so that I can get to the first mark with the leaders and not have to play catch up the rest of the race. But additional lift can be achieved without the expense of additional drag. Additional lift can be achieved by a deeper keel while reduced drag can be obtained by having a keel with minimum chord length. All of these are compromises for the sake of good all around performance in a wide variety of conditions and sailing angles. Here is my opinion on the optimum all around keel: • Maximum depth (additional lift) • Minimum chord length (reduced wetted surface) • Section widths closer to the minimum (minimum drag) • Median leading edge radius (better at high angles of attack or chop) • Minimum trailing edge thickness or radius (minimum drag) • Maximum thickness approximately 40% aft of the leading edge (greatest lift to drag ratio) • Max aft position (better balance) And don’t forget symmetry. The lift characteristics of an asymmetric keel vary on each side resulting in differing performance on opposite tack. Simply stated, an asymmetric keel is just plain slow. Rudder Much of the same applies to rudders. Interestingly, a rudder produces a higher percentage of the total lift than one might believe. That is because windward helm actually provides additional lift. But too much helm comes at the expense of drag. So here are my criteria for rudders: • Minimum depth (for least drag) • Minimum chord length (reduced wetted surface) • Minimum section width (least drag) • Minimum trailing edges (least drag) • Median leading edge radius (good lift an higher angles of attack) • Minimum weight (less pitching moment) 3. FAIRING A “fair” hull promotes laminar flow and reduces turbulence. So what do I mean by fair? A fair hull is one that is devoid of major and minor undulations to the surface. That is, the surface flows in a continuous curve with no high spots (bumps) or low spots (hollows). As the water rushes past your hull, it accelerates as the hull grows in width, and then begins to decelerate as the hull narrows. If it encounters bumps or hollows, this natural acceleration is interrupted and results in the initiation of turbulence. Any aerodynamicist Page 3 of 16 will tell you that all flow over a surface eventually becomes turbulent, but the trick is to maintain the laminar flow for as long as possible.