Questions from Archy on Magicseaweed:
Hi Roy, I'm also interested in a couple of design points:1) Why the combination of a relatively narrow tail with what appears to be a considerable amount of tail rocker? My understanding is that this could possibly retard the board's ability to build and maintain speed for the compromise of greater control possibly? Simmons held that a wide tail with little rocker could be very functional, so I was just wondering...2) The rails also appear to be rolled in the tail-would this not release water as well as a sharp rail through the tail section?ThankyouGreat questions, I'll do my best to answer them, and thankyou for askingFirstly my fastest boards have almost zero tail rocker and underwater lifting surfaces which increase effective tail area and tail lift, as they also have pronounced nose rocker they are similar in some respects to the Simmons boards, although this might not be apparent visually. Some also have wider tails with hard edges in the stern.You are asking about the FP design though, which as you say has more rocker than some boards, soft tail rails and a narow tail, all of which might seem to be detrimental to speed. The design has shown itself to be fast and able to make sections which other boards can't make, provided that there is a little bit of power in the wave it has 'long legs' and a good turn of speed.How is this possible?Basically the design is all about maneuverability and control. It makes distance and gets speed primarily because it is always able to reposition itself into the optimum position on the wave, and it can do so without making lots of drag through turns. So in spite of what people say the board is incredibly maneuverable and excells at positioning and turning at speed. The soft rails and narrow tail allow the board to roll rail to rail without corners digging in and causing drag. .. . so the lack of release is actually a drag reducing tactic in those situations.The story doesn't end there though. Now comes the part which is hard to explain: The planing hull theory which Simmons and Lindsay Lord subscribe to assumes that the lift comes from the hull. We know however that lift during turns ( and when trimming, as the board is effectively turning when in trim) can also come from fins. The FP boards are designed to use a lot of fin based lift. In order to use fin based lift from a vertical singlefin fin ( as opposed to a horizontal lifting foil or canted fins ) the fin needs to be presented at the appropriate angles of attack by the surfboard rail.Now,presentation of fins to fins at an angle of attack to the water flow is done via an angle between the rail and the fin . In the cae of a board with rail fins ( like the Simmons board) this is done via parallel rails and fin toe in. With a singlefin the fin is not toed in, instead the rails converge toward the tail, creating an angle between the fin and the rail.Ok, so when the board is turning and trimming the fins can provide lift. Now here comes the crux of the matter: When the board has a lot of rail convergence like the FP does, it adpots a nose down outside rail down attitude when trimming. This is because engagement of the tail rail does this automatically due to the tail rail convergence. Now the happy result of this is that this trim angle also angles the fin slightly horizontally. . .. . this in turn means that the fin produces vertical lift, taking load off the tail and the surfboard hull. So the feeling is that the hull gently rolls and squeezes up and down the wall, keeping the fin on an accurately controllable downwards glide path , with a slightly horizontal attitude.That is why the fin is so big. . . . it is there to provide loads of lift. . . . and doing it as an underwater foil is more efficient than relying on the hull only for lift.So doesn't the Simmons board do the same thing ? No it doesn't do it anywhere near as effectively ( not saying that it is wrondg, it's just a different approach) for several reasons:1) The straight parallel rails do not give good control of the angle of attack on the fin , as there is basically a set angle of attack. . . this makes it harder to use the fin effectively and harder to reposition and adjust the line.The FP pintail has a lot of curve in the rail which enables the fin to be presented at a wide range of angles of attack by using more or less rail. The soft round rails also make this easier as they do not lock in or track, they can roll and release in and out of the wall with ease ( a different kind of release from the hard tail edge release usually spoken of)2) The Simmons rail fins are much smaller and are low aspect ratio. . . there's less lift to be gained from them ( I use the Simmons board as a pure example of planing hull theory )With the FP on the other hand we have a very large powerful fin, which can produce a massive amount of lift.The net result of this is a board which thrives in hollow waves as it can reposition and maneuver effortlessly ( and it appears, sometimes invisibly :lol: ) it also thrives in choppy water, and in waves which require frequent repositioning and line adjustments, waves with sections, boils, double ups, and so on. This ultimately leads to a good turn of speed, but the rider needs to be actively looking for the optimum position (and the high line if possible ) at all times in order to make gains via optimum positioning. . . . sometimes these adjustments are subtle, but they give big gains.Two further points are:1) that rocker is relative to wave curvature. . . . so when the wave gets hollower the rocker is effectively flattened. That's why boards with more rocker go well in hollow waves. Now with the FP this also applies, but the wave curvature doesn't have to be extremely hollow. This is partly because the rocker curve on the board is not as great as it seems. . . . if measured in rate of curve per foot of board ( which is what the wave experiences ) the rocker is not at all extreme. . . it merely appears so when extrapolated over 12 or 13 feet. For example I have built a 10 footer on the same rocker and it appears to have moderate rocker.2) Generally speaking the Lindsay Lord/Simmons planing hull theory is based on the assumption of flat water, and in the case of Lord, turning via a rudder. When turning in a surfing situation wide tails can lose much of their gain by inhibiting maeuverability and by creating drag while moving rail to rail. Toed in fins are used to improve turning, these however also produce a braking effect during rail to rail turns. Having said that, flat rocker certainly has the potential to move fast, but it needs to be used in a way that doesn't lose the lift drag gains during trimming and turning.3) Width. Planing hull theory tells us that when planing, hull width is an advantage in terms of efficiency. That's why Simmons uses a wide tail. This is correct, however it is possible to gain the advantages of hull width and the turning and control advantages of a narrower tail, by having a hull which is wide further forward and narrower aft. This only works if the riding position is in the area of the maximum width, but it works very well indeed . The FP design is not unusually wide, however at 23 to 24 wide it has ample width for planing efficiency with the advantage of excellent control through a narrow tail. Some of our faster boards with flat tails like the thrusterbuster and X-15 have width of 27 inches at the widepoint and very narrow tails for just this reason.4) Displacement tail: The FP has a displacement tail. The last foot of the tail (in the fin area ) produces insignificant planing lift, but due to its thickness still produces displacement lift. Lift through displacement is actually more efficiently produced than planing lift, so the displacement tail is quite innocuous in terms of drag. . . it's really pod to mount the fin on, and it is able to be sunk with ease during turns and when trimming this adds control and shortens the turning acrc when necessary. .. . . . not only that, unlike a wide tail, which when underwater ( e.g when a wave breaks on the tail ) makes the board hard to turn by inhibiting rail to rail movement , the narrow tail of the FP can roll rail to rail without fuss when submerged. . . . this is GREAT in tight situation particularly when buried in a section or during a relatively tight turn.In addition, this kind of board gives a wonderful feeling of being intimately connected with the wave. . . it's a facscinating and 'trippy' feeling which is not easily seen but is felt strongly. . .. in that respect I imagine the feeling has a lot in common with the Liddle hull experience.RS
