LeeV wrote "When you guys say that the hard rail holds a high line, I will guess that you are riding thrusters and that the forward rail (what there is of it in the water) has a tucked edge. The fins are what hold the high line, with the round portion of the forward rail holding a bit. If you put the same edge as your last 4" of tail, along the entire length of your board you would see what I was getting at. You would have to constantly adjust the boards attitude to keep the track because the sharp edge would constantly be slipping." ------------------------------------------------------------------------- I have found the opposite to be true....weird?? A recent observation on one of my boards was that the sander left a hard edge that ran from the tail past center on my 6'4" but i decided to give it a go. The board was okay on the open face but in the barrel it felt "sticky" and and it was difficult to make fine adjustments in the barrel since it wanted to follow the same line or "catch" sometimes. Took the board home and went at it with some 220grit and those problems dissapeared.
A few things First of all, the spoon analogy is flawed. It is flawed because the water on a surfboard doesn't release into air. Instead it rises to the surface level. If you could observe this, you'd see that the water flow behind a "hard" rail is quite turbulent, and this creates a lot of drag (or grab), on the rail. Water doesn't release on a hard rail, in reality. It still tries to conform, but laminar flow is much more disrupted on hard rail than on a soft rail. So, the more hard the rail is, the more drag you get. A very common board today has down rails near the tail, creating drag at the rear, and rounded rails further up. I think it is pretty easy to see how this helps you turn if you apply a little mechanics to a surfboard in action and consider where the drag is relative to the center of mass. Some tail drag is pretty necessary for surfboard control. One last thing. A surfboard, once standing, is not a displacement hull - it is a planing hull. There is a world of difference. http://www.blakestah.com/surf/
When the surf gets bigger around here (Central Coast,NSW Aust)5'plus I ride my short board , a 8' thruster with super hard rails that are hard about 2' infront of the fins.The waves are steep and hollow and you need to be making your first turn as you are getting to your feet,particularly when surfing the points.You need the drive and aceleration that a hard edge gives.I do get bucked off on ocassions, possibly due to the edge running so far foward, but this is a small price to pay for the speed that can be generated by rail to rail transitions with out having to pump the board.There is no way I would try and ride my soft railers in this type of surf. I have tried and it hurts.
From what basis do your ideas arise? I`ve never heard such peculiar opinions.
Fellow Surfers, Rail configuration has everything to do with performance. This has been obvious since the days of wooden planks and skagless surfboards. Round surfaces sit down in the water. Flat surfaces sit on top of it. Round rolls - sharp cuts. If you want to go fast the less wetted surface you have the faster you go. If you want control however what ever part of what you have in the water has to have some form that has a functional reason for being there. Rails on surfboards are in a constant state of evolution simply because everyone has their preferences about how they want their surfcraft to perform. The extremes in rail design are probably best exemplified by comparing a 60's Velzy 10'0" pig hull with and modern towin board. Both boards are quite heavy and the tow board has a great size to weight ration than the old school longboard. The bottom configuration and rail configurations of the two boards is opposite. Both boards will handle rough water beautifully but for different reasons. The old school board is deep in the water and thus unaffected by rough conditions and the rounded nature of it foil makes it a very calm affair in turbulence. The tri fin tow board sits up on top of the water and is always on a rail edge (Rail change being and instantanious maneuver) planning across a steep wall or down a steep face on edge. The bottom has so much concave that the board is like a hydrofoil sitting way up on top of the water when at speed. The rails are relatively much sharper and cut through the chop much like the two hulls on a boston whaler and the pair of them creat stability when the board is on the falts. The sharp end cuts into the wave face on steep walls allowing for rapid adjustments in trim and are quite responsive. A single fin tow board is another animal. Has anyone seen one up close? Entry, Bottom, and rail configurations on this type of board is a combination of soft to hard much the way the cross section of a fin is made. Rail configuration is one of the principle elements of surfboard function. Performance is a combined function that proceeds from release to drag to release. How much and where is what counts. Rails that change in configuration perform these functions. Ones that remain the same from nose to tail are either very calm or very touchy. Some boards swoop and glide, some slash and drive and some are submarines and there's everything between a bird and snail out there. Look at an albacore sometime and you'll see and marvelous combination of foiled form and everything from round to sharp each in its proper place. The rails on the best single fin board I have go from sharp to round to sharp. There are nonillion variations on the theme and I've only seen a few. A real answer would be difficult to formalize because of that subtle difference between cutting and holding or hard and soft, which in the end is really what to difference is. An good combination of the two is where performance comes from. Some of it comes from applied observation and good sense and some of it is just a happy accident. I've had the good fortune to experience both. No Worries, Rich
I have felt the same thing but the hard edge rail was very thin or angular (like the down-railers in the mid seventies) so the edge was penetrating the surface...The "stickiness" is a good explanation of the feel...Was your edge tucked or actually at the apex of the rail?
You are taking advantage of good release to gain speed and to counteract the fins being pulled into the face. The pulled-in outline of a semi-gun is also helping hold you in and on line.
Ok...take your spoon and spatula to a swimming pool and try it...youll feel the same thing and the analogy will be easier for you to understand. As for hard edges causing drag...anything moving on or through water will create "drag". Sharp edges create less than curved edges. You theory, if I understand it, should have airplanes falling from the sky. Drag in the tail of a surfboard IS a good thing, like you say. But its from the fins more than the rails and tailblock. Yes, I agree a displacement hull is different than a planing hull.
The drag depends on the angle of incidence. I think you may be misunderestimating the angle of attack and its influence on the tail angle in the water. Take a hard down rail near the tail, and move it along nearly parallel to the water, and I agree, release will occur. Now, take the same rail, and push it in 20 degrees and pull it through the water. See what happens. Now, move it to 90 degrees. I think everyone can agree the soft rail has MUCH less drag when oriented at 90 degrees to the water. Anytime the rail is down enough to cause a cavitation behind the rail you will experience increases in drag. The drag is exactly the reason the rail doesn't slip as easily when crossed on a steep wave face. Airplanes flying is about maintaining attached flow, and deflecting that flow by angle of attack, with the flow deflection also creating a reactive force (an opposing vector in direction and magnitude) creating lift at the wing. It has nearly nothing to do with how a planing hull works. These are not hydrofoils, they work differently. As for where I got my ideas, I usually find them in boxes of Cracker Jacks along with my diplomas and dotcom stock. http://www.blakestah.com/surf/
Aaaaahaaaa, now I get it...I agree, I think. Its too bad I can't draw pictures here, it would be so much easier. When you add in the angle of attack it starts to complicate things. I was initially just trying to simplify things to only two concepts and, as usual, with a surfboard there are too many things going on at one time including fins, rocker, thickness and rail shape that affect the feel. I still think the spoon/spatula thing works though...