I just posted this frame grab my buddy shot yesterday in the Post Hull Pics thread but wanted to share it with others who may not check that one, at least I thought it was pretty interesting!
My friend Steve rode behind me on a wave yesterday while it was nice and glassy and i was stoked to pull these out of the clip for visual reference in regards to water flowing over the rail of a hull on the toeside, and how effective a hard edge is in releasing water…check out where it stops wrapping, right at the hard edge and midpoint of the fin (for hulls its generally said that anything from the fin backwards is drag). these are taken from the exit of a bottom turn…also loved how clean the water is left in the wake:
Those pics are not a very good example of what “wrap”/suction is/does in relation to rounder v. edged rails. I’m in agreement with those who suggest the big “lump” of water is the water being displaced, not sucking up. Also, the speed and direction of the flow have a lot to do with how the low/high pressure of the rail design effects the ride.
My own experiences -
Have a board with thin 30/70 rails in the tail, rode pretty well, not as fast as I’d like. I added sharp 90 degree edges from about 5" in front of the front fins, and the board was much faster.
Have a board with distinct “tucked” release edges all the way from nose to tail, sharper in the tail. This is the board that really helped me understand how the mid and fore rails work for me. The board always wants to “release” from the wave under my front foot, thus I found it to be less front foot pocket riding friendly than I like.
I made my next board with round rails under my front foot, and then I was able to do more subtle front foot adjustments in the pocket/tube - not feel like the board was “fighting” me. I also put the hard edges up to the 1/4 length point - in conjunction with rocker tail kick at that point. The board was very “snappy,” broke out of the water when I stepped on the tail, but didn’t want to do “round houses.” I took off about 6-8" of the edge, back to about 4-5" in front of the front fins, and then I could do smooth “round houses,” and it is still snappy, just not quite so radically.
All this reading and thinking has me considering going back to trying “release edges” full length on my bigger guns, as I don’t find myself doing much front foot based pocket surfing on them, and the higher end speed I’ve found w/my edge fin quads have enabled me to make some waves I wouldn’t have made on my tri’s. And here I thought I had all the speed I needed… Ha!
Looks like that was “The Corner”. You’re on to something here. When I sit and watch guys surf that is what I’m studying…the water leaving the board. You’d be surprised at the differences. These are great pics. Double concaves are real interesting to watch too. I’ve got to admit it is the planing and glide that hooks me. That inside rail says a lot… as much as the spray.
Interesting - several things kinda illustrated there:
The planing area in use/contact with the water is nowheres near symmetrical. I kinda doubt the lift generated per unit area is either.
The water path along the rail seems to be parallel with the direction the board is travelling through the water.
Very interesting - I suspect a lot could be learned from more of these, or short videos, so you could track the path the board is taking versus ( for instance) the direction the centerline is pointing.....
I posted a thread a few months ago with similar pictures, albeit from underwater, on a different type of board, and different type of surfing, that shows similar (or maybe not) flow.
The water in a wave is moving UP, and when it hits the surfboard hull, it changes direction. The change in direction and extent of the change is determined by the angle of the board relative to the flow, the bottom contours, the rail contours, and the rocker.
it may be an artifact of the photo, but it almost looks like the heel-side rail edge is above the water and not directly engaged…like the board is riding (and releasing) on a narrower surface within the outline.
I agree. You also have to realize that the water behind the board has already been ‘displaced’ by the hull/rail, and it is now in the process of filling in that space.
Greg, it seems to me, the water right under his feet on the inside rail there is NO cavitation. It shows the planing aspect. The board just doesn’t ride on top of the water. The softer rail forward sucks up the face and where it gets hard, it begins to push away and cause turbulence. And on the outside, it’s a total RELEASE of the water. On a concave bottom you will see a less uniform sheet of water and thinner than what we see here. There is a good chance I’m full of it, but I’m only a Hack. What say the Intelligencia on the matter?
hi greg i think it is because the rail in the tail is a shorter radius so it tucks away from contact with the water. ad in a direction change and there you have it. the photo would look very similar if the rail had a soft edge all the way imo
How about this, Guys with water cams start getting this shot on all types of shapes and waves and conditions and start a new thread. This would be a great comparison survey. Wherever you are, and you have the camera try, and post this shot at your break. See how bottoms, tails, and fins, ect. affect the wave.
But the funny thing to me is that we are all looking at the same pic and seeing different things. No wonder we (everyone on Sways) have such a hard time agreeing on board design.
BTW, It is easy enough at times to turn around as you are riding as look at the tail water. Hmmm. Of course we will all see it differently. But still instructive.
