Here is a thought. I don’t think enough attention is given to how water exits off the tail (trailing edge) of a board. Look at how water flows over the deck and off the tail; sometimes at an angle and sometimes just straight along the stringer. When it leaves the deck and rejoins the tail wash, I think there is some better science we should be applying. I’ve been looking at a lot of tails lately (yes I have) on mainstream boards and how they transition the rear deck down to the water off the tail and it looks like almost all are very inefficient (drag inducing). I’m also thinking as a side thought that the rear deck pads must add a lot of drag to the flow of water off the tail.
I’m dredging up some boat and airplane trailing edge related stuff to post, but in the meantime I thought I’d see if this gets a rise out of the crew.
hey greg, as of late, release has been a major criteria of mine…recently i was fortunate to review a DHD design where the the back 1/4 of the board had a sharp square RAIL (edit: not tail)…release from the bottom and top…i’ve been implementing this as well as a crispy tucked under edge running the entire length of the board…so much speed in small waves its rediculous…
i’m on it!
PS- i’d be real carefull with release in bigger waves
I think a good place to start is with the best way we’ve found to end the lines of sail and engine powered vehicles that plane over the water. There is a class of sailboats, I don’t know the name, I’m sure T.O. does, that is built around a planing hull that has a squared off transom. They are sloop rigged, as I recall, very fast and ride very high in the water unlike most other sailboat designs. All engine driven planing and semi planing hulls have square transoms. So in the nautical world when it comes to power boats the square tansom is the best way to end the transom line anyone has come up with to my knowlege. As we know on a surfboard this configuration doesn’t facilitate the turning process or rail to rail change so adjusting to the everchanging face of the wave becomes more difficult with this type of tail configuration. Part of the challenge in building a surf vehicle is to create one that facilitates searching the wave for its speed along with drawing as much natural energy out of the wave as possible. The squashtail on a modern shortboard is an excellent compromise from a square-tail and it’s very popular because it gives so much lift and is very speedy in moderate surf conditions. Softening the corners has a very possitive effect on smoothing out directional change.
Boats that sit down in the water have more drawn in lines at the transom so that they will create less of a stern wave. A stern wave is created on all objects as they pass through the water. In order for one to begin to plane it has to escape its stern wave. Surfboards are all about planing. Their maximum displacement speed is very slow as the longer thinner object will create less of a stern wave than a short wide one. If you’ve ever been on a power boat you’ve notice how the boat will suddenly begin to move effortlessly as it overcomes it’s stern wave. A square transom give the boat the lift to overcome it more quickly than any other configuration. On a surfboard the drop-in moment is when we overcome their stern wave. Some boards plane more effeciently than others because of configuration differences. The ones that ride very high in the water act very differently than one that ride very low i.e. convex vs concave bottom. The ones that ride quite high in the water will become unstable in broken water more quickly than those that ride deeper. So when it comes to tail design one with drawn in lines will be more stable in steep and rough conditions because it won’t get jostled around as much, but in quiet water a wider configuration will provide a more efficient and stable platform.
I’m sure lots of the pros here on the B.B. will have some pertinent observations on how tail shape affects speed and creates or quiets turbulence.
As I ride different wave conditions I learn how different foil configurations perform. Every board or fin foil ends in its trailing edges so maybe thinking backwards will help. They say that’s what wizards can do. I know there are some out there and I’m look forward to their perspectives.
Meecrafty, can you post a hand drawn pic? Or maybe a real pic? Can you have too much release, too much speed? Speed is good. More speed is more good?
Halcyon, That is where I started, but with water flowing over the deck and off the tail, I think iwe need anotehr model to follow. I sail dingys also, and the fast ones go for the sharpe edged transom. But there is no water flowing over the top. I’m looking to the trailing edge of a wing for guidance.
Here is a thought. I don't think enough attention is given to how water exits off the tail (trailing edge) of a board. Look at how water flows over the deck and off the tail; sometimes at an angle and sometimes just straight along the stringer. When it leaves the deck and rejoins the tail wash, I think there is some better science we should be applying. I've been looking at a lot of tails lately (yes I have) on mainstream boards and how they transition the rear deck down to the water off the tail and it looks like almost all are very inefficient (drag inducing). I'm also thinking as a side thought that the rear deck pads must add a lot of drag to the flow of water off the tail.
I’m dredging up some boat and airplane trailing edge related stuff to post, but in the meantime I thought I’d see if this gets a rise out of the crew.
I’m not convinced that a lot of water does flow off the tail. I don’t see the water flow in a ‘nose to tail’ direction, like say a boat or plane. I feel that a more accurate guage is to consider the wave as a ‘rail to rail’ flow across the board as the wave draws. This then places utmost importance on the rail shape (usually at the widest point) for best flow release, rather than the tail. This is also one reason why deeper Vs are slower…the water has further to travel across the board.
yeah cb good point…theres more water flowing off the rails than just the tail…
Greg, i meant to say square RAIL not tail…making a square rail is easy…just dont shape the outline there…i think it helps most when your on rail…imagine a hard rail turn where the board is really banked, the upper corner is now a second point of release preventing flow over the deck…also helps when your sloggin a bit with the board low in the water…every little thing helps
Lee, i dont think you can go too fast on this feeble coast…the faster i go, the better my board i perform, the more fun i have…also, my local waves tend to be very sectiony where getting past closeout sections is the key to better rides so i like fast turbo charged boards with megga release…not your everyday, mass market, soft railed intermediate designs…i guess i get most of my control from good technique and 27 years of experience…like you often say, everyone is different and its up to each individual to decide whats best for himself…right now, fast and flighty is giving me the most fun by far
Running down the line in high trim is not the most fun way to surf.
Are we from different planets? Much of my time is spent searching for big long walls that are just barely makeable. The best is when it’s clean enough to go full throttle on my fish, but I still enjoy a long lined up face even when it requires the stability of a pintail. For me, the best waves are the ones where the left rail never touches the water.
The wide diamond tail bonzers have me interested - they might just offer the down-the-line speed of the fish without the schizoidness the fish develops in big bumpy waves.
There are only two kinds of people; those who think there are only two kinds of people, and those who don’t.
Greg, About a year ago there was an interview with Bob McTavish in one of the surf mags where he addressed some of the issues relating to water over the deck. The gist of it was, that he was trying to get “dry deck” turning as a means to quicker response. (No flow of water over the deck). His conclusion at that time, as I understood it, was to square up the rail (vertically as the board sits in the water) in the tail section so water was not able to hug the rail. The board would then skate on top of the water more.
That’s the opposite of what a noserider needs, which is a tail that definitely wants to hug the wave. Which makes me think of some of the Cooperfish noseriders. The tail is concave…on the top. Water wraps around the rail and is channeled through the concave as it is released out the back. I’ve never ridden a Cooperfish, but it looks to me like the tail would be very stable when the rider is on the nose.
Two different applications for tail release. It just depends on what you want the tail to do. This stuff is so dad-burned interesting, I can’t stand it. Doug
Doug, thanks for the reminder on that article. I think it was SJ. I’m going to re-read that.
Mee, I also surf the speed challenged east coast of Florida and like to take speed where ever I can get it. I mostle ride a twin fish with some Vee in the tail and that seems to avoid water over the rear deck better than my concave thruster. Not sure what to conclude from two data points.
I’ve looked back at the board’s tail while carving and just racing down the line and noticed a fair amount of water coming over the rail and exiting near the tail. I"m just thinking that when the deck water reattaches to the water behind the board, drag is induced if not handled correctly. A long time ago I saw Greg Loehr experimenting with temporary bondo on the tail to easily test different shapes. I wasn’t paying attention at the time, but I’d now love to know what he learned.