@ Melikefish,
7’10’’ x 21’’ W, 14’‘N, 13.5’’ T, (3.5’’ thick) to a 7’’ sq tail, is my favorite size board for waves under 20 feet on the NS. 15 foot Sunset, on that board, was an absolute joy. Single fin, of course. You’re on the right track. Geev’em!
Hi Bill,
You are right on the money. I am getting ready to build the board we talked about. Picking up the blank this week. I just hope I can do her justice:)
Cheers,
Jason
Pull the tail in a little - a narrower tail with a more rounded back 20" will turn a bit better and smoother than something with a wider tail. Also, tail theory is a whole other discussion, but the shape of the tail can also dictate a lot - for example an 8" wide flat squash tail won’t turn as easily as an 8" round tail
Here’s where I see it - maybe we’re talking about different things when we say “hull” but I’m talking about a board with lots of belly and upturned rails. Anyone I’ve ever talked to who’s ridden a true hull often has told me it’s a learning curve - you need to use a different part of the wave and it takes a lot more to go very fast… typically it’s a pocket surfer not a race-out-past-the-shoulder kine board. That said, I don’t have a lot of experience riding them myself, so I’m just going off what I’ve heard, but the logic behind it seems sound to me. An upturned rail and nose with belly is essentially a giant dish in the water - there’s nowhere for the water to flow smoothly across the surface and therefore it plows water - you can tell that’s obviously the case if you just look at the pillows of wake it creates around the board when paddling or riding - That’s where the more modern shapes (flatter bottoms, downturned rails, etc) tend to be more universally faster. It’s like the difference between laying on the back of your board and trying to paddle with the nose way up, or laying center with the board flush and paddling: Less plowing = less friction = more inertia = faster board.
Maybe I just don’t have enough experience with true hulls
Friction formulas:
F=Ntanp(phi). F tangentiel force opposit to mouvement, what you call drag, N force perpendicular to surface, phi friction coefficient fonction of materials, rugosite, lubrification. Dim of surface don ´t play directly for friction forces but as everysurfer explained: for same pressure P, if surface S is bigger, N is lower because P=F/S. Shape, macro and micro, have major influence on phi coef.
Good discussion. So by that analysis, a lighter surfer on the same board will go faster, all other things held constant?
From my observations, that would not necessarily be true. With the short, wide, flat bottom boards like a fish, a lighter surfer may not be able to get the board pumping along as fast as someone heavier. There’s probably a sweet spot for weight to size of board, but that also depends on the wave size and shape.
No because the formula i give is for solid friction, friction of Surfboards is more a fluide friction of a solid were F=kv for small reynolds number. F friction force, k friction coef (depend of shape of soli, material friction coef of solid, viscosity of fluide), v speed of solid. But for surfboards reynolds number is often high, no constant flow (that’s way all the Bernouilli reference are wrong !) so drag is an aerodynamique problem, Fx=1/2rhoSCxV², rho=masse volumique du fluide, V speed, S surface in contact with fluid, Cx drag coefficient (mostly depend of shape of surface). It’s impossible to calculate because, no constant speed (so dynamic problem) no constant S surface in water no constant Cx (shape of surface in water constantly change).
So what? finally everything play LOL. Better to more surf to be able to better use wave potential energy. Even if i like it a lot, mechanical theory is “bullshit” to optimize surfboard, empirique way: modify test, modify test, etc. Mechanical theory have a go to optimize durability because you can make constant lab comparison of build (strengh and dynamic comportement).
My neighbor is a retired professor. He taught hydrodynamics and ship design. He also had a business designing oil rig platforms for the north sea and ships used to ferry workers.
He told me designing the perfect vessal for riding waves is too complicated because the waves are always changing. Not only in size but shape and power. You can only design things for a certain number of variables. So when you tell people that you need a quiver of boards, it’s pretty much true. The size of your quiver would be dependent on the variety of the waves you ride, or the way you want to ride the waves.
From my experience, short, wide, flat bottom, with hard edges will make a fast board. For control, you start changing that to add drag in very specific places. You can also change your mind and body’s reaction time to control the board, but that’s a lot harder to do.
Agreed lemat, as I said above, the situation is far too dynamic, and the feelings and responses to boards far to subjective for science and engineering to really refine surfboard design. Although some basic principals can obviously be applied.
Spot on!
If you want to design fast have flat, wide, aspect ratio width/length = 0.4 and sharp rail edges. (Lord Board) From there adjust to something more conventional to get the desired control and feeling.
On the lines of being careful not to overthink this stuff and fully aware that this is just my own UNSCIENTIFIC opinion / observation… it seems to me that width is a double edged sword - yes there is more lift and generally I notice width having a positive effect - lift = less drag = more speed, BUT I have also occasionally noticed that it does relate to volume and rocker in that in some situations (fatter / slower wave) that the wider board actually wants to plow more and thus is pushing water and impeding progress whereas a narrower board feels less resistance. I notice this especially on the takeoff with a fat / slow wave and a wider board - the width seems to make any nose rocker a negative giving me more water to push… I think in all these analysis it is most important to remeber that the real answer is “depends…”
weight to volume?
wave steepness?
strength?
etc.
YMMV
I think your problem is the rocker and bottom contour. I’ve had that problem with various boards including longer boards. The short wide boards I’m using now don’t have that problem.
I’ve noticed that certain rockers and belly in the nose will make the board plow more in slower, fatter waves. I prefer having very flat to slight concaves in the nose and soften the rails to keep them from catching. Other issues I’ve had with smaller, flatter waves and short boards is them being to small (small high performance chips) to carry my weight through weak sections. I don’t have any of those boards these days.
About 10 years ago, the guy who was making the boards I was buying had a great small board design, but it had belly under the nose and every time I’d try to step forward to get through flatter sections in the small surf they’d bog. At the time he insisted that the design needed the rolled bottom in the nose to make drops and turn right. Several years ago I noticed he has a newer version of the board with a flat bottom all the way through. Every board I’ve ridden with that style of bottom in the nose bogs in slow weak waves when you put any pressure on the nose, doesn’t matter who the shaper is, some of them were made by highly respected shapers from all over the world.
JB,
Anyshapes you can show us that have a 24" wide 5 ft long like shape please?
Very curious as to what you did with the 0.4 ratio
Wouter