Author Topic: Bottom shape to help track straight  (Read 38093 times)

scubasteve

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Bottom shape to help track straight
« on: October 23, 2019, 10:00:52 PM »
Hi Gents

Just knocking up a new board for foiling 6'8"

I am just wondering what people's thoughts are on the bottom shape to help straight tracking....?
Was going to put in single concave running into double concave round front foot area.
Any thought appreciate.
Cheers
Scuba

Dwight (DW)

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Re: Bottom shape to help track straight
« Reply #1 on: October 24, 2019, 04:03:10 AM »
Template and rails, not bottom make the difference. You got the template, now get the rails right.

scubasteve

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Re: Bottom shape to help track straight
« Reply #2 on: October 24, 2019, 06:13:41 AM »
Bottom shape parallel rails, chinned.

PonoBill

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Re: Bottom shape to help track straight
« Reply #3 on: October 24, 2019, 10:09:21 AM »
If you're worried about tracking put a fin box up front. Some folks swear by them, Dave K uses one. I've never found them necessary, but I don't go after the size of waves Dave does--I run from those.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

fumaster

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Re: Bottom shape to help track straight
« Reply #4 on: October 24, 2019, 01:06:29 PM »
Hey Scuba,
What are you using for a blank? I bought a US Blanks and they suggested to custom order a 7'3A (profile) increased to 5 1/8" thick with -1" nose rocker, 32" wide and 1.5# density. I made a 6-0 SUP foil board, but even cutting the nose and tail down to length there was to much bottom rocker in tail to match top rocker. Had to put single concave on bottom to get it parallel to top deck, that I wish I had for more volume in that area. Right now me at 180 lbs, the water line when paddling is at deck level at tail. Also are you still using plywood inserts for your track boxes? I used your method, they’re holding up well.

scubasteve

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Re: Bottom shape to help track straight
« Reply #5 on: October 25, 2019, 12:09:53 AM »
Hi
 Just making my own blank out of Eps.
This one is 5" thick by 30 1/2" x 6'8"

Still using my plywood box support it's a great way to add strengh.

I think I will add single to double concave and see how I go with that,
Thanks for all the replies
Scuba

madeinsantacruz

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Re: Bottom shape to help track straight
« Reply #6 on: October 25, 2019, 07:05:58 AM »
What PB said

sflinux

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Re: Bottom shape to help track straight
« Reply #7 on: October 25, 2019, 07:23:26 AM »
I haven't finished making a foilboard, but concave definitely will help a board track straight.  I have Tom Wegener's Tuna and Albacore (inspired by Alaias).  They are both finless boards with a single concave running the back 2/3 of the board.  Wash a spoon under a stream of water, and you can see how it grabs onto water, without the drag of a conventional fin.  It rides like a single fin, but you can slide it out when you want to.  I love it.  Reminds me of doing a 4 wheel skateboard slide in the rain.
The Hypr Nalu guns have some cool concave on the bottom of the boards, designed for speed.
« Last Edit: October 25, 2019, 07:50:52 AM by sflinux »
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

scubasteve

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Re: Bottom shape to help track straight
« Reply #8 on: October 25, 2019, 09:08:40 AM »
All concaved up
single at the front 3rd then runs into 2 x single concaves for the rest of the board.
Sink the boxes in,
Just need to bag him up next 1x carbon 1x s glass.
Should be fun.
Thanks for your replies

PonoBill

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Re: Bottom shape to help track straight
« Reply #9 on: October 26, 2019, 08:13:03 AM »
There's not much doubt a concave can make a board track straight, the question is will it be worth it, and are there other things I could do to get the same result without as big a compromise. The board I sawed in half to make "gateposts" at my shop is there both to look cool (or strange, depending on your tastes) and to remind me to test radical ideas before committing to scale. The idea was a finless race board using a deep channel to make the board track. After weeks of work and a lot of carbon fiber I had a board that tracked so well it couldn't be turned and dragged under turning pressure like it was pulling a net.

That's all by way of explanation that I reacted to your idea without recognizing that you clearly know what you are doing, your work looks great. It's just that I get dinged about the same question carried to extremes every time I drive into my shop.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

jamallstar

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Re: Bottom shape to help track straight
« Reply #10 on: October 29, 2019, 12:13:33 PM »
Call me a sailor but concaves in the bottom of hulls (boards) is nothing but drag, it may help with stability but your foil hanging off the bottom will do that.
I did a 5' 10" x 26 board with large concave rails, effectively making a "stabilized short board" on take off and touch down. In my opinion its fantastic, super easy to paddle and tracks better than my old 6' 10 which had a kalama style under side with a canard fin up front, even in flat water take offs and my long upwind paddles into onshore breezes for micro downwinders.
I will definitely be doing this again on my next board

Sent from my SM-J260Y using Tapatalk


SUPeter

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Re: Bottom shape to help track straight
« Reply #11 on: October 30, 2019, 04:21:41 AM »
Well, here is what I have done and absolutely love it.  My board tracks well and is forgiving on takeoff.  The board also has little stick on the high speed touch and goes.  Whether or not this has to do with the rippled surface, I do not know.  It was just an experiment with inducing turbulence to decrease the boundry layer.  I hope my pics go through.  Most of the step is forward, diminishing to zero towards the tail.  This picture is taken from the nose towards the back and is also showing the nose lifter.  The black stripes are 24K carbon tow bands.  Glass was vacuum bagged over these bands to create rippling.  All in all I am very pleased.  The vertical side wall acts much like the ventral fin being used on some Kalama boards.  6 ft x 29" if I remember correctly on width.  If I were to change anything, I would pull the nose planshape in some.
« Last Edit: October 30, 2019, 04:31:36 AM by SUPeter »

SUPeter

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Re: Bottom shape to help track straight
« Reply #12 on: October 30, 2019, 04:26:30 AM »
Another photo?

scubasteve

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Re: Bottom shape to help track straight
« Reply #13 on: October 30, 2019, 04:49:43 AM »
Both ideas looking good,
I was going to concave the chine rail but went for very sharp slight concave on bottom rail edge to the start of rail bevel.
😉

 


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