Fin Toe In

npsp

Michael Peterson status
Dec 30, 2003
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Senor Sopa, you might be right on all those points - I am not an expert so cannot argue with any certainty. I didn't mention the boundary layer - I think I need to do more reading and how it relates to flow separation. However the vortices I mentioned are a type of turbulence - or aren't they?

The Reynolds number equation for a pipe is different from a foil from what I can see - foil being a fin, wing, hydrofoil - I assume that's what you call flat plate? I realise now my mention of surfboard hull is completely wrong for the foil comparison (it has no low pressure surface).

Stephen Hawking said in one of his popular books on physics dumbed down for the masses, that there is no difference between throwing a ball inside the carriage of a moving train or a stationary train - it is still travelling at the same speed relative to the train and all speed is relative to other objects so a flat plate travelling in a stationary body of water would be the same as the body of water moving and the flat plate stationary.

Yes I have had fin hum from badly made home made fins - I didn't know they were turning the water to steam. I have experienced what is thought to be ventilation on a sailboard - when trying to sail too close to the wind and say hitting a lump of chop which would lift the board a bit - air from the surface is sucked down the length of the fin on the low pressure side and hold is lost - the board could go sideways for some considerable distance. Someone I followed on instagram posted quite a convincing picture of his foil board mast ventilating - sucking down air from the water surface - the air is not steam.
Sopa is correct that the pipe/foil comparison is apples to oranges in most cases. I just used it to show that turbulent and laminar flow can exist proportionally together. it's not just one or the the other. You are right that there is a point of separation, a bubble starts to form indicating the transition from laminar to turbulent flow.
Fin cavitation is an odd one but I feel it does occur to some degree but it is not the same type of cavitation we experience with a pump impeller inside of a casing where you have bubbles collapsing during phase change at low pressure. To be honest, I have no idea as to what makes the hum, whistle or in a couple of instances a popping sound with some odd foiled fins but I feel it is some sort of cavitation.:unsure:
 
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tom@daumtooling

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Jan 10, 2002
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I think there’s been a few attempts, but nothing that has stuck. Maybe @tom@daumtooling can chime in on that.
Yes, Blakestah did have Surf Trux a few years back. I haven't seen any in a while. We've been working with One 80 fins https://one80surfboards.com/
They have a self aligning toe system for the boxes. You can adjust how much range they will allow toe in from water flow and rider in put.
There is also 4Way fin system from South Africa which you can adjust the toe, cant, position and fin template.
 
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sushipop

Gerry Lopez status
Feb 7, 2008
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The Dagobah System
Yes, Blakestah did have Surf Trux a few years back. I haven't seen any in a while. We've been working with One 80 fins https://one80surfboards.com/
They have a self aligning toe system for the boxes. You can adjust how much range they will allow toe in from water flow and rider in put.
There is also 4Way fin system from South Africa which you can adjust the toe, cant, position and fin template.
Very cool to see how far Bob has gotten with this! thanks for sharing, i had a feeling you would have the intel...
 
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Mr J

Gerry Lopez status
Aug 18, 2003
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This is so off

You adjust the toe in for what you desire on that board

The distance from tail to these 2" marks at the nose should not determine anything ;-)
The method of aligning a fin to a point either side of nose tip means that shorter boards have more toe in (unless the shaper uses some length adjustment for distance either side of tip), so do your shorter HPSBs not have more toe than your longer ones?
 
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Maz

Billy Hamilton status
May 18, 2004
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Innzid
That was my thinking too, Mr J. Unless bottom contours are very different, I've found it a good method.

Off the top of my head, here are two types of board where I'd deviate from that formula:

1. Wide-tailed twin keel fish. Less toe-in.

2. Mid length/Funboard. More toe-in.
 
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griffinsurfboard

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Oct 31, 2004
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The method of aligning a fin to a point either side of nose tip means that shorter boards have more toe in (unless the shaper uses some length adjustment for distance either side of tip), so do your shorter HPSBs not have more toe than your longer ones?
My 9' longboards have the same 1/4" toe in as my 6' boards
Is that good enough ;-)

I do use 1/8" toe in on boards sometimes below 7' which is lower than this 2" off the nose would result in

Its for the effect I want - same as placements
 
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Mr J

Gerry Lopez status
Aug 18, 2003
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McKee published it all at a time when shapers were still trying to keep their sauce secret. Fin distance from tail too. It shows that he has confidence in his system.

Yes, Maz, Mckee's shortboard distance from nose 1 7/8" very similar to Dave Verrall's 2" (which works nicely for me). There are 3 basic ways that I know of for laying out toe in.

1. Point fins a certain distance ahead of nose.
2. Point fins a certain distance to the side of nose.
3. subtract distance between leading edges of the fins and the trailing edge - shapers squares are available to make this easy.

I have been in the habit of measuring my boards with an aluminium batten and found that the accuracy can vary - some almost as much as 1" difference using method 2 above. Using a long batten is more accurate because method 3 tends to amplify any inaccuracies in toe in over just the 5" fin base length, however battens can be difficult to handle and keep in place.
 
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Maz

Billy Hamilton status
May 18, 2004
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That's what I've always done, Mr J.

The idea that you mark out 1/8" or 1/4" with a fat pencil over a very short distance (length of fin base) seems crazy and likely a big source of error. Long aluminium batten for me - and that way you don't need to trust the trueness of the stringer.

Edit: I use a thin but wide batten. It flexes freely, so can easily be aligned from fin dot to chosen spot near nose, but remains perfectly straight.
 
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GromsDad

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That's what I've always done, Mr J.

The idea that you mark out 1/8" or 1/4" with a fat pencil over a very short distance (length of fin base) seems crazy and likely a big source of error. Long aluminium batten for me - and that way you don't need to trust the trueness of the stringer.
Bingo. A few years ago I got one of those magic clear fin layout templates. I changed what I'd always done and used it. When the board was done I put the fins in it and sighted it. The worst fin job I'd ever done. Way off. Got the template back out to recheck my work........spot on. That was the first.......and last......time I used one of these. Back to the long perfectly strait edge.

 
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Mr J

Gerry Lopez status
Aug 18, 2003
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The idea that you mark out 1/8" or 1/4" with a fat pencil over a very short distance (length of fin base) seems crazy and likely a big source of error. Long aluminium batten for me - and that way you don't need to trust the trueness of the stringer.

Edit: I use a thin but wide batten. It flexes freely, so can easily be aligned from fin dot to chosen spot near nose, but remains perfectly straight.
its actually quite difficult to have a system that overcomes stringer trueness deviation. By far the easiest thing to do is to use the stringer to align the middle fin.

The 3 machine cuts I have had for my self builds came with a sort of seam where one side was cut then the blank turned over and the other side done. The cuts were very good but there can be a little alignment shift which becomes evident when I used the shapers square to set the rear trailing edge dots, so I tidied up the rails in the tail area to be equal distances from the stringer. I find the shapers square good for just the rear dots - getting them the right distance from rail and checking that the stringer can be used as a source of alignment for the rear fin.

Also exactly what you described about the batten - wide so that it remains straight, but flexible enough so that it can partially adapt to the rocker of the board which makes getting the distance from nose easier.
 
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Mr J

Gerry Lopez status
Aug 18, 2003
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Bingo. A few years ago I got one of those magic clear fin layout templates. I changed what I'd always done and used it. When the board was done I put the fins in it and sighted it. The worst fin job I'd ever done. Way off. Got the template back out to recheck my work........spot on. That was the first.......and last......time I used one of these. Back to the long perfectly strait edge.

Yes GromsDad, Line of sight is quite an accurate way of assessing fin toe in.

Regarding your worst job ever with that instrument, it is one of the better layout rulers too - it is 12" deep which would give a better alignment to the stringer than the 5" one I have used. I have seen another one which was maybe just 4 or 5" deep, but had a triangular extension in the middle to help with this, but not as much as 12". Even with the stringer alignment accurate what Maz said - an error just the width of a pencil line when extrapolated over the rest of the length can show quite big deviation at the nose of the board.
 

Mr J

Gerry Lopez status
Aug 18, 2003
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Machine cuts wander to one side up to 1/8"

Making the stringer not the centerline
yep, that's what I meant by "seam shift" where the deck cut was just a tad out of alignment with the hull cut. I mentioned what I did to get the fins equidistant from stringer and rails. I don't know how other shapers deal with that - with a total of 3 machine cuts under my belt I am now an expert ;)
 

Mr J

Gerry Lopez status
Aug 18, 2003
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A few years ago I got one of those magic clear fin layout templates...
Yours is a good one, this is my last build and the one I borrowed to set the rear dots in the JD workshop. Not much depth to align with stringer, but used in combination with an aluminium batten to get the front dots.

The batten approach can be prone to the "damn it moved" sort of error. Dave Verrall uses a batten that is exactly 2" wide and marks along the outside to help with this. That one is narrower so I used a 2" block at the nose and marked along the inside of the batten.
FinToeIn.JPG
 

GromsDad

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Yours is a good one, this is my last build and the one I borrowed to set the rear dots in the JD workshop. Not much depth to align with stringer, but used in combination with an aluminium batten to get the front dots.

The batten approach can be prone to the "damn it moved" sort of error. Dave Verrall uses a batten that is exactly 2" wide and marks along the outside to help with this. That one is narrower so I used a 2" block at the nose and marked along the inside of the batten.
View attachment 94346

Depends on what you use for a batten. The way I do it leaves zero chance of it moving.What if your batten was made out of the same material as the clear plastic fin template so it could easily conform to the rocker of the board and had a hole in it so you could pin it at the nose? What if the batten was a simple piece of paper? Think outside the box. But yes, your rigid batten is prone to the oops it moved error. Cheers. :coffee:
 
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