Sometimes is the devil in the letters. Sorry : Wolfgang

Please look: www.surf-forum.com
Finnen. Rake 50? Grasfinnen. I can only there give pictures in. I have to learn. Wolfgang

I have found the Delta's fins work great for me in a twin fin configuration almost eliminates the issue with spin out in chop. However have never been happy with them as single fin's. They need to make a twin fin speed board! Then again it might work in real world shallow weed spots, sure you will give away some speed in increased drag but will gain some in confidence in the board not spinning out and being able to ride even smaller fins in shallower weedier spots. Not that there is much weed here other than down at lake George in Summer but there are killer carp which tend to lead to broken booms after hitting them at 30 plus knots. a weed fin with lots of rake helps to turn them into speed bumps! I will stick with the Delta in my twin fin but am going to try the Gun Weed Control as it is only 5 degrees less rake than the delta in my single fin boards.

Legless,

Is it true Gun call a 50 degree fin 40 and 40 degree fin 50?

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yoyo said..

Legless,

Is it true Gun call a 50 degree fin 40 and 40 degree fin 50?

Yoyo,

I have measered it at 50 degrees, Originally Gun Sails called it 40 degrees as they were measuring it the wrong way. They have now updated there website to 50 degrees the correct rake for the fin

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legless said..


Yoyo,

I have measered it at 50 degrees, Originally Gun Sails called it 40 degrees as they were measuring it the wrong way. They have now updated there website to 50 degrees the correct rake for the fin

Hmm I'm not sure about wrong or right in this context, it's just not not the normal convention.
It's equally correct to say the fin is at 40degrees to the board as it is to say it has 50 degrees of rake.

When I first got into weedies I found it very confusing, to me an upright fin was 90 degrees, not 0. But I guess that an upright fin is the norm, and the convention is to describe a fin by it's deviation from the norm. But this isn't fully specified, so a fin with 20deg of rake is called a 20 deg fin, (instead of a 20 deg raked fin) when in fact it's actually a 70deg fin.

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decrepit said..

legless said..


Yoyo,

I have measered it at 50 degrees, Originally Gun Sails called it 40 degrees as they were measuring it the wrong way. They have now updated there website to 50 degrees the correct rake for the fin

Hmm I'm not sure about wrong or right in this context, it's just not not the normal convention.
It's equally correct to say the fin is at 40degrees to the board as it is to say it has 50 degrees of rake.

When I first got into weedies I found it very confusing, to me an upright fin was 90 degrees, not 0. But I guess that an upright fin is the norm, and the convention is to describe a fin by it's deviation from the norm. But this isn't fully specified, so a fin with 20deg of rake is called a 20 deg fin, (instead of a 20 deg raked fin) when in fact it's actually a 70deg fin.

Yes I agree it is confusing and wrong and right are the wrong terms to use. I guess the norm has become measuring the fins rake from the upright position 90 degrees. As you can get fins with negative rake maybe the measurement should be through a 180 degree range from the hull of the board.

The other confusing number with weed fins is length now some use equivalent size rather than actual. Maybe equivalent is more useful indication as actual depth means little without the rake, construction and design of fin as all will affect how the fin performs.

Depth is a very useful measurement, especially if you're in shallow water! Area and thickness will give an idea of how much lift is available, length isn't all that relevant if you have these.
I hate the use of "equivalents"! Especially if that's all the info you get.
But maybe as an annotation at the end of the actual specs, they could serve some purpose, other wise they just lead to confusion.

I'm wondering now, where our rake convention came from? How widely used is it? If Gun uses a different convention, is it a national thing? Or maybe aeronautical/marine difference. Is it yacht keels versus plane wings?
\Any wise one out there with the solution to this puzzle?

Wing-tip rake:
(′wi? ¦tip ′rak)
(aerospace engineering) The shape of the wing when the tip edge is straight in plan but not parallel to the plane of symmetry; the amount of rake is measured by the acute angle between the straight portion of the wing tip and the plane of symmetry; the rake is positive when the trailing edge is longer than the leading edge.

A mast can be vertical to the hull and is said to have no rake. Only when the mast is angled back is it said to have rake.

Keel-haul. To haul (an offender) under the bottom of a ship and up on the other side as a punishment. Also called keel-rake.

Just noticed Select is also measuring its rake the other way round the have a 40 degree rake fin and a 50 degree rake fin and the 40 degree rake fin has more rake. More confusion

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fangman said..
Thank you guys. I have an evenings reading ahead of me now.:-)

One major diferance when talking about Aircraft wing over ground effects is obvious and no one here mentioned it. Air, not water, Air compresses readily water does not. Basically Aircraft travel on a "cushion" of air it is compressable flexible and prone to density changes. Water craft travel on a body of water which whilst flxable and prone to minor density changes it seldom compresses. The Paddler in your example is pushing water out of his crafts way hence the drag in shallow water and him feeling it. We can discount Displacement/Boyancy as effectively we when plaining displase very little. We as windsurfers travel on the surface as a result of TPI in the old language thrust per inch squared, or the harder you push on it the faster you can go. More thrust more speed. Surface tension is far more relevant than depth. The cushion effect is negligible in water.

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peterowensbabs said..

One major diferance when talking about Aircraft wing over ground effects is obvious and no one here mentioned it. Air, not water, Air compresses readily water does not. Basically Aircraft travel on a "cushion" of air it is compressable flexible and prone to density changes. Water craft travel on a body of water which whilst flxable and prone to minor density changes it seldom compresses. The Paddler in your example is pushing water out of his crafts way hence the drag in shallow water and him feeling it. We can discount Displacement/Boyancy as effectively we when plaining displase very little. We as windsurfers travel on the surface as a result of TPI in the old language thrust per inch squared, or the harder you push on it the faster you can go. More thrust more speed. Surface tension is far more relevant than depth. The cushion effect is negligible in water.

Peter, I think I disagree. Somewhere/time I came across the definition of planing as, "riding your own bow wave". As you say in shallow water the bow wave is bigger because it's harder for the displaced water to move away from the craft.
I agree that water can't be compressed, but I think that enhances the effect rather than detracting from it.
So the benefit of shallow water (apart from it being flatter) is because your riding a bigger bow wave when planing.
But it's harder to get on the plane because of the same reason.

whether it's correct to compare this to aircraft ground effect I'm not sure, in an aircraft's case it's the increase of air pressure under the wing, there's no bow wave. But then I guess there is an increase in water pressure under the hull, because it's harder to displace the water when it's shallow.

As decrepit says, you are probably incorrect - apparently the science says so:
www.sailspeedrecords.com/news/58-wssr-newsletter-no-156-water-depth-rule-050708

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When the water is shallower than the width (beam) of the planing surface, the reduction of drag can be dramatic and in the extreme case when the water depth is less than half the beam of the board, the drag reduction can be as much as 50%.

So looks like there is a case for a wide tail and shallow fins/s The increase drag of using 2 small fins would be overcome by a 50% reduction in hull drag?
Not sure how shallow the water I want to sail fast in. Knee deep is shallow enough I think, offers a bit of protection as long as you aren't going straight down.

fangman how did you go with the delta order , I spoke to a guy today and he said the g10 fins are hard to come by , he said there making them in carbon but not g10 ,

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keef said..
fangman how did you go with the delta order , I spoke to a guy today and he said the g10 fins are hard to come by , he said there making them in carbon but not g10 ,

No real problems Keef. The only hiccup was the timing- because it was the start of the Euro season the stores had been buying and depleted their stock so a couple of the slalom sizes had to be adjusted e.g. a slalom 21 was changed to a slalom 22. I was told that if we had waited for 6 weeks more they would have had time to restock. There are solid G10 and honeycomb G10 in the 20 - 24 cm sizes versions, but my understanding is the carbon versions are limited to the really big buggers 24. - 30 cm formula version - but don't quote me on that, as my wife points out that in all discussions with her I am generally wrong, so there is a chance this might spill over to life in general..

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legless said..
I have found the Delta's fins work great for me in a twin fin configuration almost eliminates the issue with spin out in chop. However have never been happy with them as single fin's. They need to make a twin fin speed board!

Decrep, whadya reckon if I find an relatively wider tail board ( there was one on gumtree down your way) and we gaffer tape two 15 cm deltas on as a twinny speed board? Will the theoretical physics from all the above posts outweigh the increased drag from the extra fin - given they are already pretty draggy fins?

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fangman said..


Decrep, whadya reckon if I find an relatively wider tail board ( there was one on gumtree down your way) and we gaffer tape two 15 cm deltas on as a twinny speed board? Will the theoretical physics from all the above posts outweigh the increased drag from the extra fin - given they are already pretty draggy fins?

You're on my wavelength fangy. I already have an ancient board of mine I converted to a twiny about 07 or 08. Trouble was I only had wave fins in it, and now I realise the leading edge on them is too thick. The board accelerated like mad to about 28kts then went sideways. I think the double concave right where the fins are didn't help.
So I'm now thinking of getting rid of the concaves and making some 10cm 50deg speed fins for it. But as you know, I have a couple of boards and fins to modify first.
The rental property is coming along, if I can get the kitchen sorted this week, maybe I can get back to windsurfing stuff next week.

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fangman said..

legless said..
I have found the Delta's fins work great for me in a twin fin configuration almost eliminates the issue with spin out in chop. However have never been happy with them as single fin's. They need to make a twin fin speed board!

Decrep, whadya reckon if I find an relatively wider tail board ( there was one on gumtree down your way) and we gaffer tape two 15 cm deltas on as a twinny speed board? Will the theoretical physics from all the above posts outweigh the increased drag from the extra fin - given they are already pretty draggy fins?

thanks fangman I had a look on there site and they don't make g10 above 24cm which is understandable