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Old 27th June 2007, 03:28 PM   #1
valentine
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Join Date: Jun 2007
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Default tuning by sandpaper

Hi pros.

How tuning by sandpaper can increase the speed ?
What is the best 400,600,1000 for board and for fin?
Many thanks.
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Old 28th June 2007, 06:07 PM   #2
Ian Fox
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Default RE: tuning by sandpaper

Hi Valentine,

It is a debateable point, with many issues and variables.

In most cases, you will compromise the original finish and graphics on the board (fin)
and - unless at the very highest levels - any speed difference will be minimal.

If you're not sure of what you are doing, the best advice is probably don't do it.
Or at least not without some direct further instruction or on hand guidance specifically from someone with proven experience and skill with this. In all cases, if the process went wrong, it could reduce performance, destroy the product and cancel any warranty on the product. Please be aware of that.


For boards: (most typically, performance boards like Race/Slalom/Speed)

Use quality wet and dry sandpapers only (3M is a good brand)
Use something around 400 Grit.
Use it only wet and in good (clean) condition.
Use a very straight and even sanding stick or block for boards.
Use only VERY light sanding pressure.
Use a very very even sanding motion - along the water flow line.
Do not allow the paper to clog up, or dig in the edge while sanding.
Concentrate your efforts on the back half of the board, where most of the hi speed planing occurs.
(what you are looking to do is make a perfect flow line, and leaving a fine, regular pattern of small scratches running perfectly in line with water flow along the bottom of the board.)
You will find that some class rules for racing ban the "excessive" re-finishing of production boards from manufacturer's finish.

For fins; (most typically, performance fins like Race/Slalom/Speed)

You can use a finer grid like 800 or 1000 as the flow is different.
You have to be really careful, as the foil shape is much more 3 dimensional - and over a much shorter dimension - than the (relatively flat) underside of a board. The leading edge area is the most critical on the fin, but it's also the most easily disturbed or damaged by unskilled or over ambitious sanding.
Here it is really easy to sand a flat (where there was once a subtle foil) or minutely change the profile (radius) of the leading edge - and in doing that, turn a good fin into a dog.
Or the even less likely situation of turning a bad one into a great one.
Sanding the trailing edge to a razor sharp finish has small performance potential, but a much bigger potential to cut your foot, hand etc...Ask someone who knows..
You will find most guys wisely take good care (on and off the water) of the original finsih of hi performance fins, avoiding the need to sand them, rather than risk damage by trying to refinish them.
(of course, if the fin needs refinish, it will be better to have it done correctly than not, and if the operator REALLY knows what to do, it's not so risky).

And so just to be sure that everyone understands that we are giving information
but NOT recommending this technique, let's repeat the original warning again :

If you're not sure of what you are doing, the best advice is probably don't do it.
Or at least not without some direct further instruction or on hand guidance specifically from someone with proven experience and skill with this. In all cases, if the process went wrong, it could reduce performance, destroy the product and cancel any warranty on the product. Please be aware of that.


Cheers ~ Ian
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Old 29th June 2007, 01:38 AM   #3
valentine
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Join Date: Jun 2007
Posts: 18
Default RE: tuning by sandpaper

Hi Ian,
Thanks a lot for so detail ansver.Probably I will restrain to do it by myself.
I have another question.I am intermediate windsurfer ,but use to be
pro skier.In the pro ski area, impossible to imagine whithout special
wax and powders,which can dramaticaly reduse friction,especialy on a wat snow(more then 50%).
Is there something iqual in pro windsurfing?
Thanks a lot .
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Old 29th June 2007, 05:49 AM   #4
Ian Fox
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Join Date: Aug 2006
Posts: 532
Default RE: tuning by sandpaper

Hi Valentine,

There are a lot of factors involved here, but in simple summary, no, there are no surface treatments or processes in hi speed (planing) windsurfing that will "dramatically" reduce friction by anything anywhere near 50%. No magic bullet.

In planing windsurfing mode, the use of small directional surface scratches (400 grit, directional) theoretically allows a very fine layer of water molecules to "bond" to the bottom of the board surface, thereby producing a "water flowing over water" situation, which in theory, in this mode, delivers the lowest effective coefficent of friction.

It's also worth adding to my above comments that the bottom surface finish on current / recent production Starboards, and the surface finish of the fins is optimised to an efficent finish right out of the factory (especially the hi performance boards and fins, where a "perfect cosmetic" (visual) finish or a shiny polished look is compromised by a directional sanded finish - often referred to as "pro" finish or "whitewashed" ).

Yes, like most things there is a small potential to spend a lot of extra time and detail and marginally improve on the original, however (at a practical level) the importance of these gains also relates to the conditions of use: at 45kts and going for 50, every little detail counts - especially considering the exponential nature of drag. Most planing windsurfing occurs at speeds of 15-20 kts, where any gains achieved are much less significant. (and especially when balanced against the very real risk of potentially damaging the product or reducing performance if the tuner is not so expert).

In non planing activities ( where hull speeds are much lower and operate in displacement mode, Serenity or America's Cup .), complex drag reducing treatments, coatings, or skins have been shown to have some performance edge, but irrespective of any claims made, the actual on water improvement is also marginal, rather than anything near "dramatic".
(However, in America's Cup, even the smallest margin is "dramatic". A bit like their budgets.
Which is why they moved to ban such coatings in 12 racing. But you can be assured every aspect of those hulls are faired in very, very nicely indeed.)

Cheers ~ Ian
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