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-   -   Drake slalom Pro 44 whistles ??? (http://www.star-board-windsurfing.com/forum/showthread.php?t=1466)

Pacs 23rd March 2007 03:30 PM

Drake slalom Pro 44 whistles ¿?
 
Hello,

The fin i use on my iSonic122 whistles when I go to speed.

The whistle is sharp and strong and I have curiosity.

Also the explanations / solutions that I receive they are very contradictory.

Which is the cause / explanation is?

Does it suppose some problem for performance?

Is it necessary to avoid it?

How?

Thanks too much.

Paco

Ian Fox 23rd March 2007 06:30 PM

RE: Drake slalom Pro 44 whistles ???
 
Hola Paco,

Mostly sharp, strong fin whistle comes from the trailing edge finish.

Each fin is slightly different from the (hand finish) in the factory, so without being able to view the fin up close, the general cure can be to VERY LIGHTLY sand the back trailing edge TE of the fin with some fine (400 - 800 Grit) Wet+Dry sandpaper. Best is to use a firm block or similar to support the paper flat across the TE, not allow the paper to "wrap" around the TE as you sand.

Secret is to hold the block on a mild angle, so rather than sand the very fine TE "square" (or flat at 90' to fin centerline), you actually hold the paper/block on a slight angle to 30-40 degrees when viewed vertically looking down the TE. Just a couple of very even but light strokes should solve the situation.

Often if the TE is finished too symetrically, the waterflow "collides" as both sides of the flow come together off the back of TE. By angling the TE slightly, you minutely shorten the flow on one side, which disrupts the harmony of the flow/s, and they actually merge more smoothly, without the whistle, which in turn often can indicate some minor loss of efficency.

Saludos ~ Ian

Paco, can send you a diagram/email if the description is not clear.

Pacs 23rd March 2007 06:58 PM

RE: Drake slalom Pro 44 whistles ???
 
Hello Ian,

Thanks too much!

I understand it... but, If you have a diagram, i would apreciate too much.

This asymetrical sand can cause some directional problems?

Thanks!

Paco

Roger 23rd March 2007 07:32 PM

RE: Drake slalom Pro 44 whistles ???
 
Hi Paco,
Ian has it right, but I do it slightly differently.
Run the sanding block down the TE of the fin with the block perpendicular (90 deg. or a "T") the first couple of strokes with the sandpaper to create a very tiny flat surface that's 90 deg. (perpendicular) to the front to back axis (and the water flow) of your fin.
Then run the block down each side of this tiny "flat" at a 30-45 deg. angle so you slightly "chamfer" or dull the sharp edges where the surface of the foil meet the tiny flat created in the first 2 strokes of the sandpaper.
Also, get a straight edge or dowel pin and run/roll (the dowel pin) down the TE of the foil and look for any little "hollows" just in front of the TE. The hollows create "thinned out' area that can whistle as well.
To correct the hollows, sand the foil in these areas (blending in with the surrounding area through the use of a sanding block) until the hollow areas disappear.
Then break the sharp edge as Ian suggests, and put the tiny chamfers on.
As far as causing directional problems, you aren't going to be taking off enough material to cause any sort of "asymetry" so there should be no worries.
Also, even is you are correcting for "hollows" you are going to be working on the very last section of the foil, right at the trailing edge, so you would only really change < 1% of the actual foil.
Very fine wet/dry sand paper only removes < .0005" (0.0127 mm) per stroke.
Hope this helps,

Pacs 23rd March 2007 08:34 PM

RE: Drake slalom Pro 44 whistles ???
 
Hi Roger!

I will look for hollows and try a bit 2 ways...

Thanks too much Roger!

Paco


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