Painting Foils

Originally posted by Rupert The other theory I have heard is the idea that the matt finish traps a layer of water and keeps it still,

The good old surface tension theory. Complete ***** as the foil is underwater of course...

Originally posted by Rupert but one of the America's cup teams put alot of money into the idea a while ago, and 3M came up with a stick on sheet which reduced skin friction. I believe it got banned.

Riblets. Yeah, but what you have to know about that stuff is that it was a specially textured surface which had to be aligned precisely wth the local water flow on the boat and only worked within a very limited speed range. As the old 12 metres only worked within a limited speed range it did work on them. It was a world and a half away from a rough surface...

I've sanded off my pimples - they all contained water!  What do you reckon - is this osmosis?

A gloss painted surface is quite bumpy especially if it is brushed on.
To get best performance you should flat it back with wet and dry and cutting paste and end up with the perfectly polished surface.

The mat is fast argument is because wet and dry with 800 to 1200 grit is much better than shiny un sanded gloss paint. Fully polished is better than 1200 grit but not by that much

Rupert - the difference between the feel of a matt and gloss surface is down to the area of contact with your hand. A sanded surface is made up of valleys and peaks. Your hand only contacts the peaks, so the frictional force will be less. When it's running in a fluid, the fliud is in contact with the entire surface. This is a bit of a "flat earth" argument, all the science is on the side of the highly-polished foil.

Tom, I think you're missing the distinction between "smooth" and "fair". If a surface is perfectly smooth, it will be reflective, and therefore shiny.

Neil

I think the matt finish arguement holds true compared to a gloss paint finish, rather than V's a polished surface. If you run your hand over gloss paint, you can feel it "stick". 1200 grit it and your hand slides much more easily. Polish it, and it is better still, but not by anything like as much.

As for the "you'd do better spending more time sailing" argument, sand and polish the boat and foils after the sun has gone down, at home in the "warmth" (I wish) of the garage. Can't sail then anyway.