Gloss or Matte ?

[Peter_Frank]

Hi

I dont know...

What I DO know is, that this has been discussed since the early days of sailing, surfing, windsurfing, kitesurfing, hydrofoiling and so on.

tkettlepoint claims they are 2-5 knot faster when matte (but I dont know what the references are ?).

Does anybody have some tests confirming one or the other ?

Often it is "rumors" or things taken from one context, carried over to a (wrong or right) context.
Some rumors has some truth in them though, and matte surfaces has been used a lot by racers too, indeed.

It is not as simple as we think at first...

But besides water tunnel tests, there should also be real world tests head to head, repeatedly - to confirm the differences.
With real reynolds numbers (not taken from another sport that is).

It is interesting, but not simple - since it is still being discussed over and over and over
Could just be the fact that it is hard to imagine why a gloss surface should be slower ha haa !


There could also be contradictions, things working for and con for each type, thus giving the confusion

Could be interesting to discuss and link to scientific tests or other tests, regarding this very topic

Are all windsurf and kitesurf racefins matte, or are some gloss ?

They are quite close to hydrofoils, but not fully, as they have a risk of ventilation that dont exist for hydrofoils, so crossflow importance is different.

Maybe the mast and the other below water surfaces should be treated like different objects (I personally think so)

PF

[Robsw6]

Try and get a close up picture of an AC72 foil - bearing in mind they were developed with almost an unlimited budget, I am sure they have the answer.... looks smooth matte to me? V similar to the finish of F1 carbon?

Below is an AC72 Rudder Elevator, but it seems the finish is the same as the foil, just cant see a decent photo anywhere?

[FrederikS]

AC foils for Oracle were buffed and shiny just like the hulls. No point in sanding the surface because fouling is not a problem for boats that are only outside and in the water while racing. Dinghies that are stored outside can benefit from running over the surface before sailing but I do not see the point for foils.

Even airplane manufacturers er looking into buffed wings.

Experimented with a set of fins for my raceboard no difference there whatsoever to note. Of course there is more board in the water the fins are still the only thing providing lift.

[Robsw6]

Agreed looks buffed on this....
http://forums.sailinganarchy.com/index. ... 1&page=120

[Tone]

We have a speed comp here tomorrow (thankfully we also have 40 knot winds forecast).

I have taken the shine off the bottom of my speed board and hope to see a difference. It certainly isn't a course finish, but compared to before it is dull.

It was more an accident as I was repairing the board due to chewing up the rail yesterday when practicing (damn shells just under the water).

I guess I will find out tomorrow!

don't know if my research will be of any use whatsoever, time will tell.

[Robsw6]

We have a speed comp here tomorrow (thankfully we also have 40 knot winds forecast).

I have taken the shine off the bottom of my speed board and hope to see a difference. It certainly isn't a course finish, but compared to before it is dull.

It was more an accident as I was repairing the board due to chewing up the rail yesterday when practicing (damn shells just under the water).

I guess I will find out tomorrow!

don't know if my research will be of any use whatsoever, time will tell.

Look forward to seeing some pics, your results & gps trace

[Peter_Frank]

A wetted surface "on the surface" is a very different thing IMO.

As here the wetted area changes constantly, whereas a foil below the water is always fully wetted.

So boards and submerged foils not necessarily comparable at all.

PF

[FrederikS]

Pretty much all of the bigger competitive classes have buffed hulls as well. Look at AC, VOR, A-Class cats. Not that they are comparable but it seems that it is the preferred finish when money is no object.

[Tone]

We have a speed comp here tomorrow (thankfully we also have 40 knot winds forecast).

I have taken the shine off the bottom of my speed board and hope to see a difference. It certainly isn't a course finish, but compared to before it is dull.

It was more an accident as I was repairing the board due to chewing up the rail yesterday when practicing (damn shells just under the water).

I guess I will find out tomorrow!

don't know if my research will be of any use whatsoever, time will tell.

Look forward to seeing some pics, your results & gps trace

The forecast is full on mental.

I just it doesn't get too sketchy. I was out on my 7m today and twin tip as I wanted to rest my legs for tomorrow and the gusts were just mental. We had consistent 38 knots with gusts of over 40 and today wasn't meant to be the windy day!

will posts up as much as I can

Cheers

tony

[BWD]

You can feel the difference in how slippery a wet sanded finish is compared to a glossy
finish. If you don't believe, try it. Sand a glossy surface to anything over 300 grit and notice the difference as you run your hand across the wet surface.
At some point, there may be a diminishing return as you sand or polish to finer grits and the wet surface will feel less slippery. Doesn't seem scientific enough, I know, but it does reveal the basic principle.

Obviously your hand running over a wet board to feel it has a different hydrodynamic condition than riding at speed, so this is not how to prescribe the right grit for a speed board or racing boat, for that you need more and different information.
Anyway, there are rules of thumb. In practice, sanding along the 0 axis with grit between 600 and 1000 is what seems to work best in wind sports, for speeds 0 to 40 or so knots.

For normal hydrodynamic situations, there will be a point at which the water molecules try to stick more to the surface than to each other, in a very thin layer, this is good for speed. What "grit" to get this may depend on many factors from foil shape, "reynolds number" (and other "numbers") to temperature and chemical/electronic properties of the surface, and obviously, speed range.
And other hydrodynamic factors can be equally or more important, so there is no "miracle finish" for speed, but sanded beats rough or polished I think.