Starting a new thread for this, since we hijacked another one. Here's the discussion that started it:Select to expand quotecolas said..kobo said..
A little off topic but, do you know about the difference between a sanded finish vs a gloss finish in regard to foil performance ?
A sanded finish will be faster and keep the laminar flow longer, that's true for all submerged surfaces. But I have not seen specific data other than the classic experiments in basins with boat hulls & torpedoes.
I have stumbled upon this blog that details an empirical sanding method for foils however:
www.riftboards.com/sanding-your-hydrofoil/
- sand the foil with 500 grit
- sand parallel to the leading/trailing edges (to promote small vortices that will act as "ball bearings" between the foil and water)
- except the leading edge, smooth it to 2000
The blog is wrong however on the trailing edge, you should do a Donaldson trailing edge, not the unreliable method he presents, as it is too dependent on the ratio of the actual height of the square edge to the water speed to work.
www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/The-definitive-solution-to-fins-and-foils-whistling-humming--The--Donaldson-trailing-edge-
I'll be experimenting with this for surf-foiling. So far I found that filling gouges with bondo and sanding to 600grit didn't have a very noticeable effect. Colas pointed out that we'd be better off testing at the boundaries of performance in order to notice a small difference more readily.
I found some more discussion about this from the kite racer guys:
Possibly just worth noting- Kitefoilers are currently doing 30-35kt speeds and Am Cup yachts are doing 40-50kts. A bit faster than what we are talking about here- the sheer drag caused by the size of the wings ( or maybe the draggy rigs) we are using would seem to be the main issue. Robby Naish was using an 800cm2 Kitefoil Wing in his latest video and could still only manage low 20kts going fast and deep off the wind. My understanding of the filling and sanding process on Kitefoil masts was mainly to minimise ventilation at speed by eliminating pinholes and other surface disturbances that could induce turbulence ( happy to stand corrected by any experts / racers though, not my field of expertise). Gonna need some small slim ( kite?) foil wings to really crank speeds higher methinks !
Select to expand quotemikesids said.. Gonna need some small slim ( kite?) foil wings to really crank speeds higher methinks !
And some tall riders 
Select to expand quotejondrums said..
Starting a new thread for this, since we hijacked another one. Here's the discussion that started it:colas said..kobo said..
A little off topic but, do you know about the difference between a sanded finish vs a gloss finish in regard to foil performance ?
A sanded finish will be faster and keep the laminar flow longer, that's true for all submerged surfaces. But I have not seen specific data other than the classic experiments in basins with boat hulls & torpedoes.
I have stumbled upon this blog that details an empirical sanding method for foils however:
www.riftboards.com/sanding-your-hydrofoil/
- sand the foil with 500 grit
- sand parallel to the leading/trailing edges (to promote small vortices that will act as "ball bearings" between the foil and water)
- except the leading edge, smooth it to 2000
The blog is wrong however on the trailing edge, you should do a Donaldson trailing edge, not the unreliable method he presents, as it is too dependent on the ratio of the actual height of the square edge to the water speed to work.
www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/The-definitive-solution-to-fins-and-foils-whistling-humming--The--Donaldson-trailing-edge-
I'll be experimenting with this for surf-foiling. So far I found that filling gouges with bondo and sanding to 600grit didn't have a very noticeable effect. Colas pointed out that we'd be better off testing at the boundaries of performance in order to notice a small difference more readily.
I found some more discussion about this from the kite racer guys:
and
I sand mine back when they start humming due to damage. Gets rid of noise but I do not feel I am transported at light speed because I have wet and dried my foil.
