Polishing Foils

CaptainAhab

Active Member
As most sailors have heard there are 2 trains of thought about smoothness of hull/blades. First is smoother the better, second is at some point(400 or 600 grit) it doesn't matter, because its water on water.

Frank Bethwaite's book High Performance Sailing says that he tested 2 Laser rudders. Both sanded to 1200 grit then one was buffed. His testing showed a 23% reduction in steering force at 11 knots of speed. 1200 grit is very very smooth. Its amazing that the buffing is has such a dramatic effect. I wonder what the difference is from 400 to mirror.

He recommends that all hulls and foils should be buffed to a mirror finish.

Has anyone done this to their rudder and noticed any improvement on stalling?
 
When I refurbished my daggerboard some years back I wet and dried it after painting using 1200 grit in a horizontal motion to any 'scratches' would be in line with the flow of the water over it. This made the foil noticeably quieter when planing so it must have made a difference in that there was less wasted energy (sound).

I really need to do it again and the rudder too!
 
At the academy we have all the foils touched up every year. they get buffed to a mirror finish and look outstanding. I suspect this has also contributed to improved performance of them. For us it's just important to keep every blade perfectly similar to the next.
 
That's a very cool article on Bethwaite. I highly recommend his book. He is best known for designing the Taser, Laser 2(became the Laser 3000) and many innovations for Aussie skiffs. His son Julian designed the 29er and 49er skiffs and invented the asymmetric spinnaker.
 
where i work we take all boats and foils to 1500 grit before using 3M high gloss gelcoat compound with plenty of water you should be able to see your own eyelashes in it before we send them out just use lots of water with the cutting compound but not so much that you wash it away and they'll come up better than new.
 
not that much probibily a few muinets per hour your better spending your time practicing sailing or polishing your hull or startching your sail
 
You'd be very lucky to gain 10-20 seconds on a board which was already in reasonably good condition. Doing 10 minutes taking practice over 6 days, is likely to gain you 3-5 seconds per tack on the race course. The main advantage even in polishing your hull comes from finding cracks etc that need to be repaired, rather than any performance advantage.
 
Alan,

I would expect the gains not come from tacking. The real improvements would come at higher speeds like planing. That is the time when a rudder will stall, the centerboard starts whistling. Upwind there could be a decent improvement in lift.

Personally, I just club race. The minor improvement would be nullified by capsizing or going the wrong way.

My blades were in need of some touchup. I recently broke the top corner of the board by the handle with my knee(Yes it hurt). The repair I made is perfect, but needs to be properly painted. I was able to sand the rudder to 1200 grit. I filled the defects in the board then sanded it to 220grit ready for paint.

It was blowing 25-30knots the other day so I went out without painting the board. It stopped humming altogether on a plane. I had assumed Laser's always hummed when planing. I now believe it is caused by improper flow across the dagger board from surface defects. I've been sailing frequently in heavy air and often experience a bit of stalling in the rudder(which was in very good shape) when surfing the waves while planing. This was likewise eliminated after smoothing out the rudder.
 
What do you use for filler when repairing surface dings/chips? What about to cover the repairs, gelcoat? epoxy paint? My dagger board is in need of some attention, its been on the to-do list since the fall.
 
What do you use for filler when repairing surface dings/chips? What about to cover the repairs, gelcoat? epoxy paint? My dagger board is in need of some attention, its been on the to-do list since the fall.

I generally use Marine Tex for small dings and don't cover it with anything else. I sand it down until it just starts to feather in to the surrounding surface. I guesss it isn't a perfect match, but it is white.
 
I generally use Marine Tex for small dings and don't cover it with anything else. I sand it down until it just starts to feather in to the surrounding surface. I guesss it isn't a perfect match, but it is white.

I do the same
 
Defects on the leading edge cause turbulence, which slows the boat and reduce lift.
Defects on the trailing edge, even a too-wide square trailing edge, cause humming and drag.
Captain Ahab wonders "I wonder what the difference is from 400 to mirror?" I can report the difference from rugged, with flaking paint and chips, to 2000grit is few minutes in a 40minute race. Noticeable differences are the humming noises and rudder stall. The worst is coming out of a tack in strong winds and both centreboard and rudder stall, so the boat tends to round up into the wind. Even sitting back and heeling to windward, it's hard to get the boat to bear off and it just slids sideways instead of accelerating forwards. It's true that the tight vang didn't help this; need to invest in one of those turbo vangs one day, but 1 thing at a time!
Getting the foils and hull smooth and shiny is the difference between getting left behind, and having a shot at the race win. It's worth doing.
 
I agree that a high finish is very important on foils. Frank Bethwaite has put that one to rest. By all means, finish to as a high a quality as you can, but do not wax or polish. I found this out quite quickly when I could not grip or climb onto the CB after a capsize.
 

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