Lovely article on finishing your boat.

All in all for us guys it says "polish it!"

There was a time when the merlin class polished the hull but it does not help. If you polish you car and the spray it with water watch what the water does. It runs in to drops on the surface and stays there. This is not going to make the boat faster it actually makes it more sticky. If you want an smooth hull you need to either sand the bottom couple of planks with the finest wet & dry you can find or burnish it.

It may not help hydrodynamically in fact I don't beleive it makes any difference apart from maybe a psycological one as skin friction will be a very minor factor in the equation. But a coat of wax will not harm the boat in fact it will seal any microcracks in the gel coat and that can't be bad.

This is an article published in Seahorse, issue "June 2000". 
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It has always been a discussion: To polish or to sand with 400 grit. Although water seems to run smoother over the sanded surface, is this what we want? Is friction really decreased by sanding? Read what Frank Bethwaite has to tell about it:

Polish and skin friction

Our overriding object in building what has since become the 29er was that "it should sail like a skiff to train for a skiff". This meant designing for tacking downwind, with downwind speeds approaching wind speed. However, this was always going to be increasingly difficult with this smaller boat, because small boats do not enjoy the speeds natural to bigger boats.

The "dynamically humpless hull" offered one path, but because nobody knows what makes a hull "humpless" this was a case of try it and see. Julian suggested that his current to Eighteen footer design would scale down  better than the 49er would. So I did the sums to size the new boat for two healthy adolescents, lofted the smaller boat and got on with building it from narrow timber planks edge glued and glassed inside out.

It was always a possibility that the scaling down to 0.79 the size of the Eighteen might alter its dynamic characteristics. So as soon as it was fit to float, we towed it at various speeds and weights to establish whether or not this smaller shape developed the hump in it's drag curve, which is normally expected, or whether it remained another of the strange "humpless" genre that we seem to have happened upon. Its surface, undercoated and dry sanded with 80-grit paper, was fair but not polished. Not surprisingly the drags were higher than expected. Further, there was a hump, but this was a different sort of hump. A dynamic hump would have given a steep drag rise from about six to eight knots, in other words, just above it's 5kt hull speed, and this would have become steeper at heavier weights. What we had measured was a very steep hump between four and six knots, which did not change at all between light (160kg) and heavy (230kg) total weight. We concluded that whatever the reason, this was not a dynamic hump, so we had what we wanted and proceeded. That was in March '97.

Two years later we measured the drag of a polished production 29er. The drag curves, both at 500lb (230kg), of the polished and the unpolished hulls are shown in Fig1. What they show is the different effect on drag of 1) skin friction and 2) a turbulent boundary layer.

Skin Friction.

The smoothest surface always gives the smallest friction, so at all speeds the polished hull will have a fraction less drag than the rough one.

Boundary layer.

A laminar boundary layer will give about half the drag of a turbulent one.

What Fig1 shows are three separate boundary layer regimes as between the two boats.

1) From rest up to some very low speeds the boundary layer is always laminar. In this case this speed is about three knots for the boat with the rougher surface. (You can see that by looking at your wake close to the transom when the boundary layer flow begins to become turbulent.) So from rest up to about three knots the small difference in drag is due solely to the greater skin friction of the rougher surface.

2) At about four knots the rough surface trips the boundary layer of the rougher boat into turbulent flow over the whole wetted surface. The smooth surface of the polished boat continues to run laminar. At five knots this trip into turbulent flow has nearly doubled the drag of the rougher boat.

3) At about six knots the boundary layer over the polished hull begins to trip from laminar to turbulent. This starts at the stern. As speed increases the transition point moves progressively forward towards the bow, until at 10 knots the polished hull too is running almost entirely turbulent and there remains only the small difference in drag due to skin friction.

David Maiden, President of the 49er Association of Australia, commented that he had used a slow-dissolving detergent as a tracer, in order to find out more about the flow over his 49er. He measured that the transition line from a laminar to a turbulent boundary layer was 3ft or 4ft aft of the bow at a speed of about seven knots.

All these measurements suggest that it does pay to polish, and to polish well.

Frank Bethwaite.

I remeber reading that ages ago people used to first sand the hull and then 
fill all the scratches with graphite. After everything was really smooth it was finally painted with egg white. The graphite seems logical but the egg white sounds a bit strange.

Been trying to find the provenance of this one which I have read somewhere.  This was a gamesmanship thing where one of the top teams many years ago (I thought I had read it in one of Ian Proctor's books but can't find it) applied a mess of egg-white and graphite to the bottom of the boat after the day's racing in full public view, only to wash it off again in deadly secret before putting the boat in the water the next day.  Their imitators who performed part 1 of the procedure but not part 2 were somewhat disadvantaged on the racecourse.  I now think this is in that vastly useful go-faster book "Sod's Law of the Sea" but as I cannot find my copy cannot confirm.

This reminds me of a story I heard about Rodney Patisson in the run-up to the '72 Olympics.  As he was thought of as the god of the FD, and he wasn't going very fast for some reason and was concerned about his qualification, he decided to utilse some gamesmanship...

He turned up to a major regatta with several large holes sawn out of the middle of his centreboard.  With amazement the rest of the competitors watched him fit this state of the art affair into his boat and go out for a practice.  Then panic set-in.  If Rodney had it then everyone surely needed a centreboard like that otherwise they would stand even less of a chance.  

So off they went to beg/borrow/steel jig-saws to make nice rectangle shapes in their only centreboard.  Next day Patisson won every race by a leg with his proper centre-board fitted!

I'm not sure if the above is apocraphal, exaggerated or just plain untrue, but I hope not...

I remember John Oakleys book mentioning the egg white, but it was suggested as a proper idea, not a trick! He never mentioned secretly washing it off!

Another tale - Rodney Pattison turned up to an FD champs with loads of electronics gadgets (from yachts) in his boat. Everyone looked worried, but Rodney turned it all off and ignored it once the 10 min gun had fired.

A word of warning about "waxing" your boat-DO NOT use ones containing teflon, unless you plan to either a)sell the boat soon to someone you don't like, or b)never, ever have to repair it/repaint it. Reason is the teflon is almost impossible to remove from the surface, and makes sticking anything to it, like a repair, or new paint, also impossible, or at the least, very difficult.

I think things like teflon, graphite paints etc are now banned from the RRS...