a question i would like to know

So far as I know there are no coatings that actually seem to reduce drag, though a poorly faired, or sanded surface can. There have been some films that could be applied that actually work but they have all been outlawed by rule. Typically these have regular grooves like shark skin that help promote laminar flow.

Otherwise it's just wet sand and polish (though there is some debate about how far it is necessary to go).

 

Rainex works fine on windows. Expensive to put on hulls as the boat would have to be hauled for each application.

 

I think my thread title is spot on, If I knew the answer i would know the question. Also I never heard of people doing that before, But then again i Haven't been around boats that much, But i do agree with you, It probably is bad for the health of the fish and other marine life.

 

"a question I would like to know (the answer to) " ? That fixes it !

 

Semantics aside:
A question about water repellent coatings (impact on performance)

Would have done just fine...

 

Prince, water repellent coatings are not what we believe to be the best solution for drag reduction. As a matter of fact we would like the immersed surfaces to be wet. All this gets to be a technical issue about boundary layer.

There is ample evidence that the most effective improvement is an ultra smooth surface. Marchaj, among others, reckons that surface smoothness quality should have roughness measured in the single digit micron range. You get that quality by using very fine abrasives such as 800 to 1200 grit wet or dry sanding paper and a lot of very careful work.

Is it worth the work and bother? If you are a competitive racer, particularly in a one design class, the answer is yes. You might get another quarter of a knot out of the boat and that makes a difference in fiercely contested races. For casual sailing it is probably not worth the bother. If the boat has a lot of gouges and scratches then some careful repair is worth while but micron finishes are not.

Whether super smooth or not, the cleanness of the bottom is a matter worth the bother for competitors and maybe for casual sailing as well. At regattas you will notice Sunfish, Laser, and similar boats being careened so that the sailor can wash the bottom carefully. They use cleansers like Ajax, Comet or very fine particulate cleaners like those used for cleaning glassy topped cook
stoves. That matters, especially to those with OCD like so many of us.

Wax the topsides so that they will more easily shed water and thus excess weight, but do not wax the bottom.

You have not said what kind of boat that you have or are interested in. If you are thinking of a Donzi go fast boat then don't sweat the subject. Just keep the barnacles or other marine growths off the bottom.

 

A good cleaning and a wax job will accomplish more and it will last longer.

 

Why should you not wax the bottom?