I just looked at a 41 Apache for sale that had a rough sandpaper-like bottom. I was told it is used to make the hull faster. I could be wrong, but it seems to me like that as rough as it was it would scrub speed off. Anyone have any input on this?

Sure it wasn't bottom paint?

Wet-sanding to break the shine off helps to un-stick the hull from the water. Can get you an MPH or so.

Rough? Dunno.

The blow boaters were doing it first. A slightly rough hull reduces for lack of a better word "suction"

I was over at the harbor the other day, and saw a blow boat with more than a sanded bottom. It looked like non-skid texture below the waterline, and perfectly smooth gel coat above.

Michael

wasn't someone doing a gold ball like texture on a racing sail boat to break adhesion to the water? I wonder if it ever worked out?

The rough bottom helps to break the surface tension of the water, yes giving a little more speed like Chris S stated. After a few high speed runs, the bottom will smooth back out form the friction of the water.

It is not a simple subject, but yes, some kinds of surface roughness can delay the transition from smooth (laminar) to turbulent flow over a surface. That can significantly reduce drag. The roughness of shark skin is believed to cause such passive boundary layer manipulation, and thus aid their swimming speed.

funny...when i bought my 30 Shadow Cat back in 96 it had what i would best describe as a bad case of orange peel over the entire running surface. I sanded it all down, compound, wax... the whole nine yards...probably spent an entire week doing it...only to find out it was that way on purpose...

it was supposed to create air bubbles and release the surface tension on the hull...freeing it up and making it faster...

Not air bubbles. The surface roughness can add energy to what would otherwise be a more stagnant boundary layer. That can delay the onset of turbulent flow.