smooth or rough?

My SOT kayak is nice and smooth on top but underneat is rough, like unsanded sorta.

Any advantage (other than the excersize) or disadvantage to sanding it smooth on the bottom?


idiot answer
Nice, worthless reply, why bother, go back to your games.

Most likely your SOT is poly, its finish will be pretty much what it was coming from the factory, sanding poly won’t make it faster as the scratches from sanding won’t go away. No realistic way to polish out the scratches.

Bill H.

griffin is correct, it is a chore to
sand poly, and there is no way to get the bottom as smooth as the top.

We’ve had discussions on pnet about how much difference a smooth hull finish will make, when it can be achieved. Probably you’ve seen similar discussions for power boats. Eric Nyre, who often posts on here, did coasting-to-rest trials on fiberglass kayaks that he said showed that a smooth hull is “faster.” I’ve painstakingly refinished a couple of “glass” whitewater kayaks that had gotten fuzzy and scratched, and after refinishing they seemed faster. But I have no way of knowing if they were or if it just seemed that way.

In the speed ranges we travel in most of our human paddled boats, roughness/smoothness probably makes little difference. People that race or really “push it” in fast boats may have more reason to want a high degree of smoothness. Which is why they seldom paddle poly boats.

Paint or urethane spray?
If you have a junk poly boat, you might experiment with marine paint or urethane. When paint starts to dry, you must thin it to avoid drag marks. You could practice on bottom of trash can.

don’t bother sanding it

– Last Updated: Jul-13-10 5:28 PM EST –

I'm guessing you have a Wilderness Systems boat. For some reason they've been sending some models out with textured decks and smooth hulls or smooth decks and textured hulls. I bet it has nothing to do with your use but their costs or they had too many chefs in the design shop that day.

With a little research
you will find lots of links about hull finish vs speed. Basically, a little rough is better. Texture from .002 to .005 inch is really helping you in a vessel with enough surface area that the difference can be measured, think racing yachts here. For vessels the size of kayaks, it has been determined by drag measurements that the total drag difference in mirror smooth surfaces vs textured is so small as to be pointless in comparison. The recommendation in the racing manual is “if you think you are going faster by polishing and waxing your hull, then do it. If you think you will gain and edge by fine sanding your hull then do it. The psychological value far outweighs any measureable difference.”

John Winters…
"The great disappointment for the designer is that, after reducing friction to a minimum, the paddler is unlikely to notice the effect. A 5 percent decrease in wetted surface is worth bragging about, but a single year’s scratching and banging can easily double Cf from 0.004 on a new fiberglass canoe to 0.008. This more than offsets the designer’s efforts. The cavalier attitudes of most canoeists towards their boats is evidence that a 50 percent resistance increase is not often noticed if only because the onset of its effect is so gradual. "

Some interesting reading:

Smooth is faster.
I assume a glass boat? You didn’t say how rough either? If it’s a matter of taking out a palm sander with some wet sandπaper and spending 20 minutes making it smooth, why not. A lot of things we do are a matter of concept rather than realistic benefits like washing a car. Or tuning your car when it’s called for vs. waiting until it is chugging down the road. I personally would feel happier if my boat bottom was smooth especially knowing how little effort it takes to smooth it.

I know from boating that once you get barnacles, the resistance is very noticeable.

But will a poly boat bottom sand truly
smooth? Based on small trials, I doubt it. You will get fuzz, or microfuzz.

for pete’s sake
What kind of kayak are we talking about? A rec SOT? Surf ski? Poly? Composite?

Sorry but I find this absurd. If we’re talking poly rec SOT you will never know the difference. But you may thin your hull by sanding it.

Just my opinion.