Waxing a rowing shell has benefits, such as protecting the hull from damage from the sun and from pollutants.
(Of course there are also down sides, like messing up a nice pair of pants.)
However, one of the benefits of waxing is NOT speed. A good wax job will actually slow your hull down.

What is the best treatment for a hull when you’re looking for speed?
The answer is, “Nothing!” A naked hull is usually the fastest.
You see, when a hull is gliding through the water, you want to have the smoothest possible surface that you can. Smooth is fast. The smoother the hull, the less friction . . . and that is good.
If your hull has a good paint job and is free of dings and checks, then its maximum speed will come from being clean. Think of it in these terms: “Clean is fast.”
So waxing a rowing shell can slow you down…so how do you clean the hull? In my opinion, it’s a two-step process. (For more details on this read 3 Steps To A Sparkling Clean Rowing Shell Hull.)
My first step is to use a rubbing compound. I usually treat the hull one or twice a year with the compound to remove the gunk that attaches to the hull over time. This is critical if you do wax your hull, or if you row in water that has pollution in it (and, unfortunately, today most water does have it).
Rubbing compound is an abrasive, usually in a liquid or almost-liquid form, and it comes in different levels of “grit.” I just think of it as liquid sandpaper.
There are two critical components of successfully using rubbing compound. One is selecting the correct grit (I use 1500). The other is to follow the directions, and I mean follow.
Using compound can be a mindless job, but that doesn’t mean that YOU should be mindless. Care needs to be taken that you only “clean” the hull, and not damage the paint.
Gentle strokes, usually in a circular pattern, work fine. Some people profess that using a bow-to-stern motion is best. This does have its merits, but usually only if you are using a heavier grit, or sandpaper.
My second step is to wash the hull prior to each race. I try to do this the day of the race, when the boat is ready to go. That means if we’ve transported the boat, I’ll wash it right at the race course.
That’s not usually a hardship. A bucket, a sponge, a little soap (I use dishwashing detergent), a little water (which tends to be available at race courses . . . hint, the river or lake), a little scrubbing, and in ten minutes the hull is clean. I then just rinse off the soap and let the boat drip-dry.
(For what it’s worth, one thing that I’ve noticed is that people love, I mean LOVE, to help wash a racing hull. There must be something sensual to it. Almost, without fail, every time I wash a hull people flock to help.)
So . . . if you are thinking of waxing your rowing shell, clean off the wax before race time.
Remember—naked is fast!