what would happen if you tried to ride a surfboard without any fins on it?

Answer 1

Depends upon the board. It would tend to slide but if your had hard rails you could control it. Fins were not put on boards until Tom Blake did it, back in the 40s I believe, so they can certainly be ridden that way. In one of our local "fun" contests" there is actually a division were you have to remove your fins.

There is a small resurgence of people riding traditional Hawaiian boards, such as the alaia, that do not have fins. They are very thin, have hard rails and flex like a ski allowing to hold your line.

Answer 2

it would tend to "slide out" to either side. You would not have steering control.once you stood up. With your legs still in the water you could control it like a boogie board.