You basically have two parts - liability and hull. Similar to car liability and comprehensive/collision. At that price level you can consider liability only. Like a car with liability coverage only, you are on the hook for any damage to your boat unless you are damaged by another boat that is insured. It basically covers damage you do to others.
And in spite of what kd3pc says above, I recently had a very good experience with Progressive on some storm damage. The adjuster knew boats, was very professional, and had a check in my hand within days of his inspection. When the actual repair began and some additional work was needed, again they were great. I was impressed.