Up until now, if you wanted to build a rowing dock, you had to use foam for flotation (which is illegal by U.S. Army Corps of Engineers standards) or you had to use a float that was too high out of the water. We now have a float that can ship by UPS, approved by all U.S. Army Corps of Engineers, has a tough polyethylene shell filled with foam (polystyrene) and was made specifically for rowing docks. The float, which is 8" high, 20" wide, and 72" long will support 382 lbs. The outer shell is at least  .150 thick, rotationally molded and has molded in slots for easy mounting. These types of floats are specifically made to build a dock to lay low in the water, like for use with rowing shells.