Can you guess this science riddle?

It should fall by a tiny amount tho, a rock is dense enough to sink, but while in the boat it's mass displaces the boat to equal the buoyancy needed. Thrown in it's limited to displace an amount of water equal to it's geometric displacement. Like imagine having a 1 liter cannon ball of depleted uranium in a bucket large enough to float it vs  throwing it overboard, no way it stays the same.