So you're saying the whole weight of the ship when it's floating is still on the anchor? I don't think so.
On each step, when then foot/paw hits the deck every joint in jarred by the weight of the critter. Buoyancy of the body reduces that shock. Moving through the water is harder work for the muscles, but that's the point, work the muscles without destroying the joints.
I noticed Carruthers is an old hand at dealing with needy creatures.