If carpets or slabs are placed on top of ice, a boat won't get accelerated.

Steps to Reproduce: 

Place any kind of ice down then a non-full block on top of it, such as carpet (or its moss variant), slabs, or anything else (Not including snow).

Then try to ride a boat on it, the boat remains the same speed even though there is ice under the carpet/slab. If a player walks on top of the carpet/slab though, they'll receive the expected result of ice physics being applied.