https://www.amazon.com/Oodles-Monste...ay&sr=8-8&th=1
I bought one of these and put a rope through it and I let it float on the water as a cushion between the concrete and my boat. If the edges are rubbing then raise them with the rope going through it. These do get beat up easily if constantly rub hard by the concrete so it's a toss up on not getting the hard rubber ones from a marine store.
Use a piece of 3/4" x length is your choice of pvc pipe on your tie off rope as a spacer between boat and what ever you are tied too.
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