After more digging, I think I will just get an old aluminum pontoon boat to convert and use it as a dock and as a barge to ferry a mower to the island. I can get one fairly cheaply and easily pull it from the water in winter time.

I haven't totally given up on the idea of utilizing that old steel one with either barrels or floats underneath it for something with theory we just take our chances in the winter.

[Linked Image from i108.photobucket.com]