It's a Martec Eliptec RH18DX12 and fits on a 1 1/4 inch shaft. As I've recently learned, that means 18 inch diameter, 12" pitch. It looks almost new now that it's been cleaned up, looks like it was hardly used after it was put on the boat.
Make an offer!
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s/v Driftwood
In some waterfront areas, driftwood is a major nuisance.