Re: What is this piece of sailing gear?
It is a cam tightener from the '50's-60's. It was part of a fitting that included a bullseye through which a line was led, then through a cam cleat, and then a post, all on a backing plate typically fitted to a boom or mast on a small boat. One would slide the cam tightener over the post and lead the line over the wheel and under the cam on the handle. With that, one could "tail" the line with one hand and tighten it with the other and "crank" as needed. They were commonly used to tighten outhauls and reefing lines on booms that weren't large enough to take a winch but that needed a mechanical advantage to set the lines up properly or on small boat masts. One handle was all that was needed for several fittings. They actually worked pretty well.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."