Unfortunately I can't think of a place to put the turbine that wouldn't make the boat unusable for sailing. It's no big deal now that I only use it for recreation again so even if I'm way over budget I won't notice except on long trips.

I have bought one for land and am planning on setting up a separate system with it.

Lots of people have small 300-500W wind turbines mounted on a pole in the aft of the boat. Ketches often have them on the mizzen mast,

Neither of those is a good alternative on ours, so we are looking for a rigging-suspended option like the old Ampair and Windbugger setups.

Would putting it at the top of the mast make sense? More wind up there too.

No that doesn't help. The problem with winter isn't really that there isn't enough sun, it's that there are too many cloudy days. For example in January there were like 10 sunny days when I generated about 20 kWh (plenty) but also 12 cloudy days when I generated under 2 kWh (not remotely enough).

If it was sunny all winter I could easily go off-grid.

Like said, follow the sun. For example, summer in Europe and winter in the Caribbean. Or just Cape Verde.