These sites can be of value in your research: http://www.servodatabase.com/
Servo City can help you select a good servo for your boat. Worth a few minutest to check out these sites.
On a personal note, setting up a winch system correctly requires knowledge. Setting up a sail servo using a servo arm requires less engineering and is much easier. There are many very popular rc sailboats using winch set ups, my point is when done correctly they work great.
There are many boat sold using a single double track drum set up, but those are not true winch systems - I posted photos of DENNIS DESPROIS' Gambit (one of thefinest rc racing yachts ever build)with a properly set up winch system. Hope this provides youwith an idea of what is involved.
Dennis is a well know RC sail maker and boat builder (and Champion sailor.) http://www.ddesprois-rc-boats.com/Site/contact.html
I am sure he'd be happy to give you some insights on your project.