Have you thought about running another warp of what ever length you need and just using a retrieving float and split ring instead of the winch for your deep water work?
The float / split ring is much faster and easier (IMHO) than a winch anyway. Secure the 10 or 12 mm warp on the bow and just haul it in and lower it out of a bin off the rear deck.
I use 12 mm on my Vag.
Cheers
Chimo