On alternative to using a halyard winch for trimming purposes (as opposed to just getting the sail up), and assuming your halyard is external, is to rig a 2:1 purchase that would allow you more options. I use it on my Nacra.. it is a quite common set up for mid to large dinghies and beach cats without winches.
Anyway... there is a cheek block on the mast that is the lower point of the tackle.... the halyard has a small single block tied into its length with a slip knot.... placed about a foot above the cheek block when the jib is at full hoist... there is also a cleat on the mast near the cheek block ... I use a small cam cleat with a wire fairlead.... on a larger boat like yours a "jam cleat with a horn" would work well, but I wouldn't use a clutch or power cleat in this application.
So... you hoist the sail... take the tail of the halyard through the cheek block, back up through the single block, then down to the cleat. Coil the remainder of the halyard and store it between the tensioned line and mast. With a horned cleat you can store it in the traditional way.
This extra purchase allows an easy, quick way of adjusting your halyard tension without a winch.
One other comment... You might consider rigging a Cunningham for adjusting main sail luff tension rather than the boom down haul.. It is much more effective.