Doubt that a feathering prop on a full keel
boat would make any significant difference in its sailing performance, especially when you consider Cost/Benefit. There is so much resistance and turbulent water
by the time it gets to the prop from the wetted surface of a full keel
boat that the minimal drag of a prop hidden behind all that deadwood or a feathering prop won't register.
Delivered and cruised on 3 Westsail 32s, one with a two bladed prop with the prop stowed vertically behind the deadwood and two with large 3 bladed props. The two bladed had virtually no drag when locked vertically. The three bladed props were for much bigger engines and were larger props. The two boats with three bladed props had slightly better 24 hour performance over 24 hours in near identical conditions than the two bladed. The best days run was 180 miles through the water
with a mile or two difference for the other 3 bladed prop boat. The two bladed prop boat had a best days run of 176nm. Worse than the three bladed boats but not enough to notice.
If you can justify a feathering prop for better engine
performance, have at it. Wouldn't expect any noticeable difference for sailing performance.
A while back checked on a feathering prop for my Pearson
35, similar underbody to a Bristol 39, and the only solution was to carve out a bit of the rudder
to make the aperture bigger out of the rudder. Didn't seem like a big thing to do for anyone with minimal fiberglass
skills. The cost/benifit equation luckily talked me out of it after more experience sailing the boat. The Bristol 39 seems to sail to its rating pretty well judging by its Bermuda Race
corrected time victories.