Here are my thoughts on folding and feather props. Disclaimer. I've never had one nor direct experience with the of any substance.
Sailboats go slow. The go slower in light air and to maximize speed... efficiency the sailor adapts various strategies including sail trim, weight distribution, a "slippery" bottom. A folding or feather prop fall into the last category. They are reputed to reduce drag and therefore add a bit of speed to light air sailing.
In heavy conditions a foul bottom or a slippery form or weight distribution are less or sometimes not even the issue... when the boat is driven to hull speed
The down side is performance when motoring... and maintenance
. Folding and feathering props seem to reduce some motoring performance, such as backing or failing to open or perhaps requiring more fuel
.. ie less efficient than fix blade props. There are a lot of variables so there no once size fits all answer about performance while motoring. My sense is that the trade
off is acceptable to those who have them for better light wind
sailing a reduced performance under power. And they are very expensive to boot.
Racers will be the ones to consider folding props. Less so for cruisers. It should be pointed out that many cruisers need to get to their destination
on some sort of schedule... be it arrive before nightfall in an new harbor or get to an anchorage before all the good spots are taken! Accordingly cruisers will motor
sail to get there.
I personally have a 4 knot rule
when I am going someplace.. as opposed to being out for a day sail to no where. When sailing speed over the bottom drops to 4 knots. the motor goes on. The boat as a big auxiliary engine
which can drive it to hull speed
in most conditions and we use it! Additionally, I like the prop to be very responsive in tight quarters... at quayside or in marinas
entering or leaving slips... which we do very very very rarely. A responsive prop is part of maneuverability.
Since we are not into light wind
sailing as we are cruisers there is little to no benefit to a folding or feathering prop... and several negatives. I suppose there are some speed advantages in the 4 knot
speed range, but I am unaware of the magnitude of these with a folding or feathering prop.
Frankly, I don't see the benefit of folding and feathering props on a long heavy yacht and one which is not sailed in light air and racing
What do I know?