I have had a 30' sloop with Yanmar 2GM and a Martec folding prop for more than 20 years and have enjoyed consistently good performance from both. Diesels like to work hard; motor at 2600 RPM or more unless prudence requires a slower speed.
The Martec folding prop only works well revved up. Martec claims that their folding prop can bring a sailboat from hull speed to a dead stop in four boat lengths. To test the reverse performance, in open water from a stop run the engine up to 2600 RPM with the transmission in reverse. In twenty seconds you'll be going as fast as you'll ever want to in reverse.
As John noted above, if the prop is gummed up clean it. It won't work well if barnacle encrusted. No prop does. If the prop is worn Martec engineering will refurbish your prop to original specifications refurbish.gif
. Martec recommends factory refurbishment every 5 to 10 years depending on, the enviroment that the prop lives in, amount / type of use, size of prop, and number of different operators. I have this done twice and ihave been well please with return on investment.