All sailboat propellers with the exception of Autoprop are designed to work at one pitch setting. At this point, normally the maximum engine rpm and hull speed, the sailboat propeller is at peak efficiency. Do you run your sailboat at full throttle?
Once rpm is reduced to cruising speed, the pitch for the propeller is still set for the maximum value forcing the propeller to work harder to maintain speed; this causes an increase in fuel burn and also an increase in engine emissions. This is how all sailboat propellers work regardless of manufacturer.
Tests on all 4 of the sailboat propeller types found that at 2000 rpm a feathering sailboat propeller was able to propel a test boat at 5.4 knots, but when the same sailboat was fitted with an Autoprop feathering propeller, the boat was able to achieve 6.9 knots for the same rpm and hence fuel consumption.