[okawbow]

While sailing my Bristol 24 this weekend in light wind; I checked my 2 blade prop alignment and found the mark to be 90 degrees from verticle. I watched my knotmeter as I turned the blade to straight up and down. The speed increased 2/10s as soon as the blade was verticle. I moved it back to sideways, and the speed dropped 2/10s. I have a 2 blade, 12" diameter x 14P bronze prop. The prop is completely enclosed in a cutout behind the full keel.

 

[okawbow]

My Bristol might not be a fair test, as the prop doesn't want to spin, unlocked, unless I'm doing hull speed. Even then, I can stop the shaft easily with my fingers. My keel is even wider than a Cape Dory. But, I have seen a speed decrease of .1-.2mph when the blade was locked sideways, several times. I've never noticed any difference when the prop was spinning, but I never let it spin for long.