Two blade folding Martec
Hi,
A couple years ago I installed a two blade folding Martec Prop I bought used after it had been factory reconditioned. This replaced a fixed 3 blade. I don't have measurements, but you're right to be concerned about clearance. I think the new prop is a 12x9 or 12x6; I forget.
When I first installed it, it would hit the rudder about halfway through folding/unfolding. Luckily I was test fitting this on the hard at the time. I needed a new prop shaft anyway, but the prop shop said they could have shortened my existing shaft if I was going to use it. I had a few inches of exposed shaft aft of the cutlass bearing which was too much anyway. The new shaft puts the forward edge of the hub of the new prop about a half inch aft of the cutlass bearing. No clearance problems now.
I thought I would have less power forward, and way less reverse, but it seems to be about the same. I still get massive prop-walk, but that's the nature of the beast I guess. I feel the most difference under sail. I think I could feel the turbulence generated from dragging the 3 blade prop through the rudder and wheel. It's much smoother now, and I probably have an extra half-knot most of the time.
Here's the thread with some of my photos:
http://www.ericsonyachts.org/infoexchange/showthread.php?13726-Martec-Folding-Prop
Good luck!
Dean
1970 E32