Seeing as this is my first real boat--meaning the first boat that I've cared to get to know and maintain--I had no idea that a prop is not a simple item. First off, there are a dozen different kinds of props, and that's just for sailboats.
In my haul out and survey, my surveyor identified that the zinc on the prop shaft was no more, and that had caused bad corrosion to the existing propeller. It has to be replaced.
But identifying what props work for a 1977 boat whose manufacturer is no longer in business (since 1994) and that has been repowered (from the original Atomic 4 gas engine to a GREAT Yanmar 3GM30F diesel 27 hp), is not easy.
You have to know certain things to get the right prop:
- Engine make and model--okay that was the easy part;
- Reduction ratio--this is, I learned, part of the transmission and I have a gear drive not a "sail drive" as I would've expected; and
- Pitch--this is, as I'm starting to understand it, the degree of tilt essentially.
As stated above, I have a Yanmar 3GM30F (the F standing for freshwater cooling of the raw saltwater that also passes through the engine).
The reduction ratio is stamped on a transmission plate, which it turns out on my boat is BEHIND the engine toward the aft of the boat, and only visible via a little cut out on the side of the aft quarter berth (the little bed on the back left side of the interior). So dangling my iPhone over this area precariously for 15 minutes I took around 50 photos until I was able to capture enough resolution of this lightly stamped "2.36" on the plate. Which means it has a 2.36:1 reduction rate.
The pitch remains the elusive piece. I have posts on several Facebook sailing pages, in the Ericson owners forum, and emails to two different prop shops. It seems this should be consistent for this boat and model. But it's not easily located online.
Here are a few photos of the engine plate and the transmission plate.
I'm grateful to the previous owner for all his documentation but I still need to lock down the pitch for this prop shaft. It's important I source the right prop. There's a type called a Campbell Sailor that has angled blades that are narrower than typical props and is more efficient. You can get away with a couple inches less overall prop diameter than usual because of its design. But either way, I need to get the prop right, because this boat has a 3/4" prop shaft, which I also learned is narrower than they (ALL sailboats) started using shortly after this model. Too much torque could wreck it.
So I await some answers from experts at any of the places I reached out to. Hopefully, I'll know something shortly and get a new prop ordered.