Propeller for Volvo MD1

" Hello,
I have a Volvo MD-1

" Hello,
I have a Volvo MD-1 single cyl diesel in excellent shape to use in an old style launch. The engine came to me out of a "Frisco Flyer" glass sailboat
without any other gear.

My ciphering on the prop formulas tells me I need a 12 x 9 but I have some doubts since it's a little hard to decide what horsepower Volvo meant it to be rated. Does 12 x 9 make sense?

MD-1 is from the 50's. The manual lists 7 hp "when the engine is raced" or 6HP at what I infer to be its more sensible rating.
At one point before a certain serial number the hp was 5, 6 max. Calling it 6HP for calculation should cover the bases.

I'd appreciate any help anyone can offer on what propeller to use. "

" Bob,
I contacted a friend w

" Bob,
I contacted a friend who was a Volvo dealer for many years. He says that the MD-1 would have a 1.87:1 reduction gear. For installation in a "typical" launch he would recommend a 11 x 7, two bladed wheel.
If you need further information I could put you in touch with him.
Hope that helps.
Regards, Andrew "

That's what I need to kno

That's what I need to know. Thanks.