CD28 Prop and aperature size?

[Joey]

Hello, all, I'm on my 1st official Cape Dory, although it is my 3rd Alberg design (Sailstar Corinthian 19', and a South Coast 23 previously). I just purchased a 1978 Cape Dory 28, who is a south pacific veteran of Hawaii and the Marquesas, with beefed up rigging (including exterior bronze chainplates), hull/deck joint reinforcement, and other offshore mods, but with a kaput Volvo MD7a. I just purchased a Yanmar 2GM20 which I'll be installing soon. She's still in the water, but I'm trying to get all my long-lead parts purchased. This will be my 3rd boat to repower, so I'm familiar with the process. But my question is about the prop aperture:

Vicprop's calc shows that for this engine & gear ratio, and for a 2 blade, I need a 15x9 prop, but looking at photos of the aperture with the existing 13" prop, I'm thinking that 15" diameter prop will not fit. I can use the diameter to pitch rules of thumb to get back down to a 13", since that is the factory diameter for the Volvo, but I wanted to check with any CD28 owners on what prop diameters they were able to make work on a repower. Like I mentioned, she's in the water, so I can't put a tape measure to the aperture.

Thanks everyone,

Joey
Puget Sound

[GeorgeH]

Hi Joey - a 15" prop will not work. I repowered from MD7b to a Yanmar 2gm20f last year and I had to change the prop from 13 LH 12, 3-blade to a 14 RH 12, 2-blade and it works fine and clears the aperature.

[Joey]

Awesome, I had located a 14x12 prop already, but was still hesitant... and I left the "F" off my engine, it's the 2GM20f, also. I haven't mocked up a template yet, but did you have to do anything other than raise the engine beds? I saw somewhere that there was a need to accommodate a 'bulge' near the bellhousing in the engine beds.

Thanks for the help!