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Guys:

I have a friend with a Bertram 30 that he is putting 260HP Yannmar's in and they are attached to 2:1 gears. Is anybody running this configuration on their B31 and if so, what prop size are you using?

Thanks,

Not sure what size you have now, but most with the Cummins between 250 HP and 330 HP are turning 20 to 21 inch props. 21 inches will be about the largest you can go.


I realize these are very different engines but I run 270 Cummins and my props are 20x23.

I believe Dug has the 240 Yanmars so what he turns would be closer to what you would need. Hopefully he sees this and jumps in.

Thank you Tony.

Tony,

The 260's may be the BY's while the 240's are the LHA STP's.
They may have different requirements in props.
I have the STP's, but have no idea about my props. If someone could tell me how to find their size I would be able to help in this.

Yannis wrote:Tony,

The 260's may be the BY's while the 240's are the LHA STP's.
They may have different requirements in props.
I have the STP's, but have no idea about my props. If someone could tell me how to find their size I would be able to help in this.

The other issue is that the 30 and 31 are completely different hulls. The shaft angles are different also. So what we can spin as far as size on a 31 will probably be different on a 30.

I had a 30 Chris Craft Tournament with a pair of 240 STE's with the 2:1 I was running 19X22 4 blades no cup.

The 6BY 260 is a 4000 rpm engine.

Using one of the many prop calculators on line 19x20 4 blade, 21x20 3blade. but contact local prop shop. These calculations are basic start with only a 70% efficiency.

The 240 4lh were a lower rpm engine. This is up at the 6lp range.

didnt realize they were BY's. I'd start with a 19X20 4 blade or 20x20 3 blade should be real close.

Thanks Guys!