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Bertram31.com General Bulletin Board
Cummins 370's or 330's?
Posted By: J.J. Soares
Date: Wednesday, 22 February 2006, at 6:29 p.m.
Ok guys, I know you're probably gonna tell me I'm crazy but here goes...
As you know I am restoring a B31. Been thinking about power. I like a Cummins. I was gonna go for the 330's remans but am toying with the idea of the 370's (you only live once...etc.). They are only gonna be $1000 more each than the 330's.
I've read on this board over the years that that much power (the 370's) will drive the bow down and under at over 31 knots unless I get the hull tunnels installed (which I'd rather avoid).
Now from what I'ver learned the bow is driven down and the stern up due to the 15 degree shaft angle combined with the effect of the large surface area on the big wheels one would run. I understand that the old B31 offshore race boats didn't have this problem as they were lighter, with the weight down the back but also because they ran smaller low pithed higher reving props (gas engines) which did not drive the stern up as much.
Here's my question:
If one were to have the 370's but run smaller wheels with lower pitch and surface area would the bow still be driven dangerously downwards? Of course one would use the proper gearing to keep the revs appropriate for the engines.
I don't want to do the wrong thing but then again I only plan to repower once and want
to get maximum speed without compromising handling too much. Bear in mind that the boat is only used for pleasure and will not be in big seas etc.
I won't use all that speed anyway but its nice to have it there (definitely a guy thing!)So does my theory of the 370's with proper gearing and smaller wheels make sense.
Would love to hear from you re you suggestions.
Sincerely,
JJ
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