| |
Bertram31.com General Bulletin Board
Re: Cummins 370's or 330's?
Posted By: JPH In Response To: Cummins 370's or 330's? (J.J. Soares)
Date: Wednesday, 22 February 2006, at 9:45 p.m.
JJ: I have never bought into this idea that the bow drops at over 30 knots in a B31 with >1000 pound engines and a fueled up boat. I know I've never seen it and I know many, many guys in the early 1970's with 25 cent per gallon gas routinely running their 454s wide open for fun (sadly, I was part of those booze cruises in those days). I would love to explore the origin of this topic. I do think that 35 knots is about it with regard to stability in a B31 hull though and the 370's will get you very close to that speed. All 3 6B Cummins engines (270,330,370) are running the same diameter wheel with differences in pitch and cup. The difference between 330 and 370 is 200 RPM more per engine respectively. Rarely will you use the last 200 RPM in the 370, so why not if money is no issue for you. Talk to the Yanmar 315 guys: their engines hit 30 knots at about 3600 RPM, ask them about bow drop in a B31 with engines that are 375 pounds lighter each vs. the Cummins! John Patnovic in Maryland has gotten his owners 33 knots out of 370 Cummins in a modified, slightly heavier hull of 14,000 pounds. The B31 carries weight extremely well. Tony Athens in CA (boatdiesel.com)modified a B31 with prop pockets and Yanmar 440s and got 39 knots very recently. I don't know about hull stability though at that speed. There might be a good source of information on this topic. Here's one more thing to consider; creating prop pockets lightens the stern and that'll clearly cause the bow to drop at high speeds. I'd say THE most important thing in your re-power is the correct installation (including beefed-up stringers and mount on steel) by a reputable Cummins dealer and yard who will support and service your installation after the sale. If you do go with the 370's, you can break things like windows with careless operation in rough seas. Good luck. J
| |
Bertram31.com General Bulletin Board is maintained by Patrick McCrary with WebBBS 5.12.