Gearing / Propping

[ryanleestma]

So I bought this Bering 70 and to be honest it has a few kinks in it I need to work out.

Has two QSB 6.7 engines and at speed when it’s brought into reverse it can kill the engines. I think it’s over-propped. At 8 knots the mains are running at 1100rpm’s which seems low to me. My thought is to prop higher so the engines have more torque.

Don’t want to mess up fuel consumption too much, I’m thinking 8 knots at 1600 rpm’s. It tops out at 13 knots so 2600rom which k think is the redline or damn close

Ryan

 

[rslifkin]

What power rating are your QSB 6.7s? That'll give an indication of what their rated RPM is. The QSBs are typically governed to somewhere around ~70 rpm above rated, so with a clean hull and full tanks, I'd want to see it propped so it hits the governors (and if you have a way to see the electronically reported engine load, it should be somewhere in the high 90s at that point, indicating that you're at slightly less than full power to reach governed RPM).

Based on what you're reporting, I'd bet you are at least a little overpropped.