Volvo Penta Duoprop replacement - selection?

[jwdvorak]

Hello,
I've got an old (1992) Volvo DP-C duoprop sterndrive, I plan to replace the props... the current set is B-5 series, they're aluminum, I want to upgrade to SS. The engine is a V8 350, Volvo Penta 570A, I believe it's 275 HP. Been watching Craigslist, found a set of SS C-6's available... they came off a drive powered by a 260hp V8. My question: could I safely go up a grade in pitch, from B-5's to C-6's, or would that be likely to overburden my engine?

Thanks,
Woody

 

[jwdvorak]

Re: Volvo Penta Duoprop replacement - selection?

C'mon, guys... no opinions, advice or comments?

Boat is a 26ft Olympic cabin cruiser, cruises about 28mph @ 3500rpm... WOT might be about 4500rpm or a bit higher (haven't ever pegged it). Not sure what cruise recommendation is for the engine, but I've read posts about similar engines that recommend cruise setting about 4000rpm. Am I babying her...? Engine has 775 hours.

Thanks for any advice...
Woody

 

[JoLin]

Re: Volvo Penta Duoprop replacement - selection?

Hi.

Before you go playing with pitch, you should know what your current WOT rpm is with a normal load in the boat, and compare that to what V-P recommends as the WOT range for your motor. If your motor turns more rpm's than what V-P recommends, or it's revving to the top of the recommended range, you can probably get away with a higher pitch.

Just be aware that in going from aluminum to stainless, you're already effectively increasing the prop pitch due to the fact that stainless doesn't flex as much. A 16 pitch in stainless is equivalent to a 17 pitch in aluminum.

For the record, those SBC engines usually get the best overall performance (fuel consumption vs. speed) when cruising in the 3000-3500 rpm range. You can cruise at whatever rpm feels 'right' for your boat, but you aren't 'babying' it (not sure I know what that means).

 

[jwdvorak]

Re: Volvo Penta Duoprop replacement - selection?

Thanks for the reply... so, my guess on WOT was close, VP's specs for this engine:

Technical data
Engine	570A
Production period	1989-1993
Operation	4-stroke
Cylinder configuration	V-8
Bore (in.)	4
Stroke (in.)	3.48
Compression ratio	9.3:1
Displacement (cu. in.)	350
Power (hp)	275
Max engine speed (rpm)	4600

I guess next time I'm out on flat water, I'll have to push her all the way to see how close it'll get to that. My gut hunch is it'll be right at max or a bit less, and that'd be a strong indication I should not go up in pitch.

Thanks again for the advice...
Woody