Marinette Boat Forum

I am doing a complete drivetrain overhaul and a 1.5:1 is being recommended over my existing 1:1 borg warners. I know that I can run larger props with the 1.5:1, but I am not too familiar with how it is truly a "better" setup. What pros / cons should I expect with this change?

I don't know what the pro/con's are, but I would suggest switching to zf hurth downangle trannies versus staying with inline trannies if you are thinking of buying new. That way you can go with two standard rotation engines and have one of the transmissions running in forward gear and the other in reverse. You can do that with full power in a downangle but not an inline. I don't have the budget, but my dream setup in my 28 express is a pair of 383 chevy's with a pair of zf transmissions. I would have do some research to figure out what is the preferred ratio. I would probably call a propeller company like michigan wheel or Acme prop and ask them what the pros/cons are of both, or maybe get a hold of a company that sells/rebuilds transmissions and get there opinion. You could also try getting in touch with zf or borg warner, but that might be a long shot to get to talk to someone who knows this area.

I'd be a bit nervous running a 1/5 ratio trans through those 1 inch prop shafts. The 1.5 ration requires a lot more prop, hence the prop shafts see more torque (and with the same engine).

A 28 footer with 383s sounds lie a really neat rig!

Jeff

It looks like Marinette shipped the 318 powered 32's both ways over the years, 1:1 w/ 14/10's and 1.52:1 w/ 16/15's. I think we are looking at going with the 16/15's. I have 1.25" shafts, but I need new shafts anyway, so they would be made to match if that's not the correct size.

Did this last year. I did move from 1" to 1 1/4" prop shafts. Trannys are 1.91 : 1. I have 18 x 16 4 blade props. I think the challenge is it is tough to fit a large enough prop. 18" is tight with respect to underside of boat and rudders. I am happy with the performance though. I wish I would have had 1.5 to 1 trannys.

What motors are you running with that? That looks amazing.

Small black Chevys

With regard to the original post - I am by no means an expert, but from a purely theoretical standpoint, a larger prop turning slower is (in theory) more efficient than a small prop turning faster. Propellers on big tugs and ships often turn at surprisingly low RPMs.

Given that, I would suggest that the 1.5:1 might give slightly better fuel economy at displacement speeds - maybe throughout the RPM range too - but we all know there are tons of factors that affect fuel burn.

Also, bigger props will give you more bite and power when docking...hopefully resulting in better control.

"The Propeller Handbook" by Dave Gerr is an excellent resource on this stuff, and it is written for regular guys with basic algebra skills.

One of our guys (Diver Dan) put a pair of 454 big blocks in his 32 footer using 1:1 drives and 1 inch shafts. The power blew the props away.

Yes: slower and larger is the way to go for cruisers. Small and fast turning props for speed.

Those awesome, 8,000 hp drag boats use dual, counter rotating (from a singe engine) props about two feet apart. The step UP ratio in the trans turns these super durable props at several times engine speed--we're talking 25,000 rpms here! God help you if one of them throws a blade going by!

Jeff