2 stage prop?

[powderhombre]

while driving down the road, I got behind a truck trailering a Sea-Ray 290, about a 30 foot boat I suspect. Anyway, the prop on the outdrive looked to be what I would call a 2 stage prop. A large 3 blade prop to the rear (closest to Transom) and a smaller 3 blade prop ahead of it. I never saw or heard of this kind of set up. anyone know of this kind of prop?

 

[Maclin]

Re: 2 stage prop?

That is a Volvo DuoProp drive. The props turn opposite of each other. Merc has a version as well but their props are the same size.

 

[jeff_smith_0423]

Re: 2 stage prop?

Lots of advantages, too. Quicker planing, less cavitation, better slow speed handling.

Downside? Pricey!!

 

[TilliamWe]

Re: 2 stage prop?

That is a Volvo DuoProp drive. The props turn opposite of each other. Merc has a version as well but their props are the same size.

Actually it is very likely that the drive he saw was a Mercruiser Bravo 3. Most likely not a Volvo Penta Duoprop, since Sea Ray and Mercruiser are both owned by Brunswick, and it's very hard to get a VP in one! (But it is possible) And while to the untrained eye, Mercruiser's props appear to be the same size, they are not. The rear prop is 1" in diameter smaller. Yes, I know the VP DuoProp's rear prop is much smaller than the forward, and it's obvious when looking at them.

It not a two stage prop. It's a counter rotating prop system. And it's old technology (I know of a WWII torpedo in a park in Henry, IL that has it!) that works.

Pros and cons have been discussed many many many times on here. Just search for "Single prop versus dual prop outdrive."

 

[craze1cars]

Re: 2 stage prop?

Either of these look familiar?

http://www.volvo.com/volvopenta/glo...e_engines/drives/dps_duoprop/dps+_duoprop.htm

http://www.mercurymarine.com/engines/inboards/sterndrives/bravothree.php

Nothing new and very popular actually...a large number of sterndrives are fitted with these in my area...once you get past about the 23 foot mark on most pleasure cruisers I'd say it seems more than half seem to be fitted with a counter rotating dual prop setup.