What's the deal with dual props?

[poconojoe]

I saw an ad for a boat that had dual props (on one shaft). I never saw this so I started looking around here for info on these. I'm just curious. Just trying to broaden my education. Hope these are not "dumb" questions.... How do these things work? What's the advantage? Do they spin in different directions? Do they use different helm controls?

 

[steelespike]

It's best to just look up duo prop, Volvo Penta.
Basically you have two props that counter rotate, these cancel prop torque so tracking is straight and smooth.
as you might imagine you would have amazing grip on the water and reverse has no paddle wheel affect The boat reacts the same turning in either direction.
Draw backs are the complication of the drive and the cost of the matched pair of propellers.
I think controls are essentially the same.

 

[Sea Rider]

Assume if both props turn say CW will unballance boat worst to port side, so one must turn CW, the other CCW for best steering control on straight water courses among other boating benefits. Is Volvo the only Company currently manufacturing duo props systems ?

Happy Boating

 

[poconojoe]

It's best to just look up duo prop, Volvo Penta.
Basically you have two props that counter rotate, these cancel prop torque so tracking is straight and smooth.
as you might imagine you would have amazing grip on the water and reverse has no paddle wheel affect The boat reacts the same turning in either direction.
Draw backs are the complication of the drive and the cost of the matched pair of propellers.
I think controls are essentially the same.

Ah! Thanks for that. Sounds like a good idea. Some pluses some minuses.

 

[Chris1956]

I believe the Mercruiser Bravo 3 are dual, counter rotating props as well. As was said, the counter rotating props track very straight. You will see this construct on WWII torpedoes. Those were pointed at a target and fired. They had no guidance system, so they needed to go straight.

 

[poconojoe]

Can the operator control each prop's speed separately?

 

[beech2000]

Can the operator control each prop's speed separately?

No. One input shaft with two counter rotating output shafts. Very efficient.

 

[poconojoe]

Ok. Thanks. Very cool function.