Just a pipe dream....

[Steven Vaccaro]

How cool would it be to have a "Merc Bravo 2" Style twin counter rotating system on a scale boat.

The motor could be the key.

[Darin Jordan]

How cool would it be to have a "Merc Bravo 2" Style twin counter rotating system on a scale boat.

The motor could be the key.

Hmmmmmmm......

[ReddyWatts]

It has 6 wires, must be a seperate motor for each prop. interesting!

[Darin Jordan]

It has 6 wires, must be a seperate motor for each prop. interesting!

Appears to be two outrunners hooked together in the middle...

[ReddyWatts]

So it would need two controllers and batts. hmmmm.............

[Dr. Jet]

So it would need two controllers and batts. hmmmm.............

You could use one bigger battery. These are low-current (+25 amp max) motors so batteries should not be an issue.

The motor closest to the props has a hollow shaft that contains the more distant motor's shaft.

[ChaKane]

Wouldn't the action of the closest prop as it passes through the water cause the second prop to be less efficent due to the water already moving. It may also cause the second prop to cavitate. You would have to run the motor slower to prevent this.

[Dr. Jet]

Wouldn't the action of the closest prop as it passes through the water cause the second prop to be less efficent due to the water already moving. It may also cause the second prop to cavitate. You would have to run the motor slower to prevent this.

I believe full-sized boats get around this by using a different diameter/pitch on the two props. The counter-rotating props almost act like an impeller-stator arrangement in a turbine pump to straighten out the water flow.

[AndyKunz]

Planes do the same thing. So do coaxial helis.

Andy

[Steven Vaccaro]

Interesting stuff. It would definitely be scale only, since there would be lots of resistance.

Also I had a brain fart in my first post. Its a Bravo 3, the Bravo 2 is the heavier and larger cabin cruiser outdrive.

[Ocean Racer]

on my dads boat from what i can tell they have the same diameter and pitch. ill look at it tomorrow to make sure im right and give a little more info on how they set it up. ill probably post it in the afternoon for all those interested. Steve i have to say i have also givin this some thought. the only way i can see this work is if you use a similar setup like in the EP and straight shaft outdrives. if you did a flex i can see hair flying and flex's breaking.
just my 52 cents

[ReddyWatts]

It would be kinda cool to mount one on an airboat.

[Ocean Racer]

ya it would it would look really cool especialy if you made a nice cowl to cover it.

[bonewar]

VERY INTERESTING, I HAVE A FRIEND THAT OWNS A 34 FOOT ALUMINUM MONO WITH A SEG LEG THAT RUNS COUNTER ROTATING PROPS TOGETHER ON THE ONE SHAFT, I'D LOVE TO SEE THAT ON A MODEL BOAT . NICE ONE STEVEN

[Jeff Wohlt]

Some info on how the DUO prop lower unit did on a big boat.

Not sure it has any benefits to our boats but the top speed was a significant increase (read below) Maybe cornering would also have some benefits...not sure.

Our (Boat-Talk.Net) test boat, a 25. ft, FourWinns cabin cruiser, experienced a JUMP in fuel mileage, from 2.1 mpg, to an UNBELIEVABLE 3.8 mpg! (test boat appx. 6000 lbs.) Considering the stupid prices we all pay for gasoline, a 48-percent reduction in fuel is welcome by anyone who 'works for a living'.

The huge increase in fuel economy is largely due to the fact that we could keep our boat at 'hull design speed', just above minimum speed to stay 'on-plane', at lower rpms.

The dead spot "no mans land" that occurs with any planing hull, at just below planing speed - is gone. This makes the boat' speed more 'hooked-up' through the full RPM range. The net result is more control in tough situations, such as slowing down as you approach other vessels, and when turning/ maneuvering in tight and dangerous situations.

Our minimum speed, to stay on plane, 'used to be' 23. mph. With the previous 'Single Prop' drive, going any slower than 23 mph was impossible, so we used to have to cut down to 11 mph in bad situations (weather, or heavy boater traffic). Not so with a duo-prop. We can now run at any speed under planing speed, with a level of control and confidence we never had before!

The top speed gain (35.mph to 42.mph) was 20% -not bad either. As captain, you will appreciate the better handling, throughout the entire speed range. BACKING-UP at docking maneuvers, is also perfectly straight. This may not seem important, until a gust of wind 'comes out of nowhere', or another boater gets in the wrong place, at the right time.

THIS JURY IS IN. The duo-prop is the future. VOLVO-PENTA is known around the world as 'bullet-proof' in propulsion and innovation, and they have our 100% endorsement.