converting from a sigle prop to a duo prop

[bgeddeis]

do I need to buy anew lower unit to make this possible?

 

[JB]

Re: converting from a sigle prop to a duo prop

Howdy, bgeddeis

Welcome to iboats.

We need a lot more info before we can give you a useful answer to that.

What, exactly, do you have?

 

[tashasdaddy]

Re: converting from a sigle prop to a duo prop

sounds like a VP answer yes, they counter rotate,

 

[bgeddeis]

Re: converting from a sigle prop to a duo prop

I have a 2000 four winns 210 horizon with a volvo 7.4. i think it had a sx outdrive on it.

 

[Boatist]

Re: converting from a sigle prop to a duo prop

Yes you have to buy a complete out drive. Not cheap. Take a life time of heavy use to pay for it in fuel savings.

 

[Texasmark]

Re: converting from a sigle prop to a duo prop

Well, beins the subject has been opened, would you folks in the know mind explaining to those of us folks in the don't know and tell us what this setup buys you.

I read about prop efficiency, vs # of blades I guess because of the turbulence of one interfering with the input to another. This counter rotation, with one blade immediately ahead of another seems like star wars stuff.

"It ain't cheap" comment is obviously very true. Now you need 2 concentric shafts (one hollow, the other inside) supported in 4 places (I guess the drive is up top so you have a pair of vertical and horiz shafts supported by bearings on both ends). Then you need two sets of gears cut identical yet exactly opposite to get the two shafts spinning in sync in opposite directions. Then you need two SS props; but I don't know if the pitches are identical. Maybe the gears aren't cut identical and one runs at a different rpm than the other.

I know the Russians do it with air on the Bear bomber, but that's air.

Thanks,

Mark

 

[BF]

Re: converting from a sigle prop to a duo prop

I saw a VP video some time ago... the one thing that seemed like a big improvement was the dual prop thingys seemed to back up way better.. makes it much easier to dock. You'd think there would be other advantages that would make it worth the all the extra complexity to make a lower unit like that. (?) Maybe way less slip = more efficient (?).

 

[Boatist]

Re: converting from a sigle prop to a duo prop

The outdrive is more effecient. This means fast to get up to speed and faster to plane and bettery fuel mileage. Also eliminates the sideways kick of the stern when you put in gear or change directions.

Boat tracks better going stright or in turns.

I actually like to use the stern sideways kick when put the motor in gear to make faster turn in tight area like making a 180 degree turn between docks.

http://www.volvo.com/volvopenta/na/...rives/DPR+Duoprop/the+benefits+of+Duoprop.htm

 

[gcope63]

Re: converting from a sigle prop to a duo prop

I am looking to do the same and have found out all you have to do is change out the lower unit from the SX to the DP-S. You will just need to figure out what the gear ratio should be. A new DP-S lower unit is $4295 on dougrussell.com which is a little expensive but your old lower unit may be worth something which lowers the overall cost.


Gary

 

[Don S]

Re: converting from a sigle prop to a duo prop

Moving to Mercruiser, Volvo and OMC I/O or Inboard Engine Problems forum.

Yes, you can change just the lower unit. Most of the big blocks run a 1.78:1 gear ratio.

 

[njlarry]

Re: converting from a sigle prop to a duo prop

What will you get for the increased cost and complexity? Volvo data shows no real difference for my 5.0 FL between the two. One standard prop costs less to replace than two duo props. One guy at my marina named his dx "stump grinder" but the stumps always seem to win over the props.

 

[Don S]

Re: converting from a sigle prop to a duo prop

Volvo data shows no real difference for my 5.0 FL between the two.

What data are you referring to? You have obviously never run a similar boat with a DP to see the difference, or you would never have bought one with a single prop. Read Boatist's reply again. It's fact.

One guy at my marina named his dx "stump grinder" but the stumps always seem to win over the props.

Perhaps he should try boating in the water, not in the woods.

 

[njlarry]

Re: converting from a sigle prop to a duo prop

According to the performance manual under fuel flow pages 23 and 24 (downloadable from Fourwinns.com); the 5.0 FL at 3000 RPM the SX produces 31 MPH while the DX produces 32 MPH, both have a fuel flow of 8 GPH. At WOT the SX produces 45 MPH, the DX 46 MPH both with 17 GPH. They do not specify the props but on page 21 under performance they list identical top speeds for the SX with a 14.25x21 and the DX with D6 props, both 44-47 MPH. The SX has a cruise range of 120 vs the DX range of 130 miles. These figures are for a 1996 200 Horizon. The results might be different for a bigger boat. The data is similar for the 5.8 FSi.
One MPH is not worth over $4,000 to me, maybe for others. Agree with Boatist, the stern kick can be useful for manuvering. Also there is alot to be said for simplicity.