Duoprop Compatibility - advice needed

[BJB]

I have a 1985 Contessa that has a 5.7 Volvo and what I think is a Volvo 280 outdrive. It is pretty underpowered so what I am thinking is that I want to try a duoProp DP-S instead. Now I am not sure what it might take to attach this outdrive to my engine but I am hoping bolt-on is one of the answers ;] I have found a complete unit in unknown condition online and am contemplating taking the next step. Before I do does anyone have any experience with this sort of thing or some relative knowledge of Volvo outdrives? Thanks,

John

[longliner45]

yes I do , we had volvo duoprops on our fishingboats ,powered buy 210 turbo diesles ,the thing about duoprops is they are only funtional at certain speeds ,no matter how much power you have they will only function at about 40 knots,,,physics?,,longliner

[BJB]

Thanks for the info longliner ... I am looking for something to get me out of the hole, not neccesarily drive me at a significantly higher rate of speed. With my current configuration I can *barely* plane and I heard the duoprop would provide access to 40% more of the available horsepower. If you are correct I wouldn't even get to use the duoprop. The 5.7 and leg seem to be running very well but the engine only gets to 3800 RPM when I open her up. Somehow that doesn't seem right. And I have checked the throttle cables and body to make certain they are reaching their maximum throw ...

Myabe more horsepower is the only solution? A friend is selling a rebuilt 440 Chrysler Marine that had a v-drive but I am afraid that trying to mount it and match it to the existing Volvo outdrive would be more of a headache than anything else.

[tuantom]

You can bolt a DP lower gearcase onto your existing drive without having to
mess with anything on the transom or engine. I wanted to do this to my
270 drive, however that's as far as it went. You just have to shim a little to make sure the bearing crush is within spec between the new lower gearcase and the intermediate housing. A Seloc or comparable manual will cover that pretty well.

I don't believe the DP-S will match up. Though I've never actually played with one, I'm pretty sure that would require changing everything up until the engine.

- Tom

[BJB]

Thanks for the info Tom - I have been looking for a DP lower unit that needs re-building. Has anyone else found that duoprops only function at high speeds?

John

[longliner45]

the duo props function well at speeds between 0-40 IM saying after 40 they dont function well,,,,,,,with the duoprops you have vertually 0 cavitation fuel economy is maximised and hp is maximized but like I said after 40knots it dont matter about hp, they just dont seem to want to go any faster,

[BJB]

Ah - thanks again longliner, that clears things up. I don't intend on exceeding 40+ knots (although over 25 would be nice ;). It sounds like the DP lower unit should work more effectively for me than an SP if I'm able to find one.

JB