Volvo penta I/O prop size

[DreamCatcher]

I was just curious what props others with VP outdrives run on their boats. I have a 24 ft Seasport duoprop w/ 5.7L EFI 280HP. Fully loaded around 7500 lbs. The boat was purchased with F5 stainless props. With this setup at wide-open-throttle it will run 4200 rmps. I generally cruise at 3100 rpm = 22 knots and burns about 9 gph. Is this in the ballpark for prop size?

[BrianW]

Been a few year since I owned my cabin cruiser. It was an old 24' Fiberform, but I repowered and put in a new duo-prop outdrive too.

I seem to recall D6 as the number. I switched from stainless to aluminum to prevent impact damage from reaching the outdrive. At the same time, I was able to add some cash and buy a spare set of props. I used the spares too after hitting a branch in the water. Stainless may have just chopped thru that though.

Seems she'd top out at 4500rpms and maybe 33mph. Usually ran 3600rpm and 28mph. Think I was buring around 10-12 gallons per hour at cruise.

[skydiver]

Wot?

What's the recommended WOT for that engine? Seems like maybe 4200 is a little low and you may be overpropped? Nice boat, by the way.

[olympic runner]

Yeh I agree with Skydiver, you should be 4200-4600 WOT. Not sure if you were fully loaded at 4200RPM.
Looks like dropping down a prop to F4 or (B4 aluminum) may be a better option...spendy PROP-osition though, but a back up set of props are good to have on board.

[Fish Witch]

Volvo DuoProp Size

I have a 26 Osprey with the 5.7 EFI DuoProp and just switched from C-5's (stainless) to C-3's. I could only get a little over 4000 rpms before and had a hard time getting up on step with a full load but now get close to 4600 rpms and get up on step much better. Fuel burn is still about the same at the same cruise speed per my Floscan but I need to turn about 300 rpms more to get the same speed. As a rule, you can figure about 300 rpms per DuoProp size number, eg I went down two numbers and got the WOT up by 600 rpms. I've got the C-5's for sale if anyone needs to change that I'll let go for a lot less than new.

[DreamCatcher]

Thanks!

Thanks to all former and present VP owners on your help. I did some more checking and my engine/outdrive should be turning out 4600-5000 WOT. Stepping down to F4s should get me in the ballpark. I called a dealership in Seattle and they typically install F4 on my set up. I'm over-propped with F5s. Also was told I should do WOT test with trim tabs up (which I didn't do). Live and learn. Thanks again, this forum rocks!

[BrianW]

Might want to trim the outdrive up a bit too, once on plane.