Am I propped right?

[Footloose]

Picture a 43 foot long, 10'4" beam 14,000 pound Donzi with arneson surface drives and twin 502 430 HP motors (one counter-rotates.) The old props were 3-blade 19-inch diameter, 20-inch pitch and are the original dinasaur surface props. Boat could not get over 38 mph or over 3800 rpm. Way overloaded.

Had props redone at 19-inch dia, 17-inch pitch but with lots of cupping (12) for more bite and thrust. Now runs very well and very fast and is more controllable but cant get past 4300 rpm and 40 knots or 47 mph.

I honestly dont care about WOT speeds - question is- will the motors be overloaded with these props or do I need more work done and get to the 4700-4800 rpm or higher WOT numbers to have right loads?????

Come on technical folks- someone has to know.

[BUIZILLA]

Were you out at Elliott Key the Sunday before last??

[gcarter]

Maybe remove some of the cup?
Also, if you had transmissions and some reduction, you would probably be a little happier, but you would have to change props again.

:wavey:

[JimG]

Must be that beautiful Harley!

You're on the right track. I'd keep reducing pitch until I got to 4600-4800rpms. I don't think you are going to hurt those motors right now, but you'll enjoy the boat a lot more with the right pitch.

BTW: I love those big props!

JimG

[Footloose]

Yup- we were on Elliot a few weeks ago - cruised to Boca Chita, No Name Harbor (changed fuel filters there), and stayed overnight at Stadium - very cool area. Where were you?

Thanks for the replies guys/gals, I didnt realize I posted this twice so ignore the other post (I'm losing it I guess - next year I'll be hiding my own easter eggs at this rate).

If it wont hurt anything, then I will run them for a while and see if the motors get revving better as the motors loosen up and I get more experience driving the arnesons and tuning the tabs and prop trim. The conditions were rougher than I would have liked when I did the testing Sunday afternoon -couldnt believe we were getting "air" in a 43 foot boat in the gulf stream induced 3-foot swells. What a beast and a handfull - starting to see why racers have a throttle man. To be honest I plan on spending zero time at WOT - gas is too pricey and I hate beating on boats and passengers.

[Footloose]

so did some more testing and it's official - top speed seems to be around 42 mph at 4200 rpm...after that it is all noise and not much more "go". The new prop work had really improved the launch and cruise from 3000 rpm up is much more controllable and just sounds better. Unfortunately I dont think the motors breaking in is going to give me another 500-600 rpms so I may need to get the props looked at again....also been advised to toe-in the drives about an inch for more lift. Will check that this weekend.