Prop size and Pitch Larsen 274/ Volvo Penta 5.7?

[Larsen 274]

I just bought a 2003 Larsen 274 Cabrio with a Volvo Penta 5.7, single prop outdrive.
The owner's manuel say WOT is 4600-5000 rpm
It will easily go over 5500 rpm currently
Current prop pitch is 17, I can't find size.
Anyone know what factory prop for this boat/ engine is?
Also, how big a deal is it to convert to duo prop?
Thanks

 

[steelespike]

Re: Prop size and Pitch Larsen 274/ Volvo Penta 5.7?

What is the speed at wot.If needed you can run it over 5500 briefly to check.
Judgeing by the pitch of your prop I would say your tach is reading high.
At 5500 with a 1.60 gear ratio 17" prop at 10% slip the speed would be around 49 mph.
awfully fast for single motor 6,000lb boat ,and highly unlikely.
Check the selector switch and operate it a few times to clean the contacts.
Perhaps borrow a shop tach to verify the rpm.

 

[tpenfield]

Re: Prop size and Pitch Larsen 274/ Volvo Penta 5.7?

You could easily go with a 19" pitch or maybe a 20" of same/similar diameter. A 21" might be a little too much.

 

[Larsen 274]

Re: Prop size and Pitch Larsen 274/ Volvo Penta 5.7?

What is the speed at wot.If needed you can run it over 5500 briefly to check.
Judgeing by the pitch of your prop I would say your tach is reading high.
At 5500 with a 1.60 gear ratio 17" prop at 10% slip the speed would be around 49 mph.
awfully fast for single motor 6,000lb boat ,and highly unlikely.
Check the selector switch and operate it a few times to clean the contacts.
Perhaps borrow a shop tach to verify the rpm.

Thanks for the quick response.
Speed at 5500 is only aboout 30MPH
Engine sounds like it's going 5500 rpm
Also, I am willing to bet prop is smaller than 17".
Not mentioned before, I am using this boat largely for cruising (I have an older bowrider for tubing etc).

 

[steelespike]

Re: Prop size and Pitch Larsen 274/ Volvo Penta 5.7?

If my other estimated info is correct for 5500 to produce about 30 you would have about a 10" pitch.Not available as far as I know. I think 10% slip is reasonable for big heavy boat if I go to 20% (very high)Pitch goes to about 11.5 to produce 30 at 5500.still a very small pitch. 11" props are available.How is the hole shot now?If your running an undersized prop hole shot should be brilliant!
As far as a factory prop goes Props uaually are applied based on the owners needs ie: speed or power. Or specific activities.Regardless of the purpose you would try to prop for near max rpm at wot.Sometimes a prop for water sports or heavy loads would require an eye on rpm so as not to overev.