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Under-propped. 2004 FV270

vwtoastervwtoaster Member Posts: 34 ✭
in General Boating Discussions
So I think I’m under-propped. I have a Volvo Penta, 5.7 Gi new to me boat. Top speed is around 31mph at 5000 rpm. Seems very slow. Any thoughts?

Can anyone tell me what pitch they are running on their  FV270?
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    vwtoastervwtoaster Member Posts: 34 ✭
    My duoprop is F3 front and rear. 
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    What is the RPM range for your motor at WOT. That is the only way to tell if your boat is properly propped. Speed is irrelevant if your motor's RPM falls outside its proper RPM band at WOT. IMO if your engine's RPM at WOT is 5000 you are pretty close to the upper end of it's proper RPM band. Changing a propeller merely to get more speed or better acceleration can cause the motor to over rev or lug the engine, depending on what an owner mistakenly changes a prop for - both long term fatal. Some guys on the forum have gotten better results with different blade configurations but again it is folly to have your engine operating outside its proper RPM band at WOT. I have always aimed for the highest RPM possible within my engines' specified RPM range at WOT when the boat was under its most common load and weather conditions.

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    Aqua_AuraAqua_Aura Member Posts: 2,537 ✭✭✭✭✭
    5000 RPM sounds correct and the speed seems right as well. Is the boat bottom clean?
    1997 Bayliner 3988
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    PickleRickPickleRick Member Posts: 3,886 ✭✭✭✭✭
    edited August 2021
    Agree with @Aqua_Aura

    Heavy boat, small block Chevy single motor.   Right at max rpms for most 5.7 motors.  Sounds plenty fast to me.   The 270 could have benefited from a big block.
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    laureniac1laureniac1 Member Posts: 253 ✭✭✭
    Hill Marine 4x4 props will help get you on plane ! No speed increases- check the forum 
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    Cableguy GregCableguy Greg Member Posts: 5,012 ✭✭✭✭✭
    @tniggel has the same boat with the same engine. He can get up to 40 on his 270. Not sure what props he has. 
    2008 280 Express Cruiser, 6.2MPI, B3, Pittsburgh, PA "Blue Ayes"
    Go Steelers!!!
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    Aqua_AuraAqua_Aura Member Posts: 2,537 ✭✭✭✭✭
    Also make sure your speedometer is accurate. If you don't have GPS speed on board you can download a phone app. 
    1997 Bayliner 3988
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    vwtoastervwtoaster Member Posts: 34 ✭
    Thanks guys. It is GPS speed. WOT is correct. Hull was freshly bottom painted from clean this spring. My marina owner thinks it should likely have f5 prop. @tniggel what do you have for props? Comes out of the hole without great struggle. 
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    vwtoastervwtoaster Member Posts: 34 ✭
    I just thought top end should be closer to 40 mph and cruise should be around 28 mph at 3800-4000 rpm. Maybe I need to adjust expectations to 24-25 mph. 
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    J3ffJ3ff Member Posts: 4,060 ✭✭✭✭✭
    I'm in the same boat with a383, I think I'm way under propped
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    randy56randy56 Member Posts: 4,083 ✭✭✭✭✭
    Your rpm's are correct, and you should be running 38 to 40. check speed with gps, app on phone.
    Boat Name : 

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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    @Alswagg.....absolutely!
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