How to add speed on a boat

Discussion in 'Powerboats' started by Davidz, Sep 5, 2010.

  1. Davidz
    Joined: Sep 2010
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Seattle

    Davidz New Member

    I bought a used Chapparal 1930 SS and i was riding on the lake today and noticed that at 4000 rpm it gained 25 mph. Now i have a 4 blade proppellor. Its a 14x20p. I have a 5 liter mercruiser engine. I want to know how to add more speed on it. Please i if you can help me out i would be very grateful. Thanks
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Okay, you'll need to post the make, model and year again, this time checking that all is correct and also some pictures of the hull type would be very helpful. I know this is your first post, but we need to start with a reasonable base of information.
     
    1 person likes this.
  3. Ramius41
    Joined: May 2007
    Posts: 30
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: The South

    Ramius41 Junior Member

    How fast are you wanting to go?
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Add a nitrous oxide kit to your engine and re-prop.

    -Tom
     
  5. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Something wrong with my eyes here. Do I see Mr Par 'take the screws out' :eek: Bloody long vacation you were on. I hope you have looooots of fishing photo's to show us eh ;)


    Welcome back.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 13,766
    Likes: 431, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If it was only going up to 4000RPM before, it was overpropped. The four blade is probably going to be worse.
     
  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed Gonzo, assuming a 305 Chevy, Mercruiser turning 200 HP or the "Captain" running 225 HP (aren't these 5.7's?) he should be pulling at least 5,500 RPM, maybe more like 5,700. That 14x20 sounds way wrong, how about 14x16.
     
  8. Landlubber
    Joined: Jun 2007
    Posts: 2,640
    Likes: 124, Points: 0, Legacy Rep: 1802
    Location: Brisbane

    Landlubber Senior Member

    ...hello PAR, nice to see your name again mate.
     
  9. gonzo
    Joined: Aug 2002
    Posts: 13,766
    Likes: 431, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

  10. Vulkyn
    Joined: Jun 2010
    Posts: 597
    Likes: 46, Points: 28, Legacy Rep: 654
    Location: Egypt

    Vulkyn Senior Member

    err ill steal a quick post and say welcome back PAR, read a lot of your posts and glad to see you posting again :D

    sorry for the hijack davidz :D
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 473, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Well, I was way off on RPM, 4,400 to 4,800 for the 5.0 (ditto the 5.7) at WOT (thanks Gonzo).
     
  12. gonzo
    Joined: Aug 2002
    Posts: 13,766
    Likes: 431, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Still, at 4000 the engine is lugging. Assuming the engine is in good shape, the boat will go faster with a smaller diameter or less pitch prop
     
  13. GG
    Joined: Jan 2008
    Posts: 190
    Likes: 4, Points: 0, Legacy Rep: -30
    Location: MICH

    GG offshore artie

    Hey guy just curious have you ever taken a straight edge to the bottom of the boat to see if you have a hook or not because something as simple as blueprinting the bottom of the hull can sometimes get you some fairly good gains with a little work .
     
  14. pantar
    Joined: Sep 2010
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Slovenija

    pantar New Member

    You should definitly try to change the diameter or pitch of your prop. Try contancting a local dealer for props and ask if you can test some of the props to see wich one gives you the best preformance on your boat.

    It worked for me.
     

  15. WickedGood

    WickedGood Guest

    Cruise speed on a Chevy small block 5.0 or 5.7 is 3,800 RPM. any more and that engine wont last long.

    If you want to go faster, yank out the small block and drop in a Chevy 572

    something like this should be economical


    1040HP @ 5900 RPM @ 8lbs BOOST! 91 OCTANE

    [​IMG]
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.