Boat overpropped - need help please.

Discussion in 'Props' started by yodani, May 20, 2016.

  1. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Ok, I trust your rpm readings. If you are not aiming at top speed, you will get slightly lower fuel consumption with some "overpropping". In this case you will find a reasonable compromise with a diameter of ~19,5"; ie 495 mm. Max engine rpms will be ~2680 rpm.
     
  2. yodani
    Joined: Nov 2010
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    Location: Danube Delta

    yodani Senior Member

    Thanks Baeckmo,

    So I should go with a reduction in diameter from 22 to 19.5" and stay with the 17" pitch?

    If they decide that the pitch can be modified should I go with 21x15" as given by propcalc?

    Thanks,

    Daniel
     
  3. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Yes, and yes (and your'e welcome).
     
  4. yodani
    Joined: Nov 2010
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    Location: Danube Delta

    yodani Senior Member

    Hi Baeckmo,

    Thanks for the advice and I will keep you posted about rhe results.

    Meanwhile I have another problem... Just last night one of my employees called me to let me know that another tour boat of mine just lost a propeller during a morning manouvre. I'm not sure we will be able to recover it as the water is 6-7 m deep and the current very strong.

    I'm not sure what the characteristics of the propeller where as it had nothing written on it. I'm reluctant to buy a new prop as I might repower next year so I've been looking on eBay to find a matching one.

    The boat is:

    Length - 8m
    Beam at water line- 2.8m
    Draft without keel - 1m
    Engine - 45hp@2400rpm diesel
    1:2 gearbox
    Two bearings on schaft

    Propcalc is recommending a 19.1x12.3 3 blade prop and a 18x12" four blade prop.

    https://www.ebay.co.uk/itm/331856818129
    https://www.ebay.co.uk/itm/222108668647
    https://www.ebay.co.uk/itm/231928372552
    https://www.ebay.de/itm/201586495210

    What do you think?
     
  5. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    When in gear it will not exceed the 2000rpm mark. And you can feel the engine is struggling.

    Your boat may not be "overpropped" it might be setup forv economical cruising.

    A boat that plaines will require max RPM, usually to get out of the hole.

    A displacement boat will only go so fast thru the water, before the power requirements get crazy.

    An 8 meter boat will run about 6K,,, 6 nautical miles per hour.

    How heavy is your boat?

    And with 45 HP do you really expect it to plane?

    What speed do you get at 1700 or 1800 RPM now?
     
  6. yodani
    Joined: Nov 2010
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    yodani Senior Member

    Hi Fred,

    Sorry for the confusion, but this is a second boat I'm talking about. Please read the last post. The fist boat is overpropped the second just lost it's prop and I'm looking for a new one.

    2000 max rpm with the first boat it's seriously overpropped and I don't think it will be optimum for consumption. I have cleared that out with Baeckamo.

    The boat will actually semi-plane due to the added appendix. See pictures.


    I'm going to move the last one in a new thread.


    Cheers,

    Daniel
     

  7. yodani
    Joined: Nov 2010
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    Location: Danube Delta

    yodani Senior Member

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