Proper gap size between shaft and tube?

Discussion in 'Boat Design' started by Deering, Aug 28, 2015.

  1. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    I have a 1.5" shaft. I'm trying to find the allowable gap between it and the stern tube that allows adequate space for shaft alignment while limiting the amount of water that could enter the boat if the hose on my stuffing box failed.

    I'm sure I saw a reference to an ABYC standard somewhere but I can't seem to locate it.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The available stuffing boxes determine the size of the tube. A 1.5" will typically use a 2.5" hose to attach to the tube. That means the tube will be about 2" ID.
     
  3. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    That would result in a potential ~1.4 square inch opening, or a 1-3/8 ID pipe equivalent. Maybe 1,700 gph. I'll have to double check the rating on my bilge pump. Might want to increase that, or add a second.

    With no bilge pump I'd have about 15 minutes before my engine and battery were imperiled.

    I guess I can live with that.
     
  4. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Actually it is not as bad as you've calculated.
    There certainly is a bearing or bushing at the propeller end limiting the inflow of water. And your stuffing box may develop a leak, but it will not disappear completely.
     

  5. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    I would have 2 bilge pumps anyway.
     
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