Rigging question

Discussion in 'Boat Design' started by CarlJ, Dec 14, 2007.

  1. CarlJ
    Joined: Dec 2007
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    Location: NC

    CarlJ New Member

    I have an inboard boat that is designed for an 8 degree shaft angle. The gear on the boat is an 8 degree down gear. Does the motor install with the boat hull level and engine level, Level the motor from the way the boat sits at rest or from it's running angle?
  2. Eric Sponberg
    Joined: Dec 2001
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    Location: On board Corroboree

    Eric Sponberg Senior Member

    If this is a new build, then yes, level the boat (because that is how it is supposed to float at rest), set the engine level to the boat, and the gear and the shaft placement will then be determined by the 8-deg down angle for installation. A boat will always trim down by the stern when running, amd engines are usually designed to be level or trimmed a little down at the back end. Engines are not necessarily designed to be tilted down at the forward end. It all has to do with the design and location of the pick-up of the oil suction tube and the oil pan. Tilt aft up to about 15 degrees total when running is OK, but you don't want more than that. So you want to minimize the amount of down aft tilt; you want as little overall shaft angle as possible consistent with a generous tip clearance. And since the engine idles and operates at slow speed, and the boat is more or less level, you don't want any trim on the engine down by the front end. So the best bet is to level the boat, set the engine level to the boat, and let the gear box angle determine the shaft angle and placement.

    If this is a retrofit and the shaft is already in place, you don't have any choice--it is what it is, and you have to make it fit if you don't want to rip it all out and start over

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