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Thread: need advice on (re-)shaping old bronce props

  1. #11
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    Hi smittythewelder,

    the prop as it is now is definitely too large (would hit the cavitation plate), so i can not test it yet. But i will do the "minimum cutdown" first and try before cutting deeper.

    i'm very limited with engine height as my gearcase does not have a low water pickup (yet? :-D). The water entrance is behind the prop, just below the cavitation plate.
    With the current setting, the cavitation plate is about 1/2 to 1 inch above keel and cooling is still fine, but if i go any higher, i think the cooling might collapse. That's why i prefer to stay fully submerged...

    With standard aluminum props, it runs best at about 3 to 5 degrees trim (positive/up). Trim is continously adjustable, but NOT while driving, so i need to cope with the same trim position for both getting on plane and running WOT. With more trim (~10deg), the hull has less wetted surface and feels to run "higher" above the water level (guess a little faster as well), but it also starts getting seriously wobbly. Additionally, it is difficult to get on plane with such trim angle.

  2. #12
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    Trimming the motor out with the cav plate still running in the water is a major drag inducer--it also tries to pull the stern down. If you need to trim out, try gradually raising the motor until the cav plate is ABOVE the wake. And keep your eye on that temp gage (if you have one).

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

  3. #13
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    hi Jeff,

    my cav plate is already above the wake. Maybe my explanations were a bit confusing, but a sketch is worth a thousand words:

    Name:  engine-height.sketch.png
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    as you see, it is kind of borderline and there is little to no space for height variations: a little bit lower and the cav plate gets submerged, or a little bit higher and the water entrance gets out of the water.
    But the prop is still (almost) completely submerged in this condition.
    Simon

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