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Repropping to lower top speed??

Discussion in 'Props, Shafts & Seals' started by MLILIENTHAL, Jul 24, 2024.

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  1. Pascal, Jul 31, 2024
    #21
    Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    8,542
    Location:
    Miami, FL
    Yes I dug these numbers from my old notes.

    while the numbers vary slightly with each boats the overall result remain the same: the worst speed is between hull and planning. Irregardless of the boat :)

    Another boat I ran extensively was an 84 Lazzara with 1650hp C32s. Despite being significantly bigger than the Johnson 70 and having bigger engines the fuel numbers were pretty much the same In fact on plane, it was burning 5 gph less than the Johnson.

    one factor to take into account is water depth. At hull speed you will loose speed in shallow water. Here in biscayne bay for instance, even my 53 drops about a knot in areas with 6 or 7’. longer boats are affect even more; the 110 I run these days looses about 2kts in 10’ of water compared to running in 15’ +
  2. MLILIENTHAL, Jul 31, 2024
    #22
    MLILIENTHAL

    MLILIENTHAL New Member

    Joined:
    Dec 7, 2020
    Messages:
    22
    Location:
    West Palm Beach, FL
    Interesting relationship between depth and speed, never thought of that. Another factor in my case is that I've run this boat solely in fresh water, not sure how that effects things. I'll have time to rerun the numbers when I run her to Florida in the next month or so.
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