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3 blade vs 4 blade prop sizing

Discussion in 'Props, Shafts & Seals' started by MBevins, Jul 3, 2021.

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  1. MBevins, Jul 3, 2021
    #1
    MBevins

    MBevins Senior Member

    Joined:
    May 23, 2008
    Messages:
    1,172
    Location:
    Windsor On. Canada
    Does anyone know what the average derating is when going to 4 blade props?
    I have a set of 22 X 24 four blades sitting in my garage getting very old. I have an opportunity to forward them on to an individual that has 24 X 24 three blades on his Marine Trader trawler.
    Anyone have a chart of some type that does a conversion?
  2. Capt J, Jul 3, 2021
    #2
    Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
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    Location:
    Fort Lauderdale
    You take out 1” of pitch when going to 4 blades
  3. Capt Ralph, Jul 3, 2021
    #3
    Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    12,727
    Location:
    Satsuma, FL
    Even though your going to 4 blades, reducing diameter may affect the handling & efficiency of the ship.
    I would consult MTI or a proper LSD prop shop.

    If your going to try them, Go for it before making any adjustments.