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  1. #1

    Default Need advice on selecting a stainless prop for new merc 150

    Hi have a 1992 Proline center console and last year I had a new Merc 150 outboard installed. Runs great. But the boat is heavy and I feel that a stainless prop would be better. We use it in local and open waters off san diego for fishing, surfing and cruising. I don't need more top end speed. I would rather have hole shot power. Can anyone help me with prop size, pitch, 3 or 4 blade...etc?

  2. #2

    Default Re: Need advice on selecting a stainless prop for new merc 150

    High 5 is the best holeshot and power prop 3 blade will be the fastest. Pitch will be determined by what motor you have. Rule of thumb for pitch is prop for the upper end of the operating range

  3. #3

    Default Re: Need advice on selecting a stainless prop for new merc 150

    When you say pitch for the upper end of the operating range....are you talking about standard RPM under power? The motor usually runs around 3500-4000 rpm at normal speeds. I believe I currently have an aluminum 15x17 prop that came with the motor from the factory. Is it less the pitch, the greater the hole shot?

  4. #4

    Default Re: Need advice on selecting a stainless prop for new merc 150

    if your motor is rated to for example 5000-6000 Rpm you should prop to be closer to 6000 with a light load. Less pitch has the best hole shot and may allow the motor to overrev.

  5. #5
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    9,114

    Default Re: Need advice on selecting a stainless prop for new merc 150

    You need to take your boat out and run it as you "normally do" and observe the highest rpm you achieve.

    Then you want to compare it to your WOT range for your motor.

    If your motor is say rated for 5500-6000 (and I'm just picking numbers here) and you are only making 5000 rpm you have "too much prop".

    For each 1" of diameter OR pitch you change your rpms by about 200.

    So in this example you could run a 14 pitch (15 diameter) and increase your rpms by 600 getting you up to say 5600 (within the WOT range).

    Stainless flexes less than aluminum or composite so it "bites harder" and reduces your rpms (all else being equal) by up to 50 rpms for a given diameter/pitch.

    Likewise, a 3 blade bites less than a 4 blade, so going from 3 blades to 4 would drop your rpms another 50 rpms or so.

    So, again, in my example while a 15D14P composite 3 blade prop might make 5600 rpms a stainless 15D14P 4 blade might only make 5500 rpms.

    It's not always as simple as saying "this prop" will give you a better hole shot because if your motor won't turn it as efficiently then you will lose some rpms and may end up with the same hole shot as a different prop.

    And all the "charts" only give you a place to start.

    See what your boat is doing with the current prop and start figuring from there.
    Graham

    A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)

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