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  1. #1
    Ron Potts's Avatar
    Ron Potts Guest

    Default " I'm mounting a 150 merc

    " I'm mounting a 150 merc on the back of my bass boat. How far below the transom of the boat should the cavaition plate? Also I would like to disconnect the oil injection and mix my own oil but there is a hose that comes out of the bottom of the block, can I block that off or does it need vented? Should I leave The injection part alone or do I need to diconnect it also? Thanks, Ron "

  2. #2
    Sputter's Avatar
    Sputter Guest

    Default " This is not my writing but a

    " This is not my writing but a copy and paste from another sites tech info. A place to start anyway.

    Inboard Questions ?


    What is the correct transom height for my outboard engine?

    A: On average boats, it is best to mount the engine so the cavitation plate is approximately 1" below the bottom of the keel, or 1" below the bottom of boats without keel.

    For racing boats, better speeds can be attained by raising the engine to reduce lower unit drag and exhaust back pressure. Best transom height can only be determined by experimenting . . . get the engine as high as possible, or to the point just before propeller cavitates excessively. "

  3. #3
    Join Date
    Jul 2001

    Default " Ron, On a bass boat (hig

    " Ron, On a bass boat (high performance), I think you want to mount the motor such that the anti-ventilation plate is 1 inch above the bottom of the boat, with the motor full down. This should give you good performance without ventilation. Good luck, it should scream along! "

  4. #4
    Join Date
    Jan 2007
    newcastle, NSW, Australia

    Default " what boat is it going on? ho

    " what boat is it going on? how much jack plate is installed? what propeller are you running with it? how many people are you going to be carring? what does the boat weigh? how fast do you want it to go? what gear case do you have? what is your H2O pressure? what year of 1250 is it, are you using solid motor mounts, does the boat run nose high or level,

    as you can see there are many variables to installing an outboard and that little column above mine is VERY FALSE


    150 hp on a 20' 3000 lb boat with a semi V pad hull and it only runs at 50 mph, whick BTW is not considered HIPO, and its Cavitation plate is 2.5" above the botomn and could be raise even higher if i wanted....

    general rule is mount it even to the botom of the hull with the jackplate (assuming you have one) as low as it will go, then go to the lake and test it and raise the outboard in 1/4th" incronments untill one of three thiings happen.
    1. the boat looses speed
    2. the h20 pressure drops below 10 PSI at WOT
    3. the propeller can nolonger hold up the bow of the boat

    once that occures drop it 1/4-1/2 inch and LEAVE IT ALONE

    with the right propeller and setup an 18ft boat with 150 hp should see 60-70 mph depending on the variables listed above and some more that arent mentioned

    follow the set up for RACING SETUP IN THE SECOND POST!!!!! the 1" rule is for INBOARDS not OUTBOARDS!!!!

    or save your self some greef and have a professional rigger install it for you. "

  5. #5
    Join Date
    Jan 2007
    newcastle, NSW, Australia

    Default correction 150 not 1250

    correction 150 not 1250

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