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  1. #1
    Member
    Join Date
    Jul 2019
    Location
    California
    Posts
    21

    Crestliner MX21 PROP HELP

    I just purchased a new crestliner mx 21 with the merc 250 xs and a 10” atlas Jack plate….. the boat/hull is so new there isn’t a ton of info on props out there. The dealer had no idea what to do and gave me a 19 pitch rev 4 which I knew wasn’t going to work and didn’t…. I used it for break in and at the end ran it up to about 50mph easily pegging the rev limiter at 6200 rpm. I could not trim at all without porpoising no matter where I ran the Jack plate.

    Next I tried my old back up prop from my Ranger…. A 24p Fury 3 blade with open pvs holes…. With the Jack plate set at about 3” below prop to pad, the boat will get up to about 58mph at 6200rpm and will take a little trim but will still start to porpoise if I give it too much…..Also blows out just a tad during the hole shot at break over but I assume it’s probably due to the open pvs holes.

    3rd prop I tried was a 26p tempest…. Way too much prop…. Would only do about 50mph and would only rev to about 5000rpms at wot.

    I talked to a local shop here in NorCal and they were adamant that these aluminum hulls need a 3 blade for bow lift and top speed but I’m still not sure where to go next? Hard to not want to try a bravo1 xs after the good luck I had with it on my Ranger 521c but I realize we are talking apples/oranges.

    So far I love the boat, great storage….rides nice….fishes nice but I would be lying if I said I wasn’t disappointed with the top speed….. I really was expecting an easy 65mph. Thanks for your suggestions.

  2. Member
    Join Date
    Apr 2020
    Location
    Ontario
    Posts
    588
    #2
    You've got some crazy slip happening based on the numbers you provided. 28% with the fury. So if we do some math and bring the slip down to 12% which is much more realistic you've got a wot of 70mph. Where is the transducer located on the transom? You need to make sure that nothing is disturbing the water flow leading to the prop.

  3. Member
    Join Date
    Jul 2019
    Location
    California
    Posts
    21
    #3
    The transducer is mounted in the center to the hole shot plate on the bottom of the Jack plate…. It’s mounted about flush with the bottom of the step…..it should be out of the water when on pad.