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Thread: Prop Slippage

  1. #1
    Join Date
    Oct 2011
    Location
    Rocky Mountains
    Posts
    286

    Default Prop Slippage

    Hello everyone, I have a new to me boat that I am a little disappointed in the performance. It is a 1998 Lund Tyee 1950 with a 2014 Mercury 200 HP Optimax Pro XS with a 1.75 gear ratio lower unit. I am running at 6500 to 8000 feet altitude depending on which lake I go to. The problem is I am getting a lot of prop slippage. About 20% and not the top end speed I would expect. I am currently running a Mirage Plus 19 Pitch prop. The RPM's are getting up to 5150 and my top speed is 42 mph if I trim it out. The engine was mounted on the lowest hole, so I raised two holes to start to see if it would do any better. I also just removed all my water logged foam and replaced it this winter so the boat is lighter too. I actually think I lost 1 mph after all this and the prop blows out at full trim now. I expect this boat should do closer to 50-55 mph on the water, but it just doesn't get it done. I have plenty of power to quickly plane the boat, but the last inch and a half of throttle doesn't change anything but the fuel comsumption. I am wondering if I should switch to a 4 blade prop with an 18 Pitch? I have used the online prop calculators, but I just don't know which direction to start with so many options out there. I have heard there are many experts out there to help get you in the ball park of where you should be. I would really like a little more top end speed for traveling down the 60 miles lake I fish on and so I can beat my brother in his boat. LOL. Thanks for any help you can provide.

  2. #2
    Join Date
    Apr 2016
    Location
    barnegat NJ
    Posts
    2,706

    Default Re: Prop Slippage

    thebubba, the cavitation plate on your engine should be level with the bottom of the keel of your hull or darn close for optimum performance, What is the WOT of your engine, top RPM. Each inch of pitch lower will give you roughly 200 RPM increase theoretically

  3. #3
    Join Date
    Oct 2011
    Location
    Rocky Mountains
    Posts
    286

    Default Re: Prop Slippage

    Quote Originally Posted by johnnygjr View Post
    thebubba, the cavitation plate on your engine should be level with the bottom of the keel of your hull or darn close for optimum performance, What is the WOT of your engine, top RPM. Each inch of pitch lower will give you roughly 200 RPM increase theoretically
    The WOT range is 5000-5750 rpm for this motor. The cavitation plate is about 1" above the hull.

  4. #4
    Join Date
    Apr 2016
    Location
    barnegat NJ
    Posts
    2,706

    Default Re: Prop Slippage

    Is the bottom clean? Maybe have the boat+trailer weighed ? she's a 19ft. Lund?

  5. #5
    Join Date
    Oct 2011
    Location
    Rocky Mountains
    Posts
    286

    Default Re: Prop Slippage

    Yes, the bottom is very clean and shiny. They require us to keep them that way to prevent muscles here in Utah. It is a 19.5' Lund. I will see if I can find some place to weight the boat and trailer. I am estimating around 3500 pounds. It is a single axle trailer and it seems to handle it ok.

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