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  1. #1
    Join Date
    Nov 2010
    Location
    South Padre Island, Texas
    Posts
    3

    trimax surface drives

    Need help!!!! I got a 2002 sunseeker superhawk 50 with triple Yanmar 420 with trimax surface drives. I am having trouble with propulsion. I can only get the boat to do 8.5 knots with All three motors in gear. It has the original props which are in perfect condition and transmissions are full oil oil. They are zf 110 gts. At about 2500 rpm i shift into second gear and the boat slows down to about seven knots. Any help will be greatly appreciated.

  2. #2
    Join Date
    Jun 2010
    Location
    Rotorua New Zealand
    Posts
    921
    Nice boat, great engines. First off how long have you had the boat? Ok, based on the information above first I would have the engines serviced, all filters (including fuel) and oils etc and have the engines checked by a mechanic. You need to know that the engines are making the power they are supposed to. Is the fuel reasonably fresh? Check fuel filters for signs of diesel bug. It sounds very much like an engine problem to me and I would suspect diesel bug.

    Check that you have not recently added weight to the boat and also check hull is not too dirty.

    Get back to me with the results.

  3. #3
    Join Date
    Nov 2010
    Location
    South Padre Island, Texas
    Posts
    3
    I bought the boat in florida really cheap cause it sank in its slip. I had all three motors one hundred percent rebuilt. All the filters and fluids have about ten hours at the most. Also the fuel tank was removed and cleaned and it has new fresh diesel. The bottom also has fresh bottom paint as well as the shafts and props. The turbos are also brand new.

  4. #4
    Join Date
    Jun 2010
    Location
    Rotorua New Zealand
    Posts
    921
    Quote Originally Posted by captainerik View Post
    I bought the boat in florida really cheap cause it sank in its slip. I had all three motors one hundred percent rebuilt. All the filters and fluids have about ten hours at the most. Also the fuel tank was removed and cleaned and it has new fresh diesel. The bottom also has fresh bottom paint as well as the shafts and props. The turbos are also brand new.
    Ok, that eliminates some issues. Since this work has been done I would still crack one fuel filter just to confirm there is no diesel bug. Were the engines run up on the dyno? You need to know that they are developing full power. What is the construction of the hull. When it sank a timber hull can absorb a lot of water. When the boat was in the slings on the travel lift did you note the weight of the boat?

    When you are trying to get it up and going are there huge clouds of black smoke?

    With surface drives they are designed to run "on the surface", with only one blade at a time driving the boat forward. Unfortunately when the boat is running at displacement speed it puts the engines in an overloaded situation because all blades are running in the water (way too much prop pitch). Consequently they can be slow to climb onto the plane. To help overcome this usually you will find that the exhaust gas is bled onto the prop to generate some cavitation and so allow the engine to generate more revs, and so more torque and this helps get the boat up and planing.

    When all else fails one thing I have seen done is to get a faster boat, fasten a tow line between the two and then use the other boat to help your boat gain planing speed. Then you can go to full throttle and full speed to see if the engines can achieve maximum rated loaded rpm.

    Have you spoken with the last owner and talked with him about what performance he used to get.

  5. #5
    Join Date
    Jul 2008
    Location
    severn bridge
    Posts
    1,269
    what happens to engine rpm when you shift!

  6. #6
    Join Date
    Nov 2010
    Location
    South Padre Island, Texas
    Posts
    3
    when i shift the engines rpm slow down about 500rpm and boat slows down.

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