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Pontoon/ Tritoon what is the correct shaft length question?

larrywittlarrywitt Posts: 2,747 Moderator
My neighbor bought a new Tritoon powered by a new 150 HP Mercury a nice looking rig. He brought it down from Canada. When he started to use it,  in the 25 mph range it would start to over heat and the alarm would go off. So the motor was lowered and that  took care of the heat alarm. OK thought the problem was over. Nope now when adding more throttle to go faster he can hear the motor revving up but no speed in cease. He said it sounds like the motor is cavitating  so he puts on a new prop 4 blade prop same problem.  My observation is middle pontoon is creating   an air pocket causing the problem.  My thoughts are the motor should have the longer shaft to get a deeper bite in the water. I am not sure how much experience his dealer had powering  Tritoons.
 Looking for input on powering Tritoons .
larrywitt

Replies

  • kmagnusskmagnuss Posts: 3,223 Captain
    edited January 2019 #2
    Maybe try a different prop again.  I have no experience with pontoons really, so your description of the middle pontoon causing too much turbulence could be right... but I'd try a prop that's specifically designed for a half in the water bite.  I saw he tried the 4 blade but sometimes that's counter-productive depending on the make/model.
    Tarpon... everything else is just bait.
    Captain Keith Magnussen - Crooked Rod Charters
  • larrywittlarrywitt Posts: 2,747 Moderator
    OK an update. I went to look at the Tri Toon as it set on the trailer and talk to Pat the owner. He tells me that he ran the boat all summer on the lake in Canada  cold fresh water and this never did this happen at any speed. So now i start to examine the pontoons. I notice two distinct water lines  4 to 6 inches apart. Then a light bulb goes off in my head,got it. 
    Salt water versus fresh water. Salt water is much more buoyant than  fresh water  to the tune of 4 to 5 inches. My solution would be a manual jack plate with a 6 inch adjustment. And make the adjustment for each location.
     You  thoughts on what I think would work.
    Thanks 
    larrywitt 
  • Alex from GAAlex from GA Posts: 1,424 Officer
    That's a lot of difference.  Water pressure guage will tell.  I know I got more speed at the Salton Sea than freshwater lakes.  Try the backplate it's only $300 and it's not your money.
  • MelbourneMarkMelbourneMark Posts: 2,130 Captain
    Manual jack sounds like plan to me.  Also, he should be able to bring socket set to ramp to adjust.  

    I wonder how/if the offset motor will effect weight distribution of boat.  And also, make sure hyd cables/fitting clear when lowered? 
  • larrywittlarrywitt Posts: 2,747 Moderator
    Thanks  for all the input, it helps. I will be talking to him today.  He had the boat out yesterday.
    larrywitt

  • larrywittlarrywitt Posts: 2,747 Moderator
    Update as to the problem. It is a design flaw with the new 2018  Mercury 150 HP motor. There is a service update as to what causes the cavitation. There is a exhaust flow re-stricter that fits between the fits between the prop hub and the and the motor housing and locks in place and keeps exhaust from going over the prop blades.  Pat said the dealer  had them, you would think they would be free, no he had to pay for them. He bought two. I will keep you posted as to how well they work.
    larrywitt
  • tilemantileman Posts: 1,123 Officer
     The boat has a short shaft,  I do believe that boat needs to have a long shaft  because of the center tune its configuration on that boat. Someone needs to be in the back of that boat To observe where the cavitation plate is at running speed, that would be my first thought then take it from there 
    Here's ta swimn' with bowllegged women!
  • tilemantileman Posts: 1,123 Officer
    Best thing is to get in touch with the boat manufacture and see what their view is on shaft size, then IF it calls for a short  shaft start researching the fix. JMO
    Here's ta swimn' with bowllegged women!
  • K-DawgK-Dawg Posts: 221 Deckhand
    Yep, first step is to check the motor mounting height at speed rather than moving it around willy-nilly.

    Has your friend tried adjusting the trim?


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