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Trimming the motor

psfrizzpsfrizz Member Posts: 11
Being new to boating Im struggling with trimming the motor at certain water depths, We boat in the Indian River in Florida which has a  lot of shallow water, Is there a protocol or way to know when to trim all the way down or half way even at idle speeds or shallow water, I understand that in shallow water to trim up but was wondering if anyone had suggestions.


  • nquirknquirk Member, Moderator Posts: 674 ✭✭✭✭

    @psfrizz, when you're idling, your boat is not on plane.  Trimming up won't provide any value other than to raise the lower unit of the boat out of the water to give you a more shallow draft.  So if you're passing through shallow waters at idle speeds, bring your trim up to minimize your overall draft.  (The boat will sit probably 12-14" depending on your model) plus the motor depth.

    When underway and on plane and cruising, trimming up will provide you better speed at lower RPMs as trimming the motor will align the prop directly behind the boat pushing forward instead of upwards.

    Knowing its location, you can get someone to assist you.  All the way down is your starting point.   Have someone looking over the back of the boat while you're cruising,  Now trim it up until they can see the cavitation plate even with the surface of the water.  Stop there and note where on your trim gauge you are.  This is trimmed to the highest up position while boating. 

    You can then adjust within that range as appropriate.  When you're testing this, note the changes in RPM and speed as you are on plane, at different speeds and how trim impacts the smoothness of the ride.  You'll note that your speed may increase 1-3 MPH while RPMs stay the same.   Or you can simply trim up and maintain same speed, but lower RPMs.

    Your ultimate goal is to achieve the speed you require, with the least amount of RPMs and in your case with shallow waters, trimming up to minimize the draft of your boat.

    2010 Hurricane SS 188 OB
    2010 Mercury Optimax 200HP / Mercury SS High Five 19P
    2010 Trailmaster SC trailer
  • BroadwayBroadway Member Posts: 33 ✭✭
    New boater here with my newbie observation from my first outing yesterday.  I start with the trim all the way down.  Once I am on plane, I trim up a little listening to the motor "effort".  Once I hear the motor working less and sounding more smooth, I think it is positioned well.  Can any one verify this?  Also, once I am am going fast or at full throttle I drop the trim a little to listen for the "bog" down motor sound again and then go back up till it sounds smooth.  This coincidentally is right around the little line in between the "up" and "down" trim lines





    2013 FD 226

    Yamaha 150 Four Stroke

    Venture Trailer

    2nd RGR BN.

  • nquirknquirk Member, Moderator Posts: 674 ✭✭✭✭

    @Broadway, when you trim your outboard (do it with the engine off at dock) you'll hear two very distinct noises.  The first is its trim position for in water use.  This is from all the way down to its 'somewhere in the middle' range where you seem to find the boat running smooth underway.

    The second sound is when the trim pump now allows the engine to tilt.  This is where you'd position the engine when you taking it out of the water, etc.  This will go all the way to the top.  This is not a position you'd use while boating.

    What I've suggested earlier with getting someone to assist is the way to most accurately determine the location of ideal trim underway.  The 'bogging' down noise you refer to is most likely the load on the engine.  When you first acceleration the prop is positioned to push the boat up onto plane but once its on plane, the prop is now still positioned pushing upwards.   Trimming allows it to push straight forward in alignment with the boat.

    I suspect the change in sound is simply the sound of the load on the engine changing slightly.  As an owner of a big noisy 2 stroke, I don't hear those subtle sounds under the roar :O


    2010 Hurricane SS 188 OB
    2010 Mercury Optimax 200HP / Mercury SS High Five 19P
    2010 Trailmaster SC trailer
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