Transom height

Discussion in 'Boat Yard Basics' started by flaco, May 14, 2009.

  1. flaco

    flaco Well-Known Member

    So, I'm basically rebuilding a boat that wasn't designed to have a motor (project post and pics coming soon hopefully...), and I will be rebuilding the transom to support a small outboard (can't handle much over 5 or 6 hp probably, but I will be testing it with a few motors).

    My question is this: I will need to raise the existing transom and I'm not sure how to determine how high I need to build it. I was considering putting a Bob's micro jack on it to allow me to use a longshaft motor. This way, the tiller will be a little higher, and more comfortable to drive.

    Do I just measure up 15" from the very bottom of the hull to the top of my new transom?
    Is there a standard measurement, or does it completely depend on how the boat sits in the water?
    Thanks dudes
  2. Brett

    Brett > PRO STAFF <

    Transom height is determined by outboard shaft height.
    Normally a transom is either 15 inches or 20 inches tall, measured square to the underside of the keel.
    Not along the skew angle of the transom!


  3. flaco

    flaco Well-Known Member

    Thanks a lot
  4. Bob

    Bob Well-Known Member

    Do you already have the outboard you're going to mount on the modified transom?

    If you want the cavitation plate dead even with the hull bottom, 15" &/or 20" isn't always the measurement that will get you there.  In fact, it might be off by over 1-1/2".

    Ex:  A Yamaha 2-stroke model 25N short shaft is 16-1/2" from the mounting bracket to the cavitation plate.  The long shaft version is 21-1/2".
  5. The_Skiff_Shop

    The_Skiff_Shop Well-Known Member


    I agree. I'm changing the transom on a project boat to accept a 20" motor.  The height of the transom from the bottom of the boat to the top of transom will be 22-1/2".  If I had left it at 15", I would have raised it 2-1/2" for a total of 17-1/2".
  6. flaco

    flaco Well-Known Member

    Dern, I understood after the first reply, now I'm confused again.

    You're saying I build the transom based on what motor I get?
  7. Brett

    Brett > PRO STAFF <

    If you just want to go fishing, 15 or 20 inches will do the job.
    If you want the absolute best performance,
    you adjust your transom height to fit the motor exactly.
    That's why so many jackplates are sold.
    Folks attempting to obtain every bit of speed out of their boats.