transom height

Discussion in 'Boat Design' started by dreamchaser, Jun 5, 2007.

  1. dreamchaser
    Joined: Jun 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: vancouver b.c.

    dreamchaser New Member

    Hello everyone, this is my first post on here so i hope i get it right ......well when i bought my boat , a 18.6 terminator with a 70hp tahatsu ob all seemed well until I wanted to go up in power. Since then Ive had a 1981 90hp evirude, a 1983 115 evirude , and now a 1994 120 johnson all 2 strokes. the problem with this boat is the porpoising, I installed smart tabs a year ago , move all weight to the front ie; battery , which now is a 4d and 4 12lb downrigger balls, 20lb anchor 30 ft 1/4 chain for a total of about 160 lbs up at the bow .... long winded but need to let u all know where im at . shortly after buyin this boat I noticed that the transom was cut down to accomadate a 20 inch ob height , where as from the factory is was designed to be a xl leg shaft, my question is would the diff in height and transom angle being less by cuttin it down cause this porpoising ? my antiventilation plate is now set 1 inch above the bottom of the boat, and I have one more hole to go for the highest settin on the transom . Do u think the geometry is messed up with the cut transom ? thks for ur patience ....Leo
  2. spank
    Joined: Feb 2004
    Posts: 51
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Boston

    spank Junior Member

    It's hard to say, but I doubt that the cutout is the culprit for the porpoising you are seeing. Did moving some weight forward have any effect at all? I would try some real trim tabs instead of the smart tabs if they weren't of any help. I have specified smart tabs, and my general impression is that they are not nearly as useful or effective as truly adjustable tabs, and they are flimsy, so therefr prone to early failure.
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