Need advice on engine height.

[kalium]

Hello,
New to the forums! This Spring I have been renovating my old 1980 Crest 20' pontoon and I am stuck on one last aspect of getting everything right for optimal performance - the height of the engine.

This boat has a long history, my father purchased the boat back in the 80's and I can remember quickly coasting along the water as a kid when everything was in shape and properly maintained. Up until recently, the boats performance has been lackluster to say the least, especially compared to when I was a kid.

I've successfully repaired all engine components (1980 70 HP Evinrude) last year and the motor runs great, but the top speed is not even close to what I remember and I believe its due to the engine height. A repair was done to the transom a couple years back without (possibly) any consideration to the engine height. While the engine is sitting at the correct angle, the bottom of the cavitation plate sits a good 6-7 inches below the bottom of the transom and skims along the water while loaded. The transom is easily adjustable (outside of the water) and I would like to get any recommendations before launching the boat for the summer.

Here are two pictures: one of the transom - cavitation distance with red lines added for clarity, and one of the adjustable transom.

Any and all comments are greatly appreciated! Thanks in advance.

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[ahicks]

Off topic for sure, but I would be cautious of that adjustable transom. Mfgr's had smaller engines in mind when those were being built/used. Like in the 25-40 (maybe a 50) range. Suggest you replace it, or at the very least go over it and the fastening points where it's fastened to the cross members very closely. That transom is looking pretty shaky too.

That being that, clearly your engine is down way too far. For a starting point, I would set it up so the cavitation plate is about 2" above a line drawn across the bottom of the tubes. Where it's going to run best is going to depend on how deep those 'toons run at speed and a bunch of other variables, but that should give you a solid place to start.