Easy way to stop porpoising

[Keller1490]

I have read many threads, and have tried many things to stop this, but to no avail. I finally spaced my trim plate down 9/16 of an inch and I haven't smiled this much since I bought my boat. Reaches 60 mph way faster than ever before.....plains out way faster......and I can now ride through the roughest wake without a problem. I did run into a small problem when I was spacing the plate down. The left side bolt snapped off into the cast on the lower unit. I just took a 5/16 drill bit drilled a new hole and done. If you don't have a problem this entire project takes about 2 minutes and is so simple. I will definately post pictures this week. Ohh and this project will cost you less than $5.

 

[buckeye_paul]

I have the same problem but 9/16" seems like a lot to me. Did your fuel consumption go up? I have trim tabs on a different type of boat and they eat up fuel. I'm going to start out with 3/8" and see what happens.

 

[Keller1490]

Fuel consumption did go up only because the boat will run 60 all day long without a problem. After having trouble hitting 50 I now have a throttle problem because I don't want to back it down. Haha....with my transom I couldn't put tabs on because it goes to the bottom of the hull. I would start at 3/8 but it is so easy to change at the ramp it shouldn't be an issue. It literally will take 3 mins to add or remove any additional washers. Have fun

 

[buckeye_paul]

Trim Plate

Your boat does 60? That's awesome! I can't get past 40 without bouncing everyone out of their seats. I was told top speed was 50 for my boat which has the Mercury 210 Sport Jet. Anyway I moved the plate down about 3/8". I'm afraid to go any lower because it looks like the plate which the front two bolts of the trim plate go through, is bending. The last thing I want to do is crack that plate. I tried bending the trim plate a little but it is really stiff. I'll see how it rides this weekend. Thanks for the info.

 

[Keller1490]

I have easy access to a machine shop, and when I noticed the bend I put it in a brake and bent the plate another 10 degrees maybe. That plate is stronger than you think, but to fabricate one it shouldn't be too terrible bad.

 

[Keller1490]

When I bought my boat it had a blown engine.....the mercury 240. With a cam upgrade better pistons, bored cylinders, and better top end it will do 60.

 

[buckeye_paul]

update

Had it out all day today. I got us up to 50 several times without bouncing, and was able to jump waves very nice. I still had to fight the bouncing on occasion, and the boat pulls to the left now. Maybe the plate is not quite level. I think I can use a brake at work to bend the trim plate a little. I'll try that and that should allow me to lower it more.

 

[Keller1490]

If it pulls left trimmed too much on the right side....add another washer like a an washer (really thin washer) then try it again

 

[buckeye_paul]

Washers?

You say add a washer to move the trim plate down? On my boat there are 2 stainless steel washers on each side of the trim plate. These washers are there to space the recess that is in the plate for the flat faced counter sunk machine screws. There is a jamb nut for each screw. In my case the adjustment is made by backing the machine screw out of the casting then locking the jamb nut down on the washers which keeps the screw from turning. I was able to slightly bend my trim plate in a brake. This should solve my problems. Thanks for your help.

 

[stripes136]

So if my boat is pulling left, do I lower the Trim Plate on the right side by backing out the screw and tightening the jam nut?