228 Engine Height

[catchersrock]

So, I have a 2020 228 with a Mercury 250, no jack plate. On initial delivery, the boat porpoised badly. I did a video and the engine was mounted too low. I have raised it two bolt holes and got rid of most of the porpoising. Still have some at the top end and fully loaded with all bait tanks and livewell full of water. I can get it out with trim tabs.

Question is this, any of you guys have this set up with a jack plate? Can you get all the porpoising out of the boat by raising the motor? Do you leave it there? If so, what height works? Can you measure something I can compare by, Cav plate to bottom of boat maybe?

Ever so thankful!

[freezerfiller]

Best way to do it is look at the cav plate when running. If it's submerged, take it up another hole. My boat is set up correct, and sometimes if I trim out the engine for best economy it will porpoise. I can either reduce the engine trim until it stops, or give it a little tab.

[Juan]

Apr 7, 2020 15:29:02 GMT -6 freezerfiller said:

My boat is set up correct, and sometimes if I trim out the engine for best economy it will porpoise. I can either reduce the engine trim until it stops, or give it a little tab.

Mine runs exactly like that. I'm a little confused about catcher's set up. I know if I trim mine down or use the tabs, the bow lowers and so there's no porpoising so how does raising the engine help stop porpoising? I would think it would do just the opposite.

[catchersrock]

Apr 7, 2020 17:26:20 GMT -6 Juan said:

Apr 7, 2020 15:29:02 GMT -6 freezerfiller said:

My boat is set up correct, and sometimes if I trim out the engine for best economy it will porpoise. I can either reduce the engine trim until it stops, or give it a little tab.

Mine runs exactly like that. I'm a little confused about catcher's set up. I know if I trim mine down or use the tabs, the bow lowers and so there's no porpoising so how does raising the engine help stop porpoising? I would think it would do just the opposite.

The transom on these new boats has a pretty good negative angle. At full trim down, the prop shaft and cav plate is actually pointing up. As you trim up, the cav plate rolls over and if low enough, will grab water and start the porpoising. I have to trim to around 4 or 5 % on my gauge to get to a perpendicular motor. 

[freezerfiller]

I think once you get enough angle from motor to bow, it no longer keeps the bow up, but puts it so high in the air that it has to come back down once there is no water to support it's weight. raising the engine reduces the angle of upward force, but I'm guessing at this point and have no expertise in hydrodynamics.