I ran a ZX250 last year, and a 20 iClass now. Both boats are very heavy, particularly with a 250 hp Yammie. Both boats will porpoise at slow speed as a result unless you trim in the engine.

This is something that you should expect and is easily compensated when you get used to dealing with it. I usually anticipate needing to slow down from higher speeds by first starting to trim down with my blinker trim even before letting up on the throttle. Since the Yammie has a large trim range, and is fairly slow in going from one end of the trim range to the other, I start trimming early. You also gain better boat steering control and speed control by trimming down whenever you slow down, and you minimize prop wash upon stopping.

I can drive my boat all day and never porpoise...but everytime my partner drives it we porpoise because he just isn't used to trimming down appropriately with his speed.

When running at around half speed, I use about half trim...at the slowest planing speeds I trim all the way in. The only time I'm trimmed all the way out is when running flat out (actually I'm trimmed out all the way, and then bump the trim back in just a little to get top speed).

It would be unreasonable to expect any high performance bassboat to not porpoise at slower speeds without trimming down first. Once you get the timing down, it becomes simple and smooth.