Porpoising issue with medium sized planing hull

[satsuma]

i'm trying to make a medium sized boat with a diesel engine mounted just behind center of mass, but the further up the gears i travel the worse the boat porpoises. the bow of the boat lifts far into the air and the stern sinks almost below the waterline. what can i change to prevent porpoising? pics on my profile. thanks

[Supahfly_uk]

have ur props higher the lower they the more ur bow will lift

[XLjedi]

I have a small boat with rear mounted engines and a planing hull. It's in the workshop if you'd like to look at it. Smaller than yours and not the same hull design, but in my case, with my hull...

There is a speed that is almost like a do-not-exceed speed where the boat gets too far out of the water and starts to actually fly without going completely airborne. In my case the speed was right around 50 knots. So I had to limit my engines to a 3 on 3 setup (engine/prop). I had a great 4 on 3 engine setup that would push the thing to like 70 knots, but I lost all control at those speeds. So it happily plays now in the 38-42 range which is perfectly fine for a career starter boat.

I didn't have issues with porpoising but I did install hydroplane stabilizers on the hull (just like the real boat would have) and I can't say with any certainty it would help your situation, but it would definitely lift the tail and push the nose down at speed.

Also... on my boat, notice the shape of the hull in the bow section. It sweeps back with a lower angle, so that part of the hull has less (or no) interaction with the surface of the water at speed. I notice you have your pilot house on the bow, so maybe you have too much weight forward? The sweeping bow section in combination with a raised forward deck "tilts" the bow downward. You might even see the bow slightly lower than stern when not moving. Maybe something along the lines of a WWII PT boat hull/deck?

Nice looking boat so far, don't give up on it... and good luck!