I posted this earlier, but no replies...Am I doing something wrong?

I just got a New Tracker Grizzly 1860. I have a 60 HP Mercury on it and
I'm having a problem getting it to plane off. It wants to flop up and
come down hard on the water. The dealer says the motor isn't getting
"under" the boat enough, which I don't doubt. My question is, What is
the best way to solve this problem? The dealer says it's a problem
inherant in flat bottom boats and hard to fix. Any help or Information
would be appreciated!