This past summer, down on Lake Isabella, located in the high desert, an hour east of Bakersfield, a fellow new to boating was having a problem.

No matter how hard he tried, he just couldn't get his brand new 22-ft Bayliner to perform.  It wouldn't get on a plane at all, and was very sluggish in almost every manoeuvre, no matter how much power he supplied.
After about an hour of trying to make it go, he putted over to a nearby marina.  Maybe they could tell him what was wrong.

A thorough topside check revealed everything was in perfect working order: the engine ran fine, the outdrive went up and down, the prop was the correct size and pitch.  So, one of the marina guys jumped in the water to check underneath.  He came up choking on water, he was laughing so hard.
Under the boat, still strapped securely in place, was the trailer.