Ever seen a boat on trailer (less transom straps) hit an unexpected speed bump or curb? Boat and trailer go up, trailer comes down, boat comes down a little off center. Driver about shits his pants. I was behind a guy in a big department store parking lot headed toward the gas pumps and watched this take place in front of me with about a 20ft Bayliner when they cut the corner and hopped a curb. Boat jumped over a good 6-8".

That was on a single axle. I'm guessing it may have been a little different with a tandem.