Hull number
 

Anyone know where to find the hull number on a Yamaha Jetski?

Don't know. Good question.
But if it was sold as a unit or one boat then the best guess is that the one boat has one serial number.
But let others chime in.

I'm fairly certain that by law it has to be starboard of center and facing aft (unless the stern is pointed like a canoe) on the rear of the boat, and no more than 2 inches below the gunwale. It also has to be somewhere else on the boat in a less obvious place.

I'll check mine when I get home.

Just found this:
Its on the outside of the ski at the left rear of the hull on the side below the bumper.
reply:
Its on the right rear corner of the ski, take a knee and look up behind the sponson on the right side

Check the back right side of the rear deck. If you were sitting on the back of the seat look down and over to the right rear.

http://www.yamaha-motor.com/assets/s..._Shos_1527.pdf

Going crazy
 

Last year I was searching for the vin on my used seadoo. I searched online, called dasilva, and stared at my seadoo forever with no luck until I stumbled upon it. . As you face forward there was an inconspicuous black rubber patch with a faint etching of the vin in it on the edge of the right rear flat platform. I took wax paper and a crayon and rubbed it to etch the number. Registering it MA didn't matter. They could've cared less.
It was a Dummy Crane moment.
DC

Catamarans (Hobie or other brands) have one hull number per boat. It is located on the starboard hull transom.