First off, you'll need a work permit; without that, all discussions are moot.
Generally, the more time on floats, the better off you'll be in finding a job. If you're lucky, have a decent attitude/work ethic and personality, you'll get a seat in your first summer. If not, you'll probably end up working the dock, having all of the above assessed, and be in line for a seat in the fall for next summer...
Good Luck!