First, not clear on what you mean by "staff" a
charter vessel. On smaller
boats, more or less under 50' there us usually only one hired hand on a
bareboat charter and that's the
captain. Crewed charters in that size range are usually husband/wife teams.
Boats that aren't owned by a couple will still have a
captain and will be looking for someone with gourmet
cooking skills, ability to do a mirror finish
varnish job and be able to stand watch, handle
sails, do maid
service, etc.
The big fancy yachts with a larger crew will also be looking for someone with skills except for the basic maid/janitor jobs. If you are an ace
diesel mechanic and know AC and DC
electric and can do it up to ABYC code or similar then you can look for an engineering position on a big
boat.
Having
classes and certifications and taking courses can't hurt, but what will get you the job is knowledge and
experience, how you present yourself and what you can contribute. Without that then all the
classes in the world will get you nowhere.
At the same time, I know plenty of guys working in the charter
trade in a number of jobs that have never taken a class, have no certifications, etc. Just
experience and know how. Note that this is fine as long as you aren't taking passengers for hire which does require a captain's
license.
Bottom line, you need to pick up some experience and develop some skills to have a good chance at getting a job on a
boat. Start at the bottom at one of the charter companies. You'll be changing
oil,
cleaning toilets, hauling
parts around. Do this for a while, show up on time and sober and you can work your way into
delivery crew and start moving up. Or you can just look for boats looking for extra crew to help on deliveries and start building sea time.