Re: How to become a boat mechanic?
In today's economy, it's not going to be an easy thing for a recent High School grad to find a job in the industry. While there is a persistent shortage of highly-trained and experienced technicians, the same is not true of young guys with no training and experience, I'm afraid.
Given the current business climate for the boating industry, I believe I'd be seeking education rather than immediate employment as an apprentice of some sort.
If you can find and afford a specialty trade school for that industry, that'd be great. If not, training in the automotive maintenance field will also serve to get you up to speed on wrenching, specifically, and the electronics and diagnostic skills you'll need to learn from the beginning.
In the meantime, you can extend your knowledge and experience by rehabbing cheap or free boats and engines in your free time. Document what you're doing with photographs and keep detailed records of what you're doing, as well.
At some point, you'll have a nice book of work you've done that you can show a prospective employer, like a marine shop or marina, to demonstrate that you are serious about this and actually know something.
There's not going to be a fast track for this, frankly.
As has been recommended by myself and others, consider an enlistment term in one of the military branches. Talk to your local recruiter about technical fields and opportunities in the military.
Study. Learn as much as you can about the thing you want to do. Read service manuals like they are paperback books. Your local library should have, or can get from a larger libraries, service manuals for many things. By reading them, you'll gain a knowledge of terminology, tools, equipment, and more. Most have detailed flow charts dealing with diagnostic issues. Nothing is more important than learning the process of diagnosis of mechanical systems. Being a parts-changer is...well...pretty worthless if you want to become a well-paid professional technician. It is diagnosis that is the rare tool.
Watch what happens in some of the longer threads here on iboats, where problems people are having are diagnosed by experts here. Once the right questions are asked and the answers given, the problem is easy to solve in most cases. That's the key thing. Knowing the questions and the techniques for getting the answers means you can solve the problem.
It's tough being around 18 years old. You're eager to get going with your life. You can speed that up by putting in lots of time learning. I know of no faster way to learn the basics of this kind of thing than military service. Really.