I've just done a degree in boat building, BSc Yacht Manufacturing and Surveying at southampton and really wish i had done an apprenticeship now, thankfully got lots of experience as marine engineer at a mercury dealer.
Honda do an apprenticeship scheme but most outboard engineers will take you on and train you up with manufacturer courses.
boat repairs is bit of a different field, again most places will take you on and train you but no real qualifications unless you go nvqs. several options for apprentships, either requiring sponsorship or provide placing:
Marine Skills Centre, Poole
This is just the little knowledge i have gaineed when i looked into doing one but found the degree put me over the entrance level, most important thing i will say is make as many friends and contacts as you can, no matter how small.
Good luck mate and let us know how you get on.