From my experience as a boat mechanic:
Boats are not cars! Cars are so standardized and there are so many that the repairs and repair time can be estimated accurately.
Each boat manufacturer does things differently. The fuel system, electrical system, control cables, steering, instruments, etc. can all be installed in many different ways. In some boats the systems are installed prior to the decks being put on. In that case, it can be very difficult and time consuming to make repairs.
I have had people bring in boats that haven't been run in months, batteries weren't charged, no gas in the tanks, so much personal gear in the boat that I couldn't get to the controls, batteries, etc. to service the systems, no key in the ignition, and so on. The customer hasn't made an appointment and tells me that he is leaving on vacation in a week!
Boats also take more time to service because trailers are not self propelled. In service shops, boats are usually moved by forklift and it takes two people to move the boat, one to drive the lift and one to operate the hitch, block the tires, guide the operator who cannot see behind the boat and so on.
Boat shops are busiest in the spring and summer. If you want major service done, the fall and winter are the best times.
Boat shops are usually smaller operations, run by those friendly people mentioned above. If the shop owner wanted a large highly profitable shop, he would be in the car repair business.
The best advise I can offer is to be a good customer. Make sure that your boat will start, that the batteries are charged, has gas in the tank, key in ignition, make an appointment, AND KEEP IT.
When you find a good shop, buy stuff from them so they can stay in business! Schedule major service during the off season.
Remember, you are going out on the water in your boat. If it doesn't run right or breaks down, you can not only loose your vacation time, but that can PUT LIVES AT RISK!
The marine mechanic thinks about that too. Give him time to do the job right.
One more thing, if you do some work on your own boat and then take it to the shop because your work didn't fix the problem, Please tell the mechanic what you did!! I have wasted many hours because the embarrassed owner didn't tell me that he worked on the boat first.
Good boatin' to yah!