I would politley write to the marina highlighting the areas that could benefit from some improvement and ask for specific replies to your comments, all nice and friendly of course.
After that, if you don't feel you have been treated professionally there are a number of avenues you can follow. If there are serious safety issues we all have a duty of care to highlight them for yourself and others who use the facility.
As said earlier, the marina operators also have a duty of care to its users.
I woulnt feel too bad about exposing them if that duty is neglected.
Having said that, if they do make substantial improvements, expect the fees to go up.