"That's going to be a matter of contract law, subject to the terms of your charter contract, subject to the laws of whatever jurisdiction that contract is subject to."
If it were that simple, we lawyers couldn't make a living. ;-)
But I don't see these kind of issues as "legal/contract" questions. This is a customer service issue. If the vanity light in my rental car doesn't work, that's the way it goes. If the engine doesn't start, that is another matter. In neither event, however, do I pull out the contract to see what it says. As I tell clients, if we have to look at the contract after the day it is signed, that is a really bad day.
I am just not sure where the line is on a charter boat. Obviously to me, the cockpit light being out is not a big deal. But where on the charter boat continuum of problems does, as an example, a non-functioning freezer/refrigerator fall, etc.
Are the issues we experienced on the side of "no problem, mon" or on the side of "you done me wrong."