It's very rare I disagree with you on technical topics Tony, but this is going to be one of them.
If the boat is not hooked up to a reliable shoreline and left on charge, there is no valid reason at all not to have a solar array and controller fitted. Batteries left for months on end are prime candidates for at least a modest solar system, keeping them fully charged even through winter.
I agree that many battery distributors only charge stock once a month, but that's the trade-off between too much faffing and acceptable battery condition. It's also why I always check rested voltages on delivery!