My NC33 has 330Ah open lead acid batteries that exibit their typical high auto-discharge current.
My concern was only to cope with this discharge current while not leaving the boat connected to the pier power supply.
A mere 30W solar pannel connected through a very basic solar regulator (no MPPT here) is more than enough to do the job. My batteries appear fully charged whenever I visit her evey 6 weeks in winter.
This is not a charging solution, 30W is not enough at all for thet, but the effective 1A charging current during winter time (low sun or cloudy) is the same order of magnitude as the auto-discharge rate.