If my reasonable estimate of battery power is 30 ampere hours, I don't have much of a power cushion there to rely upon in a pinch. I could be thinking that's no problem because I've got an engine alternator that is always feeding it more power. That's a mistaken assumption when the engine quits. Boat builders usually provide the minimum amount of battery power necessary with no safety margin. My own view is that a 60 AH battery is way too small for even a small boat.
Battery power is directly related to plate size.
That's why we can't escape from battery size, which is a problem in small boats. You want lots of battery power, but there ain't no place to put larger ones. Somehow, someway, you need larger batteries when you propose to go offshore. If I've got two 7.5 amp bilge pumps, that's 15 amps per hour, which can bring down a battery in a hurry. Therefore, what I'd like to have is a pair of 90 AH batteries which I figure at half the rating or 45 AH each.