It depends on the length of the water line and how many points of use you have to size the accumulator tank properly. For a medium sail boat with a galley
and one head
and maybe a cockpit shower
one of the small Jabsco
is fine. I use a belt driven single
speed pump. If I open one tap fully it will cycle 7 seconds on and then the same off with even pressure. This reduces the pump operation to half. The pump has a pressure switch built in to shut off at the desired pressure. Without the tank it would need to run constantly.
They do make pumps that are supposed to eliminate the need for a tank but I'm not sure they will handle all types of situations. They don't use a variable speed but use multiple chambers. They really can't do that with variable speed.
Not all pumps systems are as noisy. The larger tank might allow water use at night without activation of the pump. Even the small tank we have can get a glass of water without the pump going on. Our pump can pressurize the tank and deliver water to one tap. With two or more the pumps runs continuously and there is a pressure drop. A 50 ft trawler
with 3 heads and such just can't get by with a small pump. The pressure loss in the pipe eventually gets you.