That's an excellent idea. If you are happy with the flow rate, the expansion tank is a better solution and is easily maintained. We have an expansion tank in our gas furnace/hot water radiator house heating system. Occasionally we get "water hammer" and we simply go to the highest rad in the house and bleed off trapped air which is giving the system a fit of the wobblies.
Here's a brief explanation of the principles. The tank needed for a boat's plumbing could be quite compact.