on a sailboat it doesn't really matter if there is a rubber divider between the water and the air or not. I built my tank with PVC pipe and it worked for the 8 years I had the boat and who know for how long after. It stopped the water hammer and gave me at least 5 to 10 seconds of water out of the tap prior to the pump turning on. That was good enough for me. I had a 1/4 inch valve tapped into the top and every few years I would pull one of the hoses off the "T" at the bottom, open the valve and refill the tank with air. It was, I believe, about a foot long and made from 6 inch schedule 40 white PVC pipe held to the bulkhead with a big SS hose clamp. How sophisticated does a 27 foot sailboat need to be. Let's see, a stainless steel, O ring gasketed, slipper sealed piston operated, 300 dollar accumulator seems a little over kill for a 27 foot sail boat but you can go there if you want. But, hey, that's just me. I'm a simple guy.