As far as I can see, the only problem with not cross connecting the water tanks would be the resulting complexity of your fresh water system and the need to get access to all the valves every time you want to change tanks.
You will need a line from each tank to the inlet of your fresh water pressure pump, and to each of the foot pumps on your boat. In addition, you would want to put a selector valve on the inlet of each pump – though I suppose you could use the water shutoff valve at the outlet of each tank to shut off the tank and isolate it from the rest of the water system. If you don’t put in some sort of valve to stop flow from the tank you do not intend to use to the pump, your tanks will still be cross connected; water will flow from the tank which is more full to the tank with the lower water level at through the connection just before the pump inlet. My 38 has 2 40 gallon tanks – one under each settee. There is a separate fill and vent for each. There is a shutoff valve in the outlet for each. Then water flows through a ½” hose to a “T” fitting under the cabin sole. The other two ½” hoses go forward and back to the sinks. The hose to the sink in the head forward goes to a foot pump. The line to the galley sink is the supply to the fresh water pressure pump, and also to the foot pump. The cross connection is down in the bilge, so even when heeled with mostly empty tanks the water in the tanks is above the suction line to the pump. If you are using only one tank, that tank is mostly empty, and the boat is heeled to that side, there is at least the possibility that there would not be water flow to the inlet of the water pump. Drawing water from the low side of the boat is not necessarily a bad thing. As far as filling all tanks from a single deck fill, the would be true in theory. But the cross connect through a ½” hose like mine would take a long time. The water into the deck fill through the garden hose would be a heck of a lot more than the gravity fed ½” connection could carry. All that said, there are times when you might want to keep one tank dry. I have 5 heavy batteries and a fair bit of added cabinetwork on the port side of my boat. Hence the boat rests with about a 2 degree list to port. I hit upon the idea of not using the port water tank the last time the tanks ran down, and shut off the valve on the outlet of the tank. That way the weight of the water in the starboard tank will offset some of the weight of the stuff to port, which took care of most of the list, and having only 40 gaallons of water is not much of a problem when not cruising. Rick Brass Washington, NC From: CnC-List [mailto:[email protected]] On Behalf Of Josh Muckley via CnC-List Sent: Tuesday, September 08, 2015 2:55 PM To: C&C List <[email protected]> Cc: Josh Muckley <[email protected]> Subject: Stus-List Water tank x-connect So I'm doing some water tank work and I've confirmed what I already suspected. My tanks are cross vented to one another through a low point loop. It appears that I could in theory fill all my tanks from one deck fill port despite having a fill port for each of my tanks. I'm thinking that tracking tank level is a challenge when they are all sluicing between one another. This doesn't seem advantageous. Why would the manufacturer do this. Is there a problem with me undoing it? Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD
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