Water Tank Valves - Isolate or Combine Tanks

[_AJ_]

My question is concerning the 3 water tanks onboard and the pro and cons of isolating them till needed.

How are folks typically operating theirs? Are they leaving each tank isolated until the online tank is empty or do folks leave their tanks open to provide equal consumption via the balance line?

I've heard of both but am trying to understand the correct way.
Our boat has 2 -100 gallon port/starboard tanks and 1 auxiliary 65 gallon tank in the aft starboard quarter.

The capacity is more than plenty for most of our short weekend trips. My concern of leaving a tank empty is corrosion and balance. My concern of leaving it full but not using it is bacterial growth or staleness of the water in the unused tank.

I'm currently flushing and sanitizing the entire water system before refilling it. What do you folks suggest for normal valve positions?

 

[jimdavi]

We have two, ( stbd/port) and they are combined. I like that they automatically balance so the boat does not want to lean with an unbalanced quantities between tanks.

 

[MYTraveler]

My boat has two FW tanks, both on the centerline. One is 200 gallons and gravity feeds the other, a 100 gallon tank, from which all pumps draw. When I have a need to conserve water, I keep the valve between them closed. It is also closed when adding chlorinated water to RO water, in order to allow the water makers to flush with chlorine free water. (The flush has a charcoal filter, which is supposed to take out chlorine but I don't really know when to change that filter, so I keep it has unexposed to chlorine as possible.) The tanks are fiberglass, so I don't have your corrosion concerns.

 

[SteveK]

With a third tank I would shut it off to have the reserve should the other two get empty. Like others have a 90 gal on each side and it helps to stay balanced.

 

[rgano]

When I had more than one water tank, I left them connected because I wanted the water refreshed in them equally. If you are worried about having too much water to keep it fresh, just carry less, still with all tanks connected. If you are going to be well off into the hinterlands or at sea in such a manner that your trip or persons would be in jeopardy if a leak were to empty you water supply, go ahead and isolate at least one tank.

 

[BDofMSP]

We have two, ( stbd/port) and they are combined. I like that they automatically balance so the boat does not want to lean with an unbalanced quantities between tanks.

Same. We have 100 on each side, but we move it through regularly as we're on the boat about 5 days a week and we do not use a dockside pressure connection (just fill the tanks). Our head is supplied off it too, and we don't hesitate to take a long shower or two.

If we were going to be away for awhile, I would just add a bit of aquabon and not top it off.

 

[hmason]

I have 3 X 100 gallon tanks on center line. I have found that if I leave them all opened I will eventually draw air from one of the tanks and the pump will shut down although the remaining two tanks will have water left in them. My boat has a slight bow up attitude so although the tanks have balance lines there is no way they will remain equal. I isolate the tanks and rotate through them as the water is used. Since we live aboard we use a lot of water which keeps all the tanks fresh.


To make changing tanks easy I replaced the original valves with 1/4 turn valves. I can change the tanks from inside the cabin and do not have to go into the ER or lazarette.

 

[caltexflanc]

One of the absolute best upgrades I made to our boat was installing an accurate water usage meter after the pumps. We could measure how much water was used by various activities (shower lengths, laundry and dishwasher settings, etc), plus knew exactly what was left in the tank. While we did not have separable tanks, it would be really useful for those who do. Once we had this, getting a water maker went way down in priority rank on The List.

Here is just one example of an all-in one; ours was made from industrial parts. I'm going to get one as a present for our friends' new to them boat.

https://www.flows.com/digital-water-meter-totalizer-only/

I should note that if your line out of your pumps is not easily accessed for reading the meter, you can buy a meter that has a pulse out put and remotely mount a resettable digital meter designed to read the pulse count into gallons. All in all a wonderful accessory.

 

[Slowmo]

I've done it both ways. Our old boat was easy to switch and a single engine so we'd run fuel and water off opposite sides to help balance. Our current boat has twins so draws both fuel tanks, thus we also keep both water tanks open. Also it's a PIA to switch them on this boat. I do separate them when I winterize to make sure I've emptied both sides completely.

 

[Frosty]

I've never had a Pacific Trawler specifically but since you are getting input from all boat types.... In general I'd say there is no one "right way." Just depends.

Last big boat had two water tanks on centerline. No gauges. We needed to keep track of our supply as we were offshore. So what we would do is run off one tank until almost empty (a certain gurgling would indicate this). Then we would let the tanks equalize and then immediately isolate them again. Now we had two tanks again each with the same amount of water (but half as much total as when they were full).

Again we'd run one tank until basically empty, then let the two equalize, then isolate one again. Now we again had two tanks with equal amounts of water, but 1/4 as much as when all full). Etc. etc.

That kept water running through, always gave us a reserve, and let us keep tabs on how much we had. We had no balancing worries as tanks were on centerline in both directions.

You probably have no reason to duplicate this exactly, but it is another way.

 

[jungpeter]

Hi AJ,

If your boat is equipped like my 2000-vintage Pacific Trawler 40, the 65 gal water tank in the hull extension is piped exclusively to the head. This obviates the need for solenoid valves and/or backflow preventers if you choose to use your potable water (your dual 100 gal water tanks) as fresh water feed to your head.

If, however, you choose to use salt water to flush your head (ugh-certainly not MY preference), then there's nothing lost with valving all your 265 gal of water capacity as common.

I found 65 gal of water, used to flush the head alone, was MORE than enough to support two persons for long-duration cruising. Typically, my wife and I went through the 200 gal potable water at about the same rate as the 65 gallons used for the head alone. And used separately, this ensures there's no contamination from the head effluent back through the potable water system, and without all the hassle of backflow and/or solenoid valves if you common your head flushing water with your potable water.

Regards,

Pete

 

[Comodave]

We have 2 tanks that are joined by a valve. I leave the valve open because it is unfortunately a gate valve that is stuck open. I am hesitant to try and force it closed because it is difficult to get to and one side is attached to one of the tanks. I don’t want to break it loose trying to fix it, oh well.

 

[_AJ_]

Hi AJ,



If your boat is equipped like my 2000-vintage Pacific Trawler 40, the 65 gal water tank in the hull extension is piped exclusively to the head. This obviates the need for solenoid valves and/or backflow preventers if you choose to use your potable water (your dual 100 gal water tanks) as fresh water feed to your head.



If, however, you choose to use salt water to flush your head (ugh-certainly not MY preference), then there's nothing lost with valving all your 265 gal of water capacity as common.



I found 65 gal of water, used to flush the head alone, was MORE than enough to support two persons for long-duration cruising. Typically, my wife and I went through the 200 gal potable water at about the same rate as the 65 gallons used for the head alone. And used separately, this ensures there's no contamination from the head effluent back through the potable water system, and without all the hassle of backflow and/or solenoid valves if you common your head flushing water with your potable water.



Regards,



Pete

Thanks for the information. I like the way yours is plumbed. My 3 thanks are currently combined at 265 gallons. You must have added a separate water pump dedicated to your head? I'm sure 65 gallons would be plenty for us too. Looks like I may have another project in my future.

 

[jungpeter]

Hi AJ,

My head was a manual head. Thus, no additional water pump needed to draw feed water from the tank. If your head is an electric head, you'll need to supply it with pressurized water from your existing fresh water supply system (with attendant attention given to making sure you don't get backflow from the head to the ship's fresh water supply).

Or, you can go to the trouble of adding a 2nd demand pump to supply water solely from the 65 gal transom tank (with attendant plumbing and electrical issues), as you suggest. Using this tank solely for head supply removes all issues with backflow, and gives you the added benefit of being able to add salt water to the 65 gal tank, should you run out mid-cruise.

IMHO, Pacific Trawler's choice of adding a 3rd water tank in the transom extension solely to supply the head was masterful. And again IMHO, valving it common with the other two tanks is a mistake. But your mileage may vary-after all, it's your boat!!!

Regards,

Pete