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Old 09-09-2020, 09:11 AM   #1
_AJ_'s Avatar
City: Anacortes
Country: USA
Vessel Model: 2000 Pacific Trawler 40'
Join Date: Jun 2015
Posts: 8
Water Tank Valves - Isolate or Combine Tanks

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?

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Old 09-09-2020, 09:23 AM   #2
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City: San Francisco
Country: USA
Vessel Name: Couple’s Retreat
Vessel Model: 2019 North Pacific 45
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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.

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Old 09-09-2020, 09:25 AM   #3
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City: West Coast
Country: USA
Join Date: Apr 2014
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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.
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Old 09-09-2020, 10:27 AM   #4
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City: Gulf Islands
Country: canada
Vessel Name: MissStress
Vessel Model: Grand Banks 36
Join Date: Jul 2019
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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.
You only need one working engine.
That is why I have two.
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Old 09-09-2020, 10:58 AM   #5
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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.
Rich Gano
FROLIC (2005 MainShip 30 Pilot II)
Panama City area
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Old 09-09-2020, 11:09 AM   #6
City: Bayfield, WI
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Originally Posted by jimdavi View Post
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.
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Old 09-09-2020, 11:32 AM   #7
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City: Stuart FL
Country: USA
Vessel Name: Magic
Vessel Model: Grand Banks 46 Europa
Join Date: Aug 2013
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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.
Magic, 1996 Grand Banks Europa
Westport, CT and Stuart, FL
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Old 09-09-2020, 01:38 PM   #8
caltexflanc's Avatar
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 6,240
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.

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.

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
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Old 09-09-2020, 01:54 PM   #9
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City: Lafayette, CA
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Vessel Model: 40' Tollycraft tricabin diesel
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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.
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Old 09-09-2020, 04:35 PM   #10
City: PNW
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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.

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