connecting multiple tanks to freshwater system (+)

[vacendak]

got a problem with installation in new boat:

There will be 4 water tanks, 2 each side, all different sizes (altogether approx 600 ltr).
Found a very useful discussion of filling such system with 2 deck fills in this thread

http://www.cruisersforum.com/forums/...ons-20577.html

Still, cannot find a solution about discharging those to boat freshwater system:
1) switching to each tank separately with some kind of "4-in / 1-out" dispenser
seems very inconvenient (an I could not find such manifold as a ready-made product);
2) discharging 2 tanks as one unit require a bottom-to-bottom interconnections, like shown below



- not possible to install because of hull construction

will be very grateful for guru's and/or experienced person's advice.

[Pelagic]

I am assuming the bottom to bottom connections are completely impossible which would give you the best natural “head” for priming the FW pump and drain the tanks completely.

Then side to side at lowest point with internal pvc angled piping to bring suction to lowest point seems to be your only other option, unless you want to get radical with small internal submersibles.

For side to side, you may need to install check valves in line unless you can loop it below side outlet on the way to FW pump.

[Pblais]

You can pull the water using a pickup tube and lift it maybe 4 ft without a lot of problems. You can't do that in an interconnected system easily unless you work one tank at a time. If you can't take water off the bottom via gravity then your only choice is to go the other route.

You do need fills and vents on each tank interconnected or not. If you pull the water from a pickup tube you can not use multiple pickups at the same time or you will suck air at some point that the first tank goes empty.

Having a gravity based system that makes the water pump self prime is best and easiest but if you can't get there from any place then the option is the other way. Combinations perhaps could let you join some tanks. That really is the only way to make water flow.

I pull my fresh water from a single tank in the keel using a pickup tube like a fuel tank. Priming it requires opening up multiple faucets to relieve the head resistance caused by some water still remaining in the line after the pump but once the prime is made good it works until I suck air off the bottom of the tank. I would avoid any type of transfer pump approach.

[lookoutnw]

Manifolds are easy to make. Look into PEX and Sharkbites. I re-plumbed my whole boat to include the Hydronic heating system with them. They are rated commercial, hydronic and behind teh wall 'no-access' for connections. I will be going to the 'plastic connectors' for the pex in my raw water galley, deck washes, and shower head.

[bene505]

I have a 4 to 1 manifold in my Beneteau 50. It's has a valve on each of the 4 incoming lines. It's in an easy-to-access location. You simply switch to the tank you want to draw from.

[vacendak]

bene505

I wonder what may happen if you open 2 valves simultaneously,
while one of them tanks is empty ?

[vacendak]

Pelagic

unless you want to get radical with small internal submersibles

found those @ Whale : Marine : Whale Pumps

what for such pumps may be necesssary ? isn't one powerful external pump better ?

[bene505]

Originally Posted by vacendak

bene505

I wonder what may happen if you open 2 valves simultaneously,
while one of them tanks is empty ?

I suppose I could try it in the spring. I think that it wouldn't work. It's generally not an issue though, and being forced to switch tanks has the added benefit of letting you know when one tank goes dry.

I have 1000 liters, with the starboard aft tank (it's located midships actually) being the largest by far. If I'm filling up often, I sometimes use just that tank, to make it easy to refill (less opening other fill ports and moving the hose between them). Then I leave the other 3 tanks full.

I might have a picture of the manifold-with-valves. If anyone is interested in seeing it, let me know.

[vacendak]

I might have a picture of the manifold-with-valves. If anyone is interested in seeing it, let me know.

many thanks in advance, would be of big use

[lookoutnw]

I am tryiong to finish my plumbing. I will be adding a filter system taht connects shore water to the plumbing where I can fill 1 of my 2 tanks at a time. The pressure relief has to be sufficient enough not to blow a seal in the tank. I will be doing a 3/4 line there. Also I will have a pressure limit on teh connection so shore water pressure does not get over 30#. Normal RV type stuff, but an added safety. Note# It appears from signs I have seen posted in more than 1 marina, that keeping a shore water supply connected to your boat on full time, is not a good idea. I guess that when, not if, the system develops a leak, they seem to have to re-float boats. It appears to happen quite often I guess...

[Pblais]

The pressure relief devices that you can buy and install come in a 50 lb and a 35 lb variety. Many RV's use the 50 lbs. 35 lbs should be what you get but make sure to read the details as the two look identical. If you connect up the shore supply to the pressurized water system you should be fine.

For the filters just buy one of the two stage filters at a home supply store and rig up a short hose so you can connect it to the supply and then use it to fill the tanks. You really don't have to have one on the connection to the pressurized supply as none of that water will ever see the tanks. It's not that you should not use it that way but you don't have to. With a fitting on the outlet you could use it for both.

Problems being connected all the time do happen and in ways you might imagine. You could be connected yet have the water turned off at the pedestal. The constant pressure often breaks old plumbing. When powered by your fresh water pump you don't leave the power on when you leave the boat so any leak that might be small goes unnoticed. When connected to 35 lbs all the time it's noticeable.

[bene505]

As promised, here is the picture. It's located on the aft side of our island.

Originally Posted by bene505

I suppose I could try it in the spring. I think that it wouldn't work. It's generally not an issue though, and being forced to switch tanks has the added benefit of letting you know when one tank goes dry.

I have 1000 liters, with the starboard aft tank (it's located midships actually) being the largest by far. If I'm filling up often, I sometimes use just that tank, to make it easy to refill (less opening other fill ports and moving the hose between them). Then I leave the other 3 tanks full.

I might have a picture of the manifold-with-valves. If anyone is interested in seeing it, let me know.

[vacendak]

bene505

thanks a lot ! what is the tube size, 1½ ?