water tanks

[Ian F B]

Does any one have any experience of connecting two water tanks together using just one filler?

I cant think of any problems,but Im always interested in learning from other peoples mistakes!!!

Seriously Im refitting out a 30ft boat and fitting a Thetford C200 electric flush,and a shower so I need to increase

the water capacity,so I want to fit another tank on the oppposite side of the boat so as not to have to reballast etc.

All suggestions,ideas,etc gratefully received.

Cheers Ian F B

[alan_fincher]

The amount of flush water used by a Thetford casette toilet is insignificant compared to any boat water tank, even a small one. If it didn't use way under a cup-full per flush, you'd have a serious cassette emptying task on your hands, on a far too regular basis.

 

OK, showers are different.

 

I can't see a problem with 2 inter-connected tanks, if you do it right.

 

Assuming filler and water pump are connected to one already, and you just connect an extension, not having another filler....

 

1) Both will need a vent and overflow, probably.

2) Both need to have their top, and overflow at same level, or you will never be able to fully fill the "higher" one.

3) The pipe joining the two will probably need to be significantly bigger than the (say) 1/2" to the pump, so you are not able to drain one too quickly, without it staying topped up by the other.

 

I'm not sure I said that very well, though

 

Alan

[MtB]

so I want to fit another tank on the oppposite side of the boat so as not to have to reballast etc.

All suggestions,ideas,etc gratefully received.

Cheers Ian F B

 

 

I can imagine the water running through the interconnecting pipe from one tank to the other whenever the boat is listing slightly to one side or the other (i.e. all the time), leading to the port (or starboard) list getting progressively more severe until a new equilibrium is reached. Then the boat will stay permanently listing to that side until the tank(s) are refilled to the top.

 

Best to have one tank (or all tanks) on the centreline of the boat, in my view.

 

Cheers, Mike

[RobinJ]

Does any one have any experience of connecting two water tanks together using just one filler?

I cant think of any problems,but Im always interested in learning from other peoples mistakes!!!

Seriously Im refitting out a 30ft boat and fitting a Thetford C200 electric flush,and a shower so I need to increase

the water capacity,so I want to fit another tank on the oppposite side of the boat so as not to have to reballast etc.

I have done it in the past on GRP cruisers and seem many similar systems.

Ideally you need to have the filler split higher than the tanks and run a pipe to each one - when filling, both tanks are filled together - when emptying the air can flow to the same point. Similarly the take off either needs a split, one from each tank, or a separate connection so the water can pass between. Problem if they are not collapsable is to ensure they are vented with little risk of contamination.

[Justme]

The interconnecting pipe needs to be able to take the full flow of the filling supply pipe not just the internal flow as previously mentioned. Or the first tank will fill & the second tank will only be getting a dribble & the first tank will over flow or you will spend ages waiting for the tanks to level out & repeatedly topping up.

 

 

Justme

[Ian F B]

Thanks for your replies,much appreciated,it looks like the way to go is to increase my present tank size and re ballast after all.

Cheers Ian F B

[Strads]

Been there done that -

 

we changed from a large plastice bag tank to two stainless steel ones ( to better use the underdeck space by adding 120 gallon diesel tank - under the stainless water tanks)..

 

reason we have two tanks is so that they fit through the doors and front deck and could be fabricated off the boat.

 

Balance pipe is 2inches dia... so no issue on filling / draining.. and breather/overflow are joined midway to the deck breather - they are approx 15mm and we have no issues since installing...

 

have fun

[Speedwheel]

My water tank(s) are actually 3. One triangular tank and two square ones. These are all connected together by 2inch pipe.

 

Never had any problems. The problem of a boat listing as water moved to one side will not happen. It will always rebalance itself so the boat won't be on a permenant angle. If this was so then balanced diesel tank either side of an engine wouldn't work. Infact, thinking about it further, if this was the case then it would happen with a single tank to.

Edited September 9, 2008 by Satellite

[alan_fincher]

In fact, thinking about it further, if this was the case then it would happen with a single tank to.

Exactly! My thoughts when it was first suggested that 2 balanced tanks would cause a problem.

 

I can see reasons why a tank each side joined by a reasonable bore pipe could be better than one big tank.

 

With a single tank, if the boat rolls from side to side in rough conditions, the whole contents of a partly full tank will slosh from side to side, not helping the stability.

 

With joined tanks the rate that water can move from one side of the boat to the other is restricted, and the water is far less likely to add to any problems of side to side roll. (A bit like having one big tank, but with baffles in it).

 

Well that's what I reckon, anyway!....

[NB Esk]

Interesting subject & one that I've given a lot of thought to, as I propose to use a similar instalation, in my NB build.

 

My thoughts were to have one tank forward & to port, the other (of the same capacity) to the starboard & aft. The thinking is that wether empty or full, the effect on trim will be neutral. (as well as the increased capacity) The boat should simply rise & fall, as opposed to rolling.

 

As to the linking, it seems to me it is essential that the tanks are linked by two pipes, at top & bottom. The top pipe is purely a breather/vent & allows the contents of both tanks to attain the same level. The take off(s) are all from the bottom pipe, allowing all of the capacity to be used.

I haven't been able to come up with a downside to this layout, & would be interested if anyone can.

[alan_fincher]

I don' think the tanks need to be joined at the top, as long as each is vented to the atmosphere.

 

Even if you joint them, you'll still need one of the vents/overflows anyway.

 

What are you thinking of fabricating your tanks from? If just ordinary steel, each will need an access hatch for maintenance and painting. I'm not quite sure how you would "maintain" the steel pipe that linked the two at the bottom, though.

[NB Esk]

I don' think the tanks need to be joined at the top, as long as each is vented to the atmosphere.

 

Even if you joint them, you'll still need one of the vents/overflows anyway.

 

What are you thinking of fabricating your tanks from? If just ordinary steel, each will need an access hatch for maintenance and painting. I'm not quite sure how you would "maintain" the steel pipe that linked the two at the bottom, though.

 

Hi Alan, the tanks would be joined at the top as well, in order to avoid venting. (thereby avoiding just another, unwanted hole in the boat)

 

I'm thinking of fabbing them from stainless, & due to it's cost, I'd like to know it will be a success.

The joining pipes will be either plastic or copper...

 

...Also, if tanks are stainless & a well fitting fine mesh strainer is included in the filler neck, is it acceptable to avoid including access panels. (constantly cruising scenario, so water always fresh)

 

Ta...

[alan_fincher]

I've no experience of stainless steel tanks, but think it would be unusual anyway to have an inspection hatch in one.

 

Very necessary with mild steel, but not stainless, I think.

[bag 'o' bones]

Same principle as a a twin fuel tank mini cooper. Two tanks either side of the boot connected by a pipe. I'm not sure if they were all like that but I read about the principle somewhere.