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Old 19-02-2017, 06:46   #1
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Gravity tank for fresh water - any experience?

Hello,
Call me old fashioned or even backwards but I do not like depending on electricity to provide me water from my tanks*.
I have on my boat a tap with a simple hand pump which is handy as each stroke delivers precise amount of water but as I'm preparing quite a large refit and just found what looks like a perfect spot for a gravity tank, I decided to think about that a moment before I commit to one or another solution. I like an idea of a gravity tank mainly because of its sheer simplicity, went with a pump only because in a current setup gravity tank would have to be either on the other (bow) side of the boat or on the top of a coachroof. None of these locations were especially attractive to me

I'm thinking about putting about 25 litres (roughly 5.5 gallons- imperial ones for all you across the pond) which would be situated practically right over the tap, around 2 ft - 2ft 6in upwards.

Any thoughts about such installation? Does anyone use a gravity tank?
And no, I won't convert to electrics. Once bitten...

*I still remember being stuck on the boat with full tanks (1000l, over 220 imperial gallons or around 250 US ones) and having absolutely nothing to make a cup of tea with as all electrics decided to take some time off. Not funny at all. Thankfully it was alongside so I could go to the shop and buy some bottled water to have a cuppa before tackling all the repairs but bad feeling stayed with me.
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Old 19-02-2017, 07:01   #2
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Re: Gravity tank for fresh water - any experience?

You asked so I'll give you my opinion: Keep the weight as low as possible. If you have not yet become comfortable with electrical power, keep your foot pump or install a hand pump.


Most boaters find electricity reliable so maybe you just need to install and maintain your electrical system properly.
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Old 19-02-2017, 07:13   #3
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Re: Gravity tank for fresh water - any experience?

I should explain it wasn't my boat I had problems with. On mine electrical systems work just fine, but I just do not like having it as means of delivering water. Especially having a refit before about a year at sea. So I would appreciate not insulting me with supposition that I cannot "maintain my electrical system properly" or "not yet became comfortable with electrical power". I asked about installation not reasons behind it.

And no, I do not think 5 gallons of water below the deck level midship will have any ill effect on 13 ton boat.
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Old 19-02-2017, 07:19   #4
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Re: Gravity tank for fresh water - any experience?

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I should explain it wasn't my boat I had problems with. On mine electrical systems work just fine, but I just do not like having it as means of delivering water. Especially having a refit before about a year at sea. So I would appreciate not insulting me with supposition that I cannot "maintain my electrical system properly" or "not yet became comfortable with electrical power". I asked about installation not reasons behind it.

And no, I do not think 5 gallons of water below the deck level midship will have any ill effect on 13 ton boat.
You asked so I gave you my opinion. If your mind is already made up, why did you ask?

If I had known I was wasting my time replying, I wouldn't have bothered.
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Old 19-02-2017, 07:20   #5
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Re: Gravity tank for fresh water - any experience?

I asked about installation ideas not a lecture about modernity
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Old 19-02-2017, 07:31   #6
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Re: Gravity tank for fresh water - any experience?

We used 5 gallon water containers over our galley sink on our 26 ft macgreggor. No problems at all!
We used the collapsible jugs. We also used the spigot that came with the container but a hose with a closable end would have been better.
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Old 19-02-2017, 07:34   #7
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Re: Gravity tank for fresh water - any experience?

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We used 5 gallon water containers over our galley sink on our 26 ft macgreggor. No problems at all! (...).

How high over the sink is your tank?
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Old 19-02-2017, 07:37   #8
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Re: Gravity tank for fresh water - any experience?

Oh for instalation our set up was just a shelf we built and used a bungee to hold the jug. 5 gallons is not a lot of weight. The collapsible jug helped get the last drop out. But with a nice gentle slope and a fiddle in front of the jug you should be able to use a hard container too., just secure it well!
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Old 19-02-2017, 07:38   #9
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Re: Gravity tank for fresh water - any experience?

The jug was about 8 inches over the sink. Not high.
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Old 19-02-2017, 07:41   #10
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Gravity tank for fresh water - any experience?

Thanks, that clarifies the issue, I wasn't sure how low can I put the tank. So 2ft difference should be plenty. I have some space in which I can actually inbuilt a small tank (OK, laminate insides of this space and keep little slope) and I wondered how low could I get with it.

Also prefer to check for unforeseen difficulties, after building it in it won't be possible to rectify without a major surgery...
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Old 19-02-2017, 07:46   #11
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Re: Gravity tank for fresh water - any experience?

Quote:
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*I still remember being stuck on the boat with full tanks (1000l, over 220 imperial gallons or around 250 US ones) and having absolutely nothing to make a cup of tea with as all electrics decided to take some time off. Not funny at all. Thankfully it was alongside so I could go to the shop and buy some bottled water to have a cuppa before tackling all the repairs but bad feeling stayed with me.

Might not have been all that difficult to tap off the waterline feed before the (electric) fresh water pump?

Which leads to... maybe a simple spigot installed between water tanks and electric pump could be an OK emergency source.

In any case, I'd want to avoid adding installed weight higher than the naval architect's original plans called for.

Foot pump for water from existing tanks would probably be my Plan F, or maybe G.

Plan A would be electric, Plan B would be spare electric, Plan C would maybe be repair kit for pumps A and B, Plan D would maybe be temporarily re-purposing another pump on board, Plan E could be making port and ordering replacement or repair, etc. You didn't ask for that, but I had a few spare moments to type...

-Chris
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Old 19-02-2017, 07:47   #12
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Re: Gravity tank for fresh water - any experience?

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Thanks, that clarifies the issue, I wasn't sure how low can I put the tank. So 2ft difference should be plenty.
With such a small amount of water there is no opposing pressure to prevent the water from flowing. You don't need to go as high as 2 feet unless that's the best spot to store your water.
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Old 19-02-2017, 07:49   #13
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Re: Gravity tank for fresh water - any experience?

Perhaps I am missing something, but you will still need to move the water from the main tank to the gravity tank.

You could manually scoop it out, but this will be difficult when the main tank is low and it will be hard to reliably seal the main tank and still maintain easy access. So you will most likely pump it out. Using a manual pump would work fine, but I don't see the advantage over using a foot pump to deliver the water directly from the main tank to a spout in the galley.

Precisely controlling the water delivery with a foot pump, leaving both hands free, is one of the advantages of the conventional manual system of pumping water directly from the main tank. This is better than a tap if you trying to conserve water, especially in rough conditions. You would lose this with a gravity tank.

However, having a separate tank that can be filled with the best quality water for drinking is something that can sometimes be worthwhile. A day tank for water in a similar vein to a day tank for diesel.
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Old 19-02-2017, 07:51   #14
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Re: Gravity tank for fresh water - any experience?

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Originally Posted by ranger42c View Post
Might not have been all that difficult to tap off the waterline feed before the (electric) fresh water pump?

Which leads to... maybe a simple spigot installed between water tanks and electric pump could be an OK emergency source.

In any case, I'd want to avoid adding installed weight higher than the naval architect's original plans called for.

(...)...

-Chris
Don't have plans, but a heavy boat so not worried about that.

My problem with electrics is not only about eventual malfunction but also with water usage. As I said - planned trip is about year long without stops so I need to think about that also. I'm quite frugal with water anyway but with limited supply I wouldn't like to make it harder for myself.
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Old 19-02-2017, 08:02   #15
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Re: Gravity tank for fresh water - any experience?

I find the poster's analysis strange. Why on earth would you build a tank when $20 or so will buy a 6 gal water jerry can? If you don't trust your electric pump or the manual backup it is a lot easier to keep a few water jerry cans on deck for backup. I'm sure he could use that space over the sink for something more useful than spare water.
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