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Old 06-04-2014, 17:26   #1
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Water Maths

I am struggling with the concept of a water maker, but first a bit of background.
I am building a 41' cat with 700 litres of fresh water tankage and it will be used for Sth Pacific cruising with a max of say 4 people so do I need a water maker.....to me the answer is not clear given the following scenario;
1. Shower in salt water and rinse in clear water = 5L
2. 4 cups of coffee per person per day = 1L
3. Clean teeth = 0.25L
4. Drinking per person = 1.25L
5. Cooking per person = 0.75L

So based on showering every second day this equates to 3.25L out of tanks and 2.5L out of water casks based on $0.35 per litre.
Allowing for 4 people equates to 13L per day from tanks and 10L per day from casks.
If so this means tanks will last approx 53 days therefore I need 53 * 10L casks or some other derivative therof.
So being realistic a 30 day cruise between supermarkets means 30 * 10L casks at $3.50 each which means $105.00 per load of water per month.
Given you cant use a water maker in a marina environment therefore you would be using cask water anyway.

So the question really becomes....whilst cruising only does $3.50 per day for cask water beat fitting and maintaining a water maker.

I think it does if you can store 30 * 10L casks at the start of the cruise.
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Old 06-04-2014, 18:28   #2
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Re: Water Maths

I would look at it from a wider perspective.

Someone on a recent voyage had his fresh water tanks fouled, and needed to ask for assistance from another vessel for fresh water. If that other vessel did not have water making capacity, they would not have had the water to spare. It would be foolish to think that your water tanks will never get fouled, it can happen to anyone. If they had water making capability, then it would never have been an issue.

Another consideration is with a water maker on board, there isn't as much need to store so much water, thus the vessel is lighter and sails better. In your calculations, you left out washing dishes and washing clothes. While you can do this with salt water, you'll still want to rinse with fresh water.

I'm a big believer in redundancy, it's good to have water stored, and to be able to make it as well. In the long haul, at those water prices, you'll be saving money making water yourself.
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Old 06-04-2014, 20:22   #3
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Re: Water Maths

Cruising in the S. Pacific and showering only every other day? Only needing 1.25L drinking water when exploring around in the hot sun?

Watermakers never make strict financial sense - but neither do outboards, diesel engines, refrigerators, etc. All can be worked around.

The wider perspective is the way to approach it.

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Old 06-04-2014, 20:28   #4
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Re: Water Maths

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Originally Posted by colemj View Post
Cruising in the S. Pacific and showering only every other day? Only needing 1.25L drinking water when exploring around in the hot sun?

Watermakers never make strict financial sense - but neither do outboards, diesel engines, refrigerators, etc. All can be worked around.

The wider perspective is the way to approach it.

Mark
Mark, I like your perspective from posts on watermaker threads. Go for the bigger capacity water maker if possible.

Don't have to ration water' and plenty available to clean equipt and salt encrustation on vessel.

Certainly on a cat will enable you to carry less water tankage.

Cheers
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Old 06-04-2014, 20:52   #5
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Re: Water Maths

Turning into a "water nazi" and closely monitoring and enforcing the amount of water that you and your crew use down to the level of even how much water they use to brush their teeth is a great way to destroy everyone's enjoyment of a Pacific cruise.

To overcome all of this I recommend that you get a higher capacity watermaker but also carry sufficient bottled water for emergency situations if the watermaker broke down. You will then have virtually unlimited water which will greatly enhance the enjoyment of everyone on board.

On a recent Pacific crossing we had onboard a Spectra Newport Mk II which produced 120 L per hour. As a result we could use water at will with no time limits on showers or any other activities and were also able to regularly wash the boat during the passage. It greatly added to everyone's enjoyment. This model also has the function that it does an automatic freshwater back flush every 5 days even while the boat is on the hardstand which largely overcomes the need to pickle the unit.
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Old 06-04-2014, 21:10   #6
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Re: Water Maths

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Originally Posted by socaldmax View Post

Someone on a recent voyage had his fresh water tanks fouled, and needed to ask for assistance from another vessel for fresh water. If that other vessel did not have water making capacity, they would not have had the water to spare. It would be foolish to think that your water tanks will never get fouled, it can happen to anyone. If they had water making capability, then it would never have been an issue..
I'm sorry.. novice here. Can you explain to me how a fresh water tank gets fouled?
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Old 06-04-2014, 21:25   #7
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Re: Water Maths

Apart from costs and the need to ration your crew's consumption - 700 litre tank + 300 litres of casks is a tonne of water. That's a fair bit of weight to load onto a 41ft cat.
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Old 06-04-2014, 21:42   #8
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Re: Water Maths

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I'm sorry.. novice here. Can you explain to me how a fresh water tank gets fouled?
The skipper didn't elaborate how his tanks got fouled, only that they did.

I can think of 5 ways it might happen.

1. Saltwater getting into the vent.
2. Bad water from the dock.
3. A hole in the top of the tank allowing seawater or contaminants in.
4. Adding too much chlorine to clean the tanks and not flushing it out enough.
5. Someone else accidentally putting diesel or something else in the tanks.

I know a guy who was told to put a capful of chlorine into his water tanks, instead, he put a cup of chlorine into 100 gal of water. It was unusable for washing, or drinking.

I know someone else who filled their entire engine crankcase up with water, she didn't quite remember what her husband actually told her.

I had a gas station attendant in OR try to put gas into my diesel truck, despite the big sticker on the gas cap and me telling him TWICE to put diesel in it. I had to yell at him to stop him from pumping it. Which explains why I'm no longer surprised at anything that happens.
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Old 06-04-2014, 21:56   #9
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Re: Water Maths

Get a water maker and get one double what you think will need. Trying to find potable water especially in the Pacific is a real pain. I can ration water...The wife will not, so our small 80e(should have gone bigger) water maker runs for 2 hours most days and for longer if we have to do a lot of motoring. Even on the east coast of Australia there are some stunning locations to get away from civilization, but without water you time there would be limited if you need to take on water. A cockpit fresh water shower with a hand held rose uses @ 12 - 15 litres per minute, by the time the better half finishes her shower the best part of 20 litres is gone but if she is happy so am I.

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Old 07-04-2014, 00:47   #10
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Re: Water Maths

Hi All

this might be a bite of Topic .. but i was wondering if you can have 2 water makers on a cat and if some have fitted this on there boat.. im not talking about making twice the a mouth of water just for safety
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Old 07-04-2014, 01:17   #11
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Re: Water Maths

Quote:
Originally Posted by Schmacko View Post
I am struggling with the concept of a water maker, but first a bit of background.
I am building a 41' cat with 700 litres of fresh water tankage and it will be used for Sth Pacific cruising with a max of say 4 people so do I need a water maker.....to me the answer is not clear given the following scenario;
1. Shower in salt water and rinse in clear water = 5L
2. 4 cups of coffee per person per day = 1L
3. Clean teeth = 0.25L
4. Drinking per person = 1.25L
5. Cooking per person = 0.75L

So based on showering every second day this equates to 3.25L out of tanks and 2.5L out of water casks based on $0.35 per litre.
Allowing for 4 people equates to 13L per day from tanks and 10L per day from casks.
If so this means tanks will last approx 53 days therefore I need 53 * 10L casks or some other derivative therof.
So being realistic a 30 day cruise between supermarkets means 30 * 10L casks at $3.50 each which means $105.00 per load of water per month.
Given you cant use a water maker in a marina environment therefore you would be using cask water anyway.

So the question really becomes....whilst cruising only does $3.50 per day for cask water beat fitting and maintaining a water maker.

I think it does if you can store 30 * 10L casks at the start of the cruise.
I'm not sure whree you got these numbers from. My recollection of "normally accepted numbers" say that 1.25 Liters drinking water per person in the tropics is already hard rationing. Better to figure 4L. Cooking obviously depends on what food you make, Showering - well some people wash in salt water and rinse with a perfume atomizer. I guess I like my creature comforts a bit too much.

As someone else mentioned, you'll probalby also want to wash the salt encrustations off your boat on occassion.

To me a watermaker (when doing an RTW or across te pacific is a no-brainer.

Just one man's opinion.
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Old 07-04-2014, 01:20   #12
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Re: Water Maths

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Originally Posted by mikethedane View Post
Hi All

this might be a bite of Topic .. but i was wondering if you can have 2 water makers on a cat and if some have fitted this on there boat.. im not talking about making twice the a mouth of water just for safety
There's no reason why you can't. I like the way you think, redundancy is a great thing to have when you're far offshore.
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Old 07-04-2014, 01:58   #13
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Re: Water Maths

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Originally Posted by socaldmax View Post
There's no reason why you can't. I like the way you think, redundancy is a great thing to have when you're far offshore.
Thanks but i was also looking in to having less water on board to save Weight .. since we all know the more weight you put on a boat the move you need to move while sailing
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Old 07-04-2014, 05:27   #14
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Re: Water Maths

Don't forget that something can happen to your fresh water system that causes you to loose your water. I was once on a boat where a hose failed during the night and nobody noticed. It was smaller of smaller capacity than yours and the bilge happily held the entire 120 liters. So much for the water supply. Fortunately we only had to sail about 50 miles to get some more and we had a supply of soft drinks to get us through the day. In the middle of the pacific that might be an entirely different story.
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Old 07-04-2014, 07:41   #15
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Re: Water Maths

The 6th way water tanks can get fouled is by old water just sitting in there. It will go green eventually and new lifeforms will magically appear. Yum. Set a jar of water on your back porch for a month and see what happens.

When I go hiking I take about a gallon and use just about all of it in a day. It is interesting how much water you use when you can see it. And that doesn't count what I drink when I get home but then it's water with barley added. FWIW.
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