What size water tank with water maker?

[dirtdoc1]

Hi Folks,

On my trawler they put a 200 gal gas tank next to a 175 gal water tank on each side of the boat. The total gas is 400 gal. with about a 600 mile range at 8 knots. I would like to get over 1000 mile range. I can use the water tanks for additional gas, which should give me well over 1000 miles at 8 kts. That leaves me with no water. After confirming with the owner of the company that I can do this he suggested using a 40 gal blatter in the lazaret for water. I was thinking about getting a water maker to supplement the 40 gal water blatter but I hate to fill up the lazaret with a 40 gal blatter. If I used a 20 gal blatter with a water maker will that work for showers? Am I wasting my time with all of the above? Has anyone done something similar? Any thoughts or comments would be appreciated.

Thanks!

 

[Benthic2]

Will your normal cruising habits require more than 600 miles of range ? If not, perhaps on the occaisions that it does you could supplement your fuel supply with a temporary fuel bladder?

 

[dirtdoc1]

Will your normal cruising habits require more than 600 miles of range ? If not, perhaps on the occaisions that it does you could supplement your fuel supply with a temporary fuel bladder?

A simple but elegant solution.

Thanks Benthic2!

 

[ksanders]

There is nowhere in North America where you need a 600 mile range.

Not even close.

I would keep your tanks as configured and go boating.

 

[FF]

"The total gas is 400 gal. with about a 600 mile range at 8 knots. I would like to get over 1000 mile range."

Slow to 7K

 

[swampu]

Its a one way trip, once the tank is used for gas it can never be used for water.

 

[Chrisjs]

Watermakers do not work well generally in coastal waters or the ICW, for example. They require relatively clean seawater. They work great in the Bahamas and offshore where the particulate load is much lower. We enjoyed ours in the Bahamas but shut it down as soon as we got back to the ICW because filters plugged so fast. Plus, any hiccup with power supply, RO membrane(s), or running out of prefilters, would mean running out of water. I would never rely on a WM as my only source of fresh water unless I only drank beer and did not shower!!

 

[Marlinmike]

Ding ding ding, we have a winner!

"The total gas is 400 gal. with about a 600 mile range at 8 knots. I would like to get over 1000 mile range."

Slow to 7K

 

[HeadMistress]

You haven't said whether your water tanks are metal or plastic, but if they're polyethylene don't even think of trying to convert one to fuel holding. PE water and waste tanks are linear low density PE...petroleum will dissolve it. PE fuel tanks must be high density cross-linked PE, which is a different material from linear...plus, plastic fuel tanks must be USCG certified that they meet strict safety standards-- all fittings on the top of the tank, constructed to prevent liquid from pooling on any surface and a couple of others I can't recall without looking 'em up.

Even if it is metal, it's a still a very bad idea 'cuz some of those requirements apply to all fuel tanks and as swampu said, once a tank has held fuel, it can't be used for anything else.

 

[dhays]

I agree with others above.

- Where do you need to go that is 1000nm between fuel stops?
- How often will you have this need?

If you slow down to 7 knots you may have a fuel burn of about 2 g/h. That is 200 hours of operation with 400 gallons. At 7 knots that is 1,400 nm. Even if my numbers are off by a bit, I would bet that you could find a cruising speed that would easily give you a 1,000nm range with a 20% reserve.

Even if that seems like too little fuel for you, then consider converting one of your water tanks to fuel to give you 575 gallons. This is way more than you would likely need but would still give you 175 gallon water capacity.

 

[Gmarr]

My question would be gas or diesel and type of engines? You say "gas" above so curious...

 

[dhays]

I am not sure how big a water tank you would need. I would figure out how much water you would use in two days. Consider cooking, washing, showers etc.... I would want to have a couple days supply so that if I was in a location where I didn't want to run the water maker I would still be OK.

 

[dirtdoc1]

I am not sure how big a water tank you would need. I would figure out how much water you would use in two days. Consider cooking, washing, showers etc.... I would want to have a couple days supply so that if I was in a location where I didn't want to run the water maker I would still be OK.

I agree. I think that's why 40 gal was recommended. I need to look at some water makers and figure out how long it takes to make 20 gal and how efficiently the water heater could keep it warm for a shower. I keep coming back to 40 as the answer but a 40 gal tank is big! That's what I have on my Carver and it's good for one for about 4-5 days. If the water maker could keep it full even during use I think a 20 gal tank might work. But if the water maker went down I would have to depend on bottled water until I pulled anchor and got into port.

I think 40 gallons is the answer. Unfortunately.

Do you have a water maker?

Thanks,

 

[dirtdoc1]

"The total gas is 400 gal. with about a 600 mile range at 8 knots. I would like to get over 1000 mile range."

Slow to 7K

One of the reasons that I want more diesel is so I can go faster and not worry about losing my range. I'm coming from a planing boat so I'm a bit worried that 8 knots will feel too slow. I've been driving my Carver at different speeds to see what it's going to feel like running at 8 knots. 10 knots is OK but 8 feels really slow to me. I've been told that it feels different in a trawler.

I guess I'll find out in September when I take possession of the boat.

Cheers.

 

[dirtdoc1]

You haven't said whether your water tanks are metal or plastic, but if they're polyethylene don't even think of trying to convert one to fuel holding. PE water and waste tanks are linear low density PE...petroleum will dissolve it. PE fuel tanks must be high density cross-linked PE, which is a different material from linear...plus, plastic fuel tanks must be USCG certified that they meet strict safety standards-- all fittings on the top of the tank, constructed to prevent liquid from pooling on any surface and a couple of others I can't recall without looking 'em up.

Even if it is metal, it's a still a very bad idea 'cuz some of those requirements apply to all fuel tanks and as swampu said, once a tank has held fuel, it can't be used for anything else.

That's why I asked the owner of the company if it was possible with the current tanks. He said it wouldn't be a problem but I will double check on the material of the tanks. This would be done at the factory so I'm sure that it will be done to USCG safety regulations. I will be sure to have an in depth conversation with them. If I go through with this.

Thanks for your input!

 

[kev_rm]

Just one comment on the bladder style tanks as I knocked this idea around for a while (before going with poly replacements)... bladders have a fixed 2-D shape. They don't actually "fit" in a space better than a poly tank, in fact, you will find the number of available dimensions of poly tanks far far greater than bladders. Once I figured that out, I saw zero benefit to having a variable height dimension.

 

[sunchaser]

IMHO you would ruin a perfectly acceptable setup for 99% of us by screwing up the tankage specs. Think resale.

 

[Lepke]

A watermaker is handy in many ways. And you can make water almost anywhere with proper filters. I make all of my water. Last dock water was 2011. I use washable 20 and 5 micron in front of my regular watermaker filters. In rivers or bays I wash them about every 1-2000 gallons of final water. No membrane problems.

 

[HenryD]

How much fuel are you going to burn running the genset, so you can run the water maker?

 

[dirtdoc1]

IMHO you would ruin a perfectly acceptable setup for 99% of us by screwing up the tankage specs. Think resale.

Good point. Although a 1000+ mile range with a water maker might change those numbers. Still, definitely worth considering. I do intend to work my way up to a true blue water trawler one day. My dream is to motor to Palau and live on the boat. I spent a couple of weeks there on business and fell in love with the people first then the island. What a wonderful place.

Cheers

 

[dirtdoc1]

How much fuel are you going to burn running the genset, so you can run the water maker?

All these thoughts are making my head hurt. I have no idea.

 

[dhays]

I agree. I think that's why 40 gal was recommended. I need to look at some water makers and figure out how long it takes to make 20 gal and how efficiently the water heater could keep it warm for a shower. I keep coming back to 40 as the answer but a 40 gal tank is big! That's what I have on my Carver and it's good for one for about 4-5 days. If the water maker could keep it full even during use I think a 20 gal tank might work. But if the water maker went down I would have to depend on bottled water until I pulled anchor and got into port.



I think 40 gallons is the answer. Unfortunately.



Do you have a water maker?



Thanks,

I don't have a water maker. The PO of my boat had one installed when he had it commissioned. He also had a washer/dryer installed at commissioning. He later pulled both of them out. With 350 gallons of fresh water, he never found that he needed the water maker and it was more trouble/expense than it was worth.

With 5 adults on the boat for a bit over a week last summer, I could have used a water maker. We never ran out of water but we were conserving. Turns out we ended up with 100 gallons of water left over but if we had a water maker my crew would have been profligate with water use.

 

[Bay Pelican]

Is the west coast that much different than the east coast / Caribbean. From my cruising experience almost everywhere between the Mississippi and South America you are more likely to need the extra water than the extra fuel. Unless you have a special purpose that requires you to keep moving as if you were doing a delivery 600 miles is a long way. However many cruisers will stay in locations for days were using the watermaker is not a good idea because of the quality of the water. Watermakers also fail, regularly in fact, and then the you are faced with pulling into a marina or making frequent trips to fill up the water.

 

[FF]

Probably the best thing about a water maker is it is a nice heavy load and will help keep an oversized noisemaker from an early death.

 

[dirtdoc1]

Is the west coast that much different than the east coast / Caribbean. From my cruising experience almost everywhere between the Mississippi and South America you are more likely to need the extra water than the extra fuel. Unless you have a special purpose that requires you to keep moving as if you were doing a delivery 600 miles is a long way. However many cruisers will stay in locations for days were using the watermaker is not a good idea because of the quality of the water. Watermakers also fail, regularly in fact, and then the you are faced with pulling into a marina or making frequent trips to fill up the water.

Hi Folks,

Almost every response was against a water maker with a small tank and converting my large water tanks to diesel. And there were a lot of responses - thank you very much. This site with all the experienced members is a valuable resource. Based on the overwhelming consistency for not changing my system I have decided to live with the boat the way it is and take a wait and see approach. Thanks for your time it was fun and very helpful. I hope I can return the favor one day.

Cheers and safe travels!

 

[ktdtx]

On my trawler they put a 200 gal gas tank next to a 175 gal water tank on each side of the boat. The total gas is 400 gal. with about a 600 mile range at 8 knots. I would like to get over 1000 mile range.

I understand you have two 200 gallon fuel tanks and two 175 gallon water tanks in the boat.

I would consider converting one of the water tanks to diesel and keeping 175 gallons for water.

I'm not sure but I think 8 kts in that boat will be no more than 4 gph and with 600 gallons that's 150 hrs and 1200 miles (I know, no reserves calculated).

So, adding 175 gallons of fuel will be plenty and give you a significant amount of water.

I like a large fuel capacity and the ability to pick and choose my fuel stops to decrease the likelihood of bad fuel. I also like a reasonable amount of water as I don't waste it but I like to be able to use what I want.

Also, as already mentioned-a watermaker can break (as everything can) and you won't want to run it everywhere you go so more than 40 gallons of water would be good. Unless you pickle or flush your water maker you will probably want to run it every 3 to 5 days so you can pick and choose when and where to run it.

The only problem I see with converting one of the tanks to diesel would be balancing the boat but don't think it would be too difficult to maintain.

 

[dirtdoc1]

I understand you have two 200 gallon fuel tanks and two 175 gallon water tanks in the boat.

I would consider converting one of the water tanks to diesel and keeping 175 gallons for water.

I'm not sure but I think 8 kts in that boat will be no more than 4 gph and with 600 gallons that's 150 hrs and 1200 miles (I know, no reserves calculated).

So, adding 175 gallons of fuel will be plenty and give you a significant amount of water.

I like a large fuel capacity and the ability to pick and choose my fuel stops to decrease the likelihood of bad fuel. I also like a reasonable amount of water as I don't waste it but I like to be able to use what I want.

Also, as already mentioned-a watermaker can break (as everything can) and you won't want to run it everywhere you go so more than 40 gallons of water would be good. Unless you pickle or flush your water maker you will probably want to run it every 3 to 5 days so you can pick and choose when and where to run it.

The only problem I see with converting one of the tanks to diesel would be balancing the boat but don't think it would be too difficult to maintain.

Hi Ken,

That was my original idea but it was suggested that the difference in weight would cause the boat to list and I don't think I have a manifold to distribute fuel. Water weighs about 1 lb more per ft3 than diesel. So that would be about 175lbs more on one side of the boat. That's about one male (either young or in great shape) and I don't see the boat listing more than 0.5" with that much weight difference. How balanced can you keep a boat anyways.

Thanks for reminding and validating my original thought which I completely forgot about.

Dave

 

[rjwilliams11741]

Watermakers do not work well generally in coastal waters or the ICW, for example. They require relatively clean seawater. They work great in the Bahamas and offshore where the particulate load is much lower. We enjoyed ours in the Bahamas but shut it down as soon as we got back to the ICW because filters plugged so fast. Plus, any hiccup with power supply, RO membrane(s), or running out of prefilters, would mean running out of water. I would never rely on a WM as my only source of fresh water unless I only drank beer and did not shower!!

Except for water with oil on the surface (and this is only a problem if you have your intake near the surface) the statement that watermakers do not work well in coastal waters or the ICW is not necessarily true. Discussions with engineers from Kayadyn / Spectra indicated that the only effect "dirty" water has on your watermaker is that the pre-filters get dirtier. If you're changing them every couple of months or so there should be no problem using your RO watermaker in coastal water. One thing to remember about watermaker capatity is that an 80 GPD unit produces just a little over 3 gallons per hour. If you use 10 to 15 gallons a day this means that you would need to run the watermaker 3 to 5 hours a day to meet your needs. There are large capacity machines that would easily satisfy that kind of water requirements but you are talking 5 figures in cost and have a pretty large footprint for a boat the size of yours.

 

[Chrisjs]

I agree totally. The point I was trying to make is that depending on the water quality you need to change the filters (we had a 2 different micron sizes in series) more frequently, to the point where it becomes a pointless exercise.
How many filters are you prepared to carry so that you can change them every couple of days?? The waster in many areas is so full of sediment and organic material that the filters plug real fast. As previous, we found it pointless to run the RO in the ICW, and have you been in the Chesapeake lately???

 

[dhays]

Hi Ken,



That was my original idea but it was suggested that the difference in weight would cause the boat to list and I don't think I have a manifold to distribute fuel. Water weighs about 1 lb more per ft3 than diesel. So that would be about 175lbs more on one side of the boat. That's about one male (either young or in great shape) and I don't see the boat listing more than 0.5" with that much weight difference. How balanced can you keep a boat anyways.



Thanks for reminding and validating my original thought which I completely forgot about.



Dave

As delivered, the NP have a fuel manifold where you can select which tank is drawn from and which tank is returned to. You can draw from either or both, return to either or both. At the moment, I am drawing from and returning to both but usually just draw and return from one tank at a time. This system makes it very easy to keep the boat balanced. Normally, the NP have a cross connect line. It may or may not help keep the tanks balanced however. My boat has a transfer pump in that cross-over line which gives another method for balancing.

So, if you used one of the water tanks for fuel, I don't think you would have an issue with balance. You would want to have a manifold that would incorporate that third fuel tank.