Converting water tank to Diesel tank

[steve vilah]

Hi Folks I am new to this site and am hopeing that someone can assist me with a few questions I have I intend to purchase a late model used Beneteau 473 2003-2006 either a two or three cabin version I intend to do some extensive cruising, I want to install a water maker and am concidering converting one of the existing water tanks to a fuel tank enabling me to increase my fuel range Can someone advise me if this is viable? or possible? can I use the same tank? will the structure or composition of the tank be suitable for holding Diesel ? Any feed back or info. would be greatly appreciated Regards Steve

[StianM]

Why would you like to increase the range?
If you want to cross the oceans what will you do if your water maker brake down?

Is it posible? Yes

[Frosty]

Yes it is possible --Why dont you tell us what your tanks are made of and piping arrangements cock material etc.

I would always rather have diesel than water. If you run out of deisel what will your water maker run Off!!!!!

[Poida]

Just to put my 2 cents in about something I know bugger all about.

I would assume that the water tanks are conected so as the water is used, equal amounts are used out of each tank.

If they are either side of the craft and you convert one to diesel, one tank is going to be used more than the other.

If so it may effect the way the boat sits in the water.

Poida

[StianM]

Originally Posted by Frosty

I would always rather have diesel than water. If you run out of deisel what will your water maker run Off!!!!!

But if the water maker breake you don't nead diesel.
I think you should keep enough watertenks to get where your going witout thirsting to deat.

I think the best would be to convert some to diesel and keep just enough for water to make it home if you compromise things like shower, washing clodes and shaving.

You could also install more tanks if your boat allows it.

[Frosty]

Im sure he doesnt intend converting ALL his water tanks to fuel.

Showering Washing clothes and Shaving are extrememly important.

I would just rather die if I couldnt wash my clothes in fresh water or shave.

[ted655]

Water, water everywhere but not enough to drink! Oh to reach port in a fortnight and again, be in the bosum of my countrymen! I'll let you decide the chicken or the egg argument.
As pointed out, pay attention to the present plumbing and potential balance problems. Little things like fill necks, venting, AND... pickup point in tank. Most fuel tanks have a provision for sediment settling & water space in the bottom. Vapor space is a consideration. Some engines require a return line. Extra fuel storage may require fuel polishing system.
If you are wondering about some remaining water in the tank, there are additives for that (within reason).
You're aware there are "flex" tanks that fit in odd places all over the boat, another solution maybe.
No matter the choice you make, carry repair parts for EVERY major component on the boat.
You may be sitting in a becalmeed boat WITH diesel & water but no steering.

[Frosty]

Taking the above post by Ted into consideration if the water tank did not look too good as a fuel tank, you could get around this by using this fuel first.

Any way I think your getting the point that its possible but---

For temporary tankage for a one off trip, you might want to think about deck tanks. Or better still, to keep wieght absalutely as low down as possible, put temporary fuel tanks in the engine room, --50 gall drums lashed securley.

You can buy flexible diesel tanks that you can literally hang up on hooks, or they will form any shape. Like a big hot water bottle.

[Ike]

Frankly I would keep both water tanks and install another diesel tank.

[Polaris43]

Originally Posted by steve vilah

Hi Folks I am new to this site and am hopeing that someone can assist me with a few questions I have I intend to purchase a late model used Beneteau 473 2003-2006 either a two or three cabin version I intend to do some extensive cruising, I want to install a water maker and am concidering converting one of the existing water tanks to a fuel tank enabling me to increase my fuel range Can someone advise me if this is viable? or possible? can I use the same tank? will the structure or composition of the tank be suitable for holding Diesel ? Any feed back or info. would be greatly appreciated Regards Steve

Steve,

I'm planning to do the same thing for the same reasons. Obviously there are lots of folks on this forum who would rather second guess you or make lame remarks than provide any constructive advice. Perhaps it's because they don't know anything about boats or upgrading them.

The water tank that I plan to convert to diesel is stainless steel and the plumbing is not an issue. As you know, fuel and water tank plumbing is not rocket science.

My question is two fold - first: is stainless a good material for a fuel tank? second: how does one make sure all of the water is removed from the tank - my thought on this one is to drain the tank, leave it open for a few days, then run a gallon of alcohol (denatured) through it to displace any remaining moisture.

Your thoughts?

[Ike]

The problem with stainless is called crevice corrosion. Crevice corrosion occurs in the welded seams of the tank. Most standards, such as ABYC and others, recommend if you use stainless it be under 20 gals and have domed ends. That way you only have two welds and they are minimized.

That aside, stainless needs to be mounted so that it is kept dry. If stainless gets wet and doesn't dry out it will corrode just like any other metal. Stainless is subject to all the same problems as any metal tank. The welds in stainless need to be flawless, so that there are no or very few crevices where moisture can collect.

Getting the water out is the big problem with any tank that is going to be used for fuel. Your idea would probably work.

Frankly I prefer roto mold polyethylene tanks. They have no seams, they don't corrode and you can get them any size an shape up to about 100 gallons.

[Polaris43]

Thanks, Ike

This particular tank is original (1979) and appears to be in good condition. It obviously doesn't leak water.

Is there anything special about diesel that would accelerate crevice corrosion?

[steve vilah]

Hello Polaris43
Ike's point is accurate, corrosion occurs when tank is partially empty when air and moisture combine to create corrosion uaually at the weld seams The best way to minimise this problem is to keep the tanks topped up. As I am sure you already know Diesel is oil based therefore has a self lubricating property.
Regarding the eradication of water or moisture in the tank - If the tank is not yet in the boat the task in relatively simple, however if it is in situe your idear of flushing it out with alcahol is sound, making sure you drain the fuel lines also either using a vaccume pump or conversley pressurising up the tank, then I would do the same process again, with a small amount of diesel but I would also add approx. 5% of kerosine to this fuel.
The kero. places any remaining water into solution therefore allowing this water to be trapped in the fuel filter or being burnt off during combustion.
(In Australia it is common practice for the transport industry to keep their fuel tanks clean by adding 1 litre of kerosine to approx. 400 litres of fuel)

[Ike]

Steve covered it.

[steve vilah]

Hi folks I am trying to obtain a copy of the Owners Manual for a Beneteau 473 Any assistance you may offer to help me in obtaining a copy would be gratefully appreciated Cheers Steve