fuel tank construction

[mic]

Ok, it's time to change the fuel tanks. Just for all your information, we are talking about a 48' Aft wheelhouse Cray boat Carvel construction which carries twin 900 litre fuel tanks. The positioning of the existing tanks need to be changed and moved aft because of the new fit out plan, and also the shape. What really is the best material to construct fuel tanks and fuel lines from? The current tanks are of plain mild steel with copper fuel lines. Apparently stainless steel is no good because it is to brittle and cracks, aluminium gets electrolysis and virtually dissolves, and copper apparently fouls the injectors. I was thinking of perhaps that new plastic that service stations are using now to hold their diesel, I know they used mild steel tanks in the past. Friends tell me that mild steel is still the best material for fuel tanks due to it being easily cut & welded, & the diesel inpregnates itself into the steel to act like a preservative. Any ideas would be of great help. Thanks again,
Mic.

[seayou77]

Beautiful vessel! Consider Monel. Baffles, maybe needed in both directions. Stainless gets brittle huh, thanks a lot. I had bit of pipe welded as anchor points.
You might save some precious weight with monel over steel.

[P.I. Stazzer-Newt]

I've seen some large custom built diesel tanks done in HDPE or Polyprop - not certain which.

You'd have to find someone who can do the fabrication, and check the local rules and regulations.

[Ian McColgin]

Even nicer that steel is black iron. Pretty easy to fabricate, stong, lasts forever. In fact, make your water tanks of it as well. Black iron will oxodise a little, there's always moisture in the tank, but the rust barrior will protect against further problems.

Goblin had black iron tanks - 60 years old when I bought her - and never a problem.

[nedL]

To echo Ian, black iron is what I have always known to be the preferred material for diesel tanks. I'm sure monel would be fine (but I think the price tag might change your mind real quickly).

[Victor]

Not plastic or bladders?

[Dale R. Hamilton]

Mic- I guess I'd do it on the cheap by going to the big truck junkyards and buying diesel tanks that were used on big trucks. These would be aluminun and go up to 180 gal. You could get several, run them in series. Generally pay about $1 per gal size. I have a pair on my 50 year old Mack that are doing just fine.

[Ken Hutchins]

am suspicious of making tanks from epoxy and glass fabric over molds, or plywood... just seems to me that someday, a solvent effect from some impurity in the diesel might attack the epoxy.. but I don't know my chemistry very well to confirm or deny that...

This very thing happened on a brand new machine where I worked. The oiling system on the machine had a plastic reservor and we used the exact oil the manufacturer recommended. Well after they replaced 2 $25,000 spindles under warranty they did some serious investigating and found that the oil was interacting with the plastic in the tank which changed the viscosity of the oil and therefore restricted the flow to the bearings. The oil in the 5 gal can sitting beside the machine was good, but the oil in the plastic tank turned to something like half set jello.

[Peter Malcolm Jardine]

Mild Steel is just fine in my opinion, and probably the least expensive.... having air flow around the tank is good, with a set up that allows you to paint them is also good. Weight of the tanks on that boat wouldn't make much difference I suspect.

Very nice boat BTW.

[PeterSibley]

How long have the last set of tanks lasted mic ?..mild steel is just fine, cheap too .Not many things come cheap around boats.Don't make it expensive just on principle

[mic]

Hi guys, yeh Pete, the boat was built in 1961 and they're the original tanks so i guess they've lasted ok, actually they're not in bad nick it's just that they're the wrong shape for the new spot i've got planned . Ian what's black iron? Isn't that just plain mild steel!

[Andrew S/Y Rocquette]

I would also go for mild steel - plastic is all very well, inert, low maintenance etc., but if there ever were to be, heaven forbid, a fire...

[Ron Williamson]

In 1998 we replaced two mild steel diesel tanks cuz they were leaking from internal rust.One was original,early sixties,the other was new in 1986.
Keeping water in suspension with methyl alcohol would have prevented the problem.
R

[paladin]

whatever material that you decide to use...send me an e-mail off line and i will send construction and scantling information if you desire...

[Gary E]

"Ian what's black iron? Isn't that just plain mild steel! "

From Weirton Steel Co.
http://www.intlsteel.com/content/products/prod_hot_r olled.aspx

Black Iron
Uncoated steel product.

Black Plate
1. Any steel that has not been coated – usually has gone through Tandem mill (cold-rolled). Also defines a product, uncoated material in tin plate gauges. 2. 128 lb. (.0141 in) and lighter tin mill product which has not received any additional metallic coating during production. 3. A low carbon cold reduced steel intended for use in the uncoated state or for coating with tin and chromium.

Hot Rolled Sheets
Manufactured by hot rolling slabs to the required thickness.

Cold Rolled Sheet
A product manufactured from hot rolled descaled (pickled) coils by cold reducing to the desired thickness, generally followed by annealing and temper rolling. If the sheet is not annealed after cold reduction it is known as full hard. (See Full Hard Cold Rolled).

I have the understanding that "black iron" is actually hot rolled steel, sometimes called hot finished. It's advantage is that it cuts and forms easier than cold rolled steel. It should cost less than cold finished due to it's not having that additional processing. As for suitability for fuel tanks, I think it really does not matter, both will work fine.

Eddit to add..
Everything You Always Wanted to Know About Steel. . . But Were Afraid to Ask

http://www.steel.org/learning/glossary/glossary.htm

[ 03-19-2005, 11:25 AM: Message edited by: Gary E ]

[Paul Maselli]

I built two diesel tanks from 1/8 inch plate aluminum Tig Welded at the construction seams. They're ten years old and in excellent condition. Two Caveates: The tanks reside above deck and have sufficient air flow around them. Second before they ever left my shop and went into service they were coated with two applications of Pettit Epoxy primer. This was painted over with a 1 part polyurethane and we re-coat them every 3 years. No Leaks, No corrosion. The diesel keeps the inside corrosion free.

Fuel pickups exit the top of the tanks and have drops within 1/2" of the tank floor. This keeps the sediment out of the fuel lines. Diesel = ample filters and water traps.

Never build tanks with any welded tabs on there exterior for mounting or fixing into position. These will break off due to flexural stresses. Any tank round or square, steel, aluminum, or monel should only be fixed into position by means of chocks, strapping (non metallic) and corner blocking.

[mic]

"Never build tanks with any welded tabs on there exterior for mounting or fixing into position. These will break off due to flexural stresses. Any tank round or square, steel, aluminum, or monel should only be fixed into position by means of chocks, strapping (non metallic) and corner blocking."

Wow! I thought it would be pretty hard to mount 900 Litre Tanks with out some sort of structual flanges, although the strapping idea sound OK, the current tanks are strapped. Just before I make my decision on which material to use, I would like to get an opinion of whether copper really does foul the injectors, and whether it would be a good choice for construction material for fuel tanks. My boat currently runs copper fuel lines, and if they really do pollute the fuel is there a better replacement.

[formerlyknownasprince]

Mic

I used 6 x second hand 104 litre (25 US gallon) stainless LPG tanks. These are ex auto use.



These photos are during the trial fitting - I've hit them with a bit of cutting compund and a polisher since.

We made our own rolled straps which have a rubber insert.

No baffles as they are only just over a foot in diameter. We made up new o-ringed cover plates and welded in a drain on each tank and a breather at the other end.

One of the reasons for going this way was to preserve reasonable capacity and to limit the amount of diesel carried. I gave away about 800 litres of diesel that had gone stale in the old tanks. The centre two tanks are the only ones filled unless I go on a long trip.



Good luck whichever way you go

Ian

[mic]

Any luck with the copper question people? [img]smile.gif[/img]

[chergui]

A company called Tek Tanks (http://www.tek-tanks.com/) allows you to design your own tank and they will build the tank to your specs out of polyethylene. No corrosion, no flaking metal when the tank gets old. That's what I'm doing.

Jon

[ 03-30-2005, 11:26 AM: Message edited by: chergui ]

[Thad Van Gilder]

I got a quote from the monel people for $3,000 for a 4 by 8 foot sheet of 3/16".

There's now way in hell IVY will get new tanks of Monel!!!!!

-Thad

[formerlyknownasprince]

Mic

Don't use copper. No need to. You can use either bundy tube (avail from Pirtek or equivalent) or just run flexible fuel hose. If you use bundy tube - which is flash coated steel tube - I'd paint it with POR 15 too. Depends how easy it will be to replace it if you have too in the future.

Make sure your pipes are large enough.

I'm running about 15' from my tanks and for my Detroits I need 1/2" in and 3/8" return lines (the 1/2" is required to minimise drag over a 10' run). The Detroits pump about 30 gallons of fuel an hour, so I will be fitting a fuel cooler to each motor. Actual consumption for a 12nm run two weeks ago was 18 litres at 8 knots.

I'm using rubber hose due to the difficulty (read impossibility) of getting straight tube in under the cabin sole.

Ian

[Jamaica Mike]

Originally posted by chergui:
A company called Tek Tanks (http://www.tek-tanks.com/) allows you to design your own tank and they will build the tank to your specs out of polyethylene. No corrosion, no flaking metal when the tank gets old. That's what I'm doing.

Jon

I have a 40 gal (US) water tank built from 3/8" welded polypro plastic. I have no idea of the specs required for a much larger tank carrying Deisel oil on the water... there must be a marine standard specification somewhere. But MANY large tanks in agro and construction applications are poly.

Might be worth checking out.

JM

[LIMIN]

I use to own a 37 ft. boat built in 1914. It had copper fuel and water tanks. I owned this boat for twenty years and for eighteen I ran a diesel engine in it and had no problem (approx 2000 hours). During this time the fuel tank sprung a slight leak. After removing the tank I found the leak in a soldered seam. It took longer for the solder iron to heat up than it took to fix the leak. The tank was in exclent condition even though it was 90 years old. The copper is approx 3/32 thick. The boat and tank is still being used.

[formerlyknownasprince]

The tanks I pulled out of my boat - when they were 65 years old - were brass - which appears to have been plated originally (nickel?).

All the books say to avoid copper.

Ian