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Old 06-12-2009, 17:02   #16
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This is just a quick question and is sort of related to the topic. I currently have a 125 steel tank without any leaks or pinholes and that is functioning perfectly! But... I would like to increase my fuel storage capacity for anticipated longer trips.
I would like to know about fuel bladders or bags. I have pleanty space but in difficult to access places and they are rather odd shapes as well.
Has anyone tried these or does anyone have any comments, suggestions or advice please...

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Old 06-12-2009, 17:50   #17
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SS tanks

I have a pair of 20 gallon SS tanks in my boat, I don't know if they are original eq. or not but the boat is a '66, and Im pretty sure they were installed early in her life. They have only slight discoloration in the weld areas but no visible corrosion issues. I think one key to thier success is they were installed with an air gap to allow air flow around all surfaces. Without oxygen stainless doesn't stay stainless and you will have problems. The quality of the weld plays a large roll in longevity as well. Many experts advise against SS tanks because of crevice corrosion in some alloys and when incorrect filler rod is used.
I know of several aluminum tanks that had to be replaced due to pinhole leaks related to moisture and corrosion. But if the tank was treated as stated earlier in this thread with a product made for aluminum, the tank should last a lifetime providing the protection doesn't get breached through chafe or other damage.
I guess the bottom line is metal tanks of any type can give long service providing care is taken in the construction, preperation and installation appropriate for the material they are made of.

my .02

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Old 06-12-2009, 17:52   #18

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" make sure the new tanks have a dimple (at least 2 inches diameter by 1/2 inch deep near the center of the tank floor with a threaded connection and a place to put a drain cock."
As I was told, that is either against ABYC or USCG regulations and if the boat is insured, the insurer may reject it when they find the drain plug on the next survey. Don't know for sure--but you might want to doublecheck with your insurer before installing any drain plugs in the fuel tank OR engine pan.

Plastic sounds good, except for the fire hazard. But it also is universally white and translucent, so it encourages biomatter by allowing photosynthesis. Not a good thing in diesel tanks. The fire hazard may alos be overstated. By the time that fire has eaten through a diesel tank (and I'm sure the tank makers have some specs on that) I would suspect it is abandon ship time anyhow. The usual "one liter bottle" sized extinguisher can put out one skillet or one small waste basket--and that's all.
More likely that a pinhole leak in a metal tank would allow fuel to get where it shouldn't go, and start a fire that way.
There are drawbacks to every material.

Friends who have used bladders suggest sticking to Nauta ("the" brand name) or other premium maker, and placing something in between the bladder and the hull/compartment to prevent chafe. Something like astroturf (no mildew) or the rubber-tire-strip type floor mats, to make sure nothing rubs or punctures the bladder. They've been happy with theirs that way.
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Old 06-12-2009, 18:06   #19
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My stainless steel tanks are fifteen years old and still going strong. No problems with them yet. As long as they aren't sitting in bilge water, they should last a very long time.
Dave -Sailing Vessel Exit Only
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Old 06-12-2009, 18:58   #20
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Cole, aussie regs allow the use of soft bladder type f'o tanks in none commercial vessels, chaffe is the main problem with a slack tank the storage area used has to be very well protected.There are many in use you very rarely hear of a failure, use only top quaulity bags and fittings.

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Old 06-12-2009, 19:01   #21
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The differences SS vs Al

I can agree that either SS or Al would last a long time if they stay dry but what would be the difference? So copy and paste and add to the list.

Aluminum +
Thicker metal, thicker weld
Faster heat transfer
Cost is less

Aluminum -
Difficult to weld after contamination or erosion (salt soaks in)
Less noble then 316 SS

SS +
Can resist some salt contact if dried out
Easier to weld repair
Can be used for water if cleaned properly

Thinner metal (more flexing), thinner weld
More likely to sweat
Cost is higher


One thing to remember! Once salt water gets into a wood support or between a tank and a support it remains there until it's replaced or cleaned. Once salt is placed it continues to absorb moisture from the air around it.

An example would be; at work we cleaned and sandblasted some submerged cast iron valves (porous) on a Friday. They looked real good! We came back in on Monday and they were soaking wet and covered with rust again.

The only way to stop this process is to boil the items in fresh water several times, bake it in a oven for a an hour per inch of thickness and immediately after cooling coat the item with an epoxy or other water tight sealer to prevent the absorbency of any more moisture.

There is a product called salt away, that soaked in or sprayed on breaks down salt crystals Salt-Away Applications ... I use this when ever I flush out my outboards and leave residue in my diesel over the winter. You can spray it on motors as well vs WD-40.
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Old 06-12-2009, 19:19   #22
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Shakey Dog,
I have been looking around this site and there has been some discussion of the flexible tanks and it seems that they can be quite good providing they are cushioned and secured to stop them moving around. Do you know of any suppliers because I have tried the two main on-pine chandleries but they appear not to have flexible diesel tanks... water tanks and holding tanks yes... not fuel. I am looking at a 200 litre tank with a transfer pump to pump from it to the main tank as required.
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Old 06-12-2009, 19:24   #23
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Having replaced many aluminum tanks as well as steel due to corrosion pinholes if i were outfitting my own boat i would consider building a custom composite tank first,i would have to research it well though as i am not sure of the track record but as i would be building it myself and i would chose the correct materials i expect it would be the best choice ,my other first choice if that didnt pan out would definatly be plastic,i would not even worry for one second about the fire risk,the odds are in my favor to not have an engineroom fire with a normaly aspirated diesel and good next choice would be SS followed by properly protected steel. While coating the bottom,sides and ends of an aluminum tank with spray bedliner would help with protecting the outside where it sits on the bearers i believe,i wouldnt consider it for my own boat for any tank.Many automobiles have been using plastic tanks for gas or diesel for a couple of decades now with good results,thats millions of vehicles and i just dont hear of them either leaking or blowing up and they are a lot thinner plastic than boat tanks,
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Old 07-12-2009, 00:19   #24
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Hi,Colin, Whitworths appear to have dropped them from from there stock list, no idea why?. Google 1. Liquid 2. Flexitank [Austrailia] P/L. 3. Fabric, they all have bladders in the size you require or will tailor to your specs.

Cheers, Doug.
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Old 07-12-2009, 01:40   #25
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Lots of good avice on the pros and cons!
My current thinking is to go for stainless. The fuel tank is a basic rectangular shape with no awkward features, so should be straight forward to weld. The tank is situated below the cockpit floor, but above the bilges, so does not come into direct contact with saltwater.
I would also consider powder coating the external surfaces with a good quality polyester powder. This would help prevent any corrosion starting due to contact with any damp plywood or timber surrounding the tank. Any views on this idea?
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Old 07-12-2009, 02:44   #26
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Don't powder coat. Powder coating is porous - a honest knowledgable poweder coater will confirm this. You would be better off coating the timber or plywood with epoxy if you want to keep the moisture off the tank.
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Old 07-12-2009, 04:55   #27
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Originally Posted by delmarrey View Post

One thing to remember! Once salt water gets into a wood support or between a tank and a support it remains there until it's replaced or cleaned. Once salt is placed it continues to absorb moisture from the air around it.
That was my main concern. The water was confined to the bilge area so the wood did not get wet. The tank may sit on some foam blocks separating it from the other fuel tank and the sides of the bilge. I was concerned about getting those cleaned so they don't sit and corrode the tank. I cannot even come close to accessing them though so I may be out of luck.

Maybe that yellow film stuff that is coating the tank will do something. Does anyone know what that might be? It is almost like they coated it with epoxy or something. Very hard but is peeling around the fittings where tools are applied, etc. Is there anything that can coat tanks of any metal to reduce the corrosion?

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Old 07-12-2009, 05:47   #28
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Yes, aluminum tanks are often epoxy or coal-tar coated.

A good mounting method for metal tanks is to glue 2" x1/4" fiberglass battens every 12" across the bottom of the tank using 5200. Be sure to completely butter the battens with the 5200 and make a fillet on the batten edges with your finger. Now the tank will sit on these battens and never contact a wet spot and water can't get between the tank and the battens.


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Old 27-01-2010, 13:38   #29
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I am getting ready to have new alumin diesel tanks fabricated. I have been considering coating the exterior and interior with a product like Thiokol to prevent corrosion, thoughts would be appreciated.
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Old 27-01-2010, 14:20   #30
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I got very close to ordering custom plastic tanks (with baffles) but backed off and went with coated aluminum (with glued hard rubber pads at contact points).

My concern with plastic is that diesel keeps changing. The formulation has reportedly changed so much in the last few years in the US that refineries had to shut down and be reconfigured. So far, plastic tanks seem to have been fine but I worry that someday something might happen to diesel along the lines of when Ethanol started to melt 1980's era fiberglass tanks. I couldn't find anyone "in the biz" who said my concern was silly.

Does anyone know more about this stuff?


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