Tackling Fuel Tank Replacement

Posted by Darrell Nicholson with Steve D'Antonio at 12:26PM - Comments: (9)

Patrick Childress
Patrick Childress

Can this aluminum water tank be saved? The full report is in the December 2014 issue of Practical Sailor.

November is the time of year when the procrastinating catches up to us. The big projects we avoided all summer stare us in the face. Do nothing, and you risk a summer wasted pulling epoxy from your hair instead of sailing. If your boat is 20 years old or older, a fuel tank replacement—a bear of a project, even in ideal circumstances—might be that project you’re postponing. If it is, well, you’re in luck, because we’ve got a fair bit of information to help guide you through the process.

Marine consultant and technical writer Steve D'Antonio did an extensive article for us on tank replacement in the May 2007 issue of Practical Sailor. The following excerpt from that article deals explicitly with aluminum, but there are other options.

Aluminum is PS’s replacement fuel tank material choice for most installations. It is easy to work with, readily available, comparatively inexpensive, light, strong, and corrosion resistant, although far from corrosion-proof. There are some prerequisites when selecting aluminum for fuel tank fabrication, and some important installation details that must be followed.

The alloy used must be 5052, 5083, or 5086 series and a minimum of .09 inches thick. This gauge is ABYC approved, however, 1/8-inch (.125 inches) is preferable, and 1/4-inch (.25 inches) should be considered for “extreme” applications, such as bilge installations or where maximum durability and longevity is sought. Every fraction of an inch of wall thickness will buy more years of life, particularly if the installation is less than perfect.

If aluminum possesses so many good attributes, why use anything else? Unfortunately, as many boat owners will attest, aluminum is anything but indestructible. One of its primary foibles is its susceptibility to some corrosion, particularly pitting, galvanic, and poultice. Pitting is caused by upsetting the corrosion-resistant film formed on the surface of aluminum, sometimes due to variations in available oxygen. Once it takes a foothold, the pit grows deeper, which creates a more powerful cell, accelerating the next form of corrosion, which is galvanic.

Galvanic corrosion is the interaction between dissimilar metals in the presence of an electrolyte. In aluminum tanks, this process may take place between a copper-alloy fitting (brass or bronze) and seawater, or between a pitted aluminum surface and seawater. You must ensure that all metals that are in contact with the tank are compatible with aluminum.

To prolong the tank’s life and minimize the chance of any potential harm, bonding the tank is also a good idea. Bonding the tank is an American Boat and Yacht Council requirement for several reasons: to prevent electrocution for shore-power-equipped vessels, to mitigate lightning damage, and to prevent side-flashes (electrical current jumping between metal components during a lightning strike). According to the ABYC, the boat’s bonding system, the DC negative system (which includes the engine block and battery negative), and the AC safety ground all should be connected and remain at the same potential.

The resistance between any two components in this system should not exceed 1 Ohm. (It’s important to note that any bonding wire attached to the engine block must be sized to safely carry full engine cranking amperage.)

Bonding the tank minimizes the likelihood of damage caused by stray current corrosion, and it prevents static electricity build-up on or in the tank, which could lead to a spark and explosion (admittedly unlikely on diesel installations). If the tank is bonded, and the bonding system is properly attached to an underwater hull zinc anode, then this anode may provide some corrosion protection to the tank.

Poultice corrosion results when aluminum remains in constant contact with a wet surface, such as wood, carpeting, insulation, or stagnant water. If allowed to make contact, these demons are the harbingers of an early death for any aluminum tank. The result is prodigious amounts of white, gooey aluminum hydroxide. (It looks like freezer-burned vanilla ice cream.) This will quickly compromise the tank surface.

The best defense against this scenario is careful attention to installation details. No hygroscopic material should be allowed to make continuous contact with an aluminum tank, period.

A proper aluminum tank installation calls for 1/4-inch by 2-inch strips of non-hydroscopic material, such as neoprene or high-density plastic (Starboard for instance), spaced two inches apart and placed between the tank bottom and the shelf on which it is mounted. This will prevent the tank from resting in water, and enables air to circulate beneath the tank, while allowing condensation to evaporate. Additionally, the installer must be sure to bed or glue the insulating material to the bottom of the tank. If this is not done, water or condensation will find its way between it and the tank, and corrosion will set in. Any other mounting arrangements, such as cribs or beams, must include this insulating material.

For a more detailed discussion of fuel tank replacement see the May 2007 issue of Practical Sailor. For more on bonding, lightning protection systems, and grounding, see Volume Two of our new five-volume ebook on Electrical Systems. Ed Sherman, past contributor to Practical Sailor and education director for ABYC, also covers bonding and testing for stray current leaks in detail in his excellent book Advanced Marine Electrics and Electronics troubleshooting. In the August 213 issue, contributor Drew Frye examined corrosion-fighting fuel additives. In the December 2014 issue of Practical Sailor, which will soon be available online, we look at the way one owner dealt with his corroding aluminum tank—a water tank, in this case—without having to pull it or replace it.

Comments (9)

Wonder what cost of fuel tank replacement for thousanads or even $10k or more for some vessels versus remove fuel tanks and fossil fuel engine reftrofit with electric motors. If they can power a Tessa and submarines in WWII why not a boat. Safer, cleaner, more powerful, less complex, uses less space (maybe same as a Tessa auto) and batteries can be recharged by prop action, solar and wind.

Posted by: DockH | February 16, 2017 8:56 AM    Report this comment

Wonder what cost of fuel tank replacement versus remove fuel tanks and fossil fuel engine reftrofit with electric motors. If they can power a Tessa, why not a boat. Safer, cleaner, more powerful, less complex, uses less space (maybe same as a Tessa auto) and batteries can be recharged by prop action, solar and wind.

Posted by: DockH | February 16, 2017 8:54 AM    Report this comment

Aluminum fuel tank corrosion and leak potential seem to be an important considseration when shopping for a sailboat. Is there a good resource addressing this potentially costly risk when evaluating 30 foot plus sailboats ?

Posted by: DockH | February 16, 2017 7:25 AM    Report this comment

Aluminum fuel tank corrosion and leak potential seem to be an important considseration when shopping for a sailboat. Is there a good resource addressing this potentially costly risk when evaluating 30 foot plus sailboats ?

Posted by: DockH | February 16, 2017 7:24 AM    Report this comment

One rule: As long as the aluminum boat tank has a good air flow around metal surfaces, contact with water will not damage it. Properly installed, tanks will usually outlast the life of the boats.

and little more about Aluminum Boat Fuel Tanks, Installation and Repair at: www.craigmarine.info/accessories/fuel_tanks/aluminum_boat_tanks.htm

Posted by: silan | December 10, 2015 3:51 AM    Report this comment

Tying an aluminum tank to a zinc hull anode is not going to be effective; the anode would need to be aluminum. Furthermore, the water under the tank is probably not coupled to the ocean, so there is no protection; the anode probably needs to be connected directly to the tank, as per shore side tank installations.

Posted by: Drew Frye | May 22, 2015 12:38 PM    Report this comment

Additionally, there are fuel additives that controlninternal corrosion.

Practical Sailor August 2013

Posted by: Drew Frye | November 12, 2014 9:18 PM    Report this comment

Make SURE your new tank has some way to access the bottom in at least one location in order to evacuate accumulated water and/or sludge from the bottom using an external pump/ cleaning system. The ABYC permits users to install without bottom drains and is silent on clean out-provisions. New engines, especially those with common rail fuel systems ,require pristine condition fuel . In a tropical area such as Florida or other warm areas, this fuel quality is almost impossible to obtain using std engine or boat -mounted fuel filters alone. I just inspected several $$$$$ boats at Ft Laud boat show and find some mfgrs are opting to OMIT ANY PROVISION for diesel tank clean out ,bypass filters,etc. ( Save $$$ ) And on a poly tank, a set of remedy connections are impossible to retrofit . Imagine ones' surprise when you spend several 100K on a new diesel boat with "all the toys "--- and you discover you cannot even clean the tank , ( nor remove it ) for rehab.
John W. Roth
Diesel Fuel Management Advisor
Ft Lauderdale,FL.

Posted by: John r | November 12, 2014 11:47 AM    Report this comment

Also, never use black rubber matting as an insulating material....it contains carbon
and carbon reacts with aluminium and will eat holes in it! It took 23 years but we had four
rectangular holes in the tank, all exactly where the black pads were!
Michael, Canadian Yacht St. Leger

Posted by: stleger41 | November 12, 2014 11:00 AM    Report this comment

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