Maintain Your Fuel Tank
Don’t let this happen to you! November is the time of year when the postponing catches up to people. The huge tasks we avoided all summer stare us in the face. Do absolutely nothing, and you run the risk of a summer lost pulling epoxy from your hair instead of sailing. If your boat is actually 20 years old or even older, a fuel tank replacing– a bear of a project, even in optimal circumstances– may be that project you’re delaying. If it is, well, you’re in luck, since we’ve got a reasonable bit of information to help guide you through the process.
Marine consultant and technical writer Steve D’Antonio wrote an extensive article about tank replacing previously. The following excerpt from that short article deals explicitly with aluminum, however, there certainly are other options.
Aluminum is a common substitute fuel tank material choice for most installations. It is simple to work with, easily obtainable, relatively inexpensive, light, strong, and corrosion resistant, although far from corrosion-proof. There certainly are some prerequisites whenever selecting aluminum for fuel tank fabrication, and some important installment details which must be followed.
The alloy used must be 5052, 5083, or 5086 series and a minimum of.09 inches thick. This specific gauge is ABYC authorized, but, 1/8-inch (.125 inches) is preferable, and 1/4-inch (.25 inches) should be considered when it comes to “extreme” applications, like bilge installments or perhaps where optimal resilience and longevity is sought. Every fraction of an inch of wall thickness will buy more years of life, especially if the installation is less than perfect.
If aluminum possesses many good characteristics, why use anything else? Unfortunately, as many boat owners will attest, aluminum is anything but indestructible. Among its primary weakness is its susceptibility to some deterioration, especially pitting, galvanic, and poultice. Pitting is caused by upsetting the corrosion-resistant film formed on the surface area of aluminum, sometimes as a result of variations in available oxygen. As soon as it takes a foothold, the pit grows deeper, which produces a more powerful cell, speeding up the next type of corrosion, which is galvanic.
Galvanic corrosion is the interaction between dissimilar metals in the presence of an electrolyte. In aluminum tanks, this particular procedure may occur among a copper-alloy fitting (brass or bronze) and seawater, or between a pitted aluminum surface and seawater. You must make sure that all metals that are actually in contact with the tank are compatible with aluminum.
To prolong the tank’s life as well as minimize the chance of any possible harm, bonding the tank is also a good idea. Bonding the tank is an American Boat and Yacht Council requirement for several reasons: to avoid electrocution for shore-power-equipped vessels, to mitigate lightning damage, as well as to prevent side-flashes (electrical current jumping in 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 must be connected and remain at the same potential.
The resistance between any two components in this system should not exceed 1 Ohm. (It’s essential to keep in mind that any bonding wire attached to the engine block must be sized to safely carry full engine cranking amperage.).
Bonding the tank minimizes the possibility of damage caused by stray current corrosion, and it prevents static electricity build-up on or in the tank, which could result in a spark and explosion (admittedly not likely on diesel installations). If the tank is bonded, and the bonding system is actually correctly attached to an underwater hull zinc anode, then this anode might provide some corrosion protection to the tank.
Poultice corrosion results when aluminum continues to be in constant contact with a wet surface, like wood, carpeting, insulation, or stagnant water. If allowed to make contact, these demons are the precursors of an early death for any type of aluminum tank. The result is actually prodigious quantities of white, gooey aluminum hydroxide. (It looks like freezer-burned vanilla ice cream.) This will rapidly jeopardize the tank surface.
The greatest defense from this specific scenario is careful attention to installation details. No hygroscopic material should be permitted to make continuous contact with an aluminum tank, period.
A suitable aluminum tank installation requires 1/4-inch by 2-inch strips of non-hydroscopic material, like neoprene or high-density plastic (Starboard for example), spaced two inches apart and positioned in between the tank bottom and the shelf on which it is installed. This will certainly prevent the tank from resting in water, and also enables air to circulate underneath the tank, while enabling condensation to evaporate. Furthermore, the installer must make sure to bed or glue the insulating material to the bottom of the tank. In case this is not performed, water or condensation will certainly find its way in between it and the tank, and corrosion will set in. Any other mounting arrangements, such as cribs or beams, must feature this insulating material.
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