ucked away under the cabin sole floor boards, the fuel tank doesn't get much attention.  In fact, it will probably be ignored until something goes wrong.  Even if you're good about performing preventative maintenance, your time and energy probably stops short of a detailed inspection of your fuel tank.  There's good news about tank maintenance: it's possible to refinish that tank without too much effort and expense. It's possible to maintain your existing tank in a condition worthy of your confidence and certain to give years of trouble-free service.   The key is to do it before it's too late; new tanks are expensive.  

A typical black iron tank, painted and installed at the factory, undergoes all kinds of insults in the bilge.  Its exterior is assaulted by saltwater, fresh water, and bilge cleaning chemicals.  The paint breaks down and, before you know it, rust begins to do its thing on the undersides, even though what you can see from above may look fine as it does in fig. 1.  On the inside, if the tank is normally kept full and the owner is careful about filtering fuel before adding it to the tank, severe problems are not as likely to develop. (See "Fuel Tank Facts"  - ed.)

Several years ago we were in the market for a used pocket cruiser.  On board the nine year old Baba 30 cutter we eventually purchased, my first look at the fuel tank located in the bilge compartment raised questions and concerns.  The flashlight  beam along the sides of the black iron tank revealed puffs of rust blossoming midway down to near the bottom of the tank.  The fiberglass walls of the bilge space were very close to the sides of the tank, so it was impossible to thoroughly assess the tank's condition without pulling it out.  As built, the tank compartment was isolated from the rest of the bilge to contain any spills of diesel and probably to isolate it from the normal slosh of bilge water.  Nevertheless, somehow water had entered the compartment, probably working its way down from above, and over the years began to deteriorate the tank's gray enamel paint, initiating the rusting process.

The flashlight beam also revealed that the tank was sitting in a small puddle of liquid.  A hand pump sampled the liquid, which was mostly water with a little diesel fuel in it.  The presence of diesel fuel in the sample raised the concern that the tank might have a small leak.  Fortunately the compartment remained dry after it was pumped out and left alone for several days.  Fuel leakage through the tank walls or welded seams was apparently not a problem.  I made sure the tank was topped off with fuel for this test.  

Some might recommend conducting a pressure test to detect fuel tank leaks.  Pressure testing requires sealing all openings and pressurizing the tank with a pump to achieve 2-5 pounds per square inch pressure.  If the pressure maintains at the original level overnight, the tank is secure.  I didn't have what's needed to conduct this test,  but it is a valuable test and would have given more definitive information when making our decision  about buying the boat.  
After assessing the tank's exterior, I turned to the tank's interior.  Two gallons of diesel was pumped from the bottom of the tank  to check for problems such as microbial sludge or water accumulation.  I was looking for the telltale greenish black or brown slime caused by bacteria and fungi that can infest diesel fuel, clog filters and affect engine performance.  Fortunately, the sample was clean.  Water in the tank, either from condensation or contaminated fuel,  can provide a medium where organisms can thrive.  I made a mental note about the need to refinish the tank exterior, but the tank was left in place for a future appointment with the tank doctor.  Every time I thought of pulling the tank out and refinishing it, I delayed because the time the task might take would interfere with our sailing.  It turned out that the job, once started, took less than two weekends.  

The 30-gallon wedge-shaped, flat-bottomed tank, measuring about 36" long, 18" high at it's highest point, and with a maximum width of 16",  appeared quite heavy and was secured into the bilge across the top by three floor joists.  It had various hoses and ground wires connected to it, complicating its removal.  Finally, after several years, in the course of replacing some fuel system parts on our Volvo Penta diesel, I decided it was time to tackle that tank.  We had just returned from a 1,300 mile trip and the tank was now on the  "MUST DO" list.

The floor joists were easily removed.  The hoses and wires were detached and my 15 year old son and I lifted the tank out fairly easily.  Once removed, it was painfully obvious that the tank should have been pulled and refinished years ago.  The gray-colored factory enamel finish was rusted through over most of the lower half of the tank.  Pitting of the black iron surface had begun.  My first reaction was to attach a wire wheel brush to my hand drill to remove the rust and old paint.  After a few minutes with the drill and brush it was clear that sandblasting was necessary.

I called around to find a metal coating shop able to sandblast and then powder coat the tank with epoxy.  Epoxy powder coating offers exceptional qualities which include: high impact resistance virtually eliminating chipping and scratching; outstanding moisture, chemical and corrosion resistance. Also, there is good control of film thickness, from less than one mil to over six mils of coating.  Powders can be applied to all electrically conductive metal surfaces such as iron, steel, and aluminum.  Metals that don't rust may corrode in the marine environment, and can still benefit from the coating.  The only limitation is that the object must be able to withstand temperatures up to 400 degrees F. without damage.  In our case there was no concern over the temperature used, save for a large rubber gasket seal, at the inspection plate, which was removed before we started the coating process.

Prior to delivering the tank to the shop, the tank interior was thoroughly cleaned with rags to remove the residual diesel fuel and a small amount of sediment, mostly bits of rust.  The sediment hadn't shown up when the sample was taken.  Reducing the potential for water condensation inside the tank is not the only reason why it's a good idea to keep your tank full.  It also minimizes oxidation of the inside tank walls, eating away at your tank and welded seams.
.
Electrostatic powder coating is a high tech metal coating process which uses dry powdered paint.    The powders are applied using a special gun with a high voltage applied to it which charges the particles causing them to cling in a uniform manner to the part being coated.  The coated part is then placed in an oven at 300 to 400 degrees F  to fuse the powder to the metal surface.  It is heated for periods of ten minutes to an hour, depending upon the size of the object.  On cooling, the part is ready to be used.

The shop estimated the job at less than $100.  Garnet sand, which is hard and sharp, was used to blast the tank; it's effective in removing rust, even in the pitted areas.  The next step was to blast it with minute glass beads, polishing the tank to a silver color, and removing any remaining rust, as well as "flash rust" which developed overnight, between the time it had been sandblasted and readied for the powder coat.

The powder coating, approximately 6 mils thick, used on the tank consists of 100% epoxy, with the appearance of gloss white enamel. The epoxy powder was applied directly to the metal.  No primer is used in the process, because the electrically charged powder requires bare metal to adhere to the coated surface.  Light paint colors enhance your ability to check for further rusting, so you can avoid another major refinishing job.  

While the job involved some hard work, it was easier than we had thought and cost less than replacing the tank altogether.  The result is a tank which is as durable as the rest of the boat. With a durable tank, you'll spend your time enjoying sailing, not wondering what might happen if the tank starts to lose its contents into the bilge.
S

