Fuel Tank Life / Construction

Can any one comment on tank construction on Trojan Boats in particulaly the F-36 1985? How much time if any should I have on these tanks? They are aluminum I believe?

What are the thoughts of the group? Should the be replaced or just carefully monitored and if so what is the best way to monitor?

How many of you out there with mid 80 Vintage Boats have replaced their tanks and most importantly why did you see a problem or was this done as a preventative measure?

 

My boat is a Norwegian Draco Twincab from 1980. In 1995 I received an alarming phone call from the harbor master about a smell of gasoline near my boat.
It turned out to be a hole in the aluminum tank bottom caused by drops of sea-water that must have entered through the vent.
I had the tank repaired by cutting off the damaged bottom and welding in a new, somewhat thicker aluminum plate. Since then, every few years I remove the tank element and inspect the inside with fiber optics. The problem did not reoccur.

 

It's not unusual for tanks only three years old to fail. The reason aluminum tanks fail early is most often related to poor mounting, if your tank has gone 24 years than Trojan obviously did a nice job of installation.
If it's not too difficult to access your tank, it's most certainly due an inspection. If it's possible to remove the tank, along with an inspection I would recommend a thorough cleaning, prep, and epoxy coating.
It's often possible to greatly extend the life of a fuel tank by coating it with a epoxy or vinyl ester coating but good prep is required.
Unfortunately many boat manufacturers do not provide adequate access to their tanks which is one of my pet complaints with the US Coast Guard recreational boat construction standards. Designing and building a boat that requires a structural member to be removed ( cutting the deck out) should be criminal.
Because the inspection of many tanks is so invasive, many boat owners can't justify the expense until the vessel is no longer usable.
I tell my customers that I liked to inspect fuel tanks at 7-10 years and when I build a boat, it's designed to make that practical.
Gerald

 

I clean tanks daily, some frp, some aluminum, some ss and some carbon steel. Life span can vary greatly, however there are many factors that lead to an early demise. Trawlers are usually inflicted with leaky decks and the top of the tanks rust out. Sailboats and power boats sometimes have the tanks mounted via foam and this has proved to be problematic. Truck and farm equipment tend to rust from the inside, due to the condensation and carbon steel tanks.

Diesel fuel tends to develop a heavy algae, gas fuel tends to breakdown from the dreaded ethanol blends. When I first show up I check diesel for bacteral and fungal growth. If gas I check to confirm the percentage if any of ethanol. Then I check for water, if found, I pump that off, then start my cleaning cycle. As I stated above I clean tanks, I firmly beleive to polish the fuel via a low flow filtration system is like putting a bandaid on an infected finger. The contaminates in the tank have to come out, that's my job.

I have a Trojan 40 footer coming up and I can respond to your question better afterwards.

I also have a couple of customers in the Ft Lickerdale area with gen-sets that require annual servicing, if possible I can drop on down to South beach.

Good Luck,

Luther Carrier
Absolute tank Cleaning
www.AbsoluteTankCleaning.com

 

Luther,

Can you explain how to check fuel for ethanol? I know that it has been used to replace MTBE for several years but how would I know if it has more than that amount?

 

El Sea, what is your opinion of FBG waste, water, fuel tanks? Of course, microbs can grow on any surface but they do not rust or corrode. I ask because I'm getting ready to buy tanks on a new build. Thanks, Stan

 

Tom28571:
To check for ethanol I use two bottles, with calibrations in ounces.
In one bottle I put ten ounces of gas, In the second bottle I put two ounces of water.

Now I pour the water in to the bottle with the gas, cap off and shake.

Lastly, let set and the water will settle to the bottom and if ethanol is present it will absorb the water and the water line will rise from two ounces to whatever Ethanol blend you have. It can be from 1/2 oz. to 2 oz. above the original water line. This is very simply test, every boater should test their fuel 'often'.

Rasorinc:
Glass tanks are just as sound as any UNLESS you have gas fuel. Ethanol has been reported to react adversly to glass tanks by attacking some resins.
For microbs to exist they need water, and this is typical even on land in ponds, mop buckets, etc.

My boat has glass fuel and water tanks and poly waste. This was a positive factor when we bought.

El Sea / Luther Carrier

 

Thanks Luther,

If I understand the action correctly, the water will pull the existing ethanol out of solution with the gasoline, combine with it and precipitate to the bottom.

So the effects that ethanol was supposed to have with the gasoline is now lost and there is a non flammable mixture at the bottom of the tank. My tank is home made fiberglass with isothalic resin. If I find water in the tank, can I put in lots of ethanol or alcohol and pump that out to clean the tank. I plan to replace the tank with a plastic one.

 

Not really Tom, actually the ethanol pulls the water into the fuel. This is part of the phase separation.

To remove water from the tank, this can be done mechanically by pumping the water off, or sending a hose to the very bottom, at the low point and syphoning. Or if only a minute amount of water check my website and link on to the Sentry link. I use this product daily to treat water.

Luther Carrier
www.AbsoluteTankCleaning.com

 

Tank life is dependent on a lot of factors but a properly installed aluminum tank could last forever. However a study done in the 80's by UL for the USCG determined the average life was ten years. But I have seen aluminum tanks as young as 6 months fail. As has been stated here the typical problem with aluminum tanks is pin holes from corrosion. But there are two ways this happens.

First is from the outside. Bare aluminum has an oxide on it that protects the metal. That is why you rarely see painted aluminum tanks, or small boats for that matter. If water gets on the tank it dissolves the oxide. If it dries quickly the oxide reforms and continues to protect the tank. If it stays wet the oxide never reforms and the tank corrodes at the wet spot and eventually puts a hole in the tank. So aluminum tanks should be mounted so that air can circulate around the tank. Unfortunately a lot of boat manufacturers mount the tank on a flat surface, but to keep moisture from the bottom they put a layer of neopreen or other non moisture absorbing material between the tank and the mounting surface. Sometimes this works but far too often it doesn't and moisture gets trapped under the tank.

The second way is corrosion from the inside. Ethanol (see Much Ado About Ethanol http://newboatbuilders.com/docs/Ethanol.pdf) has been in gasoline for a long time, since the 70's. In the mid 70's the USCG began to see problems with aluminum tanks due to Ethanol (which is just a fancy name for Ethyl Alcohol) What happens is described above. After time (varies due to the concentration) you get phase separation and at the water alcohol interface you get also acids that form and eat the bottom of your tank. You store your boat in the fall with a full tank, come back in the spring and the tank is empty but your bilge is full.

Other mounting problems cause tank failure.

One practice is to put the tank in the bilge and put a limber hole in the aft bulkhead to drain the tank compartment. The limber hole gets clogged and your tank is sitting in several inches of water.

A third method is to foam the tank. I have not yet seen a foamed in tank that did not corrode out. Moisture gets between the foam and the tank and corrodes the tank.

The quickest, surest way to test your tank for leaks is to have a pressure test done. Most marine repair shops can do it. They pressurize the tank to three psi. They check all connections and fittings with soapy solution for bubbles. If it bubbles that's a leak. They also leave it pressurized for 30 minutes, sometimes more. If the pressure drops, there is a leak somewhere. If it's not at the fittings, it's the tank.

So have it tested and inspected.

One other thing. Almost all gasoline today has ethanol in it. This includes fuel sold at marine gas stations. Yes you can test it the way described, but that will simply tell you what you already know. In fact back in the 80's we used to check for alcohol the way described above. Even back then it was amazing how much alcohol was in the fuel.