Fuel tanks

do you mean Bronze?

 

yes I had a sandusky skiff it had a bronze tank ,anyway I wish I still had that baot it was the dayton river boat for the NCR park.

 

I have no experience with Bronze tanks. The only time I've even seen one was on a Coast Guard Cutter built in 1939 and the tank was for lube oil. I would think it would be expensive. It would have to be Naval Bronze to survive in the marine environment. I can't think of any advantage it would have over other materials other than you could polish it and it would look really nice. You would create a really active galvanic cell if it is connected to steel or aluminum fuel lines, unless you used fuel hose. If you used metal fuel lines they would have to be copper nickel or nickel copper (again, expensive) to prevent a current being created and causing galvanic corrosion. Whatever you do, don't use pure copper fuel lines. They would disappear in a short while.

Maybe someone else has some experience with this. I imagine this kind of thing was common on boats built before the 40's or 50's.

 

yup that boat was built in the 20s or 30s , had copper fuel lines and bronze steering rig, I puchased her in the 80s .

 

Question - Fiberglass Vs. Plastic

Ike - great info on the posts. I was wondering if you could expound upon the pros and cons of fiberglass vs. plastic. I see plastic as being less expensive and lighter, but does it have other advantages or disadvantages in relation to fiberglass? Thanks!

 

FIberglass vs plastic? Let me just talk about fiberglass first. Fiberglass tanks are pretty common in large diesel powered boats. Hatteras has used them for many years in almost all of their boats. However, it's rare to see them in gasoline powered boats. Why you ask? (sorry, just trying to keep the conversation light) Fiberglass tanks are usually built into the boat structure. However, you can't do that on gasoline powered boats. Fed regs say the tanks can't be an integral part of the boats structure, so it's easier to put in a pre-made metal or plastic roto-molded tank. Also, fiberglass resins are not all created equal. Some are more resistant to gasoline than others. Gas is a wonderful solvent. Who hasn't used it to clean auto parts? It dissolves some resins. So you have to be very cautious about picking the resin. Also you have to put a barrier coat on the inside of the tank, usually gel coat. Recently a lot of older fiberglass tanks in boats are failing due to the additives in the fuel such as ethanol and MTBE. As we all know, fuel tends to stay in boat tanks for long periods of time allowing things to happen such as phase seperation, and time for solvents to work their magic on the tank material. So fiberglass tanks have to be made very carefully for use with gasoline.

So if the choice is fiberglass or polyethylene, the polyethylene wins. It isn't affected by the gasoline, other than a slight permeation of vapor and a little swelling of the tank when it's first filled. Most of the plastic tanks made are still around so no one really knows yet what the life span of a plastic tank is. They have been around since the 80's. They also meet all of the requirements for fire and strength that all gasoline tanks have to meet.

Roto molded tanks can be mass produced, fiberglass tanks have to be made one at a time, so plastic is probably cheaper. I would suspect it is a lot lighter although I have never actually compared the two, but I can easily pick up a 28 gallon plastic tank. I don't know if that's true of fiberglass.

All that said, there are people who choose to build tanks out of fiberglass. For a one off or a limited number of boats, fiberglass might be the choice. I might add that a large proportion of the underground fuel tanks at gas stations are fiberglass. So it has it's place.

 

Why not install an aluminum tank that you can open, and place a fuel bladder inside? Here's an option. That way you get redundancy and you can inspect the entire system.

 

That's been done. In fact bladder in the tank systems have been around for quite a while, but frankly I don't see the point. Just my humble opinion.

 

Condensation, cleaning, inspection, redundancy, repair ...
IMHO.

 

Then why not go all the way and use the vaporless fuel tank? http://www.topdogsystem.com/

 

Hydraulic fluid to balance the air space? I'm not sure that's going "all the way" Ike -- surely someone can make it more complicated if they try.

 

I guess my attempt at irony didn't come through. I was the USCG's contact point with Top Dog on the vaporless fuel tank. It actually works but is very complex, and expensive. It has been tried in some boats and works fine. I've also seen it used in a car with great success. A really nice brand new Caddy. That said, I prefer a much less complex system.

 

whats wrong with foaming in fuel tanks?

 

In my opinion everything. First what are the pros.
Foaming in allows the builder to not have to put in a mounting system for the tank. I prevents the tank from moving. It provides some amount of cushioning from shock and vibration.

Now for reality: but first a little history. The Federal Regulations allow you to foam in tanks, but only under the following conditions: the foam must be resistant to gasoline, other petroleum products, bilge cleaners, etc. In other words all the stuff that dissolves polystrene foams (styrofoam). So you have to use a polyurethane or polyethylene foam. Typically polyurethane foams are used. The same stuff used for flotation.

Second; and by far most important the sheer strength of the bond between the tank and the foam is required to be greater than the sheer strength of the foam itself. This is so the foam will break before the bond does.

Requirement one is easy. There are plenty of foams on the market that are resistant to all kinds of chemicals.

Requirement two is the hard part: in reality it is almost impossible to achieve. In fact when the Coast Guard included this requirement they did it specifically to discourage foaming in tanks. They couldn't outlaw it because it was a common practice at the time (the late 70's) but they wanted to make it difficult to achieve.

In practice what happens is this. The builder puts some foam in, puts the tank in and adds foam to fill the compartment, essentially suspending the tank in the foam. They then put down the deck and no one sees the tank again until it has to be replaced.

What is important is what happens after the tank is in. Aluminum forms a natural oxide on it's surface to prevent it from corroding. If you remove or even scratch this coating and moisture is allowed to get to the actual metal you get corrosion. Normally in the open air the surface repairs itself. The oxide reforms and all is well. However to get a really good bond between the metal and the foam you need to remove the oxide. I have not met anyone yet in 34 years who does that. If you leave the oxide then the bond is not as good as it should be. Plus that, with shock, vibration, slamming and everything else that goes on in a boat the bond begins to deteriorate. As soon as that happens then moisture can get between the foam and the tank.

Additionally, the regualtions require that on gasoline powered boats, that the fittings on the top of the tank be accessible for iinspection. So the tank top is not foamed over. Sometimes the builder just foams the bottom and sides of the tanks, others foam the top but leave spaces for the fittings. This leaves a place for water to collect where it can't run off.

So what happens eventually with foamed in tanks is that the moisture gets between the foam and the tank and corrodes it.

Also, the foams used are two part foams. That is, two chemicals are mixed along with a blowing agent and the resulting compound foams up. This reaction has to take place within a narrow range of temperature and humidty. If it's too cold you get cow pies or bread dough. If it's too hot then the reaction happens too quickly and it breaks the walls of the foam cells resulting in what looks a lot like broken glass. Either way, if you don't get nice closed cell foam, the foam can then absorb water. Now you have a sponge attached to your aluminum tank. Again this results in corrosion. So, I have for years told builders to avoid foaming in tanks. People still do it though.

I have also tried to get ABYC to eliminate the same requirements from their fuel system standard, that it is say no foaming in of tanks. But I haven't been succesfull at that either. I have been involved with several research studies on failures of aluminum tanks and the vast majority of the tanks that failed in short periods of time, say 1 to 5 years, were foamed in. I even saw one that had only been in the boat 6 months and it had holes in the bottom, corroded from th outside in.

Foaming is just not a good practice in my humble opinion.

 

Finally, Boat US has published the findings of their research on the affect of alcohol on fiberglass tanks. It only confirms what I have been telling people for years, don't build fiberglass tanks for gasoline. This is in the March issue of Technical Information Exchange, aimed primarily at surveyors and marine investigators but of interest to anyone who builds or repairs boats. I e mailed Robert Adriance at Boat US and got his permission to quote from the article. For those who want more info email exchange@BoatUS.com. The following is a statement about two tanks, one built in 1967 and one built in 1970. The 1960 tank was made using ortho resins and the 1970 tank was made using iso resins.

"Ethanol exposure would be expected to cause the more rapid demise of the ortho resin based tank and while the iso based tank is more resistant to ethanol it to would follow suit (but more delayed) and lose properties more rapidly when exposed to fuel containing ethanol. Neither resin system stands a chance of long term survival in a gasoline environment when ethanol is introduced into the fuel."

In short the ethanol degrades the laminate and the tank eventually fails. How long will this take? In these cases 30 years, but there was probably little exposure to ethanol in these tanks until the late 70's and it didn't get really common in marine fuels until the 80's so at this point they can't tell how long. But it will happen and with the amount of ethanol in gasoline today, and the increasing amount in the future it will only get worse.