Fuel Tank

[man5]

Hello everybody, its me again the question guy. I have to replace the tank on the grady because its corroded. (Aluminum foamed in) I dont want to foam in the new tank. 1- what are your thoughts plastic versus aluminum? 2-the old tank was a (v-bottom?not square) belly tank, I want to glass in a plywood floor for the new tank, the only ready made aluminum tanks that I can find(40-55 gallon) to fit in the hole have the belly tank configuration. How do you attach these on a flat surface? THANKS

[jimslade]

1. plastic won't corrode. Whats wrong with a V tank bottom, it is structurally stronger than a flat bottom.Check out marine surveyers web sites and you will find the pros and cons of both also how to properly set up a new tank.

[dereksireci]

I would skip the plywood idea unless I'm not understaning what you mean.

Ditto jimslade. Go for a plastic one if you can find one to fit. Many are built with recesses or threaded inserts to hold slotted L-brackets. Leave some room for expansion as the manufacturers swear that they grow 3% when you add the gas.

If you go for aluminum leave the v shape in the hull and use a belly tank. I like the tank to have a 4"-6" flat spot instead of a point in the center of the bottom. It makes the tank easier to handle before installation, is less likely to collect as much contamination and leaves a space for water to go when the tank is installed. Put heavy neoprene under the ends of the tank and at the baffle locations. Look at the tank carefully and you'll be able to locate the baffles or ask whoever made it if you can't. Just screw the tank to the stringers and forget the foam or only foam the corners a bit. Check out how water is handled in the tank compartment so it will have someplace to go if it gets in there. Limber holes...

djs

[Ahmed]

I once had a couple of polly proplene fuel tanks, but the inspection engineers said, I should only use a metalic material, and made me change them to steel, so I suggest that you check first before using any plastic or poly based material instead of Alu...

[dereksireci]

Ahmed, not to be too nit picky but it's cross-linked polyethylene, There are thousands installed in boats in the US. There is a brewing storm on the horizon concerning the permeability of the material and that of the fuel hoses as well. Things may change in the near future. All the alcohol now in gasoline creates problems for the aluminum tanks too.

For me, if I don't have to pay and up front tooling charge for the tank, I'd use plastic. Moeller currently has 75 different molds in stock and there are other companies making the same type product. Steel?

djs

[solrac]

Be aware of the type of plastic.... most of them are degradable by fuel on short to medium time...
Petroleum companies do use double wall GRP tanks. internal layer with special fuelproof resin, and all of the paraphernalia of probe sensors you can imagine...
(think you won't need a 24000lts tank like this one for your boat...)

[jimslade]

Plastic tanks today are as good or better than aluminum just make sure you leave room for expansion. I have decided to repair my aluminum tank (pinholes that are not leaking yet) with a layer of cloth and epoxy resin. Should last a long time. make sure you set the tank 1/4 inch off the floor to allow drainage under. Water is the worst enemy of aluminum.

[man5]

The problem that I have is the tank was foamed in with only a couple of peices of 3/4 plywood between the tank and fiberglass hull. The brackets that i see available go down the sides of the tank and screw to the bottom. I definitely(sp) dont want to screw it to the hull. thanks. Jimslade what kind of epoxy are you using?

[Ike]

First, take a look a the thread on FUel tanks. http://boatdesign.net/forums/showthread.php?t=11238. I would go with polyethylene. There are four major makers. Inca Plastics http://www.incaplastics.com/, Tempo http://www.tempoproducts.com/products.html, Kracor http://www.kracor.com/. There are others. If you do a search on the internet you should be able to find them. Oh yeah, I left out Moeller. Geez, they'd never forgive me. http://www.moellermp.com/marine.htm
Uhhh. Did I mention Ronco http://www.ronco-plastics.com/. I guess that makes five.

There are a few manufacturers who make Aluminum tanks. Florida Marine Tanks http://www.floridamarinetanks.com/, KSH http://www.kshmarine.com/Boat_Tanks.htm (by the way they claim their tanks are Coast Guard Approved. No tanks are Coast Guard Approved! The Coast Guard doesn't approve tanks. The tanks probably meet Coast Guard Regulations. The tank manufacturer has to put a certification label on the tank that says the manufacturer certifies the tank meets the regs.) IMCO http://www.imcomarine.com/pages/tanks.html.

Oddly enough tank manufacturers have been switching over from making aluminum tanks to making plastic.


Oh yeah, I almost forgot. For GOD's SAKE, never ever foam in a metal tank. You might as well just toss it in the surf and watch it corrode! The foam eventually, sooner or later seperates from the tank and moisture collects, and you have no way to inspect the tank. You find out it's leaking when either you smell the fumes or the boat blows up. DOn't even consider foamimg a plastic tank. FIrst the stuff won't stick to them, second the expand when you fill them and third vapor permeates through the tank wall and destroys the foam.

Gasoline and it's additives do not degrade polyethylene tanks. They do degrade fiberglass tanks if the tank was not built right. Older frp tanks have been failing due to this, but as far as I am aware not new ones that are put together right. But fiberglass is not a good choice for gasoline anyway.

If you put the tank under the floor make sure you have an inspection plate so you can see all of the tank fittings and check for leaks. Do a system pressure test of the tank and the fuel lines at 3 psi before you screw the floor down. And screw it down, don't nail it, so you can get it back up if you ever have to go back in. Don't glass over it. You'll just promote rot in the floor. Soak it in resin to seal it or paint it with a good marine paint. Make sure you seal the edges all around to keep water from migrating into the plys.

Here's a good site with lots of links Good Old Boat http://www.boatus.com/goodoldboat/tanksalot.htm

[Ike]

I apologize for any offense, but I actually meant what I said. I have seen too many people injured and millions of dollars of property destroyed by tanks that failed. Almost all of those failures were due to improper installation. Installing a tank correctly is the key. Put it in the wrong way and it will fail, and it might fail much sooner than your think.

As for not glassing in decks, I know that this is done routinely in the industry, and I find it disturbing for several reasons. I have spent hours on the phone listening to consumers complain about how they had to tear up their boat to replace the tank that was buried where you can't get to it. I have also seen tanks fail without any warning, that if only the owner had been able to inspect the tank routinely, it wouldn't have happened. Even experienced, seasoned boat owners won't inspect a tank if they can't get to it.

I have spent years trying to convince the ABYC committee to change it's standard from "accessible without removing boat structure" to readily accesible with hand tools" without success. The people against this change think it's not a safety issue. I do. Even the members of the committee have argued over the meaning of "accessible without removing boat structure". I contend that removing the deck with a power saw is removing boat structure. Others don't see it that way. Ideally there would be a hatch over the tank big enough to remove the tank. This will probably never happen in my life time. However, maybe an inspection port that is bigger than the current 6 inch ports would help. At least make all the fittings capable of being inspected. Most fuel leaks are at the fittings.

I supposed the rising price of gas is going to make all this academic anyway.

No they are not approved. If you use that term you will get a nasty letter from the Coast Guard legal office telling you to cease and desist. Coast Guard Approved has a specific legal meaning and implies that the Coast Guard has tested and approved your product. Only specific products defined in law require approval. Tanks are not one of them. If you use that term you are considered to be using false and misleading advertising. Gasoline tanks on recreational boats are required by law to be "certified" by the tank manufacturer. Certified has a entirely different meaning. Here's link to the Boating Safety Circular. The first part of it explains what Coast Guard Approval means. http://www.uscgboating.org/recalls/pdfs/BSC71.pdf

Sorry to be such a jerk about this but I've spent many years having to tell people they can't use Coast Guard Approved and the message just doesn't seem to sink in. You only get their attention when you tell them to cease and desist. By the way, there is a hefty fine associated with this if they don't stop using it although in 34 years I can't remember ever having to assess a fine.

Plastic tanks have been around since the 80's. While I was at the Office of Boating Safety we did several studies on plastic tanks. We subjected them to all kinds of tests. So has UL and Imanna Labs, and some other testing laboratories. Other than the permeability issue that the EPA is dealing with, and the fact that they expand when filled so you have to leave a little slack in the straps that hold them place, there have been no significant problems with these tanks. An occasional problem is people installing stuff above the tanks and driving a screw through the tank top. Some builders forget to leave enough room above the tank and when it expands it lifts the deck. Also, the gaskets for the pickup and sender have to be flexible enough to take the shape of the tank. There have been recalls of the gaskets due to leaks caused by the gasket being too rigid. And there was a huge recall due to gaskets that detiorated due to the additives such as alcohol and MTBE. Anyway, what I am saying here is that fully half the boats built in this country have plastic tanks. If there were any problems with them the Coast Guard would have heard about it by now. I think 25 years is plenty of time to assess their efficacy.

[longliner45]

plastic is a petrolium by product, moister eventually evaporates from the plastic and this is what makes it brittle all plastics are different blends of different things, I would say that if you must have a plastic tank ,and to protect your investment you will have to do some research on this matter, but for a few dollars more you could go with the time proven bronze and be done with it,,,,,,,,longliner

[SamSam]

Originally Posted by jimslade

I deal with automotive restoration and in the 30 years I have been doing it, I have never seen a catastrophic failure in a metal tank, not the same for plastic. I just finished restoring a 60 year old truck and I used the original metal tank, still good. I doubt I will ever see a 60 year old plastic tank still useable. The problem is in the install. Glassed in floors are for structurall integrity.The catch 22 in tank installation is do you install water tight or allow ventilation. I prefer water tight due to the chance of failure, the leak will be confined to the tank enclosure than have it leak into the bilge where you will have catastrophic events occurring. If you want to make a firm point please do not bring God into it. It offends me personally. How would feel if I cursed using the name of someone you loved.

Get real. He brought God into it to stress a positive. To try and make people do something safely instead of creating problems. You comparing truck fuel tanks to marine fuel tanks is ignorant, apples to oranges. You can't even compare a 60 year old truck tank to a 20 year old truck tank, they are from different eras with different priorities, quality versus profit.Work in a boatyard for two years and you'll see all kinds of problems with metal tanks. The majority of the time there will be no provision or thought whatsoever by the manufacturer to make it easy to fix or access the tank, even if it's just as easy to do it right as to do it wrong. While you're on your pulpit, pray that your six strips of 5200 will hold your tank in place when you hit a wave wrong. If your religion isn't strong enough to carry you through and ignore what he said, you got problems. Keep that stuff out of here or be ready to be offended. Sam

[Ari]

The problem with plastic is that there is some additive that is poison to plastic.Plastic tank produce a few years ago might not be able to survive the attack of new generation poison. In blended mogas fuel/petrol the structure of the hydrocarbon bond are never informed to the end user. There a lot of different in petrol character depending on the base product used for this blend ,if the traditional market are straight run platformate than normally the plastic tanks are able to resist the restructuring of the polymer molycule by platformate, if catalytic crack gasoline (CCG- from a more advance cracking process) are used, then the same tank might not be able to survive the restructuring of the polymer molycule- mean it will disintergrate or melt or become brittle. With all this uncertainty of fuel type are thrown in alcohol as part of the blend, be it Methanol or Ethanol again the structure of the hydrocarbon molycule change and this will again make the character change. Methyl Tertiary Butyl Ether - MTBE are banned in some state in USA but still in used in some other country, Tri Chloro Ethane TCE or PCE is needed in the naptha craking process and they are real poison to plastic. CCG are never a stable product- given enough resident time..it will keep on changing..
Plastic are polymer, spun from hydrocarbon process, normally they are made from Naptha, Naptha are also the base for Platformate which is the base product for petrol..
In oil industries..metal is still the most stable material for even a small petrol container.A small plastic petrol tank for outboard normally will survive quite long..the reason is that the resident time of petrol in that tank is quite short. Those tank might not survive that long if it is used as a permanent storage tank. For a tank of 50 gallons size I believe it is expected to have the oil in the tank all the time. This will increase the resident time of petrol in that tank.This in effect will caused the permeating of hydrocarbon fume through the tank. How does the fume come out from that plastic tank shell ? It is by changing the molycular structure of the plastic ! So the part that been change is as good as it was drill through ! Luckily a molicule is very very small..! Why the right molycular structure is important ? Thats what holding all those polymer yarn togather ! In the long run that tank shell will become weak and deterioriate. How long does it take from "safe for use" until it become hazardous..? I don't know. I'am not against any type of tank, there is all sort of needs and application. For a plastic tank, make sure that permeating gas collected are cleared of before introducing any sources of ignition like switch on the light or any confine space entry.It can be fatal. Safety is always top priority.

[Ike]

ARi your argument sounds good but doesn't hold water.. errrr Gasoline. First, several studies of tank failures have shown that aluminum tanks last an average of 10 years. Plastic tanks have been around 20 -25 years and none of the failures of polyethylene tanks have been due to gasoline or it's additives. They have all been due to failure to install it correctly, failure of gaskets or fittings, or someone putting a hole in the tank. If you throw FRP tanks in, yes there have been failures primarily due to ethanol seperating from the gasoline when the boats were in storage for long periods of time, and these are all on FRP tanks that are 10, 15 and 20 years old. By the way exactly the same thing causes aluminum tanks to corrode from the inside out. There was one episode where over forty boats in one storage facility lost the contents of their tanks over the winter. They were all aluminum tanks and the fuel distributor had delivered Gasohol (10% ethanol blend) instead of straight gasoline.

Yes the formulation of gasoline is different in different regions. Yes some areas still put MTBE in the fuel but it is being phased out. But not because of tanks on boats failing. It's because MTBE is an environmental disaster. It leaks in to the ground water and gets into your and my drinking water. In areas like Alaska where MTBE has been used in large quantities, it has actually caused air polution resulting in people experiencing headaches and other mysterious disorders. So, first the Califormia Air Resources Board banned it (they were the first to require it in gasoline so they were just reversing their decision) and the EPA started phasing out it's use. The only viable substitute is etanol.

Contrary to what the press and the oil companies would have you believe, ethanol has been an additive in gas since the 70's. In the mid 80's the Coast Guard, SAE, NFPA, SAE and ABYC, with assistance from NMMA, got together and had the formulation for fuel hose changed, specifically to resist alcohol blends because they were causing premature failure of hoses. The same is not true of polyethylene fuel tanks. Test have shown that none of these compounds has any apparent affect on the structure of the polymer in these tanks. I'm not a chemist or a chemical engineer, but I've talked with the people who do the testing and the people who make the tanks. Believe me, in my position with the Coast Guard I would have been one of the first to hear if those tanks were having problems and it just did't happen. Not so with other tanks. I heard about them all the time.

Anyway Sam Sam, the use of terms was between me and Jimslade. I apologized and I don't see any need to go any further with it if Jimslade feels the same. I meant no harm and I think he knows that. But I learned a long time ago that certain words trigger a reaction. What may seem harmless to me may not sem harmless to some one else and vice versa. I once made a very common metaphor to a man from Libya and he not only was offended, he was outraged and complained about me to my boss. I had no idea that this metaphor commonly used in our society was a huge insult in his. So let's let it drop. Thank you for your input.

[Ari]

Thank you Ike. When I wrote about the effect of mogas on plastic actually it is in general. I did not go into detail at all. If those fuel tank in discussion are made off High Density Poly Ethylene (HDPE) and the result is suitable for the mass usage by all mean go ahead..I don't see the needs to go into very detail in the explanation, I had tried to make the explanation as simple as possible to the group of audience that I doesn't even know what is their understanding about chemistry, polymer or even hydrocarbon, anyway thats is the field that I'am in to earn a living. I doesn't discuss on method of fabricating or assembly..thats not my field. I did not discuss the effect of gasoline on aluminum or any other metal. Hope this clearified my intention.