posted 01-07-2003 08:51 PM ET (US)            

My thoughts are largely based from a safety viewpoint and the fact that one thing I certainly don't want on my boat is a fire. In this light, plastic and fiberglass are relatively easily punctured while aluminum is rather difficult to puncture. Rupture of the fuel envelope (puncture of the tank, leak or failure of a fitting or line, et.al) is a requisite of a fuel fire.

Another point of equal significance is the long term integrity of the tank. Normal operation of the boat induces dynamic fuel sloshing loads which can be quite large and with the continued operation will tend to fatigue the walls and corners of the tank. These sloshing loads increase with the length and width of the tank.

Consequently, one major reason I prefer aluminum is that baffels are frequently installed on aluminum tanks - which provide internal support to withstand the fuel sloshing loads. To the best of my knowledge, baffles are not incorporated in plastic or fiberglass tanks.

While touring BW's Edgewater facility, I observed the installation of plastic tanks in some boats. I questioned them on this practice and was told that they used aluminum on tanks over 50 gallons capacity. I don't know if their selection of the 50 gallons was based on a technical evaluation or was simply someone's subjective thought. The 56 gallon tank in my 17 OR is aluminum and is one of the first things I looked at when considering the boat. But, bringing this issue to one of my front burners, I will do some digging and provide some follow-up down the road a piece. ----- Jerry/Idaho

posted 01-07-2003 11:32 PM ET (US)            

I strongly favor the aluminum tanks. While the Pate fiberglass tanks seem to be popular here on the forum, I can see several downsides to them:

- They are not portable.
- They stick out from under the RPS.
- They can be difficult to fill if you have to slide it backwards.
- They can be a very tight fit.
- They are ugly.

In contrast, the twin 12 gallon tanks specifically made by both Tempo and Mirax to fit under the Whaler RPS are:

- Portable.
- Easy to fill by sliding them back or removing them from the boat.
- Useful in managing the trim of the vessel by keeping more fuel on one side or the other as well as giving you more warning when one tank runs dry.
- Easy to gauge the fuel level by just trying to lift one tank up and feeling the weight.

In addition, the Mirax tanks have been built of aluminum since the mid 1980’s and you can still get them now. While they are not inexpensive (about $175 each) they will be stronger and more durable than any other tank out there. They are also quite good looking!

posted 01-08-2003 08:59 AM ET (US)            

1) Translucent - More accurate than a gas gague and no gague to ever break!
2) Easily portable and will not scratch anything if I drag it around in the boat a little bit
3) inexpensive

The cons as I see it are:

1) Won't last forever in the sun
2) Won't store gas as long as metal (I use the boat year round, not a big deal)

posted 01-08-2003 01:18 PM ET (US)            

Aluminum fuel tanks leaking into bilges due to corrosion is a major problem in older boats. Aluminum will corrode if it is continuously exposed to water WITHOUT exposure to air. Aluminum fuel tanks corrode through quite often when the tanks are foamed in place (a practice many boat builders continue to use even though industry standards do not allow it). Foaming an aluminum tank in place can lead to water constantly trapped against the side of the tank, due to the tank expanding & contracting with heat while the foam stays in place. This cycle creates a small crack between the tank & the foam that will hold water from condensation. This leads to corrosion holes in the tanks & gas leaking in your bilge. I personally have replaced two aluminum fuel tanks that had holes due to corrosion & I've seen & heard about many many other cases of this happenning.

If an aluminum tank is mounted allowing good ventilation on all sides of the tank, including the bottom, it'll last pretty much forever, and the only corrosion will be the harmless surface oxidation you see on non-anodized aluminum fittings. But if it's foamed in place (as the tank on my Mako is), or if it's mounted where the tanks will be in constant contact with water at the mounting points, or if water can be trapped under a mounting strap, it will eventually lead to a corrosion problem.

I take David Pascoe's boat survey website with a grain of salt on his boat reviews, but he does have an excellent article on there on how to properly mount an aluminum tank to avoid these corrosion problems.

Corrosion problems due to improper mounting of aluminum tanks have become such a big problem that many builders are moving towards fire retardant plastic tanks. The larger ones are baffled just like custom aluminum tanks are.

posted 01-08-2003 06:37 PM ET (US)            

And yes, there are aluminum alloys that will corrode - as well as stainless steels that will rust.

posted 01-09-2003 10:06 AM ET (US)            

I'm no metal expert, but I can tell you that any aluminum fuel tank you can buy from any custom tank builder will corrode if left in constant contact with water for many years. Perhaps there are aluminum alloys that won't corrode, but if so, they're not commonly used for building marine fuel tanks. Many top quality yachts such as Bertram, Blackfin, etc have had their aluminum fuel tanks replaced because of corrosion, and those builders are certainly not using bottom-dollar tanks. (Hatteras uses fire retardant fiberglass tanks & they generally last forever).

You can look at any custom tank builder & buy their highest dollar aluminum tank & it will corrode in time if not properly installed. The more expensive ones are thicker guage, but they all seem to be made out of the same alloy (at least at the commercial shops that build marine tanks). I've shopped for tanks & have never seen different alloys offerred by anyone...only different (thicker) guages of aluminum.

I agree with you that you should certainly buy quality...I've always paid up for the thicker guage tanks...but it appears that proper installation is more important than anything in preventing aluminum tank corrosion.

Jimm, my guess is that under the bottom of the tank would be the only area that could trap water & be a problem on a Montauk on-deck tank. If the tank has tabs around the edge to prevent the bottom of the tank from sitting directly on the deck, you'll be fine. If it sits directly on the deck, adding plastic Starboard strips with 5200 as Pascoe describes would eliminate any potential problem.

posted 01-09-2003 01:44 PM ET (US)            

Jimm,

No, the aluminum tanks will not get overly hot in the sun. When filling, you ground them as Taylor describes, by maintaining contact between the nozzle and the tank itself.

There are no baffles in these tanks and there are no baffles in the aluminum tanks used on the recreational Whalers for built-in installations.

posted 01-09-2003 08:00 PM ET (US)            

An additional advantage of the Pates is that
they have a fuel guage that will NEVER fail
-- a clear window in the side of the tank.
A mechanical or electical fuel guage on a
boat tells you how much gas you MIGHT have.

posted 02-11-2003 09:47 AM ET (US)         

I certainly don't have the time or the experience to do a major job like this myself. However, if it's reasonable, it would seem like a good idea to have it done over the winter.

Man, how am I going to enjoy the time on the water if I'm constantly worring about my 20yr old tank leaking under foot with my kids on board.

Just when I thought it was safe to back out on the water again ;)

posted 08-18-2003 01:00 PM ET (US)            

First, someone said something about tanks being Coast Guard approved. There is no such thing. The tank manufacturer has to certify that their tanks meet the Federal Standards. That's why there is a label on the tank. We would need a small army of inspectors to approve all the tanks that are made every year.

Tanks can be made of any material except terne-plate. (a lead-tin alloy that corrodes like mad) However, the American Boat and Yacht Council (http://www.abycinc.org) has set voluntary industry standards for tanks that the industry uses. If you get a copy of H-24, Gasoline Fuel Systems, you will find a lot of different materials that can be used for tanks. The two most common are aluminum in the 5000 series (5052, 5083, or 5086) because it's resistant to the marine environment, and polyethylene (plastic). Both materials can passes the 2 1/2 minute fire test (they have to resist a fire for 2 1/2 minutes without leaking) and all the other tests such as slosh, pressure impulse and shock.

Studies have shown that aluminum tanks last on the average of 10 years. No one knows how long plastic tanks will last, they have been in use for about 25-30 years and we haven't seen an trend in failures yet. Usually if a plastic tank leaks it's a leaky gasket or someone has accidentally put a hole in it.

Foaming in of tanks is a really bad idea (my opinion). The law permits it if the foam adheres to the tank with a bond who's breaking strength is greater than the sheer strength of the foam. In practice I've yet to see a foamed in tank that didn't collect mositure and corrode. Most manufacturers that foam in tanks do so because they don't want to have to build in a mounting system for the tank.

Aluminum corrodes because the natural oxide on the surface of the aluminum is a.) washed away by moisture b.) penetrated by a scratch or hole of some kind. As long as the natural oxide on the tank is not disturbed the tank should not corrode. This is also why it's a bad idea to paint an aluminum tank. To get the paint to adhere you have to remove the oxide.

Thickness of the aluminum is also important. The thicker the aluminum the longer it will take to corrode through. Also on large tanks (200 gals & up) you definitely need thicker aluminum for strength. Generally though for smaller tanks the thickness used is .090 in.

You don't see large plastic tanks because they are nearly impossible to baffle using the current roto-molding construction methods. Metal tanks can be baffled relatively easily and that reduces sloshing in large tanks.

As for the comments about grounding tanks. DON'T FOOL AROUND. I have a video (taken by a security camera at a gas station) of a portable tank blowing up that was not grounded and the guy went ahead and attempted to fill it. He spent a long time in the burn center. The fill nozzle is grounded back through the system but you can still get a spark that will jump from the tank to the nozzle. This is especially so with plastic portable tanks. Liquid fuel sloshing around in a plastic tank actually builds up static on the walls of the plastic. The same is true of fuel fill hose on boats. This is why the law requires them to be grounded. Always ground a portable tank before filling.

Last but not least fiberglass tanks are discouraged with gasoline (but not illegal). You have to make sure that the resin is gasoline resistant. I've seen some really nasty problems with fiberglass gasoline tanks. Yes, Hatteras makes fiberglass tanks. They are all diesel boats. Fiberglas works well with diesel.