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Given all the controversy concerning Coast Guard regulations governing the installation of aluminum fuel tanks, I though I would look up the actual regs (imagine that) and start a new thread.
Here is a link to CFR 33, Subpart J, section 183.5XX that dictates the EXACT CG requirements:
Here are some key excerpts from the regs, as it applies to FOAM FILLED ALUMINUM TANK INSTALLATIONS:
§ 183.550 Fuel tanks: Installation.
(a) Each fuel tank must not be integral with any boat structure or mounted on an engine. (b) Each fuel tank must not move at the mounting surface more than one fourth inch in any direction. (c) Each fuel tank must not support a deck, bulkhead, or other structural component. (d) Water must drain from the top surface of each metallic fuel tank when the boat is in its static floating position. (e) Each fuel tank support, chock, or strap that is not integral with a metallic fuel tank must be insulated from the tank surface by a nonmoisture absorbing material. (f) Cellular plastic must not be the sole support for a metallic fuel tank. (g) If cellular plastic is the sole support of a non-metallic fuel tank, the cellular plastic must meet the requirements of §183.516 (b) or (c). (h) Each fuel tank labeled under §183.514(b)(8) for installation aft of the boat's half length must be installed with its center of gravity aft of the boat's half length. [CGD 74–209, 42 FR 5950, Jan. 31, 1977, as amended by CGD 81–092, 48 FR 55737, Dec. 15, 1983; USCG–1999–5832, 64 FR 34716, June 29, 1999]
(a) Each fuel tank encased in cellular plastic foam or in fiber reinforced plastic must have the connections, fittings, and labels accessible for inspection and maintenance. (b) If a metallic fuel tank is encased in cellular plastic or in fiber reinforced plastic, water must not collect between the plastic and the surface of the tank or be held against the tank by capillary action. (c) If the plastic is bonded to the surface of a metallic fuel tank, the adhesive strength of the metal to the plastic bond must exceed the cohesive strength of the plastic.
§ 183.516 Cellular plastic used to encase fuel tanks.
(a) Cellular plastic used to encase metallic fuel tanks must: (1) Not change volume by more than five percent or dissolve after being immersed in any of the following liquids for 24 hours at 29 °C: (i) Reference fuel B ASTM D 471 (incorporated by reference, see §183.5). (ii) No. 2 reference oil of ASTM D 471 (incorporated by reference, see §183.5). (iii) Five percent solution of trisodium phosphate in water; and (2) Not absorb more than 0.12 pound of water per square foot of cut surface, measure under Military Specification MIL P–21929B. (b) Non-polyurethane cellular plastic used to encase metallic fuel tanks must have a compressive strength of at least 60 pounds per square inch at ten percent deflection measured under ASTM D 1621 (incorporated by reference, see §183.5), “Compressive Strength of Rigid Cellular Plastics”. (c) Polyurethane cellular plastic used to encase metallic fuel tanks must have a density of at least 2.0 pounds per cubic foot, measured under ASTM D 1622 (incorporated by reference, see §183.5), “Apparent Density of Rigid Cellular Plastics.” [CGD 74–209, 42 FR 5950, Jan. 31, 1977, as amended by CGD 77–98, 42 FR 36253, July 14, 1977; CGD 81–092, 48 FR 55737, Dec. 15, 1983; USCG–2000–7223, 65 FR 40059, June 29, 2000]
1.) Despite all the claims to the contrary on other threads, IT IS PERMISSSIBLE TO FOAM IN ALUMINUM TANKS. If foam is used to encapsulate the tanks, it must simply comply with section 183.516 above. Many 4 lb density polyurethane closed cell foams will comply. Those that make statements to the contrary have not read the CG regulations.
2.) Section 183.552 above states “(b) If a metallic fuel tank is encased in cellular plastic or in fiber reinforced plastic, water must not collect between the plastic and the surface of the tank or be held against the tank by capillary action” .
3.) The builder must make sure the foam is not the ONLY support, supporting the aluminum tank with a stringer(s), or other structural member, in conjunction with the foam should satisfy this requirement.
I interpret this as to mean that if a NON-PERMEABLE NON ABSORBING COATING is used between the FOAM and the aluminum tank, than this is OK. Such as coal tar epoxy, or some other type of EPOXY coating or paint system. I also interpret this to mean that if cellular foam is held directly in contact against untreated aluminum, than this is NOT an approved installation.
Agreed that it is "legally" permissible to foam in tanks under certain conditions, but it is well known that foamed in aluminum tanks are much more likely to suffer corrosion problems. If I were installing a new aluminum tank, I would try very hard not to use any foam.
Don't forget about this section: § 183.501 Applicability.
(a) This subpart applies to all boats that have gasoline engines, except outboardengines, for electrical generation, mechanical power, or propulsion.
Much of this CFR looks at venting, hoses and other fuel vapor related issues which are influenced by the location of the engines (if inboard). Outboards do have different (more lenient) ventilation requirments (for example a ventilation blower is not required) than inboard gas engines.
The sections I have referenced apply only to tank mounting and installation issues, and do apply to outboards with respect to these issues, as they are not superceded anywhere in the regs by an alternative requirment.
Quote:
Originally Posted by kchace
Agreed that it is "legally" permissible to foam in tanks under certain conditions, but it is well known that foamed in aluminum tanks are much more likely to suffer corrosion problems. If I were installing a new aluminum tank, I would try very hard not to use any foam.
Ken
The point I am trying to make is that foam can be OK, if adequaltey protected from the effects of corrosion by some type of protective coating. Agreed, uprotected aluminum tanks in contact with foam are not compliant and a bad idea.
The sections I have referenced apply only to tank mounting and installation issues, and do apply to outboards with respect to these issues, as they are not superceded anywhere in the regs by an alternative requirment.
Really? All of the sections you reference are under subsection J- "Fuel Systems". The section I quoted specifically states the subjection J is not applicable to outboard powered boats.
Excuse my ignorance but how does "If a metallic fuel tank is encased in cellular plastic or in fiber reinforced plastic, water must not collect between the plastic and the surface of the tank or be held against the tank by capillary action” explain the need for a "NON-PERMEABLE NON ABSORBING COATING is used between the FOAM and the aluminum tank".
Sorry for being a pain in the a, but I'm just trying to understand this issue.
Sorry for being a pain in the a, but I'm just trying to understand this issue.
Not being a pain at all.
I’m no expert on interpreting CG regs, and there are many cases (even in the areas that I’ve excerpted) that are not well written and somewhat ambiguous.
As far as I know, there are no other sections pertaining to gasoline tank installations for outboard engines. If there is another reg elsewhere that contradicts these requirements, please post the reference. Lacking any published alternative requirement specific to outboards, these are the regs.
Rightly or wrongly, they have combined the tank installation requirements for inboard gas engines with outboard engines. Common sense will tell you that there is no difference between the physical mounting of a tank for an outboard vs. an inboard, unless you get into the area of ventilation, spark hazards, etc. With respect to these (vapor) issues, there most certainly is a difference, but not on structural mounting.
To the point about non-permeable coatings, we have section 183.550 (e) “Each fuel tank support, chock, or strap that is not integral with a metallic fuel tank must be insulated from the tank surface by a nonmoisture absorbing material”
I take this to mean that they don’t want anything to touch the tanks that is moisture absorbing. And this is why most builders that do foam in aluminum tanks use some type of barrier coating on the tank walls.
The sections I have referenced apply only to tank mounting and installation issues, and do apply to outboards with respect to these issues, as they are not superceded anywhere in the regs by an alternative requirment.
The way that I read the regs, they do NOT apply to outboards. 183.501 says so. Everything that is in 183.XXX, which includes the regs you cited, applies to inboard powered boats only.
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This controversy as most of us know is related to Yellowfin boats and their installing method of aluminum tanks which unless they use some kind of transparent isolating varnish or resin is clearly not good because of allowing contact between the foam and the bare aluminum, an installing way that is not up to the very high standards of installation of the rest of the equipment in Yellowfin boats. By the way there are surely many other builders doing the same ...... How can it happen in such a regulated country that so many boatbuilders use this forbidden by regulations method and still happily can sell their bpoats to the general public without any technical inspection ?? Invincibles, do coat their alu tanks with some kind of black stuff wich I have personally seen in a visit to their premises I take for certain that the black stuff I have seen covering invincible installations is Coal Tar epoxy resin or paint from my humble point of view showing how things should be done ( among many other boat manufacturers that do cover their bare aluminum tanks) showing some regard to the life of their isntallations and the troubles they do cause to their customers on the long term.
I suppose that the best way is probably some kind of dense strapping ( many straps) that suspends the tank allowing some minor movements with thick nylon belts which should pass thorough some kind of polietilene moulding that allow some spacing between the metal and the water absorbing nylon straps ........ any opinions about this ??
I'm not sure what you guys are driving at in regard to the applicability of the quoted subsection. It is my understanding that anything not specifically prohibited is allowed. Whether this CFR subsection is applicable to inboard or outboard boats is moot. I think the point of the thread was whether or not foam could be used in the installation of fuel tanks, whether inboard or outboard powered. Is there another subsection that deals with fuel tank installation for outboards?
It doesn't prohibit foam encapsulation of fuel tanks and as far as I know, no other subsection does either. If you know one, please cite it.
Best practices is a whole other subject. Best practices often go beyond what is "required", however, those practices can be open to debate. Everyone has an opinion as to what is "best practice".
Disclaimer: If you see emoticons, that means the above is written in jest. It is for entertainment purposes only. It is not meant to represent any actual persons, places, or things. It is the opinion of the poster that it is funny. Your opinion may vary. No animals were harmed in the typing of this post but a few egos may have been bruised.
I suppose that the best way is probably some kind of dense strapping ( many straps) that suspends the tank allowing some minor movements with thick nylon belts which should pass thorough some kind of polietilene moulding that allow some spacing between the metal and the water absorbing nylon straps ........ any opinions about this ??
You know, there are many materials to make tanks out of, and many ways to mount them. All are trade offs. Bly had some good suggestions in the YF thread as to using support strips with non absorbable material on which to rest the tanks.
This “old school” method is perfectly good and well suited for many types of boats, but when you get into high speed boats the stakes get higher.
Truth be told, the design, installation and mounting of fuel tanks is one of the biggest challenges in boatbuilding. The fuel capacities are enormous, the speeds are high, and safety is a huge issue.
Mounting an aluminum tank using some type of intermittent supports underneath and alongside the tanks can be a great solution. However, with large fuel capacities and high speeds you have to be careful of fatigue failures. Intermittent tank supports concentrate the stresses in localized areas and if the stresses are above the endurance limit of the material (due to high speeds and slamming loads) you can set up a fatigue failure which can and will fail the tank, particularly at or near a weld.
Using foam encapsulation in a high speed boat make some sense to me, as now, the supports are conformal, and the loads are spread out over a very large area, drastically reducing stress while still allowing expansion/contraction due to temperature changes. The trade off is you have to now be very concerned about moisture contacting the aluminum tank walls and causing corrosion, which will happen.
So based on the boats I’ve had built and the builders I’ve talked to, the lesser of two evils is to foam the tanks in around coated aluminum tanks. Certainly, other methods can be made to work just as well, but you do have to be careful with the fatigue issue.
You can also make tanks out of polyethylene (plastic) and this material is quite good around chemicals like ethanol, and of course cannot corrode. Unfortunately, there are limits to the size of the tanks, and they can be difficult to baffle internally. Worse, there are permeability issues with gasoline vapors seeping through the tank walls, and many owners of PE tanks report that they can smell the gas. Not comforting.
Before the advent of ethanol, FRP tanks were also a good solution, but the 10% ethanol content in the fuel has ruined this option as the ethanol attacks the resin over time.
Ethanol and the resulting phase separation of the fuel can and does create highly corrosive by products that also attack aluminum and some rubbers.
There are no slam dunk answers here-everything has it’s pros and cons.
.... How can it happen in such a regulated country that so many boatbuilders use this forbidden by regulations method and still happily can sell their bpoats to the general public without any technical inspection ??
What regulation says it can't be done the way they are doing it. The CFR says that the adhesive strength of the plastic must exceed the cohesive strength of the plastic. That means that the plastic must stick to the tank better than the plastic is at resisting breaking. I don't see anywhere that says urethane foam is not allowed to touch the aulminum. I don't know the adhesive vs cohesive strength of the foam but I do know it sticks very well to just about anything.
Quote:
Originally Posted by CANARIANFISHER
I suppose that the best way is probably some kind of dense strapping ( many straps) that suspends the tank allowing some minor movements with thick nylon belts which should pass thorough some kind of polietilene moulding that allow some spacing between the metal and the water absorbing nylon straps ........ any opinions about this ??
If I'm reading this right, you want to put the fuel tank in some sort of hammock? Sorry, I don't see that working at all. Nylon stretches, especially when wet. It wouldn't be long before the fuel tank is swinging away in that hammock. If the fuel tank is to be mounted, it should be mounted on something that is nonpermeable but glueable. The pad should be glued to the tank so as to preclude any water from getting between the tank and the pad.
Disclaimer: If you see emoticons, that means the above is written in jest. It is for entertainment purposes only. It is not meant to represent any actual persons, places, or things. It is the opinion of the poster that it is funny. Your opinion may vary. No animals were harmed in the typing of this post but a few egos may have been bruised.
A hammock is not made of thick nylon straps, I mean the kind of strong straps used to lift weights or to strap loads to lorries, and the swinging can be limited to very little if you keep those straps plentiful and tight, only allowing the movement necessary to thermal increases in size or slight vibration. The hammock as you call it could be made to measure and to the size of the tank I mean if the tank is rectangular, the strapping can also have a box shape inside which the tank can go relatively tight is then a matter of holding this box made of straps to many points around it to restrict its movement so it does not swing.
A different story is what Darbikrash pointed out about the non uniform distribution of the load imparting non uniform loads on the weld lines that could cause fatigue but i belive that if as stated the straps are plentiful ( many many) the loads will become more evenly distributed to a point where the welds will not suffer ....... off course only theories and probably much easier to heavily epoxy coal tar the tank and foam it in .......
What is clear Is that I would not accept in a new custom or semicustom boat made for me that the builder condemns me or the next owner of the boat to an almost certain mega hassle of sawing the deck and replacing the tank just because he did not care to give the tank an epoxi tar protective coat .... simply not acceptable particularly considering the price and likely profits involved in every sale ......
I knew what you meant by the straps, I was just having a little fun with the hammock comment. I agree with Darbikrash that fatigue could be an issue. I don't think your nylon strap arrangement would relieve the tank of fatigue related issues as fuel surging in a seaway would still cause the panels to flex between the welds regardless of how well the tank was supported by the straps. Sure the tank wall thickness could be increased to account for flex, but at what cost?
This forum has had plenty of small boat owners pulling 20 and 30 year old tanks that weren't leaking and talking about reusing them. Would I reuse a 30 year old tank if I was rebuilding a boat? No, regardless of the method of installation. I'm just saying that tanks can and do last that long. At what point do you say "enough is enough, this is a quality installation"?
I also agree with you on the coating process. As I stated in the other recent thread, zinc epoxy and coal tar epoxy coatings are tried and true. It is not that expensive and should be a part of the process.
Disclaimer: If you see emoticons, that means the above is written in jest. It is for entertainment purposes only. It is not meant to represent any actual persons, places, or things. It is the opinion of the poster that it is funny. Your opinion may vary. No animals were harmed in the typing of this post but a few egos may have been bruised.
The problem is that many boat builders do not clean, dry, etch, prime and epoxy the aluminum tanks. If the coating is damaged, salt water can easily get between the coating and aluminum tank in one place and then spread the de-lamination of the coating. The other problem is ventillation around the bottom of the tanks, and type of support of the bottom Finally the danger of abrasion of the coating at the area where straps touch the tank coating is another factor. I personally would rather have well coated tanks, and no foam--or trapping of salt water near the tank.
My process includes three corrosion prevention solutions! We clean,etch and apply a pre treatment developed by the navy for corrosion protection, apply a primer for use with our high solids coatings, and follow with the same coating used on the pentagon! All for around $300-$500 per tank! If you want any boat built in Sarasota tell them you want your tank sprayed with Line-X and I will take care of it! - I will give $100 cash to anyone who can peel my sample by hand! - Brian (941) 527-1387 the tank below went into a Andros who also foams fuel tanks in, Kevin at yellowfin also has a tank sample sprayed in the new Ford Blue Flame color! http://m194.photobucket.com/albumvie...nk003.jpg.html
I suppose that the best way is probably some kind of dense strapping ( many straps) that suspends the tank allowing some minor movements with thick nylon belts which should pass thorough some kind of polietilene moulding that allow some spacing between the metal and the water absorbing nylon straps ........ any opinions about this ??
(a) Each fuel tank must not be integral with any boat structure or mounted on an engine.
(b) Each fuel tank must not move at the mounting surface more than one fourth inch in any direction.
When they talk of the tank being integral with the structure they are referring to the tank being part of the hull such as a double bottom would be. The straps you describe would not be the way to fasten the tank. Most tanks have tabs welded in and the tank is secured to stringers/transverse bulkheads or similar with screws. If the tank is properly coated foaming in for extra support would be fine, the key is properly coated. The tanks should not have movement under the deck. high volumes of fuel sloshing around have alot of momentum and any tank movement will cause the fasteners to wear out resulting in the tack being free to move around. That is why i would secure a coated tank and foam it in. Just my opinion
Aluminum Fuel Tanks 
Sorry, I don't see that working at all. Nylon stretches, especially when wet. It wouldn't be long before the fuel tank is swinging away in that hammock. If the fuel tank is to be mounted, it should be mounted on something that is nonpermeable but glueable. The pad should be glued to the tank so as to preclude any water from getting between the tank and the pad. 
