PT Online

Rotational molders of fuel tanks for boats fear that new emissions requirements being proposed by the U.S. Environmental Protection Agency pose a threat to their business—and may also make boating a more hazardous pastime. Rotomolders produce roughly two-thirds of the fuel tanks for the 400,000 marine craft launched annually in the U.S. Crosslinked PE marine fuel tanks are rapidly replacing fabricated aluminum versions, especially in smaller (10- to 180-gal) sizes, due to their superior corrosion and leak resistance.

In a proposed rule published in July, the EPA is calling for up to 80% reductions in evaporative emissions from three sources: One is permeation through fuel-tank walls. A second is diurnal emissions caused by expansion of fuel vapors in the daytime. The third is leakage from filling and venting hoses that are snaked through boat hulls. The agency expects new rules to be in place by 2007. EPA has issued a menu of possible technical solutions ranging from mono- and multilayer barrier designs to surface treatment via sulfonation and fluorination.

“We are investigating the cost-effectiveness of these remedies, but the outcome is less than certain,” comments Jim Porter, founder of Inca Molded Products in Nashville, Tenn. A pioneer in rotomolded XLPE boat tanks, Inca remains a leader in this $40-million annual market, along with Moeller Marine Products in Sparta, Tenn., and Kracor Inc. in Milwaukee. At recent EPA hearings, rotomolders and other industry sources questioned the viability of these alternatives and suggested that one EPA proposal is downright dangerous.

Not like automotive

One concern is that the EPA proposal appears to assume that the auto industry’s success in meeting new fuel-tank emissions standards can be replicated across the board in marine fuel tanks as well as tanks for off-road vehicles (e.g., tractor mowers) and power tools, or even portable jerry cans. EPA is moving to institute evaporation requirements for all these applications, which are mostly blow molded except for marine tanks.

“Boat building hardly has the resources available to automotive,” says Inca’s Porter. Further, the economics of marine fuel tanks is a world apart from those for high-volume blow molding, he notes.

Meeting proposed EPA fuel-emissions requirements could mean replacing all the 2500 tools currently used to rotomold marine fuel tanks.

Some 2500 different rotomolding tools are estimated to be actively used for XLPE marine fuel tanks today. The U.S. boating fleet is highly diverse, with thousands of leisure and commercial classes, each requiring special tank sizes and designs, mostly in modest volumes as low as 10 units/yr. Porter says the relatively low cost of rotational molds has been a key to keeping tank costs in line.

Rotomolders generally agree that sulfonation appears to be the most viable immediate answer to their needs. They estimate that it would add around 20% to tank cost, possibly prompting a reversion back to corrosion-prone aluminum tanks.

Other reservations about sulfonation’s viability are that it would require sizeable investments for in-house use and it would create substation emission challenges in the rotomolding workplace. There is also doubt about sulfonation’s ability to meet EPA’s proposal for a barrier able to retain 50% effectiveness after five years of use.

An alternative is multilayer tanks, but that represents a potential “manufacturing nightmare” for rotomolders, argues George Kraemer, president of Kracor. Internal drop-box mold technology could be employed, but Kraemer says that increases cost, complicates inventory needs, and limits the ability to run different tank sizes on one machine arm.

A possible solution would be monolayer barrier tank design using nylon or other (e.g., tortuous-path) barrier materials. Obstacles to that approach are high cost and lack of barrier resin grades suitable for rotational molding.

Too much pressure?

A tougher challenge is EPA’s call for minimizing diurnal emissions via pressurization of tanks at 1 to 2 psi. Pressurized tanks would have a release valve to contain vapors that expand during daytime. A shift to pressurized XLPE marine fuel tanks would demand a whole new generation of tools. At a recent EPA hearing, Tony Riviezzo, Moeller’s technical director, told the agency that such a program could take 14 years to implement and would incur $10 million in added tooling costs. Also, he warned, internal pressurization could cause long-term “ballooning” of tanks, and would require further redesign of tanks and tools. (Copies of his testimony are available from the National Marine Manufacturers Association.)

An even more ominous risk is a sudden release of fuel vapors caused by failure a pressurized tank and entrapment of such vapors inside the boat hull. One molder said this in effect would “turn a boat into a potential torch” due to the consequent risks of explosion and fire.

Even spokesmen for companies that make aluminum marine fuel tanks balk at the pressurization idea. Chris Brown, v.p. of Ezell Industries in Cocoa, Fla., says any safety risk in boating is bad for the entire industry. He says aluminum tends to have an advantage in larger (180- to 1000-gal) tank sizes, one reason being that the incorporation of slosh-resistant baffles is easier in fabricated aluminum designs. Economics also favors aluminum in large tanks.

The ideal solution might be new technologies, Brown says. Ezell, for instance, would be most interested in a composite having barrier properties comparable to those of aluminum combined with corrosion resistance equal to XLPE when exposed to salt water or fuel.