Safety experts raised questions about the grandfathering of a crucial stability requirement for ro-ros after new revelations in the investigation into the deadly 2015 sinking of El Faro.

International safety rules require ships to stay within a certain metacentric height or GM, a key measure of a ship’s stability, when loading cargo. But ro-ros built after 2009 amendments to the Safety of Life at Sea (Solas) are held to a somewhat more stringent GM than older ships.

GM, which varies with the amount and stowage of cargo, is a measure in naval architecture that helps determine how stable a ship will be when it is rolling or heeled. Put simply, the higher the GM, the more stable a ship tends to be.

At hearings in Jacksonville, Florida, US Coast Guard (USCG) marine engineer Jeffrey Stettler delivered a report to the Marine Board of Investigation explaining that Tote Maritime’s 5,330-lane-metre El Faro (built 1975) had a GM of 4.3 feet (1.3 metres) when it set out on the final voyage. He noted, however, that the estimate could be off by as much as 0.7 feet.

Tote Maritime masters have testified that they kept the El Faro and its sistership to a minimum GM of five feet.

That GM is legal under the Solas convention’s 1990 provisions that apply to the 40-year-old vessel, a ro-ro that was converted to carry containers on its top deck.

The El Faro took all 33 crew members with it when it sank in a hurricane en route from Jacksonville to San Juan, Puerto Rico.

But Stettler said under the Solas convention’s 2009 standards, which apply only to ships that were built or that underwent major conversions after implementation, a GM of 5.8 feet would be required.

“That’s a significant increase in initial stability,” Captain Bill Doherty — a former ro-ro master and Norwegian Cruise Line safety manager who is now a flag-state inspector — told TradeWinds.

For Doherty, the grandfathered stability rules create a paradox: a newer ship built to the latest standards, which were bolstered after lessons learned from earlier ro-ro tragedies, must keep to a higher metacentric height.

“However, a ship pushing 40 years old, it’s OK to sail with 4.3 feet because she’s older,” he said. “What kind of logic is that?”

However, an official for the American Bureau of Shipping (ABS), which classed El Faro and carried out surveys on behalf of the USCG, played down the impact of GM on the survivability of a vessel.

“Compliance with the required GM curve means simply that the vessel, with that GM, will comply with the regulations,” ABS chief engineer for statutes Tom Gruber told investigators.

“It does not in any way, shape or form say that a vessel will survive in the seaway. Survival in the seaway depends upon the vessel itself, the seaway itself, the sea conditions, the wind conditions, and the ability of the master and crew to operate the vessel in a safe manner.”

Ro-ros present some of the thorniest challenges to the authors of international regulations on ship construction because of their vast surfaces on which water can slosh and their rolling cargo.

Richard Burke, a professor of naval architecture and marine engineering at State University of New York Maritime College, tells TradeWinds that safety regulations in the sector were changed in response to tragedies.

“Is this a case where we might want to think about the criteria under which the new regulations would be applied to existing ships?” he asked of the metacentric height requirements. “That’s a matter that the coastguard and ABS are going to have to consider.”

That, however, could be costly to shipowners on two counts. The ship and everything it carries, including cargo, ballast and bunkers, factor into its GM. That means owners of ships built to older Solas standards would have to change the amount and stowage of cargo, upgrade their ship, or both.

Should there be changes to the regime that has grandfathered lower metacentric heights for older vessels? That depends on whether safety concerns outweigh the impact on the economic viability of a ship.

When safety rules are enacted because a prior practice is considered unsafe and they do not apply to an existing vessel, it doesn’t mean that vessel is safe, says Burke, adding “it means perhaps the ship was never safe”.