The International Maritime Organization (IMO) has published the first of a set of two documents on the topic of second-generation intact stability criteria. Published on Dec. 10, 2020, the first document covers the interim guidelines that introduces new regulations for trial use – specifically five ship failure modes – while the second document, set to be released in 2022, will contain explanatory notes.
Intact stability refers to a ship that is in its normal operation configuration – it is functioning as intended and without consideration of unintended flooding or the accumulation of water where it is not supposed to be.
The purpose of these guidelines is to enable the use of the second-generation intact stability criteria for the assessment of dynamic stability failure modes in waves, which was requested in the 2008 Intact Stability (IS) Code. Furthermore, the primary purpose of these documents is to enable the use of the latest numerical simulation techniques for evaluating the safety levels of ships from an intact stability standpoint.
In developing these guidelines, it has been recognized that by combining design methods and operational measures is the most effective way for properly addressing and continuously improving safety against accidents related to stability for ships. The second-generation intact stability criteria should be used for helping to ensure a uniform international level of safety of ships with respect to dynamic stability failure modes in waves.
The five failure modes represented in the second-generation intact stability criteria are: dead ship condition, excessive acceleration, pure loss of stability, parametric rolling and surf-riding/broaching.
Naval Surface Warfare Center, Carderock Division’s Dr. Vadim Belenky, naval architect, Carderock’s Simulations and Analysis Branch got started working towards this agenda alongside the Coast Guard in 2005.
“In 2005 I started working alongside the Coast Guard in second-generation intact stability,” Belenky said. “From there I was involved with problems related to dynamic stability but have always kept my Coast Guard connections. With the support of Carderock’s management and the Coast Guard’s funding, Carderock was able to start supporting these developments.”
Belenky, a Russian native who grew up along the Baltic Sea, came to the United States in 1996 and started working for Carderock in 2008.
“My original background was in the stability of fishing vessels – my main specialty was dynamic stability,” Belenky said. “While working in Russia, we had similar problems with some of our ships, which is why I was hired by Carderock.”
Belenky’s Coast Guard counterpart, William Peters, naval architect, U.S. Coast Guard’s Office of Design and Engineering Standards, has been involved with the second-generation intact stability for the last 15 years.
“Certain forces may cause a ship to be disabled or to take on a list or to capsize,” Peters said. “These last two are considered bad – we don’t want them to happen. The IMO began in 1960 to look at what kind of things could be done to resolve this. They developed standards based on ships who had and had not had casualties and then compared stability characteristics and developed certain standards. If you met this standard, you were likely to not have intact stability failure.”
As technical progress has occurred, the shape and sizes of ships has changed.
“With that change came greater occurrence of stability failures,” Peters said. “Certain types of things became more and more obvious, which has led to the understanding of these five kinds of stability failures.”
The push to have an increase in modern vessels’ intact stability has been going on for the last 50 years.
“The IMO is not the fastest organization in the world, and things like the second-generation intact stability criteria usually happens once in a generation,” Belenky said. “So being approved last December, it is still big news.”
Though there has been a growing increase over the last half-century, there has been a stronger sense of urgency since 1998.
“In the late 20th century, we started seeing strange things happening with very large ships – things that would not be expected to have problems,” Belenky said. “The interest to intact dynamic stability of modern vessels was ignited by a large-scale container loss that occurred on board the U.S.-flagged container ship, MV APL China, in October 1998.”
The China experienced heavy roll motions with a port and starboard roll as great as 35-40 degrees. Of the 1,300 hundred containers on deck, one-third were lost overboard, and another third incurred differing degrees of damage and loss.
“The root cause of the incident was a parametric roll resonance appearing in certain combination of speed, conditions, heading and sea state,” Belenky said. “Billions of dollars were lost altogether. This case is similar to the Titanic in that a push was made for greater maritime safety.”
However, container ships are not the only ships vulnerable to parametric roll. In 2008, a cruise ship – then known as the Pacific Sun – rolled heavily while in gale force winds and high seas. Of the 1,730 passengers and 671 crew on board, 77 were injured with seven sustaining major injuries.
An instance involving pure loss of stability occurred in 2006 with the Swedish Ro-Ro ship, MV Finnbirch. The Finnbirch experienced heavy seas which heeled suddenly and considerably to port. The list after recovery was 30-35 degrees, causing the ship to capsize and sink. Two lives were lost, and 11 crewmembers suffered severe injuries.
“Stability failure can be either partial or total,” Peters said. “Partial failure can be where a ship doesn’t capsize, but significant events occur that causes not just cargo, but material, men and or equipment to shift on board, so that afterward you don’t have full operability.”
A similar instance took place earlier the same year, when, in heavy weather, the rail ferry Aratere experienced heavy rolling on two separate occasions – 50 degrees and 30 degrees – which resulted in five of the 381 personnel on board being injured.
Another phenomenon – excessive acceleration – can be equally as hazardous. In two separate instances in 2008 and 2009, the German container ship MV Chicago Express and the MV Guayas suffered from excessive acceleration, resulting in two deaths and another serious injury.
Surf-riding/broaching-to is when a ship is unable to maintain a constant course despite efforts of maximum steering. In 2012, the MV Rabaul Queen capsized due to broaching-to. The final death-toll is unknown as the exact number of passengers is unknown, but it is estimated that anywhere from 142-161 individuals perished.
“Surfers do on purpose what ships don’t want to do – surf on a wave,” Peters said. “The reason is that the stability of a ship in a surf-riding condition is very low, with a high likely hood that something will cause it to turn quickly and capsize. We found that this is still a matter of concern that has never been addressed adequately in other standards, so we wanted to address it.”
These accidents alone resulted in the deaths of at least 146 individuals and 98 additional injured personnel. Three of the ships sank. These instances have resulted in the push for an increase in modern vessels’ intact stability. The second-generation IMO intact stability criteria are pivotal for addressing the reasons for these accidents.
“The agenda to get this issue resolved started in 2002 – it took some time to realize this was happening more and more frequently,” Belenky said. “One of biggest challenges was trying to put the big picture together. It is only now that it is slowly being understood more.”
The second document is currently being worked on by the IMO subcommittee and is intended to be finalized by the end of this coming summer, with an estimated approval date of next May. It is currently already in the trial use stage, with universities and consulting companies performing the trials. The second document will not change anything in the first document, rather, it will further explain it and provide in-depth examples.
“When a ship sinks, we know exactly why – too much water got inside,” Peters said. “Why the water got inside is what we have to investigate and figure out. That’s what we are doing with this second-generation intact stability criteria.”