Khaleesi, with 20 people visible on deck

Originally posted by gCaptain. Reposted with permission.

Last Saturday, the 30 passengers aboard Khaleesi, a Silverton 34 power boat, were watching the Navy Blue Angels over San Francisco Bay as part of Fleet Week.  On the way back to the dock,  Khaleesi capsized and sank. Miraculously, no one died, although two children were rushed to a local hospital in critical condition.  (Initial reports, incorrectly described the boat as a recreational sailboat.)  Sadly, this incident sounds far too familiar.

This is not the first time that an overloaded Silverton 34 has capsized. Four years ago, under remarkably similar conditions, another Silverton capsized and sank with tragic results.

On July 4th, 2012, 27 passengers aboard Kandi Won, a Silverton 34, were out on Long lsland Sound off Oyster Bay to watch fireworks. Shortly after the fireworks were over, at around 10PM, Kandi Won was hit by a wave on her beam. The yacht capsized and sank. Three children – ages 8, 11, and 12 – were trapped in the cabin and drowned.

After the sinking, a team of naval architects and investigators worked together and independently to attempt to understand what caused the Kandi Won to capsize and sink. Sadly, the lessons learned from the tragedy do not appear to have been applied.

The Silverton 34 is no longer being built. Between 1978 and 2007, four different models were manufactured with slightly different dimensions and layouts. The Kandi Won, which capsized in Long Island Sound, was built in 1984. Based on the configuration of portlights and sheer line, it appears that Khaleesi was of the same model vintage, built between 1978 and 1988. If so, the accident report and technical analysis done following the Kandi Won tragedy could potentially be applicable to Saturday’s accident.

In 1992, the Nassau County Police Department investigation report, “The Sinking of the Kandi Won, July 4, 2012,” determined that the yacht had inadequate stability when it capsized and sank with 27 people on board. Of the 27, 15 were adults and 12 were children aged 16 and under. By comparison, there were more people, and specifically, more adults aboard Khaleesi when she capsized.  There were 27 adults and three children aboard Khaleesi, so it is likely that the passengers weighed more than on Kandi Won.  With a larger passenger load, it is likely that Khaleesi was potentially even less stable than Kandi Won when she sank.

What made the Kandi Won, and potentially Khaleesi, so unstable? The design of the Silverton 34, and other boats like her, make stability a challenge. Typical of planing boats, they are relatively shallow draft, drawing around three feet of water. They have considerable freeboard and a flying bridge. Unlike a classic Grand Banks dory where additional load makes the boat more stable because the weight is low, on the Silverton, each person coming aboard raises the overall center of gravity of the boat, which reduces the stability.

After she sank, the Kandi Won was refloated and Neil Gallagher, a Professor of Marine Engineering and Naval Architecture at Webb Institute, conducted a stability test, also known as an inclining test, to accurately determine the center of gravity of the boat. He then estimated the weight and position of all the passengers aboard on the night the boat sank. The passengers reported that the boat began to roll over when struck by a wave beam on. Based on the calculations, he estimated that the Kandi Won had such limited stability that a two foot wave could have caused her to capsize.  The wake from passing boats returning from watching the fireworks could have been enough to doom Kandi Won.

Khaleesi appears to have rolled over under very similar circumstances.  The passengers on Khaleesi were returning to the dock with numerous other boats during San Francisco Fleet Week. The weather was clear and the bay was calm, but it is possible that a boat’s wake was enough to cause the Silverton to capsize. Ironically, while the number of boats surrounding Khaleesi may have contributed to her capsize, those aboard the boats also helped rescue the people thrown in the water when the powerboat rolled over.

So, what is the appropriate number of people to allow go onboard a Silverton 34?  Despite all the analysis and calculations, that is not easy to answer. The boat has bunks for six and seats for 14. A Silverton manual for a later model lists a 10-person capacity.  Marine consultant Eric Sorenson believes that “eight to 12 people is a full load for a boat of this type in sheltered waters.” Naval architect Dave Gerr is slightly less conservative. “I can see no reason that boat wouldn’t be safe with 15 or 16 people aboard for ordinary coastwise junkets,” he says, “but with no more than two or three on the flybridge.”  Everyone agrees that 27-30 is way too many.

Aren’t there regulations to determine how many people can safely be carried on a yacht? Under the U.S. Coast Guard Federal Boat Safety Act of 1971, boats with an inboard, outboard, or stern drive engine manufactured after November 1, 1972, must display a capacity plate defining the safe load limits, both in terms of weight and number of people allowed to be carried. The problem is that the law only applies to boats of less than 20 feet long. European regulations require capacity limits on larger vessels, while in the US, the number of people allowed is largely left up to the boat operator, who, in most cases, is also not required to be trained or licensed to operate the vessel.

Where there are regulations, they may not be adequate. Eric Sorensen, in his article for Soundings, Analysis Of A Capsizing, wrote, “we have found that with 27 passengers on board, and guessing at actual passenger distribution, the resulting stability calculations appear to satisfy the requirements of the 46 CFR (Code of Federal Regulations) stability standards, which is surprising.”

Why aren’t there greater requirements to prevent capsizes? The answer may be that larger vessels just don’t capsize that often. After the Kandi Won accident, the Coast Guard found that over the previous five years, an average of 60 boats greater than 20 feet capsized each year. For smaller boats, the yearly average was 255.

Nevertheless, we have seen two almost identical capsizes of a very popular style of powerboat under very similar circumstances. Three children were drowned in the Kandi Won capsize and only good luck and fortunate circumstances prevented the loss of life when Khaleesi rolled over and sank. Even so, two children ended up in the hospital in critical condition.

These accidents may be infrequent, but they are not rare. Now seems like a good time to at least consider guidelines, rules, or appropriate training to help power boat operators prevent these unnecessary accidents from happening again. In this case, twice is enough.