Capacity, Stability, And Safety: How Many Is
Too Many?

The capsize of a 34-foot cabin cruiser in
Long Island Sound raises questions about
boat carrying capacities.

Published: January 2013

Boaters gather every year in Long Island Sound for the dozens of private and municipal Fourth of July fireworks displays visible from the water. Among the hundreds of boats on the Sound last year was a 34-foot Silverton cabin cruiser, called Kandi Won, loaded down with 26 friends and family members of the owner. When the fireworks ended, the Silverton joined the crush of boats heading home. At about 10 p.m., according to news reports, the boat rolled, spilling passengers into the water.

"It was very fast," passenger Lisa Gaines later told the Today Show. "The boat started to lean, and it just didn't recover." Three children, including Gaines' 8-year-old daughter Victoria, were trapped in the cabin when the boat went down, and died in the accident.

An investigation of the capsizing by Nassau County, New York police is still underway, but response in the boating community and in legislative chambers was swift. In New York, spurred on by Lisa Gaines and her husband Paul, state legislators introduced a bill calling for more boater training. Most of the response, though, has centered on the number of people aboard -- by seemingly any measure, the boat was overloaded. But the older boat had recently been purchased by an inexperienced skipper, who may not have understood the danger. Boats under 20 feet and powered by an engine are required to have capacity plates indicating the number of people a boat can safely carry. These remove any doubt about when a boat is overloaded. But boats 20 feet and over, like Kandi Won, have no such labeling. In the wake of the July accident, some experts are asking whether the capacity plate requirement should be extended to cover all boats.

CAD Drawing Resembling the 34-foot Silverton
Courtesy of: Dave Gerr
CAD Drawing created to be as close as possible to the 34-foot Silverton
and used to analyze the boat's stability.

Dave Gerr, nautical architect and author of (among other books) The Elements of Boat Strength for Builders, Designers and Owners, believes that all powerboats should carry capacity plates, and he has recommended that the American Boat and Yacht Council (ABYC) adopt the requirement as a standard. Gerr, with a group of other naval architects, investigated the sinking of Kandi Won.

"It was immediately apparent to all of us that this was crazy," he says. "You don't put 27 people on this boat." So a bunch of us said, "OK, that's our intuition, it seems like we all agree. Let's take a look at the stability numbers, and see if the numbers prove that conclusively."

The numbers, it turned out, were the easy part. The hard part, Gerr says, was reconstructing the boat. Silverton is in bankruptcy, and plans for the older boat were difficult to come by. He had to start from scratch, developing a mathematical model as well as a computer drafting simulation to analyze the boat. Once he had those models, he was able to determine the stability of the vessel when it was loaded with people.

"My original results were surprising," Gerr says, "so I had a couple of people look at it. Basically, it was quite a nice boat. Quite safe and stable. But with 27 people onboard, including eight on the flybridge, the stability was very questionable. It had almost no reserve stability at all."

His conclusion: "A boat that size was probably safe with 15 or 16 people onboard. Maybe even a few more."

A real-world test of his finding was fairly simple. Marine consultant Eric Sorenson piled weight on the rail of a similar Silverton 34 and measured the angle of heel. In a detailed article in Soundings last year, Sorenson was more conservative in his preliminary findings. "Some feel that 15 [passengers] would be permissible in calm waters in daylight if half of them are kids," he writes, "but I think this is excessive because of the complications so many people create in the event of an emergency."

Gerr thinks Sorenson's estimate is too 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."

Sorenson's Soundings article is an excellent and in-depth investigation. It is also physics-heavy and, one suspects, a bit dense for casual boaters like the skipper of Kandi Won. He concludes that experience is the best guide, or barring that, education of the sort offered by the Coast Guard and Power Squadron.

Gerr agrees that experience (and common sense) should serve as a guide. "Anyone who's spent any time on the water sort of understands" when a boat is overloaded, he says. "If you've been in a canoe, you understand. If you've been in a rowboat, you understand."

Chart of 34-foot Silverton Stability Curves With Normal Load and With 27 Passengers
Courtesy of: Dave Gerr
Gerr's model showed that the stability of the 34-foot Silverton
decreased by more than half when loaded with 27 passengers.

James Mercante, a lawyer hired by the insurance company of the Kandi Won owner, does not agree. "They were out there for hours before, during, and after the fireworks and there was no incident, no problem; the vessel handled fine," Mercante told The New York Times. "You get two or three big boats when they're together, you get a wake becoming six to eight feet. Any boat could get rolled over with a trough like that." Mercante's remarks have been disputed by Sorenson and others.

In the absence of capacity plates for recreational boats 20 feet and over, safe operating capacity is left to the captain's experience, judgment, and common sense. Charles Schumer, New York senator, would like to change that. Shortly after the July 4 accident, he wrote a letter to the Coast Guard, asking them to "require all recreational boats to post capacity information in a highly visible location for all to see. This will provide passengers, who are not familiar with boating capacity and safety measures, the option to choose whether or not they feel safe boarding the boat."

In September, Schumer introduced the "Boating Capacity Standards Act of 2012" in the Senate. It would require all new boats to prominently display their carrying capacity, in people and in pounds. The bill has gone to the Senate Committee on Commerce, Science, and Transportation. If the bill passes, capacity plates for larger boats would become the law of the land, but in the meantime, the Coast Guard is unable to make a rule on its own because larger boats just don't capsize that often.

Phil Cappel is the chief of the Coast Guard's Recreational Boating Product Assurance Branch, which keeps the numbers on the trouble that recreational boats get into every year. His team looked at their data after the Kandi Won accident and found that in 2010 and 2011, there were 26 capsizes, resulting in two deaths and six injuries on boats in the 26- to 40-foot range. Over the past five years, an average of 60 boats greater than 20 feet capsized each year. For smaller boats, the yearly average was 255.

In an email, Cappel wrote that "we don't have the justification from our boating accident database that we feel is needed to attempt to publish a regulation requiring capacity plates on all recreational boats 20 feet in length and over."

Capacity isn't really the issue anyway, Cappel says. It's the stability of the boat that matters, although the two are related.

"Operators have to be more aware of the placement of persons and gear aboard the boat rather than just the total weight allowed," he says. "Many boats less than 20 feet in length, that are required to have capacity plates, capsize each year even though they may be carrying the proper number of occupants. The simple fact of the matter is that smaller, lighter boats have much less stability than larger, heavier boats."

Gerr has recommended that the ABYC adopt a standard formula for capacity. The ABYC is undertaking a study to see if there's a statistically significant number of larger boats that capsize due to overloading. Like Cappel, Gerr says it is more about stability than capacity -- where the weight is placed is an important factor. Unlike Schumer's bill, he would make an exception for sailboats, because they heel by nature, and he would like to see a separate capacity plate for flybridges. Still, he says, the draft standard he envisions would not be overly burdensome.

"What I have in mind is not going to require a vast amount of calculation," he says. "The idea is to make it easy."

While the National Marine Manufacturers Association (NMMA) hasn't taken a position on the issue, some manufacturers already label their larger boats. Beneteau, based in France, labels their powerboats according to a European Community (CE)standard, with passenger capacities based on where they will be used, from Class A ("Ocean: Designed for extended voyages where conditions may exceed wind force 8 [Beaufort scale] and significant wave heights of 4 meters and above, and vessels largely self-sufficient") through Class D ("Sheltered waters: Designed for voyages on small lakes, rivers and canals where conditions up to, and including wind force 4 [Beaufort scale] and significant wave heights up to, and including 0.5 meters may be experienced"). Beneteau's new 30-foot Barracuda 9, for example, is CE-certified to carry four people offshore, and 10 people inshore.

What Gerr is proposing is less complicated. While he would like to see a separate rating for boats with a flybridge, testing stability would be fairly easy. "It's a little more complicated than this," he says, "but if you have a boat that you want to carry 12 people, you get 12 people and you stand them on the rail. If the boat doesn't heel more than 14 degrees, you pass."

Gerr proposes providing a simple set of calculations for voluntary use in the design phase and developing a simple stability test. "Those calculations would be in the standard for those who want to use them," he says. "So if you're a designer, whether you're working for a manufacturer like Silverton, or whether you're building a boat on your own, you could optimize your design based on those calculations. But if you wanted to test them, it would be something relatively simple. And that's important, that it be relatively simple."

Since neither the Coast Guard nor Congress are likely to enact a new standard in the foreseeable future, any immediate action on capacity plates would have to come from the ABYC's technical committee. In the absence of capacity ratings for larger boats, is there a method for calculating capacity that doesn't require a degree in naval architecture? Not really. "Anything I can think of that's simple might possibly lead to assuming a boat was safe that wasn't," Gerr says. "It would be rare, but not rare enough."

Owners of larger boats may find assistance in their owner's manual (the manual for a later model of the Silverton 34 lists a 10-person capacity) or by contacting the manufacturers directly. But as the Coast Guard's Cappel pointed out and the European Community standard for capacity labeling indicates, conditions outside the boat can have a dramatic effect on stability. There is still no substitute for training and experience.

For smaller boats, there is a formula that gives a rough approximation of the number of passengers a boat can carry. The New York Times cited it in an article about Kandi Won, but later corrected the article. Widely referenced online, the formula is length times beam, divided by 15. Asked about that formula, Gerr wondered aloud what answer it would give for the 34-foot Silverton. There was a brief silence over the phone while he calculated.

"That gives 27 people," he announced. "So yeah, it breaks down on bigger boats."End of story marker

Drawings prepared by Dave Gerr, Director of the Westlawn Institute of Marine Technology (www.westlawn.edu), and first appeared in Soundings Trade Only.


To comment on this article, please contact Seaworthy@BoatUS.com