Bayesian Stability Calculus Suggests There Really Were Only Seconds To Save Lives
Roger Long Uses Analysis From Inquiry Into Marques Sinking
Along with his many designs of sailboats and research vessels, Roger Long was retained as an expert in the inquiries following the 1984 sinking of the British sailing school ship Marques during a talls-ships race. At the time, Long was vice-president of Woodin & Marean naval architects. After retiring from his own company, Long cruised the East Coast under sail and most recently on his 43-foot Gulfstar trawler Gypsy Star. Loose Cannon recently published Long’s series of stories about the sinking of Pride of Baltimore.
By ROGER LONG
Naval Architect Tad Roberts is working on a detailed hydrodynamic model of the Bayesian with vastly more information than I had working as consultant and expert witness for the British government in the inquiry into the loss of the sail training vessel Marques.
This is a work in progress, but we can already answer some important questions about the accident, based on Bayesian stability data published by the builder, Perini Navi.
Discussion and speculation seems to focus on a scenario in which the wind heeled the vessel to the point were water began entering through unsecured openings, the weight of the water changed the vessel’s stability, and it capsized and sank.
If passengers had been asleep in this scenario and the wind suddenly came up sufficiently to begin flooding the vessel, they would have awakened at a frightening angle of heel but one in which they could still climb out of their bunks and move about the ship sufficiently oriented to seek escape as water rose in the passageways.
This graph is prepared according to standard calculations but using an approach I presented in the Marques case that is not commonly followed. Rather than grapple with the many unknowns of trying to determine the actual wind velocities of the event, I simply look at the relative differences.
This graph tells us that the experience of the passengers probably would have been very different from the self-rescue scenario above, if there was enough wind to begin downflooding. The first indication of trouble for those asleep on the high side however would have been to have been thrown or dumped out of their bunks onto the floor. Next, they would have discovered that the floor was actually the opposite wall of the cabin.
To escape, they would have had to find and open the door which was now in the floor and drop through it across to the other side of the passageway now rapidly filling with water. Those on the low side would have found themselves lying on the side of the hull with the door they needed to escape through now in the “ceiling.” The disorientation and difficulty of moving around the vessel seeking exit would certainly have raised the death toll.
How does this graph tell us that the second scenario is the most probable when we don’t even know what the actual wind velocities were? The vertical magenta lines on the graph show the places were water can begin entering the vessel.
The one at the lowest angle is only equal in area to about a 9-inch square so not very significant in a vessel of this size. The second, at an angle of 39.6 degrees is equal in area to a 22-inch square. This is large enough to let in a significant amount of water so I will used it as the base for the first scenario. Three degrees after that comes another water entry point just slightly larger.
The red lines show how wind force on the vessel decreases as the vessel heels. The value at zero degrees heel indicate the initial wind pressures, but there are too many variables and unknowns to do this precisely. However, wind pressure varies as the square of the wind speeds. We can thus take the square roots of the upright value of the two red curves to find the relative difference in wind speeds between the first and second scenarios.
This simple calculation tells us that, if the wind was strong enough to heel the vessel just to the point that it started to flood, only a 6.8 percent increase in velocity would be required to lay the vessel right over on its side.
So, we have two scenarios: The first scenario is one in which passengers would have had a reasonable chance of escape. The second has the vessel lying flat in the water within seconds and flooding through every available opening. Is it reasonable to believe that the wind speed would have remained within that exceedingly narrow range between the two?
Afterword: According to testimony before Italian authorities, the Bayesian crew had been mustered soon after the wind began to blow at 20 knots. When stronger winds hit and the yacht heeled dramatically, they scrambled desperately to rescue guests. Captain at front, they formed a human chain “walking on the walls.” Only six guests were saved. Long’s calculus of stability tends to support crew statements that they simply had no time to get everyone out.
PREVIOUSLY ABOUT BAYESIAN:
I was caught once in a sinking boat when I was in the Coast Guard years ago. I literally had to wait a few seconds for the area to flood before I could get out through the door the water was coming in through. It's difficult to imagine how strong that current can be. In my case the boat sank in about 14 ft. of water.
When I heard the news of the sinking of the Bayesian, I knew parallels would be drawn surrounding the 1984 sinking of the 120’ barque Marques.
I was crew on the S/Y Luna Quest, and after a long passage from Norfolk, VA to English Harbor, Antigua, we tied up next the Marques and the 123’ brig Cuidad de Inca.
On the docks in front of us was a huge bacchanal with all the boat crews - our timing was spot on.
I spent many happy days with the crews and they asked me to join the Marques. I met the Captain aboard Marques to seek a berth but they had none; I ended up as crew of the W. Fife vessel “Eilean.” This was in March 1984.
I was stunned to hear of the Marques sinking; but was grateful there were survivors.