Squalls associated with thunderstorms can contain some downdraft element that reaches the ocean surface.


wind heeling arm curve can be shiſted 30degs to the right. As can be seen in diagram 3, when this is done, any residual buoyancy from the deck houses is totally overcome, and the vessel goes over onto its beam-ends. So what we have from the Concordia model


is:


• a vulnerability to a rapid increase in heel angle at a relatively modest wind speed;


• a loss of buoyancy due to downflooding through open doors, windows, and vents;


• a possible inclination of the wind that overcomes any


and remaining residual


buoyancy provided by the deckhouses. In combination, these factors would result


in the rapid knockdown and capsize. All well and good—as explanations go—but


Concordia was no spring chicken; rather, it was a seasoned veteran of many ocean voyages. While we do not know if the vessel had been knocked down before and recovered, we do know that, by reputation, the vessel had always been sailed conservatively, with minimised heel angles so as not to adversely affect classes. Here’s a final element to consider: Concordia


was built in Poland and was originally flagged in the Bahamas. Te Bahamas followed the UK rules and required that the vessel have ‘squall curves’ included in its stability book (maximum steady heel angle to prevent downflooding in gusts and squalls). Tese


Ship & Boat International March/April 2012


rules were introduced in the UK following an inquiry into the loss of the Marques in 1987. When consulted by a deck officer who is knowledgeable in their use, these curves show when the margin of safety is being eroded and, therefore, when mitigating action—such as shortening sail or altering course—is required.


Two-point call for action So what happened on Concordia? Te Master handed over the controls at 12:00 to the officer of the watch (OOW) with a shortened sail plan that was “good to 40knots” and instructions to bear off if the wind increased. Te vessel was on a broad reach and making about 5.5knots in 15 -20knot winds. Te Master’s standing orders required that he be called if the vessel was at risk. Tere was no discussion of the squall curves at the handover. This is key. In fact, the OOW, who was appropriately certificated for his position, was not aware they were on board, did not consult them, and was not trained in their use. Had the stability book been consulted, it


would have shown that, in order to provide a margin of safety in typical gusting conditions, the heel angle should be limited to 24degs. Instead, as the squall approached, the angle of heel increased from around 10degs to about 23degs in wind speeds of about 23knots. At this point, the margin of safety may have just been sufficient for a gust, but certainly was not sufficient for the encounter with the squall


when it came. Te OOW, not perceiving the risk to the vessel, was not concerned. But the heel angle then quickly increased and, within a very short time, Concordia was on its beam ends with the deckhouses flooded. Te OOW’s attempt to change course was too late. Ultimately, no single factor caused this


accident. Rather, it was a combination of the inherent limits of Concordia; a lack of knowledge of these limits on the part of the OOW; the associated lack of awareness of the developing risks; and, consequently, the absence of mitigating action to reduce sail, change course, or secure the vessel watertight. As a result of its investigation, the Board


made two recommendations, which—if adopted—should help ensure that a similar accident does not occur in the future. In essence, every sail training vessel should have the necessary information onboard to define its individual vulnerability to specific weather conditions; and its deck officers should be trained to use that information. SBI


Jonathan Seymour FICS, MNI, was a Member of the Transportation Safety Board of Canada from 1999 until he retired from the Board in 2011.


1


This range of estimated wind speeds takes into account uncertainties with the value of sail heel force coefficient, which may also be thought of as the “efficiency” of the sails.


19


In-depth


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