Navigation Accidents and Their Causes
The Nautical Institute, 2015
A recent tragedy at sea once again serves to refocus the world’s attention on maritime accidents and underscores the subject of Navigation Accidents and Their Causes, recently published by The Nautical Institute. Acknowledging the contributions of an impressive group of experienced master mariners, navigation specialists and university scholars, this book examines those strands of accident precursors that lead to economic loss, environmental devastation and, all too often, tragedy. In drawing attention to a persistent challenge, the book acknowledges that it “tackles an important question … why do navigation accidents keep happening?” It addresses that challenge in an effective way.
Statistics suggest that, in absolute terms, accident frequency is decreasing, but there are other factors to consider. Vessel size and capacity continue upward, whether measured in tons of crude or thousands of TEU, with the outcome of an accident becoming less a function of frequency and more of damage and loss per accident. Further troublesome in its persistence is the issue of “human error.” Questionable crew levels and work schedules providing inadequate rest periods leading to fatigue are cited in many accident reports. Several studies indicate that over 80 percent of collisions are the result of human error and many of those, not surprisingly, are a result of fatigue.
Maritime accidents are often reported in a horizontal approach — a description of the development of a specific event from beginning to end. Navigation Accidents and Their Causes takes a more vertical approach — that is, focusing on individual factors that are critical to understanding the fine details of an evolution. This makes for an approach that can be studied, reviewed and applied to any voyage, any vessel, anywhere. Twelve chapters, each authored by an expert in the field, address specific topics.
Emphasized frequently with specific examples is the critical importance of checking position using at least two different systems, with visual seemingly being the one often neglected. The importance of maintaining a DR/EP plot is stressed, serving as a secondary independent backup of a position fixed by other means, e.g., electronic. In one incident, a navigation system incorporating a pre-programmed DR received GPS and Loran inputs and outputs to a chartplotter and autopilot, having corrected for set/drift. Responding to loss of GPS signal, the system — bypassing an available Loran signal — defaulted downhill to the DR, thence to the autopilot and the vessel grounding on a shoal. Accuracies of radar ranges, range/bearing and bearings decreased in that order, and the effects of radar beam width on tangent bearings as well as pulse length on radar ranges are noted. Parallel indexing is covered in detail, noting that that a misidentified radar target used to establish cross-index line(s) can lead to misleading interpretations. Another factor is awareness of the radar presentation being north-up, i.e. stabilized, or head-up with the possibility of misunderstanding the display.
Knowledge of under-keel clearance (UKC) is obviously critical when the water gets thin. Initially defining the derivation of static under-keel clearance (SUKC), that chapter proceeds into the more specific dynamic conditions encountered by vessels underway with possible vertical motions due to wave action, heel and squat. This seeks to determine the hull’s minimum clearance of the seabed, given the characteristics specific to the vessel at the time, the hydrography of the seabed and tidal effect.
Squat, the vertically acting trim effect of the vessel’s wave pattern, a function of its hull speed through the water as opposed to over the ground, is covered in detail. It is of particular interest and concern in the shallow water of dredged channels and canals. Appropriate calculation aids as well as suggested references to the vessel’s trim and stability book are provided. The transverse effects on UKC of roll or heel and horizontal effects of heave or pitch are provided separate attention along with illustrative diagrams. The amplifying effect of the vessel’s natural rolling period with swell period, especially on a dockside vessel exposed to a long-period swell, is underscored. This chapter concludes by drawing attention to UKC management in practice.
And then to everyone’s favorite topic: the ColRegs. By their very nature, a limited number of regulations to cover an infinite number of situations can never be perfect. This chapter puts forth a wealth of ideas, warnings and the authors’ personal observations, highlighting critical points. While recognizing the contributions of ECDIS, ARPA, AIS, VHF, etc., the authors remind the reader that each aid has its inherent difficulties, and that they are just that — aids. The long-standing importance of visual bearings, whether for position fixing or monitoring an approaching vessel for a constant bearing, recalls one master’s eloquent admonition that “it is sometimes well to look out the window.”
VHF use in collision avoidance draws attention to the fact that, while talking, the range is closing — and fast. Rules for lookout, safe speed, collision risk and action to avoid collision are well covered. Discussion of Rule 17, Action by Stand on Vessel, cautions about the perennial trap for both stand-on and give-way vessels and makes critical points. As for the latter, a 1965 article in the U.S. Naval Institute’s Proceedings by Capt. Richard A. Cahill titled “The Burden of Being Privileged” explored deeply the “burden” carried not only by the burdened give-way vessel but, in equal measure, the privileged stand-on vessel itself.
Bridge resource management, passage planning and vessel traffic services are among other topics addressed. This most recent publication of The Nautical Institute, Navigation Accidents and Their Causes, brings a unique focused approach, examining factors leading into those situations and thus how to prevent them. Numerous diagrams and provision of brief accident digests add to its value.