Sunday, May 15, 2011

How to Avoid Bligh Reef - Keep a Navigation Plot

Track of  tanker Exxon Valdez to Bligh Reef
How to Avoid Bligh Reef.

From the Old Salt Blog - Two Constants – Bligh Reef and Human Error

The Coast Guard report on the grounding on the tug Pathfinder on Bligh Reef prompts the Old Salt Blog to point out that this is  the same reef struck by the Exxon Valdez on March 24, 1989.

As pointed out, both incidents have in common Bligh Reef and human error. They also both share a lack of a proper navigation plot.

The chart (chart and times from  Visualizing the Decision Space )  above is marked with key points (click to enlarge chart).

1. At 2324  Exxon Valdez drops off the pilot
2. At 2330 Hazelwood changes course to 200T
3. At 2339 Third mate Cousins plots a fix /  Hazelwood changes course to 180 T (due south)
4.At 2353 Hazelwood leaves the bridge, orders third mate Cousins to change course when abeam Busby Light (2 minutes ahead)
5. At 2355 Third mate Cousins plots a fix abeam Busby but does not change course.
6.At 2400 (midnight)  Lookout reports Bligh Reef on the Stbd bow -  Cousins orders Right 10 rudder
7. At 0004 Cousins orders right 20 rudder
8. 0007 Cousins orders hard right
9. Exxon Valdez strikes Bligh Reef at 12 kts.(at 12 kts 1 mile = 5 minutes)

The key here is that giving verbal instructions to the mate does not suffice. It's critical that an intended track-line be  laid down with anticipated turning times labeled on the chart. When a navigator plots positions, courses and times on a chart it moves navigational information from the officer's mind, to the paper chart where it can be more easily examined by all involved.   Plotting navigation information  is both a way to determine turning times, distances to hazards and so forth but also, importantly, it is also a  communication tool.

When Capt Hazelwood ordered Cousins to "turn when abeam Busby Island" we don't know if Hazelwood  had full situational awareness, specifically the ship's position and distance from hazards and we don't know how Cousins interpret  his instructions. Placing the relevant plotting information on the chart would have closed understanding  gaps between mate and captain.

Next, the case of the tug Pathfinder.

From Report faults captain in tugboat grounding on Bligh Reef.

The captain of a tugboat that ripped open on Prince William Sound's Bligh Reef in 2009 was unaware of the boat's position when he put it on a crash course with the infamous and well-known navigational hazard, according to a Coast Guard report.
"Unaware of the boat's position". My experience is that captains and mates on tugs don't keep a paper plot. In many cases they should. If the crew is so familiar  with the area that they fully aware of the vessels position at all time, for example in a marked river channel, then a full plot is not necessary. In many other cases some form of a plot should be kept.  According to Bowditch

"a small craft navigator of limited experience may underestimate the importance of professional navigation. However his vessel's safety depends on his skill. He must plan his track and know his position at all times. Small craft navigation also requires a complete, accurate, and neat plot."

But the captain on the Pathfinder had over thirty years of experience including ten years on the Pathfinder. Not a navigator of "limited experience".  This is an example of what a ship mate of mine describes as "I'm so good I'm brain dead"

For captains this is simple, insist on a formal plot. For mates it's a little tougher. I've sailed on tugs where the captain forbid making marks of any kind on the chart. But if allowed don't accept "hand waving" when changing watch. If the off-going officer does not have a plot take the time  to lay one down before you relieve.


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