Reviewing nav method for entering harbor
Capt. Virginia Wagner's correspondence piece in a recent issue ("Ocean Star's encounter with a Cuban Reef," No. 93, November/December 1998) brings into sharp focus a number of important navigation and piloting issues.
Capt. Wagner tells a story of being tired, and of feeling uneasy about the 150° range from the sea buoy to the inner harbor, when the guide books and the chart clearly indicate you should follow a range of 140° T.
I used the Cap'n navigation program to call up the harbor chart for Marina Hemmingway. Sure enough, the bearing into the harbor is 140° T. I then laid out a two-waypoint route by drawing a range line from the inner harbor's bulkhead, through the middle of the channel, to a point outside the harbor at 23° 05.33' N, 082° 30.50' W.
In effect, I created my own sea buoy and a range line that would keep me in safe water.
Capt. Wagner talks about studying the chart and guide book. But she does not talk about plotting her position on the chart or drawing her own range line. I make the point about using a paper chart because everything I did in the Cap'n program can be done on a paper chart, although the Cap'n makes the job easier and does not fall victim to "I've been up for 24 hours" mistakes.
I assume that Ocean Star is equipped with a GPS or two. What went wrong?
1. We all get tired. I wrote this report late at night, and misread the latitude of my first waypoint. I was turning into the harbor from 120 miles to the north!
2. We all forget basic navigation practices, such as plotting our position, and laying out a route.
3. We all fall victim to relying on only one piece of information, such as channel markers.
4. We all have ignored that little voice inside that says something doesn't make sense.
As managing director of Nautical Technologies Ltd., its my job to convince folks how much safer they are when the Cap'n is plotting their position every two seconds. I try to wean recreational boats away from buoy-to-buoy navigation and into the professional world of plotting their position.
I'm not saying the Cap'n is the only tool I'd use, especially in such a tight spot. (There's only about 78 yards between two of the reefs at the Marina Hemmingway harbor entrance, the datum of the digital chart is unknown, and ordinary GPS can be off by 100 yards.)
Assuming my judgment was not impaired by lack of sleep, I would have:
A. Laid out my range on the chart and driven the vessel to the first waypoint using GPS (paper chart or digital, makes no difference, except the Cap'n does not make plotting mistakes);
B. Taken a range from the ship's compass to confirm that my jumping-off point agreed with the range line defined by my route into the harbor; and
C. Since I'm the original Chicken of the Sea, I'd have turned on my radar to get a confirmation that I was lined up on the correct range of 140° T.
Would I go to sea with Capt. Wagner? You bet. Her post mortem tells me she is a well-qualified skipper who is constantly improving her professional skills. The next time she is uneasy about a harbor approach, she'll probably stand off, make a cup of strong coffee, and dig into her bag of navigational tricks.