200267 Ancient and Modern 4

08 Mar 2002 MARS

Ancient and Modern 4
Report No. 200267

I read the very thought provoking article "THE USE OF VISUAL AIDS TO NAVIGATION" - A Nautical Institute Presentation by Commodore David Squire CBE FNI. One phrase that caught my attention, and which I repeatedly hear being discussed in my new role as a maritime training facilitator, is "the right balance" between older and modern aids to navigation. I think one of the factors to decide what is the "right" balance is the phrase in the article "reliability of each method depends also on the circumstances and location of the navigator".

 

Given below are some illustrations that portray this, some for traditional aids (I include radar as traditional!) and the others for modern aids.

Incident 1

Own vessel was approaching Keelung (Chi-lung) harbour (North Taiwan) to pick up a pilot inside the breakwater. The GPS constantly put the vessel in the outgoing channel whilst the fairway buoy indicated the opposite! Unfortunately, the rocky (partly above water) shoreline gave a very unreliable radar fix though the lights were prominent enough for us to be sure we were in the correct channel. The approach has some extremely sudden, erratic and strong tidal streams. A notice to mariners received later clarified our doubts - the WGS correction was found to be 0.15' to the West! In this instance, it would have been foolish to rely on the GPS.

What about places where such corrections have not been published - a wrong assumption is worse than none! I also wonder what we might have done, had visibility deteriorated to the extent that we could not see the fairway buoy let alone the lighthouse!

Incident 2

While approaching the mad house that is the approaches to Changjiang Kou river estuary to pick up our pilot, the seeming confusion was further accentuated by 5 vessels picking up a pilot at the same time in the same location WITHIN the channel. There were also strong tidal streams which did not agree with the BA tidal atlas, a plethora of fishing vessels and stakes, local coasters and language problems! The BA chart clearly states that the positions of buoys is continuously changed due to changing depths of the estuary. The closest "fixed" navaid (a small island) is a good 13 miles off, buoys do not have the same markings as the BA chart (apparently the Chinese chart is more reliable), the place is choc-a-bloc with fishing vessels, and RACONS do not work! The only two navaids that we could put more trust in were the GPS and the echo sounder. Ah - did I forget to add that visibility is usually 0.2 to 2 miles in this busy shipping lane most of the year? In this instance, it is wise to use the GPS.

Incident 3

English channel - overcast skies, morning daylight, force 7 winds, rough seas, zero visibility. We could not see the buoys, lighthouses or the coastline. The only means of plotting the position were the radar and the GPS. Speeds varying between 3 knots and 12 knots (this was on a 25,000dwt general cargo ship, 4 years ago). Thankfully, the last time we had passed this place, we had used BOTH visual fixes and radar fixes - thus making identification of a confusing situation easier. Why confusing? Two reasons - one - the coastline had either too few or too many projections, and - two - there were TWO vessels going in the wrong lane making us wonder if it was them or us who were in the wrong lane! (Where is the VTIS when you need it??!!! - The comedy that is life).

Incident 4

Own vessel was approaching Port Klang. Both the GPS's gave the same position, 1 to 3 miles away from what the land visual and radar fix gave. We decided to trust the latter and the distinct channel buoys (mangroves do not have lighthouses - for all those who would judge using a buoy as a position indicator as a cardinal crime!) supported our judgement. I still do not know the reason WHY the GPS's did that. (No, they were not on DR mode, DOP was fine, and they later gave proper positions)

Hurrah - visual navigation.

See also reports: 200214, 200244 and 200266