Wednesday, April 17, 2013

4/17/2013 Oceanography


File:Sandy Island on 1908 chart.jpg
Sandy Island Was Near The Center of this 1908 Chart.

 Out in the Pacific which has drawn so much of our journalistic attention of late there are still a few navigational and geographical mysteries left. We noted in our coverage of the USS Guardian's grounding off the Philippines that the well known coral reef that this U.S. mine sweeper grounded on was 8 miles off of its latest charted position. This wasn't some grievous modern error of the British Admiralty or our NOAA charting organization. Such errors which are constantly being discovered and corrected simply reflect the magnitude of the cartographic work that organizations like the British Admiralty Charting Organization and our own NOAA corps undertake. Today it is un-glamorous and under funded work. Some of the Pacific charts still rely in part on positions of reefs and islands based on the reports of Captain Cook in the 18th Century. Many modern charts especially in the vast Pacific are a mixed bag of data some very old, and some very new, and lots in between. Unfortunately it takes more research than most modern navigators are accustomed to do to determine the reliability of data making up a navigation chart. 

 STCW requirements for detailed voyage planning obligate the navigator and master to more carefully review the reliability of data for specific regions. The voyage plan should include such measures as enhanced look out procedures, perhaps reduced speed in areas of potentially inaccurately plotted obstructions.  The case of the grounding of the USS Guardian is an example of what can happen when a real obstruction is inaccurately charted due to a carry over in the cartographic process of obsolete information. The case of the disappearing "Sandy Island" is an example of uneconomic voyage planning in avoiding a hazard that isn't there. But was it ever there?

 We believe that the mystery of the islands previous existence or non existence is now resolved. Certainly today, despite the continuing depiction of this Manhattan sized island on "current navigation charts" we know it is not there. More over given that the water depth in the vicinity of the island's reported position is over a mile, it did not simply erode. Was it ever there? The  "island " was first reported as a low "sandy island" in 1876 by the Whaling ship VELOCITY. It appeared in its 1876 reported position on British Admiralty charts in 1908. The 1908 position is pretty much where it is depicted on today's British and American charts. The French removed the island from their charts in the 1970s. However one American Defense Mapping Agency chart in the 70s showed the island in its 1876 location with the notation "First Reported 1876, Reported 4 miles East 1968." A recent Australian expedition now confirms there is nothing anywhere near the area and the water is at least a mile deep. What happened?

 Last year we reported on a pumice island floating in the Pacific for weeks. In areas of volcanic activity which includes the area where "Sandy Island" was reported. these occur sometimes after a large volcanic eruption. Pumice is a hard mineral with a lattice work like structure that can trap air. It can float for quite a while. It has a mild adhesive quality and can coalesce into a massed structure of considerable size. The one we reported on stayed afloat for weeks and was several miles long. We simply believe that the VELOCITY mistook a pumice raft for a low lying sandy island. We believe who ever reported a new position on it in 1968 simply observed a different Pumice raft. This information is important to the voyage planning team. If you voyage anywhere near the vicinity you might want to make a pencil notation on your charts of "Pumice rafts occasionally reported". You do not want to collide with a pumice raft any more than with a sandy island. No doubt that a modern steel hulled ship would probably plow several hundred yards into one without hull damage. But your water intakes, perhaps cooling system, screws, thrusters, and under hull transponders will likely be ruined after a relatively short incursion into the body of a pumice raft. Here's a night mare for the ship master, imagine running into a particularly wide but thin one on a dark moonless night. All your watch standers on the bridge might experience might be a slight slowing of speed. But basically your intakes are taking in pumice and everything else on your submerged hull is getting the equivalent of a wet sandpapering. These things may be miles wide. 

 We don't want you experiencing a wet sandpapering in the middle of the night so we are loading our OCEANOGRAPHY and NAVIGATION sections with free aids for voyage planning. We especially draw your attention to BEN's TECH CORNER where you can find links to web sites that will turn your wireless laptop into a force multiplier for all of your navigational efforts. Also don't forget in your foreign voyage planning to take piracy into account, we have real time piracy activity updates and other information on piracy in the NAVIGATION section and in the NEWS section. The wise seaman plans his voyage down to the last detail from dock to dock before throwing the lines off.  The International Convention on Standards of Training, Competency, and Watch Keeping (STCW) now requires you to be that "wise seaman".  Not merely competent, wise; research and plan those voyages in depth. 

Johnas Presbyter, Editor 

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