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Mark Milburn’s Cornish Wreck Ramblings, Part 1: Accuracy, inaccuracy and alternative co-ordinates
We are in a marvellous age of technology, where we can pinpoint a needle in a haystack within inches. In the days before GPS and even Decca, there were transits. Transits can be good or bad; a good transit can be as accurate as any GPS. A bad transit is just bad.
I once went looking for a plane wreck. It hadn’t been dived for a long time, and we wanted to see what was left. It was a forty five minute boat ride but the transits were supposed to be good. We had to line up a telegraph pole with the third tree, out of four, in the hedge behind.
Something had happened to one of the trees; there were now only three, all spaced out a little… so which one was the original third tree? We used the sounder to look but found nothing, so we guessed at one of the trees…. and found sand. So a good transit had gone bad!
Decca was an improvement over transits when you were further offshore. Towards the end of its life, the last version of Decca was quite good, but eventually GPS took over. GPS was a little all over the place to start with, so along came Differential GPS (DGPS), which used a known fixed local transmitter to correct any errors. These errors were deliberate errors used by the Americans, so the rest of the world would be at a disadvantage. Once the Americans no longer added their “fudge factor”, the D was no longer needed.
So, what could possibly go wrong now? A few years ago, there was a news item on the BBC about a wreck called the Antoinette. It had become exposed as the sand shifted in the Camel Estuary. The report stated it was on the Doom Bar; it also stated that the bomb squad had been tasked with removing the remains of the wreck as they were a hazard to shipping. I headed over with my camera, but found nothing, just sand. I then headed back to Padstow to say ‘Hi’ to the staff at the lobster hatchery. While there, I could see something going on in the middle of the river. I was told it was the bomb squad about to blow a wreck up. But that was Town Bar not the Doom Bar – they are over a mile apart. Not the most accurate of reporting! That was quite recent though; when looking for old wrecks, with old information, the difference could be a lot worse.
Surely though, modern GPS is infallible? It is very good, as long as the numbers are accurate. They could be written down wrong, accidentally or deliberately. They could be from an alternative dataset. Most people use WGS 84, World Geodetic System, which originated in 1984. Some people don’t.
Myself and some friends wanted to dive the wreck of the St George, which lays twenty miles off shore in a depth of sixty five metres, and we wanted an accurate position. We asked around, got some accurate marks, and headed out. Once in the area, we watched the sounder as we went over the co-ordinates, but all we found was a flat sea bed. We repeated this several times, but still nothing. Time was running out to dive at slack water, but the sea bed was completely flat all around us.
Then one of us remembered that the person who gave us the co-ordinates liked to use OSGB 36, a different dataset. We quickly changed the GPS to OSGB and headed off. We arrived at the new location, and lo and behold, there was the wreck. So the co-ordinates were right… just an alternative right.
So, every form of position fixing has potential errors. Sometimes, there is nothing you can do about it… except guess!
Find out more about Mark and Atlantic Scuba at www.atlanticscuba.co.uk.
Today we are diving one of the outer reefs from an inflatable. As we reach the bottom, a reef octopus eases its way into the cover of a small crack in the coral while displaying it’s incredible ability to change colour. They are arguably one of the most charismatic of reef dwellers and it is always exciting for me to simply hover and watch. I would have spent longer and waited for it to come and investigate me, but as dive time is limited we wanted to move on and find a turtle.
The waters around Somabay are well protected and hold a rich variety of marine life. The reef edges are thriving colonies of coral and shoaling fish, while nearer the sea bed plenty of wildlife is still to be found.
Then we located the turtles. They are very used to divers and so show little concern when slowly approached. In fact occasionally one will come over to see what you are doing. There is always huge excitement when diving with a turtle. The shear thrill of sharing a moment with another species.
What a fantastic way to finish a wonderful few days diving and I would like to thank SOMABAY, ORCA DIVING and THE BREAKERS for making my stay such a good one.
I had a great time, with diving everyday either on the house reef or on one of the offshore reefs by inflatable or larger day boat. Orca diving provided high quality equipment and facilities while the staff were all very friendly and welcoming. The Breakers was right on the coast with nice rooms, good food and once again friendly staff making the whole trip a real pleasure.
Soma Bay covers an entire peninsula and is home to several resorts as well as residential compounds.
As well as scuba diving, Somabay caters for many other sports and activities, and so is perfect for families as well as individuals and/or groups. And of course there is always time to lay peacefully on the beach under the Egyptian sun.
Book your next Red Sea dive adventure with SOMABAY! For more information, visit www.somabay.com.
Stay at the Breakers Diving & Surfing Lodge when you visit! For more information, visit www.thebreakers-somabay.com.
Find out more about ORCA Dive Clubs at SOMABAY at www.orca-diveclubs.com/en/soma-bay-en.
Day three of my trip to Somabay and we were spending the day on the Lady Christina and diving on the wreck of the Salem Express.
Diving wrecks for me is always one of mixed emotions. The excitement of diving a wreck is more than often tempered by the thought of loss of life when she sank. The Salem Express was a passenger ship and a roll-on/roll-off ferry travelling from Jeddah, Saudi Arabia to Safaga, Egypt. Most passengers were of poor class travelling home from their holidays while around 150 people were returning home from their pilgrimage to Mecca.
The ship struck a reef and sank within 20 minutes. Passengers were trapped below deck and the ship was filled with fear and panic.
The wreck area is strewn with personal belongings from the crew and passengers such as a transistor radio and a flat iron for clothes. A diver at sometime has put them in a prominent place to be seen.
Tragically only one life boat was launched while the others went down with the ship. More than 600 men, women and children lost their lives here.
It’s a stark reminder that the sea can be unforgiving and so when we dive on such wrecks we should do so with humble regard.
Returning to the surface, shoals of fish are gathered under our boat and seem to be welcoming us back into the light.
Back at the Breakers I sat in the dining area with a beer and a very good meal while my thoughts still remained with the day’s dive on the Salem Express.
Check in for part 3 tomorrow for Jeff’s last day of diving with Somabay on the off-shore reefs looking for turtles.
Book your next Red Sea dive adventure with SOMABAY! For more information, visit www.somabay.com.
Stay at the Breakers Diving & Surfing Lodge when you visit! For more information, visit www.thebreakers-somabay.com.
Find out more about ORCA Dive Clubs at SOMABAY at www.orca-diveclubs.com/en/soma-bay-en.
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