Oct 10 - South of the Equator
Update (10th October 2004)
Noon Position : lat 20° 23.95' N, long 38° 20.6' W (Bearing: 061 T, 311
from Rio de Janeiro)
Air temperature @ noon today : 26.2°C
Sea temperature @ noon today : 24.8°C
Wind: NNW Force 3
South of the Equator
This week has seen us leave the northern hemisphere and cross to the south of the equator. I'm sure the water is a nicer shade of blue down here! The view from the bridge window hasn't changed much, and contrary to popular myth there was no bump as we went over the line. King Neptune was notably absent during our Crossing of the Line, perhaps he had bigger fish to fry. However, we still had a barbecue to celebrate our new latitude and it was probably the farthest from anywhere I have ever been at a barbecue before! On the charts we are now heading parallel to the coast of Brazil, although still out of sight of land for a while yet.
Time on board ship has been spent in maintenance and drills. It is very important to maintain safety whilst at sea and we have regular drills to this end. This week the exercise was a fire in the galley with one victim overcome by smoke inhalation. After the initial muster, teams of firefighters don their breathing apparatus whilst others man the fire hoses and the medical team prepare to accept the patient. As you can see from the photographs we all get quite warm when putting the protective equipment on in the tropical heat.
More Maths in the Middle (but not too much!)
Following on from last weeks navigation lesson, the cadets have been trying to teach me about gyro errors. The ship has a very accurate compass, called a gyro compass, which uses gyroscopic motion in order to give a heading in degrees. This type of compass is a lot more reliable and precise than a normal magnetic compass, but it is still susceptible to errors. The best way to check the error of the compass is to take a bearing of the sun from one of the gyro "repeaters" on the Bridge wings. When this sight is taken, the time and position from the G.P.S. ( Global Postioning System ) are noted down, and, using a sets of tables, the "true" bearing of the sun at that position and time can be found. This is then compared to the bearing taken from the repeater and the difference, if any, is the gyro error. If the bearing taken from the gyro is more than the true bearing of the sun, the error is high, and if it is less, then the error is low. This can then be applied to any navigational work in order to obtain a higher level of accuracy.
A hotly debated topic of discussion this week has been which way the water goes down the sink. As soon as we were in the Southern Hemisphere I was told that I should be able to see the
water spiral down the plughole in an anticlockwise direction. Now, a quick experiment confirmed that we have the wrong type of plugholes to test this! No spiralling seen at all -
but I looked into it all a bit further. It is the Coriolis force which causes weather patterns, sea currents and water down the plughole to spin in a clockwise direction in the
northern hemisphere and anti-clockwise in the southern hemisphere. The best explanation for the Coriolis effect that I found was at the Ohio State University Physics Website. Most importantly for me it had a section called, 'Water going the wrong way down
the sink'. This points out that water going down a plughole moves at only metres per second over a small distance. Therefore the equation governing the 'spin' generated estimates a
change in direction of only a fraction of a degree per second over the course of the entire draining of the sink. Under perfect conditions a noticable difference can be seen but things
like leftover spin from filling the sink, irregularities in construction of the basin and convection currents if the water is a different temperature to the basin will be more than enough to
overwhelm the very small Coriolis effect. So the bottom line is, water in the sink doesn't go far enough to trigger any noticable north/south deflection. Usually it just spirals out of
the sink in the same direction that it spiralled into the sink.
This week has seen a fair bit of wildlife accompanying the ship. The most noticable are the flying fish, which leap to escape predators. Occasionally they will land on the deck of the ship and need to be given a helping hand back into the water. The so called 'wings' of the fish are expanded pectoral and pelvic fins that enable it to glide, rather then truly fly. Apparently these fish can glide for up to 100m about 1.5metres above the surface. Unfortunately, our companions had not been in training and were barely managing a paltry 20m in most cases. Still too fast for my camera I'm afraid!
Following on from the fish (not surprisingly) were the birds. There were a dozen mask-faced boobies escorting us for several days this week. It was quite incredible to watch them fishing. They would glide effortlessly along beside the bridge then suddenly espy some poor, unsuspecting fish. Instantly they tuck their wings into their sides and plummet, torpedo like towards the waves, sometimes directly in front of the bow of the ship. Seconds later they will bob to the surface gulping down their dinner. An enormous amount of effort is then required to become airbourne again, but after a herculean effort they will resume gliding through the air looking for the next morsel.
More of a mystery were the frigate birds. These very large birds did not do any fishing during the time they followed the ship. They seemed content to watch us and make sure that we were just passing through.
I must apologise for those looking forward to Tom's Mickey Mouse impression last week, a technical error caused the photo to become corrupted. Sorry about that, it is now all sorted and the photo of Tom can be seen in October 03 diary....
I shall leave you this week with another sunrise from the bridge, taken by the officer on watch.
Bye 'til next week, Lisa