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Gday All...
The picture to the right shows the bow breaking the ice. As the ship keeps pushing - without moving, cracks gradually appear in the ice ahead and slowly widen - enough for the boat to slowly move on (at 1cm per second). Sometimes an ice lump becomes stuck under the bow, and the ship has to be put into reverse. The Aurora Australis (AA) has a single oversized (about 4m diam) variable pitch propellor and rudder. It also has two main engines (V12 & V16) which are coupled together through a monster of a gear box and down a 500mm diameter shaft to the propeller. When the ship is in ice-breaking mode, the RPM rate of the propeller increases but the pitch of the propellor is decreased. While this is less efficient, it decreases the chance of the propeller breaking on lumps of ice - with a small pitch the propeller cuts the ice like a knife. The last thing you need stuck in the ice is a broken propeller which sort of happened last season. The way the AA breaks the ice is by having a shallow and toughened steel bow. The AA pushes itself up onto the ice and the weight of the ship drops down cracking the ice. Some blocks slide under the ship and pop out the side, while others slide all the way under the ship and pop out the rear. Most of the ice scrapes down the side of the ship, and sitting inside the ship at the ice-line near the walls, there is a very loud scraping noise. When the AA gets stuck it has to stop, go into reverse (by changing the pitch on the propeller) and take another run-up and try again. If this happens too much then the overall motion of the boat can become so slow that you could walk faster. Most of the time this does not happen because the crew are using ice charts and satellite imagery showing the ice thickness. Also, they are using their years of experience in picking a path through the thick ice (usually very white in colour) and the thin ice (grey in colour). At night this task becomes very difficult, even with three very powerful search lights on the bow of the ship. The search lights are very nifty, since they can be controlled in the up down, left and right axes by a joystick on the bridge, and the beams are able to shine out to at least 1km!.  Last
night, the task of picking a way through the ice became too hard,
and the boat stopped for 6 hours. It was interesting to see on the
GPS track log how the ship had actually moved relative to the earth
while stuck in the ice - because the whole ice sheet was moving !.
Yesterday we nearly crushed two Emperor penguins!.. They were standing out in the middle of the course of the AA. They kept looking at the boat as it approached then in about 20metres from the boat they flopped down onto their bellies and motored along by pushing with their feet (very funny to watch :-))... one veered under the bow out of view, but luckily it altered course away from the boat and disappeared down a crack in the ice. There was plenty of cheering on the bridge as we saw the two penguins escape successfully !.. The reason the AA doesn't steer around the penguins is that it's turning circle is still quite large (300m) and penguins - like dogs on the road - have no ice (road) sense ! We are now within 300 nautical mile (1nm = 1.85km) range of Mawson. The helicopters on the AA have two ranges. One is the maximum one-way flight where they have to be guaranteed to be able to land at Mawson, and the other is the safe return limit where they can fly from the boat to Mawson and if they cannot land due to the weather, they can turn back and land safely on the AA. We are currently inside the one-way limit but the AA is heading for the safe return limit which is 180nm from Mawson. At our current rate we will be at this limit tomorrow or Wednesday - ice thickness dependent. The helicopter flight time will be about 1.5 hours with each trip holding up to 8 people and some luggage. The AA is scheduled to stay near Mawson for at least 3 days - and hopefully we can get all our luggage off the ship. So... This will be my last email from the Aurora Australis - the next from Mawson. Cheers for now... Kym
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Well,
we are well and truly into the pack ice. So much so that often the