Monday, July 14, 2008

July 13, 2008 - Darwin Dash, Day 16

Bush Fire

To get from the Arafura Sea to Darwin, on the shores of the Beagle Gulf, it is necessary to transit the Van Diemen Gulf. Timing the approach to the Van Diemen is crucial, as it has strong currents flowing through it. But unlike the Torres Strait, where we could just pick a rising tide and ride the flow west, the currents in the Van Diemen are influenced by both the tides in the Arafura, which only rise and fall 6 feet, and the tides in the Beagle Gulf, which can rise and fall up to 24 feet. The trick is to hit the Dundas Strait, the entrance to the Van Diemen Gulf, 4.5 hours before high tide in Darwin. Keep your boat speed up, and you should have favorable currents in the Dundas Strait and then again on the other side of the Gulf at the Clarence Strait. In the middle of the Gulf, you'll have some counter current, but it won't be as strong as the favorable currents in the straits.

A few days ago, Nick on Kika sent us an email with the Darwin high tides and the corresponding times to arrive at the Dundas Strait. Nick noted that there was diurnal inequality in the Darwin tide cycle. Some days there is one high tide in Darwin. Others, there are two. If we chose the wrong high tide, we'd have a shorter period of favorable current to transit the Gulf. I worked through two additional sources of tide information and confirmed his analysis. We all decided to try to time our entry to the Strait to have a longer time to transit the Gulf. We knew we had the theory right. So how did it work in real life?

We ended up arriving an hour earlier than planned at the mouth of the Dundas Strait. We entered the Strait with half a knot of current against us. It eased off, and soon we had a favorable current. We were able to sail for a while, then the wind came forward and then promptly died, and we motor sailed for the rest of the day. At times, we had 3 knots of current assisting us. After clearing the Clarence Strait, we rode the flood tide into Darwin. Sten kept congratulating me for nailing the timing. I graciously accepted his praise, and made a note to myself that I owe Nick a round or two for making me look so good.

Spending the day motoring through flat water gave us a chance to clean house. Sten worked on deck most of the day, washing the salt crust off of everything he could reach. He also inflated the dinghy and got it ready to launch so that we can get off the boat as soon as humanly possible once Customs clears us. I spent most of the day cleaning down below. It seemed a waste of a hot engine room not to use it to raise some dough, so we made pizza for dinner, which had the added benefit of allowing us to cook up the last of the meat in our freezer - some ground beef and sausage. There is very little left on board for Quarantine to take. Luckily, we have three sweet potatoes left so that they'll have something to show for their visit.

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