Monday, April 23, 2012

Expect major and unpredictable changes in speed and direction. Assume no prediction possible"

It has been more than two weeks since I had a sail.  The forecast - a sunny day  8 to 10 knots gradient Westerly wind  Sea water temp 23 C. Air temp  lower for most of the day.  20 knot expected around 5 pm.  I plan to go at about 12.30 and get in well before the 20 knots..  I worked out the stability index before going. The stability index is a creation of Frank Bethwaite, explained in his book "High Performance Sailing", as a way of try to predict the kind of winds we sail in. So before going out I made this calculation.

Stability index 
  • low dominant   1 pt
  • colder wind over warm water 1pt
  • gradient wind 1 pt
score 3 pts

For the lowest possible score of three points, Bethwaite  says "Expect major and unpredictable changes in speed and direction. Assume no prediction possible".  In other words highly unstable.

I launched at Sirius Cove and sailed out into the harbour  in 5 knots ready to do some practice. But before I could settle into it,  a huge black thunder cloud started forming in the NW,  lighting was flashing inside the cloud, dark rain streaming out, high in the sky.  I needed to get to a beach. The nearest, Syringe Cove the one next to the zoo was about 500 metres away. I was about 40 metres off the beach when the storm approached. The trees on the high hill above the beach just went crazy. The squalls arrived 15 seconds later, the gusts swinging side to side. When the boom went in the water there was no hope and the boat went over.I never stood a chance.  It seemed unwise to try to get back up again, so I swam pulling the bow of the laser on its side towards the shore. If I had been out in the main harbour, I would have sat on the upturned hull, turtle style hoping the commercial vessels would dodge me.

It was slow going and took about 10 minutes to do the 30 metres to get my feet  touching the ground,  thinking all the while about bull sharks.

This is the Seabreeze record, gust peaking at 30 knots at Fort Denison, 35 in the main harbour.

It was a lucky escape. The harbour was a white out, the wind gale force. So I held the boat in the shallows on its side for 20 minutes or so, wet but safe -  ate an apple from my pocket.

With the storm passed I went back out to do some practice. I was a little shaken  but determined to make the best of the day. After only  20 minutes of practice  another storm cloud starts developing in the NW. Not again -  and so reluctantly we (me and Laser 176894) head back to Sirius Cove. I made it up the bay as the next squall came through. The trees went crazy again along the shore, I kept the boom very loose, ducking lots and keeping the boat level. We inched the last 20 metres and  got to beach unscathed. That's the second peak on the chart.

In my experience this is quite unusual weather I have only been caught in this kind of squall half a dozen times in 50 years of sailing on Sydney Harbour. Any way that's what I am telling myself. The boat is safe, I am not hurt and I got home for a hot shower and cup of tea by 3.00pm.

The Frank Bethwaite told me before I went out, "Expect major and unpredictable changes in speed and direction. Assume no prediction possible". 5 knots to 35 knot squalls, that's major and unpredictable.

There is more information on the stability index in the wind tab.

Time lapse video

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