Monday, April 2, 2012

Halfway - Day 13

Well - we are more than halfway to Hiva Oa, passing the halfway point (as the seagull flies) at mile 1308 around 2 pm local time yesterday.

We have begun to pass through rain showers and impressive cloud formations. During the first good morning shower, we stripped off and jumped into the cockpit, lathering up and then dancing around in the cool clean heavy rain - lovely!

We also finally had suitable conditions to do a noon sextant site, following instructions drafted for us by Kurt ('Kaptain Krunch') off S/V Raven.

Here is how we did this:

1. Adjusted our clock to a time signal broadcast over the SSB radio so that it was correct for Greenwich time.
2. Looked up when the real local noon (sun as far overhead as possible) was according to our rough current position.
3. Took a series of sextant 'shots' that bracketed this time, to determine a) the maximum height above the horizon of the sun and B) When exactly that height was reached (local apparent noon). This is quite a fun exercise as you swing the sextant back and forth, watching a little red ball (the filtered sun) arc back and forth like a pendulum. The trick is to know when the bottom of the red ball just grazes the horizon. This is not always easy on a rolling boat with 6 foot swells getting in the way.
4. Adjusted these numbers for factors such as how high we were above sea level (about 2 meters), errors in the plastic sextant, and the half diameter of the sun.
5. Looked up various values in the 2012 nautical almanac that use these data to obtain lat and long.

According to our GPS, we were only off by 4 miles in our sights - very good for our first attempt using Kurt's instructions. We tried this once before using the simple instructions from the sextant manual and only achieved a 30 mile accuracy!

Our position as of 14:30 zulu this morning was N 07 04 and W 126 38 for a day's run of 126 NMs with 123 of them in th right direction. Winds became light and shifting with lightning and showers in the early hours this morning, which has slowed us down.

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