Thursday, June 03, 2010

Finding Oneself at sea by the Stars

I’ve not yet sailed in the Ocean.   The idea of it is daunting, and yet the draw is greater than ever.  There is lots of time apparently to spend doing something other than exhausting paperback novels and possibly my mother’s Suduko.  One option is to have a backup Sextant and to actually use it.  GPS should it fail [sic], would then neccisitate finding one’s way quickly away from whatever it is one needs to get away from, fast!

Firstly said it is complicated.  Secondly accuracy.  Seasoned and professional mariners, like Bob’s father would get within a mile of two of knowing exactly where the Wanderer, his schooner was in the pacific ocean.  Bob learned this as a child, he would take three or four sights a day and have to calculate the position and then compare them with his fathers observations.  If he was wrong, he was to recalculate.  If still wrong, then it indicated his sightings were wrong.  Well it’s easy to understand how this could be possible. 

The sextant the instrument that evolved from the yardarm, itself may have some internal error, that needs to be subtracted from the reading itself. [see sextant errors ]

The atmosphere may be cloudy, the celestial orb not visible or poorly so, and early morning or late afternoon sightings of the sun could be difficult to read due to errors of parallax and refraction.

Your clock may be off, the radio broadcast of time-ticks may be  unreachable so syncing your chronometer to GMT or Universal Time may not be possible.  Who knows what if you don’t know what day it is or what hemisphere you think you are in, well this is admittedly a rare scenario of ocean shipwreck survival, unlikely.

Nearby planets, the moon, and sun are physically closer to earth, so their orbits and significantly changing.  These are recorded in the sighting tables, and do make the calculations more complex.  Not good when under pressure in rough seas.  It’s better to use the stars to Navigate as they are further away and require no corrections. 

Understanding the calculation is fairly repeatable and with a good form to fill out and having the correct almanacs I'm sure with practice I’ll be able to work out my relationship with the heavenly bodies. 

Extremely thought provoking stuff, not immediately practical, but something to keep the old brain lubricated.  I’ll write more once we go do a sighting on Rodeo Beach one clear Sunday, hopefully soon.

1 comment:

Grant said...

A few weeks later we calculated the poistions, it took hours to do, but in the end I was within 3 miles for my first reading