Tuesday, April 29, 2008
In response to a comment on the previous post I am detailing what navigation equipment we used.
We bought a 1923 Plath Vernier sextant for £10 from Harold Hayles Chandlery. He was selling it on behalf of Eric Hiscock who had been presented with a new one at the London Boat Show. If you refer to his book “Voyaging Under Sail” you can see it on page 189, plate 35. He used it to sail around the world in Wanderer III. My father has had it sitting in his cupboard for the last 39 years and you can see from the photos here that it has deteriorated somewhat in that time. Dad is thinking of donating it to the museum if they are interested.
We didn’t have a chronometer, but Dad had an Omega Seamaster watch which only gained a few seconds each day. The only radio we had was a Philips shortwave receiver on which we received time signals and corrected the watch when necessary. At times we couldn’t receive a radio signal in mid ocean but we didn’t have to be so accurate there with no land anywhere near us. We also had a battery operated electric clock on the bulkhead down below and we adjusted this to the time of the watch whenever needed.
Dad would take the sights (not an easy task with the boat bobbing up and down with the waves) and call out "Now" to me and I would take note of the time on the clock, then he'd hand me the sextant and I would read what he'd taken and write it down. I tried to take the sights as well at first, but as my son commented when we took the attached photo “Gee this is heavier than it looks”, I found it very tiring on the arm to hold it up to your eye for long enough to take a sight.
So we settled into a routine of Dad taking the sights and me working them out. I had to teach myself how to do this from Eric Hiscock’s book “Voyaging under Sail” and Mary Blewett’s books “Celestial Navigation” and “Navigation for Yachtsman” as Dad’s working out of the sights was clearly not accurate (see earlier posts). The sextant was also difficult to read as the vernier measurements were so small, so it was easier for me to do that with my young eyes.
“Sight Reduction Tables for Air Navigation” Volume 2 Latitudes 0-39°, Declinations 0-29°
and Volume 3 Latitudes 40-89° and Declinations 0-29°
These were purchased from an Admiralty Chart Seller in Bristol, along with charts that covered as much of our journey that we could. We hoped to buy some charts of the Pacific in Panama which we did. Dad has also kept the charts and Sight Reduction Tables all these years.
We tried taking lunar sights a few times but found that we were able to accurately work out where we with just a morning and noon sight most days (after our first fiascos between England and Las Palmas - see previous posts). There were only a few occasions when the sun didn’t come out and we couldn't take sights as you will read when we get to that part.