Re: eBay - The Ebbco Sextant - Finding your location before GPS...



John Wilson wrote:
On Tue, 28 Feb 2006 19:00:37 +0100, Peter =?UTF-8?B?S8O2aGxtYW5u?=
<peter.koehlmann@xxxxxxxxxxx> wrote:

toad_oftoadhall@xxxxxxxxxxx wrote:

Martyn Thomas wrote:
The Ebbco Sextant - Finding your location before GPS...

Decca was finding your location before GPS...

This one will not help finding any accurate location at all
It is OK as a backup for the backup-sextant
--
You can use a plastic sextant and achieve fairly good accuracy - many
years ago I used a very cheap Ebbco plastic sextant and - provided I
checked index error before and after each sight or series of sights,
and averaged the two errors, usually managed to get within about 2
miles at sea - confirmed by finding oceanic islands where they ought
to be in the days before GPS. A couple of miles error sounds terrible
nowadays, but until relatively recently tens of thousands of large
ships travelled the world without knowing much more closely where they
were in mid-ocean.

The problem with the Ebbco was that index error varied almost by the
minute, by a minute or two, and the plastic lenses of the telescope
was pretty poor quality.

I occasionally use a metal sextant now (it's older than I am) because
I can now afford one, it's a nice piece of equipment, and a pleasure
to handle, and partly also because the telescope optics are so much
better, and my eyes are worse! But you can take perfectly good sights
with a plastic sextant, and I have been on a yacht deep sea with three
GPSs and most of the rest of the electronics all dead through
over-liberal application to salt water inside the cabin, so sextants
and tables still do have a place (as does a waterproof mini Garmin
sealed inside a couple of plastic bags !).
John Wilson
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I believe they used an Ebbco on the Torrey Canyon.


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