NavList:

   

Reply

george huxtable skrev  15.09.2005 17:25:

> Mike Hannibal wrote, about tests on certain sextants-
>
>> the outcomes were around
>> 1-2 miles intercept for the C&P, 3-7 miles intercept
>> for the other metal sextants, and between 12 and 23
>> miles for the two Davis plastic sextants. Whilst there
>> may be small anomalies in my memory of the numbers I
>> think that I have been faithful in my recollection and
>> certainly the order of magnitude of the plastic
>> sextant errors is pretty right.
>>
>> Make what you will of that.
>
>
> =============================
>
> I think Davis have produced several widely-different grades of plastic
> sextant, though I am familiar with none of them. Unfortunately, Mike
> doesn't state which model was tested, to give those appalling results.
> Clearly, those were not proper altitude-measuring instruments at all, but
> toys, simulating sextants.
>
I am a beginner who has been using a Davis Mark III (the cheapest and
simplest of the Davis plastic sextants available now) since early spring
this year. My last intercept here in Oslo using a Davis artificial
horizon and the mean of six measurments was 1.5 nautical miles away.
This summer I spent some weeks training every day with a sea horizon
froma balcony on Lesvos (in the Aegean) where my main problem was to
figure out how high above the sea mu POV was and so the dip. After
testing and training myself in the use of the sextant I took two seats
of sun shots, and the intersection of the two LPs was about 3 nautical
miles away. Given the way the Davis Mk. III works I believe it is
difficult to come any closer than 1-2", and that yes, one should move
the arm in the same direction for all the shots.

Espen Ore
Oslo

   

Reply