06-08-2018, 11:49 AM
My Astro IIIb and Davis mk3 were stolen in the US a number of years ago. Who ever stole them probably wouldnt even know what they are let alone know how to use them. I really cant afford one now and wouldn't trust a good deal on Ebay- even shipping would be cost prohibitive.
I am in the hopes that one of you wealthy sailors (if there is such a thing) will have pity on a poor old expat sailor living on the economy in South-East Asia and perhaps donate a reasonable sextant.
I currently practice taking observations with my own altitude creations; a back-staff-like carpenter's square and a modified 45 that acts like a Gunter quad. As I mentioned to the forum admin I even made a few Bris sextants. The carpenters square is not marked in degrees so I use the cm scales and some trig to get the altitude.
I promise to the best of my ability the sextant will receive great care, and that any donated sextant will never be sold in my lifetime, and upon my death I will have my wife return the sextant to society by way of donation to a likely individual or school with the same stipulation (or perhaps returned to the donator).
Part 2... I also need some info relative to the HP correction tables. I could use it before but now I am a bit confused about how to use it properly. I know what HP is, but the table is a bit confusing. Perhaps the instructions are in a paper almanac, but my almanac was obtained from this forum's host site without it.
Part 3... Then there is the matter of a typical refraction error correction.. If refraction error is combined into the Sun altitude correction table, then why is there a separate refraction table? Im a bit confused and worry that I am mis-reducing my Gunter observations. I actually do pretty well, but I wonder if I can do better. When taking a Gunter sun shot I usually use star alt correction or Ha+LLc-SD+-T/P. There is no DIP or IC correction with the Gunter.
By the way - when using my Gunter like instrument I never look into the sun. I drilled a small hole at the front which allows a few rays of light to project onto an aligned white card at the back where the image of the sun is centered... I then rotate the Gunter locking the weighted string onto the degree scale. I then instantly stop a stopwatch which has been coordinated to GMT (UTC). I usually do best if i wait a minute or two for the string to center on a whole or half degree mark. Of course I am not taking the observation in the wind or on a rocking boat - I might not then be so lucky with my accuracy... :) Moon, planet, and star shots seem to work out pretty well although they are a bit more difficult to align on the Gunter. One of these days Im going to make a marine astrolab. Ive also been experimenting with permanently positioned mirrors in the tradition of the Bris... and developing some ideas on how to make a Bris act like a sextant or octant (bris glass is self aligning, unlike sextant mirrors)... necessity IS the mother of invention.
Any help would be greatly appreciated.
Joe
I am in the hopes that one of you wealthy sailors (if there is such a thing) will have pity on a poor old expat sailor living on the economy in South-East Asia and perhaps donate a reasonable sextant.
I currently practice taking observations with my own altitude creations; a back-staff-like carpenter's square and a modified 45 that acts like a Gunter quad. As I mentioned to the forum admin I even made a few Bris sextants. The carpenters square is not marked in degrees so I use the cm scales and some trig to get the altitude.
I promise to the best of my ability the sextant will receive great care, and that any donated sextant will never be sold in my lifetime, and upon my death I will have my wife return the sextant to society by way of donation to a likely individual or school with the same stipulation (or perhaps returned to the donator).
Part 2... I also need some info relative to the HP correction tables. I could use it before but now I am a bit confused about how to use it properly. I know what HP is, but the table is a bit confusing. Perhaps the instructions are in a paper almanac, but my almanac was obtained from this forum's host site without it.
Part 3... Then there is the matter of a typical refraction error correction.. If refraction error is combined into the Sun altitude correction table, then why is there a separate refraction table? Im a bit confused and worry that I am mis-reducing my Gunter observations. I actually do pretty well, but I wonder if I can do better. When taking a Gunter sun shot I usually use star alt correction or Ha+LLc-SD+-T/P. There is no DIP or IC correction with the Gunter.
By the way - when using my Gunter like instrument I never look into the sun. I drilled a small hole at the front which allows a few rays of light to project onto an aligned white card at the back where the image of the sun is centered... I then rotate the Gunter locking the weighted string onto the degree scale. I then instantly stop a stopwatch which has been coordinated to GMT (UTC). I usually do best if i wait a minute or two for the string to center on a whole or half degree mark. Of course I am not taking the observation in the wind or on a rocking boat - I might not then be so lucky with my accuracy... :) Moon, planet, and star shots seem to work out pretty well although they are a bit more difficult to align on the Gunter. One of these days Im going to make a marine astrolab. Ive also been experimenting with permanently positioned mirrors in the tradition of the Bris... and developing some ideas on how to make a Bris act like a sextant or octant (bris glass is self aligning, unlike sextant mirrors)... necessity IS the mother of invention.
Any help would be greatly appreciated.
Joe