NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: UNK
Date: 2015 Feb 28, 21:34 -0000
Thanks Henry,
This is really a very interesting historical thing. Just found Dutton 1805 on Google who quotes the original Kelly method as described dating from 1797! So you could do lunar clearance in 1797 easily using these simple graphical techniques? Dutton claims they were accurate to 5’? Perhaps they were not? Otherwise why were they not taken up as routine?
I shall look into it.
Thanks again.
Francis
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Henry Halboth
Sent: 28 February 2015 17:27
To: francisupchurch@gmail.com
Subject: [NavList] Re: LOP's without DR Position
Francis,
From the "American Practical Lunarian & Seamans Guide" by Thomas Arnold, c. 1820, or thereabouts.
Henry
On Sat, Feb 28, 2015 at 1:26 AM, Francis Upchurch <NoReply_Upchurch@fer3.com> wrote:
Thanks very much Henry,
Very interesting. May I ask where this comes from and who wrote it?
I’m interested in some of these old ideas and methods. Not really as a modern practical alternative. As Frank points out, it’s not very useful or sensible really. Just part of my interest in the hobby. My mind works better with graphs/pictures etc than pure numbers. (so I like to use slide rules to do the maths, not because it as good as calculators. (actually ,Fuller 2 not far off), but because I enjoy the organic/analogue/graphic feel of the thing. With the Fuller, you can see the moving log scales adding up/subtracting (i.e. multiplying/dividing) to give the answer. Bingo! So I will try this method, just for fun. (sorry Frank!)
Part of my interest in all this stems from reading Maskeyne’s early, pre Nautical Almanac lunar clearance work. Took even him up to 4 hours to do the number crunching using logs etc. So a bit surprised that some of these simple ,graphic type methods were not developed earlier to help the poor average, probably semi innumerate navigators (like me) of the day!
I’ll try to do a comparative test run on some of these, versus my normal clearance method using formulae from John Karl’s book and either calculator or Fuller slide rule.
Thanks again,
Francis
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Henry Halboth
Sent: 28 February 2015 03:42
To: francisupchurch---.com
Subject: [NavList] Re: LOP's without DR Position
Francis,.you wrote,
"Also, intriqued by the possibility of reducing lunars by purely graphic means. Could you show me an example if this can be done?"
At the risk of incurring Frank R.'s ire, I attach a proposed method of clearing a Lunar Distance by part graphical & part mathematical means. There is really nothing much new in navigation - it's just a matter of knowing where to look! It goes without saying that I have not tried this method and present it purely as a matter of possible interest.
Henry
On Thu, Feb 26, 2015 at 5:06 AM, Francis Upchurch <NoReply_Upchurch@fer3.com> wrote:
Robin,
that is interesting!
I'm no mathematician, and don't really understand simple numbers, never mind complex ones! However, am I right in thinking that if you had sterographic projection charts (flat), you can place circles of equal altitudes directly on this and get a fix with 2 intersections? i.e, like using the big globe idea, but instead using flat (stereographic) charts? Is that correct? If so, any advice on where to get stereographic charts to do this?
Also, intriqued by the possibility of reducing lunars by purely graphic means. Could you show me an example if this can be done?
This could save me a lot of engineering work. was thinking about building a globe to do this! would rather use stereographic charts if feasible.
Best wishes
Francis
Attached File: 
(img/130500.clearing-a-ld-by-projection.pdf: Open and save or View online)
