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Questions - pabrides - 08-04-2018
This post has several parts so bare with me please. If these subjects came up before I have not seen them.
1. I just learned that the 2017 PRACTICAL NAVIGATOR (Bowditch) is available. I downloaded it here and looked over a few chapters - it's really a wonderful piece of work.. If a young person was only interested in the sea this pub would give him everything he needs to function as a well rounded sailor in several disciplines. There is so much information the format now includes a second volume.
2. I know this forum is about CN, but forum members might also be interested in the other arts of navigation as well - I am, anyway. However, I'm having trouble finding good examples on how to use the Haversin tables. I know what a haversin is and the actual formula to find distance between two points, but an example of table use has not come to my attention... Has anyone a clue??
3. I dont know how well I can explain this, but the calculator in my cell phone (CP), which includes trig functions, does not arrive at the same answer as my electronic calculator or trig function tables. I have been learning, for the first time, how to use these tables as well as log tables with great satisfaction and fun, but my CP calculator really threw me for a loop when the Sin, Cos, and Tan functions spit out different numbers than what the purpose-built electronic calculator or tables say.
For example: Sin 40
Scientific Calculator - .64279 (rounded up)
Trig function Table - .64279
Cell Phone calculator - .74511
I can find no options in the Cell Phone calculator which might give me a clue as to why the numbers are not the same... Any Thoughts???
4. I would appreciate if anyone could give me a few plain examples on how to use the traverse tables. Meridional parts and conversion, Log of trig, and Amplitude tables also give me trouble... I have no idea as to their use.
I may not be much of a navigator or mathematician, but its not for want of trying... :) My goal is to acquire the same skills as those navigators who plied their trade before the advent of batteries and electronics. Dont get me wrong - I appreciate the modern convenience of GPS and all the other cool navigation stuff, but give me a Gunter scale and some tables to occupy my free time and Im as happy as a sailor with a beer in one hand a cute girl in the other.
Thanks in advance
joe
RE: Questions - LouisC - 08-04-2018
Joe,
Thanks for telling us about the updated Bowditch.
As to Haversins, can't help you much about that for finding the distance between two points. I use this formula for that;
Distance = 90 – Sin -1 (sin(Destination latitude) x sin(Your present latitude) + cos(Destination latitude) x cos(Your
present latitude) x cos(Difference in longitude between Your Location and Destination Location)
Multiply answer by 60 to get Nautical miles.
The "Sin-1" means arc-sin.
A Casio calculator is the only calculator I use- cellular phone one isn't convenient or easy.
Are you trying to find a Great Circle route and waypoints? Pub. No. 229 presents a way to do that.
As to electronics. Ugh, yesterday I was trying to tighten a bolt on the boat trailer hitch and needed the ol' trusty flashlight. Would the batteries work?! Of course not! I was "on the hard" but was a' cussin' like a sailor.
Lou
RE: Questions - pabrides - 08-05-2018
(08-04-2018, 11:57 AM)LouisC Wrote: Thanks for telling us about the updated Bowditch.
Distance = 90 – Sin -1 (sin(Destination latitude) x sin(Your present latitude) + cos(Destination latitude) x cos(Your
present latitude) x cos(Difference in longitude between Your Location and Destination Location)
As to electronics. Ugh, yesterday I was trying to tighten a bolt on the boat trailer hitch and needed the ol' trusty flashlight. Would the batteries work?! Of course not! I was "on the hard" but was a' cussin' like a sailor.
Lou
I thought perhaps 2017 Bowditch might be old news.... your welcome
Your formula seems similar to the one for finding Hc. Ill try it for fun, but I still want to learn the haversin table as well as all the nav tables no longer popular.
As a side note; last week one of my English students volunteered to work long (5 significant digit) math problems by hand while I used the log tables. I consistently worked the problems in half the time with fewer errors. The log tables work well.
I read that with distances of <600 miles the difference between the great circle and mercator is insignificant, and even at the longest distances the difference is still only about 4 percent; which might be significant in aviation terms, but to ships at sea very little.
I laughed at your loose bolt experience; "...cussin like a sailor."
While in the Navy, especially at sea, I always carried a flashlight on my hip in a Velcro loop holster for emergencies - and I made triple sure it was working (the idea of being caught below decks in a darkened ship scared the bejeezes out of me). Nevertheless, I went to use the flashlight in my tool box a month ago and it was flat dead... I still haven't replaced the batteries.. Its funny how our priorities change.
joe