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Come one, come all - celestial navigation w/ Steve Hodges (Frolic)

G

Gamayun

Kynntana (Freedom 38)
Celestial Navigation - A Brief Primer with a focus on Noon Sights

Have you ever wondered how navigation was done before GPS? Steve Hodges (winner on corrected time of the 2014 Singlehanded TransPac and I think he won the Celestial Navigation trophy in 2012) will be teaching an introductory seminar on the art of celestial navigation, with a focus on noon sights. The first day on Tuesday May 16 (1800-2100) will be held at Island Yacht Club, and will include a brief description of the notions involved, such as geometry, position plotting and an introduction to the nautical almanac.

The specifics of how to obtain latitude and longitude from a noon sight of the sun will be presented on Thursday May 18 (1130-1300), with the location on Alameda to be determined, but it probably will be near Ballena Bay Yacht Club.

There will be an opportunity to handle and operate sextants in the meeting room on Tuesday, and then, sky permitting, we will “shoot the sun” on Thursday. Below is the outline of the seminar. Please post questions here, and one us (Steve, Dave Herrigel or I) will answer for everyone.

Some recent discussion and info about celestial navigation can also be found here: http://www.sfbaysss.net/forum/showthread.php?1788-Navigation-class-recommendations

We're looking forward to seeing you all!

Presentation Outline

• Overview
– Sight Methods
– Plotting Standards
• Theory
– Geometry & Time
– Noon Sight Reduction
• Equipment
– Noon Sight
– General Sights
– Nice to haves
• Hands-on Practice
• Resources
 
Would really like to do this, but, my nephew is graduating high school that Thursday.

I have one of the Davis sextants to practice with and I watched a couple you tube videos...
 
Daydreamer said:
Would really like to do this, but, my nephew is graduating high school that Thursday.

I have one of the Davis sextants to practice with and I watched a couple you tube videos...
Click to expand...

Well, that's Thursday (congrats to your nephew). You could attend Tuesday only, if you'd like to have a refresher and a fun evening rolled into one!
 
When I was in graduate school, back around the time of Inquisition, I took a physical oceanography course. One of our lab activities was to pass a sextant around the class while we were standing on top of the sand dunes at Moss Landing Marine Lab and shoot the sun. We got shots more or less every 2-3 minutes for about 45 minutes bracketing LAN. Then as a class we graphed them...time on the X axis and angle on the Y axis. "Graph" meant with an ancient invention called "graph paper". Upshot...you drew a smooth curve through the points on the graph and adjusted for the height of the dunes and son of a gun but if we didn't get our latitude to within about 4 miles.

I did some reading and figured out how to get longitude from that measurement as well. "All" you need is a reasonably accurate digital clock set to Greenwich time. I was so intrigue'd by the whole process that I bought a secondhand Tamaya sextant in 1996 and went out to Half Moon Bay a few times to practice before I went to Hawaii that year. I took 3-4 noon sights on the way over that year, and discovered that taking sights off the beach is easy compared to taking sights off a small boat!

I subsequently sold the Tamaya, but now have the "better" model plastic Davis sextant in my garage.

Years ago when I was working at the Marine Science Institute, I used cheapo plastic Davis sextants to teach kids how to fix their position on the Bay with horizontal sextant angles and a three-arm protractor. It's pretty remarkable how accurate that is.
 
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If you plan to come to the Tuesday evening session next week, I suggest you take a look at the Sun data in a Nautical Almanac. You can buy the book, or download for free from this site:

https://www.thenauticalalmanac.com/

During the session we will plan a noon sight for Thursday, 18 May. For that activity you will only need the Sun data for 18 May, and the 'Increments and Corrections' pages (two pages available from the same site). That’s a total of three sheets of paper.

I will also bring some sextants for hands on practice. If you have a sextant, feel free to bring it!
 
We had a nice session! Thanks to attendees for your interest and participation. Thanks to Carliane Johnson and Dave Herrigel for help organizing this.

The brief I presented and the noon-sight form we discussed are available here:

https://drive.google.com/drive/folders/0ByoWPQ0Bj_ywemN1U09YYUNmbVU?usp=sharing

The weather looks good for a noon sight from Alameda this Thursday. I plan to be at the Encinal Boat Launch Ramp (adjacent to the Encinal High School) about 1130 this Thursday (18th) with several sextants for loan. LAN is 1305 PDT.

Encinal Boat Ramp
Alameda, CA 94501

https://goo.gl/maps/Qj1zXLtJ7Cw
 
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We had a productive noon sight session. Thanks Randy for chronicling the event with images.

I didn't catch the Sun's altitude at meridian passage but bracketed it to obtain a LAN at 13:05:45 which gives a Lo of 122°19.7' (GPS 122°17.4')

I did get a complete noon sight yesterday and posted a summary of that in the google drive folder listed above.
 
I have a Davis 15 sextant I could part with. Used by a little old guy for celestial nav class and then for one trip to Hawaii - it worked! We won! Almost as new (in cardboard box in plastic case, everything there). New = $140. Little old guy used one = ??? Make me an offer. Pat "Little Old Guy" Broderick.
 
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