Hansen’s Ex-Meridian Tables
April 18, 2019
Day 195
Noon Position: 11 33S 24 42W
Course(t)/Speed(kts): WNW 5
Wind(t/tws): E 10
Sea(t/ft): E 3
Sky: Hazy cirrus; some puffy cumulus.
10ths Cloud Cover: 9
Bar(mb): 1016+
Cabin Temp(f): 88
Water Temp(f): 85
Relative Humidity(%): 64
Sail: Working sail, reaching to starboard
Noon-to-Noon Miles Made Good (nm): 131
Miles since departure: 26,615
Avg. Miles/Day: 137
Leg North Days: 29
Leg North Miles: 3,665
Avg. Miles/Day: 126
Not sure if wind fell lighter overnight, causing us to slow down, or if we were slowed by taking the wind aft of the beam. In any case, we were slower. Winds are steady but quite light; rarely over 10 knots.
I should be flying the big genoa, but we are back to wind just forward of the beam this afternoon, and that sail is a bear on a reach. At least that’s my excuse. I’ve not changed sail in so long, I’m not sure I recall how.
A bird. A small petrel: larger than a stormy, smaller than a small gadfly; long, delicate wings. No idea what it was. Only bird in days.
—
I have been dabbling in a new-to-me set of celestial navigation tables. Published originally in 1930, they are, in fact, not new at all, but were a part of the collection of tables my father used when he was an officer in the American Merchant Navy.
The book is titled HANSEN’S EX-MERIDIAN TABLES. According to the inside cover, dad bought the book in 1944 in Liverpool, when he was serving on the S/S F.H. Newell. It’s been tucked away aboard Mo this entire voyage and was only broken out a few days ago.
The tables have been compiled by a Capt. L. F. Hansen, and his instructions in the preface, written for the professional mariner of the 1930s, took some study on my part but have yielded a simple technique for getting one’s latitude.
As you may know, a favorite sight of the sailor is the noon shot for latitude, “the cornerstone of the navigator’s day,” to quote Tom Cunliffe. The sight is easy as it does not require time to the second of GMT; the calculation is also easy and produces a latitude directly; e.g. 47 degrees 27.7 minutes south.
The calculations for forenoon and afternoon sun shots require more look-ups, more steps, and give you intercepts, i.e. lines on a chart, and where they cross, there you are. All fine and good, but it’s reassuring (and did I mention easy?) to know ones latitude.
The problem is that the noon shot has to happen at your local noon. If you miss it, it’s gone until tomorrow.
Enter Capt. Hansen, whose tables calculate where the sun will be for a time AFTER noon.
So, if a cloud was blocking your sun at noon but the cloud is gone by 12:45pm, you can take your “noon” shot at 12:45pm, consult Hansen’s tables, dig out a correction for degrees and minutes to add to your working, and there you are. You’ve got your latitude, cloud be damned.
I’ve used the book these last six days. It took the first three to get the interpolations down, but now my off-noon sights are nearly as close as those of noon.
The sun is said to be “on its meridian” when it is directly overhead; thus, “Ex-Meridian Tables.”
As far as I can tell, the tables aren’t made anymore. Fell out of favor. Don’t know why.
Fascinating. I’ve recently been rather taken with Self-Contained Celestial Navigation with H.O. 208 by John S. Letcher, Jr. It is a very compact and convenient table and I wonder as you do why it fell out of favor. The book is wonderful, particularly his explanation of finding the time by lunar distance and time by lunar lines of position. Are you familiar with this work Randall?
Love following your voyage. Wishing you good winds (preferably reaching just forward of beam!)
Very interesting concept – extending the window for solar meridian passage. I’m going to look for a copy in the used book world.
Kurt
Very interesting! I’ve found a publisher who sells a revised edition in the UK: https://www.skipper.co.uk/catalogue/item/hansens-improved-ex-meridian-tables.
Captain LF Hansen is my great grandfather and I just read his autobiography Adventures of a Sea Rover up a fjord in British Columbia Canada in a canoe with my dawg… His blood runs in my veins!
Cheers to You and stay safe!
What an excellent comment. Ian, thanks for reaching out. It was fun to use Hansen’s tables for the experience of them and as they had my dad’s notes from when he used them back in the 1940s. Three cheers for your great grandfather. And to you for your adventures. Thanks for sharing. ~RR
Ian I was just given a copy of Adventures of a Sea Rover. It has an inscription to my grand father Leonard M Hansen. I am tying to understand if there was a family connection. If you would reach out. I’d love to understand that side of my family tree more.
Thanks, Kevin M Hansen
A search for the book nets only one copy…already sold. The description:
Adventures of a Sea Rover; autobiography–While Capt. Hansen is best known for Hansen’s Simplex ex-meridian tables which was the essential reference for every ship captain, here is his rare autobiography which provides insight of an authentic biographical nature in the last day to sailing ships and the transition to the age of high-powered steam ships. He ran submarine blockades in two world wars, was marooned in hostile Patagonia, fought an enraged tiger who got loose on a cattle boat (see the front dust jacket). Printed in a small print run less than 8 libraries have copies and most of those are museums on maritime subjects as well as both the U.S. Coast Guard Academy Library and the U.S. Naval Academy Library at Annapolis. A very nice copy bound in green cloth, spine lettering giltin unclipped pictorial dust jacket with large chip to head, smaller chipping to corners, spine faded. A scarce work.
I’ll keep looking.
Nories Nautical Tables includes ex-meridian tables. Nories is packed with useful information.