celestial navigation

[David M]

Originally Posted by dhhudson

The best single volume I have come across for teaching oneself celestial navigation is Mariners'CelestialNavigation written by William Crawford. The book starts with an explanation of time and time diagrams and runs you through to taking a typical celestial fix. Sunlines, LAN, sunrise, sunset, as well as times of lunar phenomena are fully explained in short, humorous chapters that are really, if you apply yourself, self teaching. Crawford emphasizes the use of the Nautical Almanac and Publication 229 which are partly reproduced in the tome, as well as use of the Rude Star Finder. (Anyone still got one of those?) Crawford also revels in the lore of seamen, explaining many of the sayings, habits, and beliefs that have developed over the ages.

The book is currently out of print, but there always seem to be copies available on line at Alibris.com or Amazon.com.

By the bye, if you learn nothing else about celestial, learning how to find your latitude at LAN is a simple task that will answer 50% of your questions about "where the hell am I?" It was good enough for the Europeans to find the New World.

Same goes for shooting Polaris.

[GordMay]

Like money in the bank, it’s good practice (and reassuring) to have back-up equipment or skills, supporting any important function.

Last weekend, we delivered a brand new (to owner) C&C33 from Duluth to Thunder Bay (about 160nm, coastal).
Upon our 6:00PM departure from Duluth, we established a plotted course by compass heading.
The course didn’t seem right according to visual bearings, so we fired up my pocket GPS, and obtained a track, which was significantly different (about 20 deg. CE) from our compass heading.
There were no obvious external conditions that would have set our course off heading (leeway).

Accordingly, we used our GPS Track as a True Heading (separately determined on each leg*), and sailed an accurate course home (over 2 days and a night).

* The compass error (deviation) varied between 5 & 25 degrees, depending upon heading.

Upon reflection, I supposed that the new S/S shifter & throttle levers (binnacle mounted) were causing the compass error. A subsequent test proved that the levers (and mounting set screws) are magnetic.

In this case, the back-up skill was an approximate true heading obtained by visual fix, and the GPS backed up the compass. In fact, the Knot-Log was non-functional, so the GPS also backed up our speed estimates.

[sandy daugherty]

I just realized my previous post was critical of Celestial Nav for no reason. It is a fine traditional skill worthy of respect and useful in real life situations. I shouldn't let my questionable ability, and infatuation with gadgets allow me to lose it. Hello, Mary!

[David M]

Originally Posted by sandy daugherty

We don't even require celestial nav at the Naval Academy anymore, it's strictly an option for Mids who want to qualify for offshore racing.

Fortunately the Coast Guard does require celestial for Third Mates licenses. Looks like if the GPS system goes down, the naval ships will be out on the ocean doing circles while the merchant ships will be finding their way to the next port.

[sandy daugherty]

Good point, but we still have Inertial Nav, RDF, Loran, and (mumblemumblemumble)

[David M]

Originally Posted by sandy daugherty

Good point, but we still have Inertial Nav, RDF, Loran, and (mumblemumblemumble)

Yeah I know. I just thought it was a funny image seeing the grey stack fleet going in circles.

[SkiprJohn]

Aloha Sandy,
Apology accepted. I was in the Navy nearly 30 years. Didn't learn celestial until I wanted to make a Pacific crossing in my own boat prior to GPS and affordable SatNav. They don't teach celestial to enlisted unless you are a Quartermaster which I wasn't.
Although I only use it from time to time I am very proud of the skill I learned independent of the Navy. Many people say that it is easy. I disagree. It really is one of the most difficult things I've learned and I'll continue keeping my skills up to date not matter how many gizmos and electronics the corporations come up with. I do use GPS. It is easy. Just push a button but I will always have a backup and encourage others to as well.
Kind regards,
JohnL

[Ex-Calif]

Originally Posted by GordMay

* The compass error (deviation) varied between 5 & 25 degrees, depending upon heading.

Upon reflection, I supposed that the new S/S shifter & throttle levers (binnacle mounted) were causing the compass error. A subsequent test proved that the levers (and mounting set screws) are magnetic.

Gord - I personally would attribute that to maintenance error.

Anytime a large metal object is placed or replaced near the compass it should be swung. Anytime electronics near the compass are changed the compass should be swung.

We carry a handheld compass for backup to the bulkhead mounted one. If in doubt we send someone to the foredeck with it.

We also have a "secondary" flux-gate mag course in the autopilot window.

I have also stated in the past that the compass should be swung with all "standard" equipment running and should be tested with no equipment running to understand if there is a difference.

And like 90% of everyone else we are usually carrying at least 2 GPS units although rarely using them at present.

[GordMay]

Originally Posted by Ex-Calif

Gord - I personally would attribute that to maintenance error.

Anytime a large metal object is placed or replaced near the compass it should be swung. Anytime electronics near the compass are changed the compass should be swung.

We carry a handheld compass for backup to the bulkhead mounted one. If in doubt we send someone to the foredeck with it.

We also have a "secondary" flux-gate mag course in the autopilot window.

I have also stated in the past that the compass should be swung with all "standard" equipment running and should be tested with no equipment running to understand if there is a difference.

And like 90% of everyone else we are usually carrying at least 2 GPS units although rarely using them at present.

Dan is quite right, in all respects.

The new owner installed the shiny new binnacle-mounted levers, without consideration for the possible (magnetic) consequences.
I also found it odd that both the levers and set screws were magnetic, coming from a reputable marine supplier.

I believe our first check, upon becoming suspicious, was the hand-held compass. Conditions were a bit “lumpy”, and I wasn’t totally confidant in my sighting, so confirmed /w GPS track.

This reaffirms the wisdom of utilizing multiple, cross-confirming, skills and equipment wherever practicable.
Plan "A", plan "B", plan "C" ...

[JiffyLube]

Has anyone tried to use a GPS to check a compass?

[GordMay]

Originally Posted by JiffyLube

Has anyone tried to use a GPS to check a compass?

Yes; see my post from 25-05-2008.

[anotherT34C]

I took celestial nav when I was at the MMA. It was a requirement at the time, at least for us "deckies". No idea if it still is.

My sextant sits in a rarely opened plastic box.