Celestial Navigation - how good were you?

[RichMac]

Celestial navigation in the old days before gps was very satisfying when you got it right. A good sun or a star sight can be quite accurate, but you can be a long way out of position after long periods of dead reckoning between sights.

My brother was a skilled navigator, he could position an oil rig better than 1/2 a mile in the late ‘60s by taking sights continually for a day or two. But in a small yacht with rough seas, cloudy skies and a current, he sailed 25 miles off course and arrived at the wrong Indonesian Island.

One night, our log impeller failed, and the sky was overcast in the morning. Our DR position was 12 miles out, and we ended up surrounded by reefs, it was like a maze to escape. Looking back, I'm quite embarrassed by some of my navigation incidents.

We were on an old 80ft dive chart boat, somebody opened the wrong wheelhouse door in a severe gale, and our charts blew overboard. We just kept Australia to port until we recognised something!

How good were you before gps, perfect landfalls every time, or some interesting stories?

[Pete7]

An odd shaped cocked hat some distance off the skippers DR position. But since we were in the middle of the North Atlantic at the time it didn't matter too much and close enough for "government work". That was on a 20T yacht. On our yacht which is 5T, no chance unless its flat calm. I sold it when the price of secondhand Davis doubled a couple of years ago.

Pete

[Paul L]

When I tried to be a purest and reduce the sight by hand without a calculator I ended up in the Arizona dessert as often as in the ocean.

[Scott Berg]

Just takes practice (and a good worksheet helps). My students usually get the rough idea in two 2 hr classes. Sun lines are usually down in the first week along with noon sights, and are getting reasonable cocked hats with morning stars after 8 weeks. Most find kneeling on a small boat easier that standing but each person finds their own best shooting position. The key is to keep at it until both skills (sight taking/timing) and reduction are 2nd nature. I recommend putting a cover on the GPS that says don't look here, grab a sextant and figure it out! (then check your work!). Pro hint, if you are by yourself have a stopwatch around your neck, click it on the sight, then subtract the elapsed time from the chronometer when recording sight time. Easier than looking at your watch and stopwatch at the same time.

[LittleWing77]

My "best" reductions were within 10 miles of our GPS positions. Helps you understand why, back in "olden times" there were so many shipwrecks! (Methinks) <Gulp>

Best,
LittleWing77

[slug]

Originally Posted by RichMac

Celestial navigation in the old days before gps was very satisfying when you got it right. A good sun or a star sight can be quite accurate, but you can be a long way out of position after long periods of dead reckoning between sights.

My brother was a skilled navigator, he could position an oil rig better than 1/2 a mile in the late ‘60s by taking sights continually for a day or two. But in a small yacht with rough seas, cloudy skies and a current, he sailed 25 miles off course and arrived at the wrong Indonesian Island.

One night, our log impeller failed, and the sky was overcast in the morning. Our DR position was 12 miles out, and we ended up surrounded by reefs, it was like a maze to escape. Looking back, I'm quite embarrassed by some of my navigation incidents.

We were on an old 80ft dive chart boat, somebody opened the wrong wheelhouse door in a severe gale, and our charts blew overboard. We just kept Australia to port until we recognised something!

How good were you before gps, perfect landfalls every time, or some interesting stories?

My experience is that I seldom get a fix with celestial...only LOPs

They lines are very useful when combined with an well kept DR

How accurate are my celestial observations...a few miles

Combine this with other inputs such as a RDF and everything works out


I can remember sailing boats from the East coast USA to Bermuda with only basic navigation ..a very challenging passage.

Once we got in the vicinity of Bermuda we would slow dow..them look for airplanes approaching Bermuda or shipping traffic...to help verify out assumed position

[Sailnav]

KC-135 air refueling tankers used periscope-equipped sextants via a through-hull in the ceiling. Circular error after six hours at 350 knots was typically 7 nm.
BTW, a hose fitted to the through-hull made an excellent vacuum cleaner for the cockpit.

[skipmac]

If I took a series of sights on the same bodies, graphed the results, tossed out the odd ones, drew a line down the middle of the rest and picked a best point on the line for each body I could get within 5-6 miles.

Doing a latitude by Polaris I was often dead on.

[roland stockham]

I came on deck one morning to find a seasick skipper slumped over the tiller with no idea where we were and no DR plotted (in the southern north sea). Solution, we headed towards the Belgium coast making a course at right angles to it having checked the were no offlying dangers. When we go close I read the place name off a chip shop on the front. We had tried getting a radio fix from the coast guard but they where 100miles out. We knew that because they put us in the only bit of deep water in the area and we had less than 20m.

Sometimes I think GPS spoiled the fun (until I hit fog or heavy weather!!)

[Cpt Pat]

Noon sights, bouncing around in my little boat: 8 nm. Standing on a dock facing south to sea: 3 nm. That's with a cheap Davis sextant.

Here's a cheat for single-handers: dial in WWV (2.5, 5, 10, 15, or 20 MHz) on the SSB, turn up the volume so you can hear it on deck, and count clicks between minute announcements. The 30-second click is missing, if you lose count.

No clock needed. You can't find a more accurate time source.

And if you use that signal with an RDF: a male voice is Colorado, a female voice is Hawaii. In the Pacific, if you switch frequencies, you can often hear Colorado on one band and Hawaii on another. Don't try RDFing if you hear both.

[skipmac]

Originally Posted by roland stockham

I came on deck one morning to find a seasick skipper slumped over the tiller with no idea where we were and no DR plotted (in the southern north sea). Solution, we headed towards the Belgium coast making a course at right angles to it having checked the were no offlying dangers. When we go close I read the place name off a chip shop on the front. We had tried getting a radio fix from the coast guard but they where 100miles out. We knew that because they put us in the only bit of deep water in the area and we had less than 20m.

Sometimes I think GPS spoiled the fun (until I hit fog or heavy weather!!)

Sounds like navigating to Hawaii in the old days. Never did it myself but heard the plan was to leave California, dead reckon until you're a few days or week out of Hawaii then follow the contrails from the jets flying into Honolulu.

[saillr]

I had two occasions to check accuracy.
In 1967 we were sailing from I think Palmerston Atoll to Nukualofa Tonga and realized a submerged reef was close to our rum line. Beveridge reef had been a final destination for sailing ships for many years. We decided rather than try to avoid it we would try to find it. From memory I believe it is about 4 miles long and about 2 miles wide. At low tide you can see a little surf breaking depending on wind and swell. I was able to get a moon LOP near dawn and sun sites each 1/2 hr until our expected TOA about noon. Anxious eyes glued to the horizon sure enough we were lined up with the southern most part of the atoll and since I was aiming for the south to middle my accuracy was about 2 miles. Not bad for sun shots. We anchored inside the lagoon in pure white sand for 3 days feeling very accomplished in those early times. I took many star shots during the early part of the voyage but found they were much more difficult to be even close due to the motion and dealing with such a small pin point of light. Keeping it in view and reducing it to the horizon was enough to give you a significant headache as well as arm ache. Holding a heavy Plath sextant for any length of time was painful and you had to get the shots quickly as the horizon doesn't stick around long in the tropics. Then you had to work out three LOP's and in 67 I don't think we even had a calculator.
The second situation was sailing from Malacca Straights to Southern tip of Sri Lanka. Each day we were greeted at close to noon site time with the double boom of the SST Concord flying overhead at greater than the speed of sound from Singapore to India. Our tracks were very close and we could tell if we were slightly to the right or left of our intended GC track.

[captmikem]

Well, it was hard to tell, because you had your fix and only dr etc to compare it with. Once Sat Nav came into use you would get a fix four or five times a day to compare it with but you were moving and advancing a fix on an ocean chart where a pencil point is a quarter to a half mile.

In 1986 I took the fist civilian GPS across the Atlantic on Alden 54. Back then we only got fixes at various times during the 24 hour day but it was way more frequent than SatNav. I did not fully trust it so I kept up my sights.

After a round of stars on a clear night my star fix and any GPS fix that was close was always within a mile. One time I was about an eighth of a mile, (using as plotting sheet) but that could have been an anomaly.

It got to where I would use the GPS fix as my AP (when I could) and if my intercept was a mile or less I would plot the GPS fix as good.

Bear in mind I was an officer on ships and had thousands of sights under my belt. This may seem like a lot but I would always shoot a body 3 times and average the times and sight to reduce errors. Doing morning stars, sun and moon sights during the day and evening stars adds up pretty quickly vs the person who just does noon sights and Polaris.

M

[Scaramanga F25]

We also used a radio direcrion finder, that worked very well. ( RDF )

[slug]

Originally Posted by Scaramanga F25

We also used a radio direcrion finder, that worked very well. ( RDF )

RDF was how we would find the Azores when sailing across

Sextant got you in range ..RDF got you into the harbour