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CelNav- no batteries, no electronics but... - craigsl - 12-19-2015
If your chronometer is broken and time is unknown or you can't get a WWV or WWVH signal you're going to have a hard time determining Longitude. Latitude can be obtained easily enough from the blessed noon-sight. No time...no position fix.
Have any of you tried "the recovery of time" technique. I think it requires a known position and the GHA deriving the Hc specific to the position. Beyond that, I know nothing about.
Looking at Bowditch Chapter 26 Emergency Navigation
"Section 2612. Finding Longitude" (page 10) mentions something about determining meridian transit time and correcting the chronometer for same. There has to be some explanation for this?
I hope.
Craig
RE: CelNav- no batteries, no electronics but... - Lipr - 12-20-2015
(12-19-2015, 01:34 AM)craigsl Wrote: If your chronometer is broken and time is unknown or you can't get a WWV or WWVH signal you're going to have a hard time determining Longitude. Latitude can be obtained easily enough from the blessed noon-sight. No time...no position fix.
Have any of you tried "the recovery of time" technique. I think it requires a known position and the GHA deriving the Hc specific to the position. Beyond that, I know nothing about.
Looking at Bowditch Chapter 26 Emergency Navigation
"Section 2612. Finding Longitude" (page 10) mentions something about determining meridian transit time and correcting the chronometer for same. There has to be some explanation for this?
I hope.
Craig
Bowditch Chapter 26 page 10 says,
"Either of these methods can be used in reverse to set a
watch that has run down or to check the accuracy of a watch if the longitude is known."
That's the difficult part if you don't know your longitude- you can't use GHA to calculate time.
But if you do know you Longitude here's the formula to assist you in determining time-
Determine GHA (with knowns of Hc or Ho, Ap. Lat., Declination & Ap Long)
(360 - Cos-1((Sin(Hc) – Sin(AP Latitude) x Sin(Declination)) / Cos(AP Latitude) x Cos(Declination)) + Longitude) - 360
The 360º figure is only if Body azimuth is less than 180 (before MP).
Wish I could be of more help.
Larry
RE: CelNav- no batteries, no electronics but... - c_davidson - 12-21-2015
Most likely the best approach lacking accurate time is to refer to the DR Log book that was being kept and make an assumption from the last accurately known time and position (assumed position or fix). From the last accurate position or fix, estimate the further course and speed of your vessel to provide a MPP (Most Probable Position).
Estimate the number of hours from the last fix/position based on vessel speed and distance to obtain a new time to reset your "chronometer" to. This assumes you've got a knot and Distance meter that work.
This shows the need for a backup of the time keeping system. Carry several watches and check and compare them often. Reset as necessary.
It won't be accurate but if you've in the middle of the Atlantic headed to France land will not be immediately ahead.
Hailing another boat or ship might work? Ask 'em what time it is.
Clendon
RE: CelNav- no batteries, no electronics but... - Rdutton - 12-26-2015
For me the notion of not knowing what time it is or not be able to ascertain the time is a "dooms-day" scenario. However, relying upon a chronometer or watch is a weak link in the celestial navigation process. Nothing's perfect.