A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Byron Franklin
Date: 2010 Dec 25, 10:43 -0800
I must read "THE FRANKLIN PILOTING TECHNIQUE Ernest B. Brown and Bryon E. Franklin Vol. 14, No. 2, 1967 IoN", now .
I would send this to better understand the Technique along with the 1967 ION.
Bowditch of 1977 also is a good understanding.
Compass Error Licked, Byron Franklin, page 1.
The Franklin Piloting Technique
Compass Error Licked.
In 1958 I reported aboard the USS Outpost AGR 10. The AGR was a radar picket ship modified from a Wold War II Liberty Hull. She was very top heavy with high radar antennas and the same gyro she was originally built with. Her mission was to track any thing heading toward the United States and report anything that was unscheduled. A jet fighter plane from the main land would investigate the intruder. Accurate navigation was important to ensure we were on station, using the gyro, Loran A and the sextant. The old gyro was good enough to run the open sea, but was always slow moving about the meridian, so that visual cross bearings in restricted water were difficult. As the quartermaster chart plotter I could give good navigation recommendations to Officer of the deck (OOD), but I was not happy with the charted fixes that my recommendations were based on. I had noticed that when coming into the last leg and heading north to the pier, there were two charted well-spread Navigation Aids (Navaids) close by to port-side. Also, the ship was visually in the middle of a north/south channel with buoys on both sides. IT WAS EASY TO SEE THAT WE WERE IN THE CENTER OF THE CHANNEL. The third and only other Navaid was to the south and very far away. The line of position (LOP) from the well spread close by (>2000yds) Navaids always crossed in the center of the channel where we were visually between the buoys. The only other Navaid was far to the south (> 6000yds), This Navaid�s LOP was always outside of the 100 yards wide channel.
The AGR moored, I was tired after the two months at sea and piloting the AGR for about the two-hour transit to pier-side. I boarded a buss to go home, Newport RI. The compass error problem would not let me rest, so I went over in my mind, the two close-by charted fixes always in the channel and the far Navaid falling outside of the channel.
It became apparent! An idea that I could use the close by well-spread Navaids to get my fix.
I needed the third LOP to make the fix legal (according to the book, three LOP�s) so I can correct each of the LOP�s by using the bearing of the far Navaid as true from the center of the buoyed channel �FIX�, the observe sighted bearing difference was error, I can use the same correction for all three, collapsing the triangle. I found that I could use this technique anytime to find and maintain a fix, while monitoring the movement of the compass. I no longer needed the buoyed channel as a guild and I could use the far LOP to give me both direction and amount, any time or place to correct the compass.
With this idea I tamed the monster of compass error. It became a pussy cat to me.
My complete mechanics to Cross Bearings � The Franklin piloting Technique.�
Compass Error Licked, Byron Franklin, page 2.
Mechanics to Cross Bearings
Geometry of Piloting
The chart plotter and navigator should have a complete knowledge of plotting geometry to insure accurate fixes. Plotting geometry is predictable, uncomplicated and easy to use once understood.
Geometry Special knowledge.
A. single line of position (LOP) has two (two) dependable predicable traits (1) direction (2) offset
1 Direction. When facing each NAVAID.
a. When compass error is present, each line of position (LOP) will miss the observer to the left hand when the error is WEST and to the Right when the error is EAST. See figure1
2.Offset. when facing each Navaid, the line of position (LOP) will offset distance of the closest point of approach (CPA.)at the observer
a. When compass error is present, the (offset) CPA distance will depend on the distance to each Navaid and the amount of gyro/compass error in degrees.
b. Close Navaids will have a closer (offset) LOP to the observer, far Navaids will have a farther CPA. The offset can be, (but not needed) computed by using the rule of sixty (Radian rule)
B. LOP�s will have either (1) systematic error or (2) a random error
1. Systematic error is, the true angle between the LOP�s is correct, but the true north ailment is off the meridian. This may be a gyro, bad repeater alignment or seeking the meridian.
2. Random error is, the true angle between the LOP�s is not correct and may be caused by bad observation, ship movement between observations or compass card not centered.
The magnetic compass with the problems of ship movement is normally random.
3.Any two Navaid LOP�s that are systematic will cross somewhere on a circle that includes the observer position. If a third Navaid on the circle and its LOP are added, all LOP�s will cross at the observers position on the circle, but the three, if in systematic error will fall on the circle to the west (left hand) or to the east (right hand)of the observer the greater the error the greater the distance. -Still intersecting on the circle-. . 4. Navaids LOP�s that are random will work in the same manner but will be not be as accurate. The Franklin Piloting technique will improve fixes with Random error such as the magnetic compass. (with or without variation or deviation.) See Franklin piloting Technique.
5.Any combination of Navaids will work with the Franklin technique except the case where all three Navaids are on a circle with the observer. This is easy to recognize on the chart and a rare happening. In this case the center Navaid would be the farthest( This situation using a three arm protracter will be a swinger and will give a non fix..
The far Navaid can give near 100% total compass error when not between the fixing navaids
it will give less than total. When the far Navaid is opposite the fixing Navaids the far Navaid will give more than total error.
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com