The map below shows a plot of data from several USS Liberty logs that contain navigation data.  (Copies of these logs are exhibits attached to the Naval Court of Inquiry proceedings document.)

The DRT (Dead Reckoning Trace) Log was written by the Radarman on watch, in CIC (Combat Information Center).  It contained computed latitutue and longitude data, for the ship's position, entered on an hourly basis.

The Deck Log was maintained by the OOD (Officer of the Deck), in the ship's pilot house, adjacent to CIC.  It recorded general events affecting the ship or crew, speed changes, course changes, and occasionally cited bearing data.  (Note: the Deck Log for June 8, 1967 was rewritten/written at least several days, if not weeks, after the attack and, thus, it may contain incomplete or unreliable data.)

The Bearing Log recorded time and bearings, in true degrees, as sighted from the ship to a fixed land object: the El Arish minaret in this case.

The gross mismatch of navigation data, shown on the map, raises questions.  Is the commonly accepted course (known as the "AB" leg or the planned "ABC" patrol course, shown by the gray dotted-line) true?  Further, does data from the ship's other logs support the AB course or explain navigational data variance?

BT (Boiler Tender) Log supports doubts about the ship's course:

The BT Log shows boiler number two was off-line from midnight until the attack, and only boiler number one was on-line.  At 1109, cleaning soot from boiler number one's tubes started.  This consisted of blowing steam through the boiler's tubes and out the stack -- a procedure known as "blowing tubes."  Boiler tube cleaning ended at 1125.  (Note: The 1109 to 1125 blowing tubes event was recorded in both the BT Log and page 831 of the Engineering Log.)

Depending on wind direction, the ship may temporarily change course to blow tubes, to prevent the black soot from falling on its decks.  For example, a course change is shown on the map, and recorded in the ship's Deck Log, for blowing tubes between 0600 and 0700.

The 1109 to 1125 blowing tubes event was not cited in the Deck Log, as well as no course change during this time.  Of course, wind direction may have been favorable for blowing tubes, without the need for a course change.  The Weather Log has an incomplete entry for 0900Z (1100 local time); it shows a shift of wind from the west to being from the north.  The next Weather Log entry at 1000Z (1200 local time) shows the wind shifting back to being from the west.  If Weather Log entries are true, then there would have been no need to temporarily change course for blowing tubes, and this would allow a constant course during this time -- as depicted by the AB course.  Otherwise, the green-colored DRT Log's data plot shows a possible diversion or change of course to accommodate blowing tubes, with the wind coming from the west.

Other data found in the BT Log was fuel oil usage.  The BT Log shows the ship burned, on average, 318 gallons of fuel per hour, on June 8, 1967, from 0000 (Midnight) until 0800.  Between 0800 and 1100, this average usage rate decreased to about 303 gallons per hour.  At 1100, one burner on boiler number one was turned-off and oil consumption dramatically dropped to 130 gallons per hour (a 43% reduction) until 1200.  Between 1200 and 1300, oil consumption increased to 220 gallons per hours.  Between 1300 and 1400, the oil consumption rate was not recorded, due to the attack.

Much like an automobile, a ship's rate of fuel usage is dependent on its speed and distance traveled, as well as the energy (i.e., high-pressure steam) needs to operate the ship's electrical generators and other auxilary equipment.  Considering the relatively minor difference between the average rate of fuel consumption before and after 0800, it appears that the ship's speed did not change much.  But keep in mind that during hot daylight hours the need for air conditioning would significantly increase, thus increasing fuel usage.  So, even though it is relatively minor, the decreased fuel consumption from 0800 to 1100 appears consistent with a slow-down in the ship's speed as indicated by the AB course shown by the gray dotted-line.  Although, depending on the ship's actual movement between 0800 and 0900, the DRT Log's data plot also offers a fairly good match for fuel usage rate, except for the 0900 to 1000 time period.

The point at which fuel usage and the AB course grossly part company is between 1100 and 1200.  Fuel usage dramatically dropped from an average of 303 to 130 gallons/hour.  I asked Gary Brummett, a former BT (Boiler Technician) and USS Liberty attack survivor, about the significance of burning an average 303 v/s 130 gallons/hour. Gary's comment was:

"Burning 130 [instead of 303 gallons/hour] means we had slowed down ... and were barely moving."

Indeed, this is exactly what the DRT Log data plot shows from 1100 to 1200 where the distance traveled is about two nautical miles in one hour or two knots speed.

Overall, the hour-by-hour BT fuel usage profile correlates well with the DRT Log's data plot, except for the apparent slower speed depicted by the 0900 to 1000 time period.  On the other hand, the BT Log correlates well with the AB course, except for the apparent slower speed implied by reduced fuel usage from 1100 to 1200.  So, while the BT Log's data offers some insight, it fails to explain the DRT Log's 0900 to 1000 exception; although, it does support the DRT Log's navigation data for 1100 to 1200.  Clearly, this is a confused and mixed finding that raises more doubt than it resolves about the ship's true course.

'Bearing Log' entries make matters worse:

As you can see on the map above, the two bearings for 1112 and 1145 appear only about one nautical mile apart; i.e., about 2 knots speed.  Additionally, the 1145 bearing is after the 1132 time, cited in the Deck Log, for changing course from 253 to 283 degrees.  This simply does not support the ship changing course at 1132.  On the other hand, it supports a slow-down in speed as implied by decreased fuel usage during this time period.

Bell Log and Engineering Log support AB course:

The Bell Log recorded requests for speed changes and hourly readings of the propeller shaft's revolution counter; and the Engineering Log reflected the Bell Log's entries.  At 0901, the Bell Log recorded a speed change request for five knots.  From 0901 until 1400, propeller shaft revolutions were recorded each hour as exactly 25 revolutions per minute (RPM) -- not one turn more or less.  The Engineering Log's data entries agreed with the Bell Log.
 
The AB course is 16 nautical miles.  Using DRT Log data from 0000 to 0800, the ship's average speed before 0901 was 11 knots, and the Bell and Engineering Logs indicate the ship's propeller turn rate was set for 10 knots (45 RPM).  Using the 11 knots average speed, between the AB course's 0849 and 0901 (12 minutes) points, the ship would have traveled about 2.2 nautical miles (NM).  This leaves about 13.8NM to travel from 0901 until 1132 end point of the AB course.  If we assume the ship suddenly slowed from an average of 11 knots to 5 knots, it would have traveled 12.5NM from 0901 until 1132.  Of course, due to its inertial energy, the ship did not suddenly slow.  So, the ship would have traveled farther than 12.5NM by 1132 -- perhaps as much as a bit over one extra mile to 13.8NM.  Thus, Bell and Engineering Logs' data supports the AB course, not the DRT Log's data plot.
 
Bearing Log entries make matters worse -- again:
 
Unfortunately, Bearing Log data reflects distances and times that simply do not agree with Bell and Engineering Logs' data, or match the AB course's times, as show in the analysis below:
                                          Bearing Log Data Analysis
                               Time Period   Distance   Time       Speed
                                0849 - 0930:  3NM         0.68Hr    4.4 knots
                                0930 - 1039:  5.5NM      1.15 Hr   4.8 knots
                                1039 - 1112:  4NM         0.55 Hr   7.3 knots
                                1112 - 1145:  1NM         0.55 Hr   1.8 knots
                                1145 - 1132:  3NM        -0.2 Hr    -15 knots (reverse direction)
 
If there was a speed change from about 10 to 5 knots at 0901, then from 0849 until 0901 (0.2 hour), the ship would have traveled about 2NM before the speed change.  With about 3NM between the 0849 point the first bearing at 0930, this leaves 1NM traveled between 0901 and 0930 (0.5 hour) -- a speed equivalent to 2 knots.  This is an impossible result, if the ship traveled at about 10 knots until 0901, and 5 knots thereafter.  Thus, Bearing Log data does not support the AB course plot, nor agree with Bell and Engineering Logs' data.

Deck Log and Underway Log entries conflict:

The 1132 course change, at the end of the AB course, was recorded in both the Deck Log and Underway Log (maintained in CIC), as shown below; although, suspiciously, handwriting for this entry in the Underway Log is different from its immediately proceeding entries.

As you can read, the Underway Log does not agree with the Deck Log for the 0849 course change to 253 degrees.  The Underway Log shows a course change at 0838 to 255 degrees, not a course change at 0849 to 253 degrees.  Changing course earlier, with a slight difference in heading, favors the DRT Log's data plot, and casts doubt on the AB course.

Also of interest is the difference in time for the 10 to 5 knot speed change.  It was noted as occurring at 0901 in the Bell Log, 0903 in the Underway Log, and 0905 in the Deck Log.

Summary and Conclusion: 

As presented above, the Bearing Log's data does not support either the AB course or the DRT Log's data plot; although, the Bell and Engineering Logs' data support the AB course plot, and not the DRT Log's data plot.  On the other hand, a result derived from data in several logs indicates an apparent significant decrease in speed between 1100 and 1200 (during the time the ship's boiler tubes were cleaned) that does not support the AB course, and hints that the DRT Log's data may be correct. 

Additionally, there is a critical course change datum entry in the Deck Log that does  not match an entry in the Underway Log.  Assuming one of these entries is correct, it will either favor the AB course plot, if the Deck Log is correct; or the DRT Log's data plot, if the Underway Log is correct.

All things considered, it is very odd that the DRT Log reliably recorded navigation data until 0800, and then suddenly became unreliable for only the AB leg of the planned ABC patrol course, but this appears to be the case -- even though support data for the plotted AB course (i.e., gray dotted-line) is questionable too.

In conclusion, the gross mismatch of logged navigational data is troublesome and suspicious.  It muddies the water for clearly seeing USS Liberty's June 8, 1967, navigational course.  Nonetheless, in general, all logged data reviewed herein supports that the ship slowly approached El Arish, from a 253 or 255 degree heading, possibly executed a temporary course change, issued a cloud of dark smoke by blowing tubes, and then slowly departed the area on a 283 degree heading -- all while remaining within international waters.