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AEGIR RIDGE OBS AND DREDGING SURVEY 2010

Click to see plot of ship position, track line, weather ++.

Click to open photo album.

Aegir Ridge OBS and Dredging Survey, May/June 2010 (map by A.B.).

SURVEY, PROJECT DESCRIPTION

Survey duration

27 May 2010 - 14 June 2010

Project name

"Hotspot Rift Interaction & Geochemistry of the North Atlantic Mantle: The Aegir Ridge 'Hole' in the Iceland Hotspot"

Project leader

Prof. Rolf Mjelde, Department of Earth Science, University of Bergen, Norway

Project funding

The Research Council of Norway

Project duration

May 2010 - June 2013

GEOPHYSICAL EQUIPMENT

• List of equipment (PDF) delivered by Dept. of Earth Science, Univ. of Bergen. (Spreadsheet original)

HSE

• Mini-streamer oil: MOBILECT-44

LOG SHEET

• Recording logsheet

DATA AND SOFTWARE

• First version of Data Tables.

Software

• pre-process-timestamps.py Δ
• OBS-2010-make_OBS_UKOOA_P1_90-line1.py Δ
• OBS-2010-make_OBS_UKOOA_P1_90-line2.py Δ
• LatLongUTMconversion.py (from external library, put in same directory)

OBS positions

• DeplLine1_2_Aegir2010.txt

Transit data

• 28 May 2010: 280510C001.npd.txt
• 29 May 2010: 290510C000.npd.txt
• 30 May 2010: 300510C000.npd.txt
• 31 May 2010: 310510C000.npd.txt
• 11 June 2010: 110610C000.npd.txt
• 12 June 2010: 120610C000.npd.txt

Gravity data (raw)

Select from this directory

• Day 147 = Tue 27 May 2010
• Day 164 = Sun 13 June 2010
• Format description: Marine mode

Gaps in gravity data

There are two gaps in gravity data. Both are outside both profile and main transit periods. They are caused to forgetting to activate Spring Tension after Daily Check. (It has only happened on this survey.) Spring tension will remain constant, and raw beam position will slowly move very far from center.

NOTE: After Spring Tension is activated again it will still take some time before data are valid - check/plot data to investigate.

Gap 1

• Start of gap:
  Day=152, 01 June 2010, 11:23:30, File= 2010_152.DAT
  From file: TRANST 2010152112330 9557.71 9551.22 4.57 -13.5 ...
• End of gap:
  Day=152, 01 June 2010, 15:05:00, File= 2010_152.DAT
  From file: TRANST 201015215 5 0 9571.22 9551.22 22.55 3699.0 ...

Gap 2

• Start of gap:
  Day=155, 04 June 2010, 20:34:10, File= 2010_155.DAT
  From file: TRANST 2010155203410 9685.99 9685.07 .62 -4.8 ...
• End of gap:
  Day=156, 05 June 2010, 07:36:40, File= 2010_156.DAT
  from file: TRANST 2010156 73640 9701.57 9685.07 4.72 13255.0 ...

GRAVITYMETER BASE READINGS

Summary

• Base readings in Bergen, 27 May and 13 June 2010
• Gravitymeter: L & R, S/N: S-38
• S₃₈ = 0.9994

 Delta gabs = 
 Delta hw = 
 Delta av = 

 Drift rate = ( hw*0.3086 - S38delta av ) / delta tv

27 May 2010

Gravitymeter still reading:

  Day, time     DG       ST      CC   RAW   TC
  147:19:24:00  9203.4  9204.0   .0   -21   -0.3

Measurements Realfagbygget:

Measurements Nygårdsvik:

Distance to sea surface: 2.10 m

Gravitymeter still reading:

  Day, time     DG       ST      CC   RAW   TC
  147:20:50:00  9203.5 9203.6   .0   -41.0  -

27 May: Last-minute change in Spring Tension

• 21:07 UTC: New spring tension (ST) setting: 9157.6, a reduction of 46.0 counter units.
• This was due to lack of ST synchronization between ST on gravitymeter itself, and ST value in gravimeter software. Should normally have been discovered earlier.
• Ship sailed 21:11 UTC.
• Compare this to Spring Tension reading slightly more then two weeks later, on the same location, with a small difference in water level: 9155.5

Excerpt from relevant log file 2010_147.DAT (raw data on gravitymeter hard disk).
Green background:Time.
Yellow background: Spring tension stable before change was made.
Red background: Spring tension at new target value.

NOTE: Spring tension change is not instantaneous, so it will take some time (> 1 min) before the new value is reached. But it seems that spring tension software switch was not touched during this operation, as spring tension value continues to change after target value is reached. Ship left pier very shortly afterwards.

  MY_LINE # 201014721 7 0 9203.53 9203.56    .00   -43.3      0.      0.      0.      0.      0.      0.      0.      0.      0.00FFFFFF   11.
  MY_LINE # 201014721 710 9203.53 9203.56    .00   -43.3      0.      0.      0.      0.      0.      0.      0.      0.      0.00FFFFFF   11.
  MY_LINE # 201014721 720 9203.53 9203.56    .00   -43.4      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 730 9203.53 9203.56    .00   -43.4      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 740 9203.53 9203.56    .00   -43.5      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 750 9203.54 9203.03    .00   -43.5      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 8 0 9203.53 9200.09    .00   -43.6      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 810 9203.53 9194.92    .00   -43.6      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 820 9203.51 9188.70    .00   -43.6      0.      0.      0.      0.      0.      0.      0.      1.      0.00FFFFFF   11.
  MY_LINE # 201014721 830 9203.49 9182.44    .00   -43.6      0.      0.      0.      0.      0.      0.      0.      0.      0.00FFFFFF   11.
  MY_LINE # 201014721 840 9203.44 9176.78    .01   -43.4      0.      0.      0.      0.      0.      1.      0.      0.      2.00FFFFFF   11.
  MY_LINE # 201014721 850 9203.38 9172.01    .01   -43.2      0.      0.     -1.      0.      0.      1.      0.     -1.      3.00FFFFFF   11.
  MY_LINE # 201014721 9 0 9203.28 9168.20    .01   -43.4      0.      0.     -1.      1.      0.      1.      0.     -2.      2.00FFFFFF   11.
  MY_LINE # 201014721 910 9203.15 9165.24    .01   -43.8      0.      0.     -1.      1.      0.      2.      0.     -1.     -1.00FFFFFF   11.
  MY_LINE # 201014721 920 9202.98 9163.01    .01   -44.1      0.      0.     -2.      1.      0.      2.      0.      0.     -3.00FFFFFF   11.
  MY_LINE # 201014721 930 9202.76 9161.34    .01   -44.3      0.      0.     -1.      1.      0.      2.      0.      0.     -5.00FFFFFF   11.
  MY_LINE # 201014721 940 9202.49 9160.09    .00   -44.3      0.      0.     -1.      1.      0.      2.      0.     -1.     -5.00FFFFFF   11.
  MY_LINE # 201014721 950 9202.14 9159.16    .00   -44.3      0.      0.     -1.      1.      0.      1.      0.     -1.     -5.00FFFFFF   11.
  MY_LINE # 20101472110 0 9201.72 9158.48    .00   -44.0      0.      0.     -1.      0.      0.      1.      0.     -1.     -4.00FFFFFF   11.
  MY_LINE # 2010147211010 9201.22 9157.98    .00   -43.8      0.      0.     -1.      0.      0.      1.      0.      0.     -2.00FFFFFF   11.
  MY_LINE # 2010147211020 9200.62 9157.61    .00   -43.5      0.      0.     -1.      0.      0.      1.      0.      1.     -1.00FFFFFF   11.
  MY_LINE # 2010147211030 9199.91 9157.35    .00   -43.3      0.      0.      0.      0.      0.      1.      0.      2.      0.00FFFFFF   11.
  MY_LINE # 2010147211040 9199.09 9157.17    .00   -43.1      0.      0.      0.      0.      0.      1.      0.      2.      1.00FFFFFF   11.
  MY_LINE # 2010147211050 9198.15 9157.04    .00   -42.8      0.      0.      0.      0.      0.      0.      0.      3.      2.00FFFFFF   11.
  MY_LINE # 20101472111 0 9197.09 9156.95    .00   -42.7      0.      0.      0.      0.      0.      0.      0.      2.      2.00FFFFFF   11.
  MY_LINE # 2010147211110 9195.89 9156.89    .00   -42.4      0.      0.      0.      0.      0.      0.      0.      2.      2.00FFFFFF   11.
  MY_LINE # 2010147211120 9194.57 9156.85    .00   -42.1      0.      0.      0.      0.      0.      0.      0.      0.      3.00FFFFFF   11.
  MY_LINE # 2010147211130 9193.13 9156.82    .00   -41.7      0.      0.      0.      0.      0.      0.      0.     -2.      3.00FFFFFF   11.
  MY_LINE # 2010147211140 9191.56 9156.81    .00   -41.3      0.      0.      0.      0.      0.      0.      0.     -4.      4.00FFFFFF   11.
  MY_LINE # 2010147211150 9189.88 9156.80    .00   -40.9      0.      0.      0.      0.      0.      0.      0.     -3.      5.00FFFFFF   11.
  MY_LINE # 20101472112 0 9188.11 9156.79    .00   -40.4      0.      0.      0.      0.      0.      0.      0.     -1.      6.00FFFFFF   11.
  MY_LINE # 2010147211210 9186.25 9156.79    .00   -39.9      0.      0.      0.      0.      0.      0.      0.      1.      7.00FFFFFF   11.
  MY_LINE # 2010147211220 9184.33 9156.79    .01   -39.4      0.      0.      0.      0.      0.      0.      0.      3.      8.00FFFFFF   11.
  MY_LINE # 2010147211230 9182.36 9156.79    .01   -38.5      0.      0.      0.      0.      0.      0.      0.      5.     13.00FFFFFF   11.
  MY_LINE # 2010147211240 9180.38 9156.79    .01   -37.3      0.      0.      0.      0.      0.      0.      1.      5.     20.00FFFFFF   11.
  MY_LINE # 2010147211250 9178.40 9156.79    .01   -36.3      0.      0.      0.      0.      0.      0.      1.      4.     23.00FFFFFF   11.
  MY_LINE # 20101472113 0 9176.45 9156.80    .01   -35.9      0.      0.      0.      0.      0.      0.      1.      2.     20.00FFFFFF   11.

13 June 2010

Gravitymeter still reading:

  Day, time     DG       ST      CC   RAW   TC
  164:05:21:30  9155.7  9155.5   .0   20.   .1

'Measurements Nygårdsvik:

Distance to sea surface: 2.85 m

Measurements Realfagbygget

Measurements Nygårdsvik:

Distance to sea surface: 2.45 m

Gravitymeter still reading:

  Day, time     DG       ST      CC   RAW   TC
  164:07:12:50  9155.5  9155.5   .0   -31   .0

K-check, 13 June 2010

 ST OFF
  Slew ST +30.0, wait > 5 min. -> TC = -28.5
  Slew ST -60.0, wait > 5 min. -> TC = 28.7
  Slew ST +30.0, wait > 5 min. -> TC = 0.0 
 ST ON

 MARINE OPERATING SYSTEM: 2.04
 FOR METER S-38

Calibration table land gravity meter:

Calibration table land gravity meter used during gravity ties. Click to enlarge.

Gravity reference "REALFAGBYGGET, BERGEN"

• Realfagbygget, gravity reference point

Data format, hard disk logging gravity PC

• Format description NOTE: WE ARE USING MARINE MODE LOGGING FORMAT

MINI-STREAMER DATA

Credits B.O. Ruud (GEO) for assistance in mini-streamer data handling:

Processing steps in Seismic Unix:

  segyread tape=1535.sgy endian=0 | sugain tpow=1 | \
  sufilter f=15,30,60,90 | suattributes | suop op=ssqrt | \
  sustack key=fldr | sumix mix=1,2.2,2,2,1 | suximage perc=99 d2=0.2 &

Suggestion by A.B.. Use sugain mbal=1

Click to enlage:

Line 1 Mini-streamer data - click to enlarge.

Line 2 Mini-streamer data - click to enlarge.

TRACKLINE, WEATHER

• Data.txt (6.1 MByte)
  These are raw data used in plot of position, trackline, weather:

UKOOA P1-90 NAV DATA FILES

UTM Zone, reference point on vessel

All UTM data are relative to UTM Zone 30.

All coordinates are also relative to the position of the gravitymeter on board the ship.

Gravitymeter is placed at frame 40.

Frame distance is 0.6 m. Thus, gravitymeter is 40 x 0.6 m = 24.0 m from the stern.

Airgun offset distance

Airguns are positioned 60 meter behind the stern.

We have to add offset between gravitymeter and stern, to obtain the total offset between source and positions given in navdata files.

Thus, total offset between source and positions given in nav data files is: 60 m + 24.0 m = 84.0 m.

UKOOA P1/90 navdata format

Output from nav data processing should be in UKOOA P1/90 format, slightly modified to accommodate three decimals in time value.

The UKOOA P1/90 format specification can be downloaded from SEG. It's a fixed-position format without any <SPACE> or <TAB> delimiters between fields, so it can be hard to read. However, by inserting appropriate comment field in the header, it can be made much more legible, as this example shows. The first part is the header; the individual shot points are at the end (six lines) :

   H0100 SURVEY AREA ISFJORDEN, SVALBARD
   H0101 SURVEY DETAILS SVALEX-2005
   H0102 VESSEL DETAILS R.V. HAAKON MOSBY
   H0104 STREAMER DETAILS 240 CH GECO NESSIE-3
   H0200 SURVEY DATE AUGUST - SEPTEMBER 2005
   H0201 FILE CREATED 16-Jan-2006
   H0202 FILE VERSION UKOOA P1/1990
   H0300 CLIENT SVALEX-2005
   H0400 GEOPHYSICAL CONTRACTOR UNIVERSITY OF BERGEN, NORWAY
   H0500 POSITIONING CONTRACTOR N/A
   H0600 POSITIONING PROCESSING O.M. UNIVERSITY OF BERGEN, DEPT OF EARTH SCIENCE
   H0700 POSITIONING SYSTEM
   H0700 SURVEY COMPUTER SOFTWARE NAVIPAC, EIVA, DENMARK
   H0700
   H0800 SHOTPOINT POSITION CENTRE OF SOURCE
   H1000 CLOCK TIME UTC
   H0900 OFFSET SHIP SYSTEM TO SP 70.0 M BEHIND
   H1200 SPHEROID AS SURVEYED A,1/F WGS-84 Spheroid 6378137.000 298.2572236
   H1300 SPHEROID AS PLOTTED A,1/F WGS-84 Spheroid 6378137.000 298.2572236
   H1400 GEODETIC DATUM AS SURVEYED WGS-84
   H1500 GEODETIC DATUM AS PLOTTED WGS-84
   H1700 VERTICAL DATUM SL : ECHO SOUNDER
   H1800 PROJECTION 001 UTM NORTHERN HEMISPHERE
   H1900 ZONE 33X NORTHERN HEMISPHERE
   H2000 GRID UNIT 1 METRE
   H2001 HEIGHT UNIT 1 METRE
   H2002 ANGULAR UNITS 1 DEGREES
   H2200 CENTRAL MERIDIAN 15 DEG E
   H2600
   H2600 00011111111112222222222333333333344444444445555555555666666666677777777778
   H2600 78901234567890123456789012345678901234567890123456789012345678901234567890
   H2600 -NAME-><->---<-SP-><---LAT--><--LONG---><--EAST-><-NORTH-><-DEP><D><TIME>-
   SLine34-05             18781022.23N 141348.31E 482384.58677774.7 215.8242180734
   SLine34-05             19781023.47N 141353.32E 482416.98677812.8 214.7242180755
   SLine34-05             20781024.73N 141358.24E 482448.78677851.4 212.3242180816
   SLine34-05             21781026.00N 1414 3.08E 482480.08677890.4 209.6242180837
   SLine34-05             22781027.28N 1414 7.88E 482510.98677929.7 207.6242180858
   SLine34-05             23781028.53N 141412.83E 482543.08677968.1 206.2242180919

UKOOA P1-90 navdata format structure.

The shot point (SP) parameter, for instance, is located from column 20 to 25, as shown below. The two column numbering lines, together with the parameter name line, is an aid in determining the column position of the different parameters. These three "assist" lines are not common - they are only inserted by the software we use to generate UKOOA P1/90 files.

  +--------> Column 20
  |
  |    +---> Colomn 25
  |    |
  222222
  012345
  <-SP->
      18
      19
      20
      21
      22
      23

"OBS" modification of UKOOA P1/90 navdata format

OBS refraction surveys means that source (airguns on ship) and receivers (OBS placed on the bottom, or on land, as an extension of the profile) must maintain a common, accurate - to the nearest millisecond - time base. This is accomplished by special oven-controlled oscillators in the OBS instruments, and GPS locked clocks in land based instruments. On board the ship, the exact time of the shot point is recorded by two time-tagging systems operating in parallel (details provided in table of geophysical equipment above).

The time field in the UKOOA P1/90 format only accommodates seconds without decimals. The format has been modified to permit storage of shot times with six decimal places, of which only the three most significant decimals are used.

An example of modified file:

   H2600 FILE FORMAT MODIFIED TO INCLUDE SHOTPOINT TIME IN COLUMNS [7..19]
   H2600
   H2600 00011111111112222222222333333333344444444445555555555666666666677777777778
   H2600 78901234567890123456789012345678901234567890123456789012345678901234567890
   H2600 <--SP TIME--><-SP-><---LAT--><--LONG---><--EAST-><-NORTH-><-DEP><D><TIME>-
   SSM-1 101921.956000     1632728.92N  74033.97E 732982.37045135.6 171.3297101921 
   SSM-1 102109.690000     2632728.28N  74019.50E 732783.87045101.1 172.4297102109 
   SSM-1 102251.455000     3632728.66N  740 5.07E 732583.57045098.3 176.4297102251 

"EIVA" Survey Computer shot event log files

The format of these shot point log files is as follows:

 Event       Date         Time    Easting    Northing St.d.  Gyro      Dal    Dol      Kp    Object    Data
 -----------------------------------------------------------------------------------------------------------
 000057 2010.06.02 02:51:41.914 0334654.77 07118140.71 00.90 038.1 00000.15 005.14 000.000 "H Mosby f " 3002.22 9449.08 52045.27 "" 01
 000058 2010.06.02 02:52:59.662 0334792.73 07118285.63 00.80 037.7 00200.24 005.27 000.200 "H Mosby f " 3010.88 9448.82 52040.90 "" 01
 000059 2010.06.02 02:54:19.285 0334928.16 07118432.47 00.80 037.6 00399.98 002.25 000.400 "H Mosby f " 3019.18 9449.93 52035.06 "" 01
 000060 2010.06.02 02:55:36.205 0335067.61 07118575.91 00.70 037.9 00600.02 004.48 000.600 "H Mosby f " 3027.67 9451.44 52025.12 "" 01

Parameters are given in first line. Most are self-explanatory, except these:

Gyro

Heading of ship (which could be different from the course the ship is following, due to current or wind direction).

Dal

Distance Along Line. NOTE: This is distance along current line SEGMENT, where new segment start at position of each OBS.

Dol

Distance Off Line (deviation from course line - we have manual steering of vessel).

Kp

Kilometer Post - total distance covered along the line.

Object

Description of Survey Computer navigation data handling. Complete text is not included in log file; it should read "H Mosby filtered", meaning that GPS positions (incl. differential corrections) are subjected to a filtering algorithm (Kalman).

Data

Data values, delineated by "", selected by Eiva Survey Computer operator; in this case Depth (from Simrad EK60 Echo Sounder on board), Gravity and Magnetometer.

The last item in each line ("" 01) can be ignored.

Shot time stamp files

Time values in files generated by University of Bergen time stamp unit is given in UTC.

 $PUIBR,TTT,,02:51:42.7163,5595,7812*00
 $PUIBR,TTT,,02:53:00.4707,3677,7812*00
 $PUIBR,TTT,,02:54:20.0914,714,7812*00
 $PUIBR,TTT,,02:55:37.0041,32,7812*00

Parameters are comma delimited. Record structure mimics NMEA GPS telegram format. Using first line as example, parameters are:

Field #1 - $PUIBR

Telegram header. By convention, "P" stands for "proprietary" (meaning not covered by the standard). "UIB" = University of Bergen.

Field #2 - TTT

Time tag identifier

Field #3 -'''

Empty

Field #4 - 02:51:42.7163

Event time stamp, in UTC. Four fractional digits.

Field #5 - 5595

Internal housekeeping data: Event occurred at this Timer0 interrupt value. Interpolated event time is then the ratio between this number, and the number in field 6.

Field #6 - 7812

Internal housekeeping data: Number of CPU Timer0 interrupts last second. This number should be constant. It indicates the smallest time resolution interval: 1/7811Hz = 128.0 µseconds

MAINTENANCE

1. Replaced 4 ea airgun cables, attached to Port/Starboard junction boxes under deck. Length new cables: 3.5 meter
2. Scheduled maintenance: Replace airgun depth sensor cables, 2 ea, attached to same junction boxes. Length: 3.5 meter.
3. Magnetometer:
   • New slip ring on winch.
   • Added adapter cable used in tow fish.

TECHNICAL ISSUES

Thanks to D. Snartemo for notes regarding Deployment and retrieval of equipment, Magnetometer, Streamer, Torque values.

Deployment and retrieval of equipment

OBS skyting 4 melkespann (hvert melkespann 1200 inch³ ):

• Start ca to timer før profilet starter, bruker ca 2 timer på å sette ut alt utstyr. Unngå looper da utstyret lett henger seg fast i hverandre.
• LMF kompressoren produserer nok luft til 4 melkespann, skyting hver 200 meter, ca 70-80 sekund mellom skuddene. LMF kompressoren produserer 10,4 m³ pr. minutt ved 1 bar. En Junker produserer ca 1,8 m³.
• Hvert melkespann 1200 inch³ = 10,66 liter
• 20 meter lengde på blåse tauene (8 + 12 meter)
• IKKE bruk blylodd på kanonene når 20 meter tau på blåsene nyttes.
• Kanonene nummerert fra 1 til 4 fra styrbord side, (noteres tydelig på hvert juletre)
• Luft til kanonene montert to kanoner på hvert juletre.
• Kanonplassering:
  • Kanon 1 montert på bommen (arbeidswinch)
  • Kanon 2 montert på kran styrbord side
  • Kanon 3 montert på stor kranen
  • Kanon 4 montert på kran babord side.
• Ved utsetting sett ut kanon 2 først deretter kanon 1, så 3, til slutt 4.
• Sett deretter ut ministreamer, (hvis den brukes) til slutt magnetometeret.
• Ved utsetting av ministreamer påse at den ikke henger seg opp i noe av utstyret satt ut tidligere. Hvis mulig er det lurt at en person prøver å styre den i en åpning mellom blåsene.
• Påse at slanger, kabler som ligger over rekken ikke får gnag, bruk filler under slangene, kablene.
• Kanonene finjusteres etter at alle kanonene har startet å skyte, slik at boblene kommer til overflaten samtidig. Justeres ved å trekke inn vaier, eller sleppe ut.
• Be matrosene sjekke at kran wire ikke siger ut under produksjon, sett på brems der det finnes.

Magnetometer

• Husk å sikre med låsebolt etter utsetting av magnetometer.

Streamer

• Ved bruk av streamer (256 kanaler) må streameren settes ut først, deretter kanonene. Enklere å plassere kanonene, to på hver side av streameren.
• Husk å sette på brems og sikre med kjetting fra hull i skinken til fundamentet til streameren. (Kjetting med store sjakler)

Airgun volumes

 1 liter = 1/1000 m3

 1 inch3 = (0.0254 m)3 = 0.000016387064 m3
 1 inch3 = 0.016387064 liter

Some common airgun volume sizes:

  300 inch3 =  4.916 liter
  240 inch3 =  3.933 liter
  136 inch3 =  2.229 liter
   90 inch3 =  1.475 liter
   60 inch3 =  0.983 liter
 1200 inch3 = 19.664 liter    

Airgun: Torque values

Moment på mutter til stempel stang luftkanon:

  1500 kanon  --  475 Nm --  350 feet * lbs
  1900 kanon  --  203 Nm --  150 feet * lbs

Bolter til feste av magnetventil:

  22,6 Nm  --  200 in * lbs

    Nm = Newton meter 
   lbs = pound 
    in = tommer
  feet = fot

Airgun autofire

6 June 2010: This problem was caused by intermittent failure in wire harness running from vessel to airguns. Initially, failure was only present when the guns were firing; it became gradually more regular. Spare harness also had similar fault.

3 June 2010:

The Gun Controller often reports auto-fire in the second airgun, as shown on figure below.

Gun controller (GUNCO) reports auto-fire in the second gun.

The GUNCO timescale only extends to 70-80 ms after Time Break (=zero time). It's not possible to hear any misfires in between the normal shots, which occur approx .every minute. Thus, it was tempting to write off this auto-fire as an electrical interference, and disable auto-fire warning for this particular gun.

After connecting an oscilloscope to the airgun sensor signal line, and letting the GUNCO Scope FTB trigger the scope, the reason for the auto-fire report became clear.

As shown in figures below, there is a signal approx 300 ms after time break, which is not supposed to be there. The erroneous signal could have one or two peaks. It can only be seen when GUNCO reports auto-fire on the affected gun.

Erroneous sensor signal.

Erroneous sensor signal.

For comparison, a normal situation is shown in picture below.

Normal sensor signal.