Retrieved Field Log No. 2
Uneven Tides
NORTH ATLANTIC COASTAL SURVEY
FIELD LOG
Primary subject: Coastal soundings, tidal variation and chart verification
Observer: Captain Femke Ashcroft
12 September
Anchored north-east of Blackglass Head at 16:40.
Barometer steady.
Wind west-north-west, moderate.
Charted depth at present position: 96 fathoms.
First sounding: 94.
Second: 95.
Difference acceptable given drift.
Tide predicted to begin falling at 17:12.
Observed change in waterline at 17:26.
Fourteen-minute delay.
No significance attached.
13 September
Survey commenced at 06:10.
Three sounding stations completed before noon.
Depths broadly consistent with Admiralty chart.
Station C produced an anomalous reading of 61 fathoms where 88 are charted.
Repeated twice.
62 fathoms.
61½ fathoms.
Moved vessel approximately 400 yards east.
Sounding: 87 fathoms.
Returned as closely as possible to Station C.
Sounding: 63 fathoms.
Possible submerged ridge absent from chart.
Marked for further examination.
14 September
Returned to Station C at high water.
Depth: 84 fathoms.
This is inconsistent with yesterday’s readings.
Expected tidal variation insufficient to explain difference.
Lead returned without sand, shell, gravel or mud.
Only clear water on line.
Repeated sounding using heavier lead.
83 fathoms.
No bottom sample.
Position checked against headland bearings.
Correct within reasonable tolerance.
15 September
Low tide observed thirty-one minutes later than prediction.
Height also greater than expected.
Crew reports stronger current around northern side of Blackglass Head.
Station C:
First sounding: 67 fathoms.
Second: 66.
Third: 67.
Lead again returned clean.
Transferred a small amount of tallow to base before fourth cast.
No material adhered.
If this is seabed, composition remains unknown.
16 September
Extended survey westward.
Normal depths for first five stations.
At 10:42 recorded sudden reduction from 103 fathoms to 72 over less than half a nautical mile.
No corresponding feature on chart.
Changed course south.
Depth increased gradually to 98.
Changed course north.
Depth decreased again.
Possibility of elongated submerged bank.
Shape unusual.
Estimated width presently impossible to determine.
17 September
Mapped approximate limits of shallow region.
Results unsatisfactory.
Northern edge appears farther north than yesterday.
Western edge cannot be fixed.
Measurements suggest feature extends at least 1.7 nautical miles.
No bottom samples recovered from any sounding made within the shallow area.
Outside it, lead returns expected grey mud.
Inside it, nothing.
Chief mate suggested current may be holding line above bottom.
Tested with increased weight.
No difference.
18 September
Tide behaved irregularly throughout morning.
Water fell steadily until 08:20, rose approximately eighteen centimetres over seven minutes, then resumed falling.
No wind shift sufficient to explain this.
No visible swell.
Barometer unchanged.
At 09:05 vessel listed slightly to starboard for approximately ten seconds.
No corresponding wave observed.
Sounding at time of list: 59 fathoms.
Charted depth: 101.
19 September
Requested repeated tidal readings every fifteen minutes.
Unusual rise observed again at 07:46.
Duration approximately nine minutes.
Shallow region now appears closer to Blackglass Head.
Yesterday’s western survey markers no longer correspond.
There is an increasing temptation to describe the feature as mobile.
I will not do so without stronger evidence.
20 September
Soundings begun before dawn.
Station C: 79 fathoms.
Station D: 74.
Station E: 71.
Station F: 69.
Station G: 72.
Pattern forms a broad curve.
If charted as a bank, its highest point lies approximately midway between C and G.
No bottom material recovered.
At 06:58 line at Station F tightened sharply after lead had stopped descending.
Assumed snag.
Line released itself after approximately twelve seconds.
Lead returned.
Surface scratched.
No marine growth attached.
21 September
Examined lead from yesterday.
Scratches are parallel.
Three grooves.
Each approximately six centimetres long.
Could have contacted rock.
No fragments embedded.
Surveyed same position.
Depth: 91 fathoms.
No snag.
The shallowest portion of the feature appears to have shifted south-east.
I am recording this statement because measurements require it.
I am not proposing an explanation.
22 September
Fog from 04:30 until after midday.
Suspended near-shore work.
Soundings taken at anchor.
06:00 — 78 fathoms
07:00 — 75
08:00 — 72
09:00 — 68
10:00 — 71
11:00 — 76
12:00 — 82
Tidal cycle does not account for this pattern.
The vessel remained at anchor throughout.
Anchor line showed no evidence of dragging.
At 09:12 all loose objects on deck shifted approximately two inches toward port.
No wave observed.
23 September
Fog cleared.
No shallow feature found at yesterday’s position.
Charted depth restored: 104 fathoms.
Surveyed outward in expanding circles.
At 13:17 found reduced depth 1.3 nautical miles east.
Sounding: 64 fathoms.
Second: 64.
Third: 63.
It is no longer useful to describe this as an uncharted bank.
Banks do not relocate between observations.
24 September
Crew increasingly attentive to sounding operations.
Ordered normal duties maintained.
No discussion of causes during survey hours.
At 07:30 observed unusual smoothness of sea approximately half a mile off port bow.
Wind force four.
Surrounding surface broken by small waves.
Smooth area nearly circular.
Estimated diameter 250–300 yards.
Changed heading to approach.
Smooth area diminished before arrival.
Sounding taken at approximate centre: 52 fathoms.
Charted depth: 112.
25 September
Repeated yesterday’s route.
No surface anomaly.
Depth at same position: 110 fathoms.
At 11:08 lookout reported dark shape below surface off starboard quarter.
I observed no defined shape.
Water appeared darker over an area perhaps thirty yards across.
Could be shadow from cloud, though sky was mostly clear.
Sounding cast immediately.
Line stopped at 41 fathoms.
Held steady for approximately five seconds.
Then descended further.
Final depth: 109 fathoms.
No bottom sample.
26 September
Examined all records from 13 September onward.
Reduced-depth measurements do not form a stationary feature.
They form a sequence.
Approximate movement averages between one and three nautical miles per day.
Direction inconsistent.
Most positions remain within ten miles of Blackglass Head.
Tidal anomalies occur when the reduced-depth area passes nearest the vessel.
This correlation may be coincidental.
27 September
At 05:52 water around vessel rose without corresponding swell.
Increase at hull approximately twenty-seven centimetres.
Duration less than one minute.
Vessel lifted evenly.
Anchor chain remained taut.
Immediately afterwards, strong current set northward for approximately ninety seconds.
Sounding cast at 05:55.
34 fathoms.
Repeated.
35.
Charted depth: 97.
No one on deck spoke during second sounding.
28 September
Moved vessel six nautical miles south before beginning work.
Purpose: verify whether anomalies are confined to Blackglass Head.
Soundings normal until 14:10.
At that time recorded 48 fathoms where chart gives 121.
Repeated twice.
49.
50.
Shallow region therefore not confined to original survey area.
At 14:18 surface behind vessel became unusually smooth.
No further work conducted.
Changed course south-west.
29 September
Maintained distance from reduced-depth readings.
Surveyed coastline only.
Tides normal.
No unusual current.
No unexplained listing.
The sea remained ordinary all day.
This was unexpectedly reassuring.
30 September
Returned north for final verification before departure.
Station C reached at 08:35.
Depth: 96 fathoms.
Matches chart.
Station D: 101.
Station E: 98.
All normal.
At 10:12 lookout reported smooth water approximately one nautical mile north-east.
Did not alter course.
At 10:27 the smooth area had closed to approximately half a mile without obvious change in our position.
Engine speed constant.
Current weak.
Ordered sounding.
Line stopped at 29 fathoms.
The lead remained there.
No slack.
No further descent.
After approximately twenty seconds, line began moving horizontally to the north-east.
Not drifting.
Moving.
Ordered line cut.
1 October
Departed Blackglass Head at first light.
No further soundings taken.
Tide tables for the previous nineteen days have been checked against observations.
The tables are not in error.
Charts are not in error.
Our instruments are not in error.
I can offer no satisfactory account of what we measured.
One final note:
At 06:40, with Blackglass Head nearly lost astern, the lookout reported a broad patch of smooth water approximately three miles behind us.
It remained visible until fog closed over the sea.
Retrieved for the Shelves.
