Aug 24 - Rosemary Bank
Date: Sunday 24th August 2003
Position at 1200 BST: 59°14'N 010°04'W Rosemary Bank - about 290Nm from Glasgow
Wind: ESE x Force 2
Barometric pressure: 1019.0
Sea state: Slight
Air temperature: 15.3°C
Sea temperature: 14.3°C
The picture below is of the James Clark Ross passing Cobh, on our way out to sea, following our departure from Cork on Saturday 16th August. I had hoped to include it in last weeks page, but only received it after the page was published. Thanks to Tony Mulcahy for taking it. Click the image for a larger version.
The vessel returned to Cobh on Monday morning to disembark two service engineers, and then steamed around the west coast of Ireland and headed north for Rosemary Bank. The journey around the Irish coast was enjoyable with some lovely views, and the ship passed within a few miles of the Fastnet Lighthouse (the famous Fastnet Yacht Race had been taking place whilst we were on passage to Cork).
One of the requests for the trials cruise was bad weather! As always, the Officers and Crew on the James Clark Ross are always keen to be as helpful as possible, and so the following entries are taken from the Ship's Logbook:
Wednesday 20th August 2003
0800 Hrs Slight sea and low swell. Wind W x S Force 4.
1600 Hrs Vessel rolling and pitching gently to Moderate/Rough sea and long deep swell. Wind WSW Force 5/6
Thursday 21st August 2003
0000 Hrs Rough sea and increasing swell. Wind S x W Force
7 to 8
2000 Hrs Pitching heavily to rough sea and large swell. Shipping frequent spray and occasional green water forward. Wind WSW Force 9
Above: Shipping water forward! Click the image for a larger version.
Friday 22nd August 2003
2000 Hrs Vessel pitching easily to slight sea and moderate swell. Wind W'ly force 3.
Swath survey of Rosemary Bank by Carol Pudsey, Principal Scientific Officer.
This cruise is intended to test and calibrate equipment and provide training for new BAS staff, but we have taken the opportunity to map an interesting seamount in the NE Atlantic. Rosemary Bank was discovered during a survey in 1929-30 aimed at finding new fishing grounds west of Scotland. The survey vessel was HMS Rosemary. The Admiralty charts of this area show a 1000m and a 500 m contour with additional soundings (fig. 1). Over the last five days we have surveyed most of the bank and its surrounding moat, and are presently filling in the area of the top.
Above: Fig 1 Part of the chart of Rosemary Bank. The blue box is the area enlarged in the perspective view below. Click to enlarge.
Rosemary Bank is a large extinct volcano: a pile of basalt erupted some 70 million years ago during the early phases of opening of the North Atlantic Ocean. Similar but smaller volcanoes were active in the Hebrides a few million years later, and some of the classic features seen today on the islands of Mull and Skye can also be imaged here on the seabed (fig 2). For example, Rosemary Bank has steep sides bearing the concave scars of large landslides, and some fallen blocks are visible at the foot of the slope (similar to the Quiraing area of Skye). The top is relatively flat with terraces tens of metres high, just like the trap lavas in northern and western Mull. Scattered over the top of the bank are small volcanic cones, probably representing the last stages of volcanic activity.
Above: Fig. 2. Perspective view of the southwest corner of Rosemary Bank. The deepest part of the moat (purple) is 2200 m deep and the red area lies at about 1200 m. Click to enlarge.
Rosemary Bank is also of interest because it forms a large obstacle to the flow of deep-ocean currents. The moat at its base and the mounds of sediment around it indicate the action of strong bottom currents over the last few million years, particularly southward flow along the west side of the bank.
Above: Peter Morris, from BAS, monitoring data received from the swath bathymetry system. Click to enlarge.
Whilst all this science work is being carried out, the ship's staff continue with the day to day operations onboard, along with 'odd jobs' as and when required. Colin Smith, the 2nd Engineer, is currently busy constructing a propane storage cabinet in the engineers workshop.
Above:Colin, armed and dangerous!! Click to enlarge.
Wind - An explanation of the term 'Force' as used in our weekly updates.
Wind force is expressed numerically on a scale from 0 to 12. This scale, which originally defined the wind force in terms of canvas carried by a frigate, was devised by Captain, afterwards, Admiral Sir Francis Beaufort in the year 1806 for use in vessels of the Royal Navy. Since his time, however, so many changes have taken place in the build, rig and tonnage of seagoing vessels that in 1874 Beaufort's scale was adapted to the full-rigged ship with double topsails of that period. With the passing of sail, this specification meant very little to those who had no experience in square-rigged ships, and the practice rose of judging wind force from the state of the sea surface. In 1939 the International Meteorological Organization agreed to the use of a sea criterion by which wind force was judged from the appearance of the sea surface, and was brought into use in 1941. The specification is shown in the table below:
The Beaufort Scale
|0||0||Calm||Sea like mirror|
|1||02||Light air||Ripples with the appearance of scales are formed but without foam crests.|
|2||05||Light breeze||Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break.|
|3||09||Gentle breeze||Large wavelets. Crests begin to break. Foam of glassy appearance, perhaps scattered white horses.|
|4||13||Moderate breeze||Small waves, becoming longer; Fairly frequent white horses.|
|5||19||Fresh breeze||Moderate waves, taking a more pronounced long form; many white horses are formed (chance of some spray).|
|6||24||Strong breeze||Large waves begin to form; the white foam crests are more extensive everywhere (probably some spray).|
|7||30||Near gale||Sea heaps up and white foam breaking waves begins to be blown in streaks along the direction of the wind.|
|8||37||Gale||Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks.|
|9||44||Strong gale||High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.|
|10||52||Storm||Very high waves with long overhanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The tumbling of the sea becomes heavy and shocklike. Visibility affected.|
|11||60||Violent storm||Exceptionally high waves. (Small and medium sized ships might be for a long time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.|
|12||64 and over||Hurricane||The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.|
The above information is taken courtesy of the Marine Observer's Handbook.
Intentions: The trials should be completed in the early hours of Monday morning, when the ship will head for Immingham, via the Pentland Firth, and should be tied up on Wednesday morning.
The vessel will then prepare for the Antarctic season, loading cargo and stores.
A crew handover will commence on September 8th and the ship is due to sail on September 10th, bound initially for the Falkland Islands.
This weeks page will be the last page until the vessel has sailed, and then the 2003/4 Antarctic season diary should begin.