NOAA Teacher at Sea: Caroline Singler
Ship: USCGC Healy
Mission: Extended Continental Shelf Survey
Geographical area of cruise: Beaufort Sea in the Arctic Ocean
Date of Post: 13 August 2010
Maneuvering in Ice – 7-10 August 2010
Date: 11 August 2010
Latitude: 71º 23.2’ N
Ship Speed: 9.7 knots
Air Temperature: 5.1ºC /41.2ºF
Barometric Pressure: 1010.6 millibars
Winds: 30.6 knots ENE
Sea Temperature: 4.8ºC
Water Depth:2952.9 mDate: 12 August 2010
Time of Day: 1900 (7:00 local time); 02:00 UTC
Latitude: 71º 10.94’ N
Longitude: 144º 40.28’ W
Ship Speed: 11.9 knots
Heading: 265.3º (WSW)
Air Temperature: 6.73ºC /44.12ºF
Barometric Pressure: 1016.7 millibars
Winds: 18.8 knots ESE Wind Chill: 3.96ºC /39.12ºF
Sea Temperature: 6.0ºC Salinity: 24.32 PSU
Water Depth:2496.0 mScience and Technology Log
I want to give you a sense of how ice can affect the progress of the ship. It was not something that I could imagine before coming on the Healy. When we first encountered ice, I was captivated by its beauty – it is a wilderness of an entirely different sort than I have ever experienced. I knew the ice would slow our progress, and I knew from talking to the scientists that it could complicate the mapping with the multibeam system. I did not realize all the ways in which it would challenge everyone involved in the mission, for example:
- the chief scientist and the rest of the science team have to decide how to alter the ship’s track without sacrificing the mission objectives;
- the ice analysts use satellite imagery and ice buoy data and try to predict where the ice may be and advise the Chief Scientist and the ship’s crew regarding possible changes in course;
- the Coast Guard officers and crew who try to keep us as close to our planned course as possible, keeping in constant communication with the Chief Scientist and with the watch standers in the geophysics lab to be sure that we are able to collect good data;
- the computer specialists have to figure out how to get the best ultibeam data, even when ice clogs the seawater intake that provides data for the sound speed profile and when sound beams transmitted from the surface bounce in all directions and cannot find bottom;
- geophysics watch standers like me have to watch for tiny clues from the instruments that the ice might be interfering with the transmission of the sound signals and the acquisition of reliable data.
Everything about working in the Arctic is a lesson in patience and flexibility; one must learn to “go with the floe”.
Since our primary objective is to collect bathymetric data, the locations of transect lines were determined before the mission to best meet the objective. Some lines provide data about previously unmapped areas; others fill in gaps between existing data tracks. We are able to follow the plan when we are in open water, but once we are in the ice, sometimes plans change. This became immediately apparent when I went on watch on the night of 7 August. We were heading north in the Beaufort Sea into thicker ice. There was a flurry of activity in the geophysics computer lab. The scientists were studying the ship’s track and the latest satellite images of the ice. We were on course to encounter some very large floes. I was about to get my first real taste of what an ice breaker does.
An ice breaker is designed differently from other ships. It is double-hulled with extra thick steel at the bow, stern and water line. It has a flat hull with a rounded bow that slopes gradually upward to allow it to ride up over the ice. (I am told that same feature makes it roll considerably in rough seas, though thankfully the Healy’s design is somewhat modified from the earlier Coast Guard ice breakers, so it does not roll as much as it could!) There are numerous mechanical modifications that allow ice breakers to work in an environment that would crush other ships. (See Cool Antarctica for a good summary of the characteristics of ice breakers.) The ship weighs over 11 tons, and the basic principle of ice breaking is to ride up over the ice and allow gravity to do the work, using the ship’s weight to fracture the ice. Healy’s typical cruising speed is 12 knots, with a maximum of 17 knots; depending on ice conditions, Healy’s speed typically decreases to 7 knots, and it is often necessary to go even slower through large floes, particularly if the multibeam is not recording good data. In the thickest ice, the ship uses a technique called “backing and ramming” which is pretty much exactly as it sounds – the ship is driven on the ice, then backed up and driven back onto the ice again. But while Healy is a powerful ship, a large tabular floe of multiyear ice has a lot of inertia, and it takes an incredible force to move it. More often than not, it is a better idea to try to find a way around the large floes instead of breaking through them.
Things got tricky after that. Notice the change in scale on the second map, which shows the ship’s progress over the next 3 hours until point “11” at 4:00 a.m. (12:00 UTC) on the 8th. In that time, we covered 15.48 nm and had to deviate off a straight line course and change direction several times to maneuver around ice. Our average speed continued to be about 5 knots, but there were times during that stretch when the speed was a low as 1 or 2 knots. Relative to the original planned straight line course, the distance covered in that period was 6.7 nm.
Map 3 shows the remaining course we followed for that transect (the right hand track line) – note again the different map scale. We covered the remaining distance along the line between points 11 and 12, about 91 nm, over the next 3 hours. The trackline on the left shows our subsequent course, about a day later.
It takes a special ship to do what Healy does, and it takes a crew and science team who are capable, flexible, and cooperative to get the job done.
Tomorrow, it seems, is Saturday. It is extremely hard to keep track of the days at sea, especially when there is not much darkness at night. Saturday is cleaning day, so we have to make sure everything is “ship-shape” in our staterooms and the science work areas. Stay tuned for some photos of my room after it’s neat and tidy!
Did you know?
Distance at sea is typically measured in nautical miles. One nautical mile is equal to approximately 1.15 statute miles or 1.85 kilometers. Speeds are measured in knots. One knot is equal to 1 nautical mile per hour or 1.15 miles per hour.