When I was first approached to write an article on ‘Survey under Extreme Conditions’ I immediately thought of two or three examples of surveys that could easily be termed ‘extreme’; after all it is the extremes that make life interesting. I then sat back and trawled through the memory-banks and soon came up with a long list of events that often highlight a particular, otherwise mundane, survey. It soon became apparent there are two basic types of ‘extreme’ that most often affect surveying offshore: extremes by design and extreme events. Then, of course, there is a third scenario where one compounds the other.

Extremes by Necessity
It is inevitable that some surveys are extreme by design. The data is usually required for good reason and sometimes it is necessary to collect such data under seemingly the most difficult conditions. One such example occurred in an estuary in the north west of England during a pollution dispersion study.
The specification called for a dye-tracing exercise to try and quantify the dispersion and diffusion characteristics of the area of interest at mid-water, on a spring flood tide. At this state of tide a tidal bore passed through the area. The dye was to be deployed immediately prior to arrival of the bore. The usual period of observation for this type of survey is up to seven hours, or until the dye is to diffuse to detect. In this case the dye was deployed as required with just enough time to get the dye patch dimensions before turning the vessel’s head into the approaching bore. After the bore had passed through, the dye took off at about 5 knots, with us in hot pursuit. Two bends later, the river widened and the dye patch spread across the entire river and was lost. The whole exercise took eight and a half minutes. We had, however managed to measure the extremities of the patch as it travelled through the area and the exercise was deemed a success.

Extreme Events
Extreme events can fall into two basic categories, environmental and human. Environmental extremes are generally weather-related and may occur on any survey. Today’s commercial pressures lead to working up to the limit of the weather as common practice. This means that recovery of towed equipment is often undertaken in less than ideal conditions. If four gun arrays and three kilometres of cable need to be recovered, the back deck can become an uncomfortable place.
Some surveys are conducted in areas where extreme events are an almost daily occurrence. Sand Banks in the Outer Bristol Channel can provide a challenging environment. In one contract the client required swathe coverage of the survey area with a depth range from drying to 20 metres. There was the whole gamut of environmental conditions to contend with, a 12m spring tide, 4-knot currents and exposure to weather from almost every quarter. Even on calm days a long oceanic swell can rear up on top of the bank, making life exciting for the helmsman already fighting to keep the vessel online with very little way due to the following current.
For all people working offshore, one of the most important traits necessary for sanity, if not survival, is diplomacy. Work in remote or unfamiliar locations it is often necessary for us to employ this least-talked-about of the surveyor’s traits. Sensitivity to other people’s customs and beliefs is essential, as we may find ourselves not only working and living with local people but reliant upon them and their knowledge of the environment to ensure timely and safe execution of the survey. Sometimes events can overtake you; twice I have had flight plans delayed by weeks due to riots and unrest and only luck as prevented me from being caught in the middle.
The vast majority of the time these more remote locations make for the most interesting and enjoyable jobs. Just occasionally events can take an unexpected and unnerving twist. On arrival at a safe anchorage in the Niger Delta a small boat was seen leaving the beach and heading for our vessel: Marine Security, the mate informed us. The Captain, having experience of this particular group of uniformed gentlemen, sent me to my cabin. On boarding our vessel the men proceeded to try and extract money with menaces and upon failing to intimidate the Captain threatened to kill one of the crew. He fortunately suffered only minor facial injuries from the marline-spike aimed at his eye. This was an extreme event and, having worked in West Africa on many jobs, the only truly threatening situation I have experienced.

Extremely Tired
Most extremes can be managed with careful planning but problems are always exacerbated by tired minds. The following problem was encountered whilst serving as a navigator on a deep seismic vessel. A single line was to be run west to east across a north-south-orientated sandbank, shoaling to 4m below Chart Datum. At high water springs we had around 4m of tide, giving 8m of water on the bank. We were towing 3.6km of cable running at 6m. To compound the problem there was a navigation buoy 300m to the south and 500m beyond the end of the line and at high water the current would still be running south. Thus we needed to begin turning to starboard to come down-tide of the buoy as soon as the line was complete.
Timing was everything. Perfect conditions were required to clear the bank, High Water and no swell. The opportunity arrived and on crossing the bank the observed water depth was within 0.1m of the predicted. Everyone in the instrument room was extremely relieved; it was half an hour before the end of a 12-hour shift, 28 days into a 30-day trip. We were looking forward to going home. The call came from the bridge “What about the buoy?” Too late! We had all forgotten. I arrived on the bridge about fifteen seconds later, in time to see the buoy on the starboard quarter. By turning to port as hard as we dared we managed to clear the buoy with all but the back section of cable. Needless to say, the drinks were on me.

Extremely Normal
While writing this article I was conducting a swathe survey in very shallow water on top of a sandbank off the east coast of England. More strong currents, drying sandbanks, interesting swell conditions – just another day in the office. That is the point: Hydrographic Surveying is Survey under Extreme Conditions. We are trying to measure something from a platform that is heaving, pitching and rolling, whilst being pushed and pulled by wind and tide. It is testament to the equipment manufacturers that we are provided with tools that allow us to fulfil this requirement with ever-increasing degrees of accuracy. Every time we put equipment onto a boat and head out to sea we are entering into an extreme environment. Anything can happen, and quite often does. That is the appeal of Hydrographic Surveying; tomorrow will always bring different problems and new challenges. It is never just another day in the office.