Fieldwork was undertaken between January 11th and March 20th 1999. The summaries of the daily data records for this period are detailed in the appendices. The relocation of devices was undertaken over a continuos period of time on each field trial excursion. Consequently, wind speed and sea state on many trialing days fluctuated markedly. In order to conduct a comprehensive matrix of relocations under comparable conditions, it is preferable for the prevailing environmental conditions to remain constant. Although the fieldwork was conducted over a two-month period, the trialing conditions did not frequently provide protracted periods of stable conditions. Inevitably, not all devices have been trialed under the full range of conditions. This was particularly the case with light intensity.
Deployment method A was used on four days and proved useful in providing initial relocation distances. The first device to be sighted on any approach drew the observer's attention immediately towards adjacent devices, thus giving a false impression of the relocation distances of other devices. Additionally they do not simulate the relocation of devices under real search conditions. The random deployments conducted on four days produced a more diverse range of relocations. In some instances, observers would unknowingly mark an approximate deployment position upon relocation of a device if a prominent landmark formed an obvious transit to it. These position fixes proved to be of little assistance however when additional relocations were undertaken on reciprocal headings or other tangents to the same device. Deployment method C was used on twelve occasions and provided the largest number of relocations. Though observers witnessed the deployment of devices whilst using this method, relocations proved difficult in many instances. The search vessels used a variety of headings and observers could not readily estimate deployment positions due to the open expanse of the deployment area. Method D was used on the last two days of trialing. These relocation distances allow more direct comparisons between devices as relocation headings were standardised for each device. The deployment and relocation of devices were plotted for most trial days and correlated with search aspect and wind direction. Figure 1 shows a typical example of these plots. These plots were used to ascertain any differences in relocation distances with change in search aspect.
A wide range of environmental conditions was experienced during the course of the research. Sea states ranged from calm to rough, with waves occasionally higher than 1.5 m. Cloud cover ranged from clear to overcast, with overcast predominating. Visibility ranged from less than 2 nm to more than 10 nm, though typically this was between 6 and 10 nm. During the period of the field trials, relocations were conducted between 10:00 hours and 19:00 hours with the typical daylight hours changing with increasing day length. Devices were relocated under a rage of light intensities from 1.4 to 175,000 lux. Daytime light intensities typically ranged from 5,500 to 175,000 lux. Light intensities of less than 175 lux typically represent failing light towards darkness. An intermediate light intensity is covered between 175-4,500 lux, and intensities greater than 4,500 lux were typical of dull, overcast days through to clear and bright days. As a guide to the dynamic range of light intensity, a bright sunny day may be 100,000 lux, office lights, 1000 lux; and a full moon 0.1 lux . The period of time for falling light intensities following normal daylight hours was relatively short during the trial period. Light intensities during the afternoon of 19th January are clearly demonstrated in Table 2.
Table 2 Light intensity with time, 19th January 1999
Light Intensity (lux)
The two values reresent the first and the last observer to relocate the device.
Distances in meters
Date: 10th March 1999
Wind direction: SSE
Wave height: 0.5-0.7m
Broken cloud with sunny spells
Visibility:10 miles plus
The range of sea states experienced during the course of the research ranged from less than 0.5 to 2.0 metres. Sea waves in excess of 1.5 m were experienced only on brief occasions. Whilst wave height increased with wind speed there was often a delay in the period of time required to manifest the corresponding wave height. Similarly, this delay was also experienced with decreasing wind speeds. It is therefore not possible to classify broad divisions of sea sate with any given range of wind speed in the first instance. For the purposes of summarising data, relocation distances were collated and grouped into wave height classes of less than 0.5 m, 0.5 to 0.9 m and greater than or equal to 1.0 m.
Data was also grouped into three broad divisions of light intensity. These were selected at less than 175 lux, 175 to 4,500 lux and greater than 4,500 lux. These divisions approximate to darkness, intermediate and daylight. Relocation distances of each device falling into the appropriate matrix of wave height, light intensity and observation platform, were extracted from all the daily data records, collated and averaged. These summaries are detailed in tables 3 to 17 and represent a total of 481 individual relocations.
Tables 3 to 17 Collated relocation distances (meters) of devices from (a) hard boat and (b) inflatable
Orange / Red Flag
AP Red Decompression Bag
AP Red Decompression Sausage
Bowstone Red Decompression Sausage
Bowstone Yellow Decompression Sausage
Pink and Yellow Buoy
2 Red Buoys
Torches observed from hard boat only
Jotrun Strobe on Flag
Pyrotechnics observed from Hard Boat only
| 35-40 mph
wave ht 1.0m
| 5-8 mph
wave ht <0.5m
| 5 mph
wave ht <0.5m
white smoke only
|Not detected at 8962
The relocation of devices from inflatable and hard boat ranged from not detected in some instances to more than 9 km. Flags and buoys typically afforded location distances of up to 3 km whilst pyrotechnics, torches and strobes were observed at distances generally in excess of this. The ranges of relocation distances from both observation platforms have been extracted from the summary tables and are shown in table 18 below.
Table 18 Typical ranges of relocation distances from inflatable and hard boat
|Strobe on flag
The folding flags were visible at significant distances. This was particularly the case for the day-glow yellow pennant that was consistently located at distances in excess of 2 km and at a maximum of 3 km. Under all conditions and for all observers, this colour proved to be the most noticeable passive relocation device. This colour was the most readily observed in all sea states, including periods of breaking wave crests. Equally, it was the colour that was located in deteriorating light intensities when it was not possible to locate pennants of any other colour. This colour was most pronounced and was never confused with numerous buoys in the area. It was noted that this pennant collected dirt and the brightness of the colour became slightly faded during the course of trialing. This did not appear to have an observable effect on the relocation potential.
Most observers found orange or red pennants were the next favourable colour after yellow. Two observers suffered from degrees of red-green colour blindness and had difficulties in relocating these colours. Occasionally these observers only located the flags at a few hundred metres. The movement of the pole or the merest flutter of the pennant often drew their attention to the flags position. Towards the upper extent of the location distances for flags of this colour, they were occasionally confused with red and orange fishing buoys that were present within the trialing area. This problem was not experienced with the bright yellow flag, as buoys of this colour are not frequently encountered in the marine environment. Red and orange flags were also more difficult to locate under intermediate light intensities than the yellow flag. The black pennant was located better than expected and was observed well in dull and overcast conditions. The A-flag was the weakest in all conditions. During periods of breaking waves, the location of this flag was extremely difficult and the white pole was frequently sighted before the pennant. The location of the folding flags was largely facilitated through their elevation above waves and in some instances when there was movement of the flagpole and pennant as a consequence of wave motion and wind speed. Relocation distances of flags were maximised when headings were made at aspects close to or approaching abeam to the wind direction. These aspects presented the greatest visible surface area of the pennant to the observers. Location of flags was more difficult when the search heading was into or against the wind direction.
4.4.2 Decompression Devices
The location distances of these four devices were very similar, providing location distances up to 1 km. The AP valves decompression bag had a slight advantage other devices. This inflatable bag was a day-glow orange/red colour and was noticeably brighter than the AP Valves and Bowstone red decompression sausages. On many occasions observers noted that this device was more prominent than the two red buoys. It was however difficult to make a positive identification on this device until much closer than the initial sighting. At distance, the device resembled a single red buoy, typical of fishing buoys.
The decompression sausages produced similar average location distances. Several observers found that the AP Valves sausage was located more easily than the Bowstone sausage. This was most likely a result of the slightly larger diameter and height. Most observers found the yellow sausage difficult to locate though the relocation distances for this device are not significantly lower than related devices.
The paired red buoys were much better to relocate than single buoys. The separation distance between buoys facilitated their relocation in areas where numerous similar coloured and sized fishing buoys were deployed. It was noticed that the separation distance between buoys permitted an independent movement of each under increasing wave heights. The buoys movement produced a yo-yo effect in these conditions, thus there was a more continuous period of time that buoys were visible to the observers. The separation distance of the two buoys varied between one and two metres. It was noted that location of the buoys was facilitated in most circumstances at the greater separation distance. The combination of two bright red buoys was marginally better than the combination of a large pink and yellow buoy overall (tables 11 and 12). The pink and yellow buoys did afford a slightly enhanced location range under calm conditions.
The diving torches produced very bright beams and were clearly located during daylight at distances in excess of 4 km increasing to 9 km in darkness. It was apparent that location was restricted when the person activating the torch pointed it towards the search vessel. Location was enhanced when the torch beam was directed towards the general position of the search vessel and moved slowly but steadily in a scanning motion (horizontally and vertically) to produce a much wider detection sector.
Strobes were only deployed attached to folding flags. Initially the strobes were attached just below the pennant, but this was found to produce intermittent flashes. This was believed to be the result of motion on the flagpole in waves, and the pole itself obscuring the lens of the strobe. Subsequently, strobes were attached to the top of the poles with the lens clear of the pole. Strobes were not observed at light intensities above 175 lux. The Jotrun strobe was observed at distances up to 4 km at light intensities lower than this. Typically, this strobe was located at an average of 2 km. The Jotrun strobe was found to be more effective than the Seeman Sub strobe, generating a much brighter and regular flash. On one occasion the Seeman Sub strobe was observed at 2 km and on two relocations at 1 km and 1.3 km.
A limited number of trials were conducted with the range of pyrotechnics. Prior arrangements with the Coastguard were required before testing these devices and the period of time for their activation was kept to a minimum. The hard boat retreated a considerable distance from the deployment position and observers viewed in the general direction of the deployment position. The observation vessel then retreated to more distant positions for subsequent deployments. The orange smoke from the day/night distress signal had a burn time of 20 seconds. This produced a smoke cloud that appeared dense at 4 km and lingered for approximately 90 seconds. As the distance was increased to 8.5 km, the smoke remained visible but appeared less dense and had a much lower profile. Wind speed on this occasion was less than 10 mph. The night flare on the day/night distress signal produced a dense white smoke in daylight that was also visible at 8.5 km. The location distance of the night flare in darkness was not established. Miniflares had burn times of 10 seconds and were estimated to achieve a height in excess of 100 m. These were observed up to 8.5 km in daylight but they appeared much brighter at distances less than 6 km. In darkness the Miniflares were very easily located at over 9 km.
It was noted that cold hands hampered the activation of the pyrotechnics. Several researches commented that they would be uncertain as to how practicably these devices would be operated by a diver wearing gloves with cold hands.
The simulated divers head was only observed at relatively short distances (up to 230 m). It was generally agreed that this device, whilst simulating a diver who was heavy in the water, did not realistically mimic the aspect that most divers would be able to maintain at the surface. A diver wearing full scuba equipment was deployed and located by inflatable and hard boat. Approaches were made towards the diver and repeated with the diver raising one arm. The location distances of the diver from both observation vessels were comparable in both instances and were doubled to more than 600 m through the diver raising one arm (see Table 17a and 17b).
4.4.8 Recovery Vessels
The location distance of hard boat and inflatable by an in-water diver was ascertained by deploying a diver on a shotline at a fixed position. The vessels moved away from the diver and the position noted when the vessel was beyond visual sight of the diver. During daylight and with a wave height of 0.5 to 0.75 m, the diver lost sight of the inflatable at 1333 m and the hard boat at 4397 m (see appendix Table 11). These distances are far greater than those for the relocation of a diver from these platforms. This demonstrates that an in-water diver without a supplementary location aid will be able to see a recovery vessel some time before the vessel is close enough to locate them.
4.4.9 Aerial Relocations
The search undertaken on 2nd February failed to locate several devices. Devices that were sighted included the Dyechem sea marker dye and the yellow flag. The marker dye produced a very concentrated plume of dye upon activation. It was noted that the dye release remained consistent for approximately two hours. Four hours after deployment the release of dye was significantly reduced. Location distances of these devices were increased at an increased search altitude. The search undertaken on the 3rd February was under marginal conditions. It is highly likely that diving operations would not normally take place under these conditions. However, weather and sea conditions may deteriorate very quickly during the course of normal diving operations and they therefore provide realistic search conditions. The devices that were located included the marker dye, yellow flag and A flag. The relocation distances of the yellow flag and dye were significantly reduced under these conditions compared with the previous search. The results of these helicopter searches are detailed in the appendices.
4.4.10 Search Exercise
The devices deployed for the search exercise and their relative location distances are shown in table 19 below.
Table 19 Relocation distances of devices deployed for search exercise
Device Lifeboat Helicopter Yellow flag (1) 1226 m Not detected Yellow flag (2) 1800 m 892 m Red flag 827 m 1901 m A flag Not in sector 396 m 2 Red buoys 482 m 898 m Decompression bag Not in sector 48 m Decompression sausage Not in sector 169 m Diver (simulated) < 50 m Not detected Marker Dye (Sea Streak) 50 m Not detected
The marker dye was activated 30 minutes prior to the commencement of the search. The simulated diver used for this exercise was a 25 litre barrel attached with a buoy covered with divers black hood and mask, and a buoyancy device. The barrel was ballasted with water to simulate the form and size of an on-surface diver with no additional location aids.
The initial search headings of the lifeboats were from West to East. The Stromness lifeboat located all devices deployed within their designated sector. Additionally, the Stromness lifeboat located three devices that had been deployed in the adjacent search area. The yellow flags provided the greatest location distances and were typical of the average distance derived for these devices under comparable environmental conditions from the hard boat observations. The relocation distance of the red flag was also typical to those relocations made from the hard boat. The diver was only located a few metres directly ahead of the lifeboat and lifeboat crew commented that the device appeared realistic. Each lifeboat required two hours to search their designated sectors. The position fixes of device relocations by the Longhope lifeboat were not reported. The helicopter covered the total search area in approximately one hour and located six of the ten devices. On completion of the exercise the deployment vessel collected devices and it was noted that the Sea-Streak marker dye did not release a significantly noticeable concentration of dye. The plume of marker dye was extremely diffuse and relocation of the buoy to which it was attached required several minutes of searching from downwind of the deployment position.
A total of 55 responses were received from recreational divers in the UK. The results of these responses are detailed in appendices. Delayed SMB's are by far the most common location device used by recreational divers. These are either used routinely for planned decompression or infrequently when unplanned decompression may be required. The most popular colour of these devices is red or orange, but largely as a result of manufactures predominantly fabricating these devices in these colours. Detailed comments on the questionnaires identified a preference for self-inflating or self-sealing decompression marker buoys as they do not expel air if they are allowed to fall over. This frequently occurs when open-ended SMB's are incorrectly deployed. Flags, torches and whistles all appear frequently as location devices. Almost 50% of divers questioned use, or have used folding flags. Similarly, red and orange are the most common pennant colours. More than 50% of divers carry two or more torches, with a small torch frequently used as a backup to a larger lantern style main torch. A similar proportion of divers regularly carries a strobe that in most cases is attached to the divers buoyancy device. Whistles are generally incorporated as a fixture on buoyancy devices. These are typically moulded plastic mouth whistles. A small proportion of divers also commented that they used air-powered sirens attached to their buoyancy devices.
Colour blindness was only reported in 5% of the divers. One diver that reported colour blindness preferred yellow to red or orange. From question 10 relating to particular colours that stand out more than others, orange is largely recorded as the most readily observed. Several divers commented that they found red and orange better colours to observe than yellow and green in bright conditions. Day-glow pink was also noted as a good colour to observe. The questionnaire responses indicate that almost 50% of divers have been missing for an average of more than 30 minutes and the device that aided relocation was most frequently a delayed SMB.
A wide selection of additional comments from question 11 on the questionnaire appears in the appendices. Many relevant issues regarding relocation devices additional to those that have been dealt with in this research appear in the list.
Several shellfish divers were interviewed on a wide range of issues regarding shellfish diving operations and diver location in these circumstances. These divers predominantly use pairs of polyform buoys attached to their line to enable the boatman to distinguish between the diver and any fishing buoys in the immediate vicinity. Some divers use a combination of large and small buoys and two buoys of different colours. The separation distance between buoys had not been considered as a factor that may promote location and none of the divers questioned used a supplementary location device.
Commercial shellfish divers periodically work in strong tidal areas utilising 'solo' diving techniques. There are commonly one or two divers in the water at any one time. These divers may be deployed in close proximity of each other or at distances up to 1 km. If multiple divers have been deployed and the divers become separated, the support vessel will remain equidistant from each. On occasions the divers can be grossly separated (up to 2 km) as a result of tides or the divers swimming on diverging courses, and during periods of reduced visibility or moderate sea states the diver's marker buoys can be misplaced. Depending on environmental conditions it may be impossible to readily locate the position of each diver. Several divers commented that they have been missing or lost by a support vessel on numerous occasions over many years of diving. The amount of time varying greatly from a few minutes too more than one hour. Some divers also reported swimming to shore on occasion. The most common explanation for these incidents is the lack of awareness of the boatman to keep the divers marker buoy in sight. The ability of the boatman to remain in visual contact with the divers is not facilitated when multiple divers are deployed in tidal areas or in non-tidal locations over an extensive area. Most divers commented that they take all relevant factors into consideration when undertaking this type of diving operation.
Many divers commented that prevailing weather and tidal conditions are always considered when deploying divers in any particular location. During periods of spring tides, many of the favoured fishing grounds are avoided due to adverse current speeds. This is not related to the risk of a working diver becoming separated from the support vessel, but because the divers cannot search the seabed effectively when they are drifting over the seabed at excessive speed. Similarly, these areas are avoided if a particular wind direction and windspeed are against the general direction of tidal movement, therefore generating moderate sea waves.