Search pattern
Search patterns are used by search teams in sea rescue to find people or ships that are missing or in distress. They can also help if a ship has lost sight of someone who has gone overboard and needs to find it again.
Basics
If people are in distress at sea, they must be found as soon as possible, otherwise there is a risk of death from hypothermia , exhaustion or, if they are still on a ship or a life raft , dying of thirst or starvation . The sea is a huge area in relation to the desired target and the target can drift away due to wind and waves and no longer be at the point where an emergency call was made or was last seen. The further away from the country what you are looking for is, the longer it usually takes until search teams are on site, so the further away it can be from the original location.
Search distances
Most search patterns use the grid spacing S ( recommended track spacing ) as the central variable for specifying the “density” of the search pattern. This depends on the size of the target object and the weather conditions. It is chosen so that every point of the search area can be viewed and the search time is minimized at the same time.
The value of S can be estimated using a formula:
Here is the uncorrected distance and the correction factor.
| Recommended grid spacing (nautical miles)
|
for merchant ships | for helicopters | ||||||
|---|---|---|---|---|---|---|---|---|
| Search object / meteorological visibility | 3 | 5 | 10 | 15th | 20th | 1 | 5 | > 20 |
| Single person in the water | 0.4 | 0.5 | 0.6 | 0.7 | 0.7 | 0.0 † | 0.1 | 0.2 |
| 4-person life raft | 2.3 | 3.2 | 4.2 | 4.9 | 5.5 | 0.5 | 1.7 | 2.9 |
| 6 person life raft | 2.5 | 3.6 | 5.0 | 6.2 | 6.9 | 0.5 | 2.1 | 3.8 |
| 15 person life raft | 2.6 | 4.0 | 5.1 | 6.4 | 7.3 | 0.6 | 2.4 | 4.5 |
| 25-person life raft | 2.7 | 4.2 | 5.2 | 6.5 | 7.5 | 0.6 | 2.8 | 5.7 |
| Boat, <5 m | 1.1 | 1.4 | 1.9 | 2.1 | 2.3 | 0.5 | 1.6 | 2.5 |
| Boat, 7 m | 2.0 | 2.9 | 4.3 | 5.2 | 5.8 | 0.7 | 3.0 | 5.9 |
| Boat, 12 m | 2.8 | 4.5 | 7.6 | 9.4 | 11.6 | 0.7 | 3.9 | 9.1 |
| Boat, 24 m | 3.2 | 5.6 | 10.7 | 14.7 | 18.1 | 0.8 | 5.7 | 18.5 |
- All values in the table are in nautical miles specified
- † Under these conditions (search with air rescue equipment in fog), success is very unlikely
- The table also shows why it is important to stay on or with the sinking boat as long as possible: it is easier to see than the life raft.
| Factor for weather conditions | The search target is a person in the water | They are looking for a life raft |
|---|---|---|
| Wind up to a maximum of 15 kn and a maximum of 1 m swell | 1.0 | 1.0 |
| Wind between 15 and 25 kn or swell up to 1.5 m | 0.5 | 0.9 |
| Wind over 25 kn or swell over 1.5 m | 0.25 | 0.6 |
Pattern for self-help
These patterns can be used when a person falls overboard on a boat and is out of sight despite the man-overboard maneuver being initiated . The last known position should then be saved immediately (usually by pressing a corresponding MOB button on the navigation device) and serves as the starting point for the search. Of course, it is particularly unfortunate if the accident is only discovered after a delay, for example because the watchman was alone on deck at night and his absence is only discovered in the morning.
Sector search
The sector search is suitable for searching in a relatively small area if a reasonably precise reference point (e.g. MOB position) is known. The given position is marked first, e.g. B. with a marker buoy, so that the drift is visible, from which the victim is also affected.
The search begins by moving away from the buoy in a certain direction - often to the north for simplicity - until you have reached the desired radius. This is often static and is between 2 and 5 nautical miles. Alternatively, the can Expected sight (ES) (ger .: Expected Detection Range (EDR) ) are used. This is the distance at which you can still see the marker 50% of the time. This is an estimate for the grid spacing S.
After triple the ES, turn 120 ° to starboard and drive ES three more times. Then, after changing course, it goes 120 ° to starboard back to the starting point and the next sector begins straight ahead. If the search for three legs was unsuccessful, start the first sector of the second circuit in the direction of 30 °.
Search in the expanding square (advanced search)
If the sector search was unsuccessful or if the last known position was only inaccurately determined, a larger area can be searched with the advanced search. However, this search pattern also does not work efficiently if the search target is too imprecise. This method is the primary search variant used by professional SAR units. However, the method cannot be used by several ships at the same time and also does not work for low-flying aircraft because the operating radius is too small and the search teams would endanger each other.
The widening square search also typically begins on a north course. Here, however, only three quarters of the ES are used as the leg length D (or 100% of the ES, if a sector search has already taken place, since the area was then already searched twice). First one drives D to the north, then once D to the east, then twice D to the south, twice D to the west, then three times D to the north, etc. After every two legs, the distance to be traveled is increased by a D, which increases one widening right-angled "spiral" is created, the legs of which lead past each other with a maximum distance D.
SAR search pattern
If search teams from SAR associations intervene in the search, a much larger area must usually be searched because either the close-up search was unsuccessful, the last location of the target is only vaguely known, or a long time has passed since the alarm was raised. These search patterns are coordinated and, if necessary, planned by the on-scene coordinator , especially if several ships or aircraft are involved .
Route search
If the position of the desired destination is unknown and one only knows its intended route, a search along this route is first started. In doing so, a search is first made on one side of the route and on the way back on the other. For this type of search, aircraft are primarily used because of the long distances.
Parallel search
Two SAR units (e.g. a ship and a helicopter) will search the search area in a grid with grid spacing S, one unit with lines in east-west and the other in north-south direction. In doing so, they try to include current and wind data from the affected area as far as possible in order to estimate the probable location of the target.
Alternatively, one unit searches in parallels from the search center to the right, the other to the left. This pattern can be carried out with any number of units.
An airplane and a ship together can carry out a combined search, which takes into account that the airplane is significantly faster than the ship, but the latter can navigate more precisely and is closer to the water: while the airplane is flying along a grid, the ship only travels straight ahead across it and gives the aircraft a navigation mark with which it can compare its pattern.
Search by technical means
Technical aids can lead to specialized search patterns, for example to find a SART buoy or an EPIRB or ELT signal . A double fly over the area and some map geometry should be sufficient to determine the position of the sending buoy with sufficient precision. This makes use of the fact that the transmission range of the signal at sea is almost exactly round, i.e. the distance from the target at which the signal gets out of range is constant.
Of course, the radar device can also be used for the search. The range of radars also depends on the size of the target object. A 10,000 GT ship can be located at around 18 nm, while a 9 m boat can only be detected at a distance of 2.7 nm on average (at 30 m radar height, at 15 m radar height only around 70% of that ).
Search ashore
Searching on land differs from searching at sea in several important ways. Due to the presence of vegetation , the target object is usually more difficult to discover than at sea, so the area often has to be flown several times. The grid spacing for searching for a person is only five to eight meters. Today, FLIR cameras are also used, with which people can be detected based on their body heat, especially at night. Searching by ground teams alone is mostly impractical, but can be helpful in small areas.
For a parallel search on land, human chains are formed who comb through the area at a given distance. So 20 to 25 people can search an area of one square kilometer in about an hour and a half.
Stop searching
There are several reasons why the search may not be successful. This can be due to an incorrect specification of the last known destination position, for example due to transmission errors or navigational errors. The drift of the object can be wrongly assessed. In harsh weather conditions, it is possible that the object is simply overlooked even though it was in the search area. The fact that a boat goes down without a trace is rather the exception, usually at least some debris or oil stains remain on the surface.
The search is usually carried out until the object or person you are looking for is found. The responsible MRCC (or, if this cannot be reached, the on-scene coordinator (OSC) must decide) can abort the search if the prospect of success is no longer considered realistic. For individuals, this limit is a few hours to a maximum of days, depending on the water temperature. The following table gives some guideline values for people floating in the water without a protective suit:
| Water temperature (° C) | Expected survival time |
|---|---|
| <2 | Less than 3/4 h |
| 2 to 4 | Less than 1½ h |
| 4 to 10 | Less than 3 h |
| 10 to 15 | Less than 6 h |
| 15 to 20 | Less than 12 h |
| over 20 | Unlimited (depending on the exhaustion of the victim) |
If ships or life rafts are searched, the search can take several weeks and result in corresponding costs. The search for the Boeing 777 on Malaysia Airlines Flight 370 took several months and has not yet been successful.
If the searched object was found, the OSC ends the search and informs the MRCC about the search result, as well as about where the recovered victims are being taken and which ships are transporting them. If necessary, he asks for further medical help for the rescued. If the ship involved in the accident poses a danger to other ships or the environment, the MRCC must also be informed so that salvage measures can be initiated and other ships can be made aware of the danger.
swell
- Keith Colwell Safety at Sea ; Delius Klasing Verlag; Bielefeld 2012; ISBN 978-3-7688-3539-8
- International Civil Aviation Organization and International Maritime Organization: IAMSAR Manual , Volume III: Mobile Facilities, 2007 Consolidated Edition. PDF