Underwater Search and Rescue Patterns You Should Know
Rachel Doornekamp | August 30, 2021
What is Search and Rescue?Search and rescue (SAR) is an operation executed by well-trained and specialized emergency services to locate and extract an individual believed to be in distress, or in imminent danger either in a remote or difficult to access area, such as mountains, desert or forest, lakes or at sea. Search and rescue differs from search and recovery in that search and rescue is only used when there is a chance to save a life. When it is concluded that the missing person may be past rescue, the mission enters recovery mode as risk to rescue personnel in an all out effort is no longer warranted.
Underwater search and recovery specifically is the process of locating and recovering victims or objects lost underwater by divers, remotely operated vehicles and/or electronic equipment on surface vessels.
Search and Rescue MethodsSearch and recovery teams need to find their target in a quick and safe manner. Whether looking for a lost victim, vehicle or other evidence, it is imperative that investigations be conducted as efficiently as possible.
Recovery teams typically plan their search area using the last known location and eye witness reports. Once the search area has been determined, search and rescue teams sweep the area looking for the target.
Whether using a side scan sonar on their boat or a sonar-equipped remotely operated vehicle(ROV), methodical search patterns are important to a thorough search. There are many common patterns that search and recovery teams use to ensure that they are searching an area completely - without missing any key spots. Using a pattern allows the team to accurately track where they have and haven’t searched.
Once the target has been identified, recovery teams can safely and respectfully retrieve the victim or evidence. Using an ROV, rescue divers or a combination of both, the team can complete the recovery.
Circle Search MethodOne common search pattern is the circle search method. Relatively simple and straightforward, the circle search method consists of a diver or ROV swimming a series of circles, gradually increasing the circumference, around a fixed reference point marking the centre of the search area. Requiring little extra equipment, the circle search is best for searches where the area of the target is known with relative accuracy.
The centre of the search area should be clearly marked by a highly visible, fixed object. The radius of the circles depends strongly on visibility and underwater conditions. There should be a small overlap between the current circle and the previous circle to avoid the risk of missing the target. If a diver is conducting the search it is useful to attach a distance line to the fixed centre point, gradually unreeling sections of line at the conclusion of each circle. If an ROV is being used, mission planning software can be used to track which areas have been previously searched.
If the target is not found by the time the circle search has been completed, the team may shift the centre point and then start again.
Variations on the Circle Search MethodThe circle search method is similar to the spiral search method, however the spiral search method is often completed without a central marking point. In lieu of the fixed point and line, distances are often measured using diver kicks or tracking distance covered on the ROV screen. While the spiral search method does not require a fixed point - and as a result is not susceptible to line tangling by underwater debris - it can be less accurate.
Another variation on the circle search method is the pendulum search, also known as the arc or fishtail search. Often used when there is insufficient space to complete a full circle, the diver or ROV stops and changes direction at the end of each arc. This variation is often used when the search area is along a shoreline or dock where a full circle cannot be completed.
Circle Search Advantages
- The circle search method is very simple and straightforward to conduct in emergency situations.
- Very little equipment is required to accurately conduct a circle search pattern.
- If using a diver, no surface tender is needed to guide the diver around the area.
Circle Search Disadvantages
- While a minimal amount of equipment is required for a circle search, the anchor point must move freely to prevent tangling. Furthermore, submerged logs, rocks, plants and other debris may tangle the line if using a diver.
- It is difficult to switch out divers while conducting this pattern. If a diver is swapped out, it is often necessary that part of the previous circle is overlapped.
Jackstay Search MethodThe jackstay search method simply entails divers or ROVs swimming along the jackstay. Used to guide divers, a jackstay is a line between two fixed points or anchors. In other circumstances a jackstay is used to guide commercial divers to and from their underwater workplaces or to support the transport of materials and equipment to the underwater site.
To conduct a search using the jackstay method, divers begin at one anchor and search along the line until they reach the second anchor. At that point the second anchor point is moved laterally to move the line. The distance the fixed point is moved depends on the underwater conditions, turbidity and the size of the target. Once the anchor is moved, the diver then switches directions and searches the area as they follow the line back to the initial anchor. This pattern continues until the area is completely searched.
Variations on the Jackstay Search MethodIf the body of water being searched is relatively small or shallow, the jackstay can be moved by the surface team as opposed to the diver. By lifting the jackstay and moving the entire line parallel to the original position, the surface team can effectively move the line for the diver.
Another method, also known as the J search involves the diver or ROV starting at the same end of the search line every time. Once the sweep of the line has been completed the same end of the jackstay is reset every time so that by the end of the sweep, the line is parallel to its original position. This method takes longer to complete however it is useful in extremely limited visibility or in cases where the target is very small as the same area is searched twice as the diver or ROV swims back up the line.
Jackstay Search Method Advantages
- The jackstay search method lends itself well to accuracy as there is a large amount of overlap between each sweep.
- It is easy to switch divers midway through the search without having to backtrack.
- The jackstay search method is useful in large, open water environments.
Jackstay Search Method Disadvantages
- The jackstay search method requires a substantial amount of equipment to set up effectively.
- The jackstay method can be confusing to implement, especially with more novice or inexperienced rescue divers - it may require more advanced training.
- While thorough and accurate, the jackstay search method can be time consuming.
Grid Search MethodTo conduct the grid search method, search teams must create a grid across the search area. Using marker buoys, teams create search squares covering the area to be searched. Much like previous methods, the size of the search squares depends on visibility and the size of the target. After the search squares are created, each section is thoroughly searched. Following the completion of each square, searchers report and log anything of interest. This is repeated across every square within the search area.
Grid Search VariationsOne common variation on the grid search method is the compass grid search. In this pattern the diver or vehicle swims parallel lines on a compass bearing and its reciprocal while conducting a visual search. The parallel lines chosen often allow for overlap to ensure accuracy.
Grid Search Method Advantages
- The grid search method is very accurate and thorough.
- The grid search method is quite successful - particularly for smaller targets.
- A large number of divers can be dispatched without confusion.
Grid Search Method Disadvantages
- While extremely accurate, the grid search method is time consuming.
- The grid search method is complicated and therefore requires highly trained divers.
- The grid search method requires a large amount of equipment.
Snag-Line Search MethodThe snag-line search method is a good method for large targets in a relatively small area. When the size and shape of the target is suitable, the snag-line search method is a quick way to find an object.
With a snag-line held tight - typically by a fixed jackstay - a diver, team of divers or ROV pull the taut snag-line across the bottom. Most commonly the line is pulled around in an arc motion around the fixed point. The line is pulled until it hooks and catches on an object. At that point, the snag line is fastened in position and the diver or ROV swims along the line until they reach the snagged object. If the target is identified as the object of the search they will mark it, otherwise they free the line to continue the sweep. It is important to note that this method is often easier with a weighted line.
Snag-Line Method Advantages
- The snag-line search method is very effective for large targets such as sunken cars, boats and aircraft.
- The snag-line method is extremely fast.
- The snag-line does not require a large amount of equipment.
Snag-Line Method Disadvantages
- The snag-line method is effective for larger objects, however it is not useful for smaller targets.
- The snag-line method can be destructive to the ocean floor or lakebed.
- Large objects may unintentionally get caught up in the line, slowing down the snag-line method.
- The object has to be a suitable form in order to get snagged by the line.
Quick Search MethodA quick search is the search done by the first arriving divers and relies on the principle that a victim will be found in a radius equal to the depth of the water. Done especially when a victim’s last known location is near a shore, boat, dock or pier, the quick search method is typically carried out by the first two divers as other team members begin to set up additional equipment.
To conduct the quick search method with a diver, one diver acts as the tender while the second diver enters the water at the victim’s last known location. From there the diver swims out in an arc while staying taut on the line held by the tender. As the diver searches back and forth in a decreasing radius to the shore, pier, dock or boat the tender keeps the line taut. This method can be conducted with an ROV in a similar fashion - using the ROV as a substitute for the diver. This is particularly useful in dangerous waters.
Quick Search Method Advantages
- The quick search method is good for quickly finding victims near a shore, pier or dock.
- Limited equipment is needed to conduct the quick search method.
- Divers can begin in minutes, with minimal set up.
Quick Search Method Disadvantages
- The quick search method is most useful only when the target has gone missing recently and close to the shore, pier, dock, etc.
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Extensive sonar options allow teams to find targets underwater in turbid waters while controller GPS empower teams by providing latitude and longitude readings as well as the automatic GPS lock for the Google Maps feature.
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