| Underwater Search & Recovery Techniques
While these techniques have worked well for me, I am not advocating their use by others. I am not a trained professional nor a certified instructor.
Historic objects Mark location and notify relevant organization. Why ? Submerged Historic Resources are often protected by state or federal law. Removal of such items (even if an isolated find rather than in situ) can place the diver into a legal nightmare. "experts" would prefer to lose access to a find and let the future "re-find it" than to have unauthorized removal of the item.
Explosives old cartridges, explosive shells, cannon balls etc are best left where they are found and your local EOD contacted. In the US this is often the Military or State Police who will have an EOD person or a contact. Why ? as propellant dries, it can become unstable and detonate spontaneously or when jarred.
Firearms - unless a targeted search, a firearm might be related to a crime. Mark the location and inform law enforcement, noting the type, size, any markings visible. If part of an organized search and recovery is mandated, marking the location via float will allow law enforcement to estimate where the weapon might have been disposed from.
source: FBI Law Enforcement Bulletin (9/2000)
|Marker Buoy - surface released
Surface released buoys essentially are stored and released fully inflated and include large mooring type, smaller water ski markers and fishing structure markers.
Common foam mooring buoys offer 30-400 lbs of buoyancy, inflatable's are 5lbs for pickup and ski markers to larger mooring buoys with 700 lbs of buoyancy
Large buoys are well suited to mark large heavy weights such as mushroom anchors used as end points for a tensioned line, and they can not be dragged beneath the surface by diver action. Smaller buoys can be yanked below the surface to provide for diver to surface communication
Marking sonar hits can utilize fishing structure markers (see diver released markers - below) or buoys can be assembled using bright containers such as clean laundry detergent bottles, with line wrapped around them and a heavy weight, which can quickly be thrown overboard and usually unreel line from around the container as the weight descends. note: wind the line carefully to prevent tangles, and clean the interior of the container thoroughly to prevent pollution before use as a marker.
|Marker Buoy - Diver released
Diver Released Marker Buoys - can be SMB's (surface marker buoys) inflated at depth and released, or fishing structure markers can be carried and released. SMB's require a method to carry sufficient line to reach from bottom to surface along with attachment to a weighted object or structure if they are to be left unattended. A spooled reel is better than use of a line winder since the time to unwind line is not conducive to shooting a lift bag to the surface ... remember SMB's can deliver significant lift
Structure markers used in fishing use light weight line, the Pelican Recovery float can not only mark, the 225 lb test line can also be used to lift small items from the surface.
|Diver released buoys|
An anchor can be anything, from a concrete block to drilled helical devices. For structure markers which I find easy to carry while diving, the attached weight is often sufficient except in high seas or current. Being cheap (I mean thrifty) I try not to leave anything of value unattended for too long. We have used 500 lb moorings to tether a large mooring ball to mark a site for long term documentation. That is the extreme I have been party to. Usually it's a quick mark and take compass and/or GPS coordinates, knowing that a return to the exact location is doubtful and will require some in water searching (thus bottom markers are left behind) if leaving a buoy to the surface is impractical or unwanted. The possibilty of theft, vandalism and severe weather need to be considered. So even with a decent marker in place, make sure you record compass bearings and get GPS, just in case.
Event: while diving, I had someone in a small boat come over to the dive flag I was towing and attempt to lift it into their boar. Surface support yelled at them and informed them that it indicated there are divers in the water. Since I was not there, I can only assume they were told in a calm manner and it was an informative positive learning event.
|Acoustic Beacons (Pingers)
The Pinger emits an acoustic signal and is attached to an object or can be dropped to mark a potential recovery location. It can be used when a anchored marker buoy on the surface would present a navigation issue or simply when overt marking is not desired. This is a two part system and required a receiver which can "hear" the pinger signal and indicates direction and proximity with a tone which increases in frequency or volume as the diver nears the pinger location, or will utilize a visible display with signal strength indicators. Some units utilize interrogator / response and programmable frequencies to allow multiple pingers in the same general area, and pingers will remain silent until the interrogator emits the command signal to start transmitting
Some of the interrogators that used to be available for salvage or research appear to have been removed from the civilian market and are only marketed to military and government entities.
Instead of a marker which is highly visible from the surface, sometimes you will not want to advertise the location of your area of interest to those on the surface. An alternative to acoustic pingers, a physical bottom marker can help you return to the location.
The bottom marker can also be useful to mark the search area lanes. What you use varies depending upon visibility, size of the item, value of the item (monetary, evidentiary or historical) and terrain.
I see strobes advertised for marking shore locations , anchor lines and for emergency use. These do not state the flash rate, or if it is a user variable flash rate. I strongly advise against using any emergency strobe in a non-emergency situation.
Before anyone yells at me that there is no restriction around the world, or that the only place that a strobe is listed as a distress signal is in US Inland Colregs. I know. But for those of you who also know that an emergency 60/min strobe is attached to liferafts, survival suits and lifejackets no matter where you fly or sail, you know they are made to attract attention. It's the frequency that is important. Another use for strobes are to mark fishing trawl nets. Those normally are set to 1 flash every 2.5 or 3 seconds. A slower rate.
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