Drift Decompression Diving

by David Miner

Diver deploying a lift bag on a free ascent decompression drift dive

Standard drift diving is a specialized form of boat diving allowing you to drift with the underwater currents during your entire dive. The boat is never anchored or moored and follows the group of divers the entire time. The different types of drift diving are: float drift and live boat drift. Float drift diving involves the use of a float with a down line or drift line that is towed by the dive leader or divemaster and always lets the boat captain know where the group is. The boat captain follows the float on the surface. Live boat drift diving requires no drift line forcing the boat captain and crew to follow the divers’ bubbles as they drift along.

However, there are also sometimes strong currents on deeper wrecks or other dive sites where you don’t want to drift during the dive, but must drift during your decompression stops on the way to the surface. There are several forms of drift decompressing after the dive is complete, anchor line drift decompressing, float/buoy line decompressing, and free ascent decompressing. Whether drifting for the entire dive or diving a wreck and only drifting while decompressing, there are things to consider and special equipment needed to safely complete your decompressions stops and surface with the boat waiting to pick you up.

First, lets define the different methods of drift decompression diving and then look at some of the equipment used for decompression drift diving.


Diver drift decompressing. Notice the grappling hook, reel use,and backup reel clipped to harness.

Float line drift decompression diving: When drifting with a float line, the dive team must ascend the line together until they reach their first decompression stop. As a team, all divers must stop and drift together, making sure to remain in contact with the line. The team must complete each decompression stop together and then surface. If a diver must surface due to an emergency or other reason without the team, that diver must ascend the line to the surface and drift with the float until the boat captain indicates that it’s safe to move away from the float and be picked up. Typically, the dive master or leader of the dive group carries the float line throughout the dive. The float is typically a larger float ball or float ball with an attached dive flag. The line is typically a small diameter line so that it drifts through the water column easily, and is typically deployed and retrieved using a standard dive reel or spool. The reel or spool must contain enough line for the depth you’re diving. Since the line is of smaller diameter, typically it is not recommended to “hang” on the line or clip into the line. The diver can hold onto the reel or spool or clip the reel or spool to a D-ring on their harness or BC. It is important for all divers to monitor their depth and avoid drifting up or down too much and violating their decompression stop.

Live boat drift decompression diving: Live boat drift decompression involves little extra equipment, but relies on the boat captain to stay in contact with the dive teams’ bubbles during the dive as well as all decompression stops. It is recommended that all divers carry a small reel or spool and either a safety marker tube or lift bag in case you need to deploy a surface marker indicator before surfacing or once on the surface. All divers must stay together during the dive and decompression stops and must surface as a group. The more bubbles, the easier it is for the boat captain to see where you are. If you’re diving rebreathers, live boat drift diving is not an option as there are no bubbles for the captain to follow. It is important for all divers to monitor their depth and avoid drifting up or down too much and violating their decompression stop.

Buoy line drift decompression diving: A buoy line is a line that is attached to the wreck or dive site upon descent. A float ball floats on the surface, but is not attached to the dive boat or anything else. The attached line must be long enough to reach the dive site and strong enough to withstand being pulled on by the seas and currents above. The buoy line remains attached to the dive site during the dive and then must be retrieved upon ascent. The dive team unhooks the line and ascends together carrying the hook to the first decompression stop. The hook can then be clipped into the line so that the divers don’t have to hold onto it. Once the line is unhooked, the divers and the buoy line begin drifting, meaning that the boat captain must begin following the buoy. All divers must remain in contact with the line as they drift throughout all decompression stops. It is important for all divers to monitor their depth and avoid drifting up or down too much and violating their decompression stop. The float is typically a larger float ball or float ball with an attached dive flag. The line is typically a larger diameter (almost anchor line size) so that it can withstand the seas and currents while attached to the dive site. Since the line if of a larger diameter, reels are not used for deployment or retrieval. However, since the line is much heavier, divers can “hang” on the line or clip themselves into the line using a Jon line. It is recommended that all divers carry a small reel or spool and either a safety marker tube or lift bag in case you get separated from the buoy line and need to deploy a surface marker indicator before surfacing or once on the surface.

Anchor line drift decompression diving: Anchor line drift decompressing involves dropping the anchor on the dive site, descending the anchor line for the dive, and then retrieving the anchor at the end of the dive. Once the dive is complete, all divers must meet at the anchor, unhook the anchor, and ascend with the anchor to the first decompression stop. The anchor can then be clipped into the anchor line so that the divers don’t have to hold onto it. All divers must remain in contact with the line as they drift throughout all decompression stops. Since anchor line is a thicker diameter and very strong, divers can “hang” on the line or clip themselves into the line using a Jon line. Since the anchor line is attached to the dive boat, the divers drift along with the boat until decompression is complete and then surface to the awaiting boat. It is important for all divers to monitor their depth and avoid drifting up or down too much and violating their decompression stop. It is recommended that all divers carry a small reel or spool and either a safety marker tube or lift bag in case you get separated from the anchor line and need to deploy a surface marker indicator before surfacing or once on the surface.

Free ascent drift decompression diving: Free ascent drift decompression diving involves having the boat drop the team of divers upstream of the dive site. The divers descend to the dive site together, execute their dive, and then ascend together to just below their first decompression stop. Each diver must then deploy a lift bag using a reel or spool. The line on the reel or spool must be long enough so that the lift bag reaches the surface. It is typically a small diameter line so that it drifts easily through the water column. The divers can then ascend to their first decompression stop. On the surface, the boat captain must begin following the lift bags on the surface as the dive team drifts along. As the dive team ascends, the line must be taken up using the reel or spool. All divers must stay together during the dive and decompression stops and must surface as a group. Since the line is of smaller diameter, typically it is not recommended to “hang” on the line or clip into the line. The diver can hold onto the reel or spool or clip the reel or spool to a D-ring on their harness or BC. It is important for all divers to monitor their depth and avoid drifting up or down too much and violating their decompression stop.

Standard drift decompression diving equipment

Drift decompression diving typically involves the use equipment outside your main diving equipment. As detailed in the descriptions above, the following pieces of equipment are used for drift decompression applications.

Reels and spools: Reels and spools are used to deploy lift bags when drift decompressing. As the diver ascends the line is reeled back onto the reel or spool.

Jon line: Jon lines are used to attach the diver to the down line when decompressing. They help to keep the diver at the correct depth, keep the diver from getting blown off the line in strong currents, and keep the diver from being pulled up and down from the boat or buoy bouncing up and down in the waves.

Float ball and float ball with dive flag: Float balls drift on the surface and are used to indicate the diver’s position underwater to the boat captain and crew. Float balls can be used with reels or with heavier duty line, such as when buoy line decompression drift diving.

Grappling hook: Used when buoy line drift diving. The grappling hook attaches to the end of the line and is used to attach the buoy line to dive site (e.g. wreck). Sometimes a piece of chain is used for the last few feet, which acts as a leader preventing the rope to be cut or scrapped on the wreck or dive site. The chain can also be wrapped around an object when unhooking the buoy line to help make it easier to undo the hook when the line is taught.

Lift Bags: Lift bags are used to indicate the diver’s position underwater to the boat crew while drift decompression diving.

Safety tube: Safety tubes are designed for use as a surface signaling device that alerts divers and boaters where you are. They can also be used to indicate the diver’s position underwater to the boat crew while drifting along if a lift bag isn’t available.

DIVING IN DEPTH TAGS

  • it is recommended that a dive team diving from an anchored boat begin their dive
  • it is recommended that a dive team diving from an anchored boat begin their dive:
  • drift decompression diving
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