A distance line, penetration line, cave line, dive reel or guide line is an item of diving equipment used by scuba divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult. They are often used in cave diving and wreck diving where the diver must return to open water after a penetration when it may be difficult to discern the return route. [1] [2] Guide lines are also useful in the event of silt out. [3]
Distance lines are wound on to a spool or a reel for storage, and are laid in situ by unrolling. [4] The length of the distance line used is dependent on the plan for the dive. An open water diver using the distance line only for a surface marker buoy may only need 50 metres (160 feet), whereas a cave diver may use multiple reels of lengths from 25 ft (7.6 m) to 1000+ ft (300 m).
Reels for distance lines may have a locking mechanism, ratchet or adjustable drag to control deployment of the line and a winding handle to help keep slack line under control and rewind line. Lines are used in open water to deploy surface marker buoys and decompression buoys and link the buoy on the surface to the submerged diver, or may be used to allow easy return navigation to a point such as a shotline or boat anchor.
The material used for any given distance line will vary based on intended use, nylon being the material of choice for cave diving. [4] A common line used is 2 mm (0.079 in) polypropylene line when it does not matter if the line is buoyant.
The use of guide line for navigation requires careful attention to laying and securing the line, line following, marking, referencing, positioning, teamwork, and communication. [3]
Cave diving: Guide lines are used in cave diving as standard procedure whenever it is possible that the divers may be confused about the way out. In effect, this is in any dive where there is no free surface overhead and where daylight is not visible at all points of the dive. By the most common definition of cave diving, this would mean guide lines should be used for all cave dives.
Wreck diving: The use of guide lines in wreck diving is very similar to their use in cave diving.
Diving in low visibility: A guide line may be used for dives where poor visibility may make it difficult to return to the starting point, and there is a safety or operational requirement to return to that point.
Other dives where it is necessary or highly desirable to return to a starting point: This may include dives where a shot line or anchor line is to be used for ascent, and other dives where a specific exit point is chosen for safety or convenience. Working divers may use a guide line to allow confident and efficient movement to, from and around the workplace. This may also be referred to as a jackstay. In these applications the guide line is generally more for efficiency than for safety, but it may also help the divers stay away from potentially hazardous areas.
Guide lines may also be used as a means of directing tourists around a dive site, between points of interest which may be difficult to find without the line. This form of guide line may be permanently placed.
Cave line, strictly speaking, is line used in caves, but the term is used generically for the type of line carried by divers on reels and spools for use as guide lines and surface marker buoy lines. It is made using the same machines and materials to the same specifications as the equivalent line used for other purposes.
Code | Diameter in mm | Diameter in inches | approximate breaking strength [kg] | approximate breaking strength [lbs] |
---|---|---|---|---|
#18 | 1.58 | 1/16" (0.0625) | 65.4 | 144 |
#24 | 1.86 | 0.073 | 104 | 230-250 |
#36 | 2.11 | 0.083 | 150 | 330-360 |
#48 | 2.48 | 0.098 | 182 | 405-550 |
1/8“ | 3.18 | 0.125 | 331 | 728 |
A reel comprises a spool with a winding knob, which rotates on an axle, attached to a frame, with a handle to hold the assembly in position while in use. [4] A line guide is almost always present, and there is usually a method of clipping the reel to the diver's harness when not in use.
Other accessories which may be present (usually not all on the same reel) include:
Reels may be made from a wide variety of materials, but near neutral buoyancy and resistance to impact damage are desirable features, which are easiest to achieve in engineering polymers such as nylon, acetal (delrin) and polyethylene.
Reels may also be open or closed. This refers to the presence of a cover around the spool, which is intended to reduce the risk of line tangles on the spool, or line flipping over the side and causing a jam. To some extent this works, but if there is a jam the cover effectively prevents the diver from correcting it. Open reels allow easy access to free jams caused by overwinds or line getting caught between spool and handle.
Finger spools are a simple, compact low tech alternative to reels best suited to relatively short lengths of line. They are simply a pair of circular flanges with a hole in the middle, connected by a tubular hub, which is suitably sized to use a finger as an axle when unrolling the line. Line is secured by clipping a bolt snap through a hole on one of the flanges and over the line as it leaves the reel. Line is reeled in by holding the spool with one hand and simply winding the line onto the spool by hand. Spools are most suitable for reasonably short lines, up to about 50m, as it becomes tedious to roll up longer lengths. The small, compact size, and low cost make them useful for various purposes where long line is not required. [4] Spools may be made from any material that is strong enough and suitable for underwater service, but engineering thermoplastics are most common.
A line holder is a simple device for storing and deploying line underwater. A simple type is an H-shaped piece of wood, plastic or stainless steel used to manually wrap a moderate length line.
It may be used in conjunction with a surface marker buoy or a delayed surface marker buoy by divers, or for a short guide line. When used to deploy a DSMB, negative buoyancy is helpful in to safely unwind the line underwater as the buoy floats to the surface, as it may not be possible to manually unwind the line fast enough to avoid being pulled upwards. For this method of deployment the line holder is dropped and left to unwind by gravity. This may not work as intended, and the line holder may unwind more line than is useful if deployed in midwater. This problem falls away when used with a regular SMB, or for a short guide line.
Cave reels are reels used in cave diving. They are often specifically designed for laying and recovering line at swimming speeds, and may differ from reels used for other purposes such as deploying a DSMB. They usually have an adjustable drag facility to prevent overrun, and a lock, but may not have a ratchet.
Exploration reels are large cave reels that can hold a lot of line, in some cases as much as 2,000 ft (610 m), and are used during major exploration dives where this length is needed. They tend to be bulky and impractical for most other purposes. They are often used to lay permanent line. [4]
Penetration reels (also known as primary or lead reels) are used to run line from a point with direct access to the surface to the start of a permanent line. This may be as much as a few hundred feet into the overhead. These reels will usually carry 300 to 500 ft (91 to 152 m) of line. These reels are also used for short penetrations where there is no permanent line. [4]
Jump and gap spools are used to bridge gaps between two permanent guide lines. Line length is generally about 50 to 100 ft (15 to 30 m) [4]
Safety spools are used in emergencies such as line breaks, searches for a lost guide line or lost diver. They generally carry about 150 ft (46 m) of line, and one should be carried by each diver. They are not intended for use under an overhead except in an emergency. [4]
DSMB spools are used to deploy inflatable surface marker buoys from depth. They have negative buoyancy and enough line to reach the surface from the planned deployment depth, and are often made of injection moulded plastic and sold as a set with the DSMB. Larger versions which can carry more line and are suitable for use from deeper depths are more likely to be machined from aluminium and are both more ergonomically shaped and more expensive.
General purpose reels used by open water divers usually feature a ratchet mechanism which allows rapid deployment of DSMBs, and secure recovery of line, using the spring-loaded ratchet to prevent unintended unrolling during ascent, but allowing deployed length to be increased rapidly under tension by disengaging the pawl, which is usually operated by a thumb lever or finger trigger. Ratchet reels are occasionally fitted with a drag mechanism to allow controlled line tension when laying guide line, and a ratchet release retainer, but these features add complexity and cost and potential failure points, and are not needed for open water use.
Line markers are used for orientation as a visual and tactile reference on a permanent guide line. Directional markers (commonly arrows), are also known as line arrows or Dorff arrows, and point the way to an exit. Line arrows may mark the location of a "jump" location in a cave when two are placed adjacent to each other. Two adjacent arrows facing away from each other, mark a point on the line where the diver is equidistant from two exits.
Non-directional markers ("cookies") are purely personal markers that mark specific spots, or the direction of one's chosen exit at line intersections where there are options. One important reason to be adequately trained before cave diving is that incorrect marking can confuse and fatally endanger not only oneself, but also other divers.
Silt screws are pegs which are inserted into soft bottom sediments to tie off the guide line when there are no suitable natural formations. A common style of silt screw is a length of rigid PVC tube cut to a point at one end, with a notch at the other to secure a wrap. These are lightweight and durable, and are easily transported by attaching them to a cylinder with bungees.
The principle of a continuous guide line between the penetration diver and open water is central to cave and wreck diving safety. [1] Procedures associated with the use of guide lines include primary and secondary tie-off, laying line, positioning line, following line, marking and identifying line, identifying jumps and exit directions, searching for a lost line, repairing a break, and recovering line.
Most reels are designed to be held in the left hand, particularly for recovering line. Line should be kept under tension at all times to avoid slack which is more likely to snag on divers' equipment. An adjustable brake may be used to provide resistance to rotation, or this can be done by pressing a thumb or finger against the spool as it rotates, which is quick and controllable, but requires some attention, and fails if the reel is dropped. The line should be kept clear of the divers body during the laying to reduce risk of snagging on the diver's equipment. This can be achieved by holding the reel away from the body in clear water. [2]
The line should be laid so that it can be followed in the worst possible visibility, and allow for other emergency procedures such as gas sharing at the time. This generally means that the divers must be able to follow it by feel. [2]
Line traps are places that a line can pass through but are too tight for a diver, making it impossible to follow the line by feel. Avoiding line traps is a large part of the skill of laying line, and generally require the line to be tied off in such a way that it does not enter line trap areas when under the necessary tension to prevent slack. As a general principle, this requires the line to be secured at any change of direction, by a placement or a tie-off. [2]
A placement is made by running the line past a contact surface in such a way that friction or geometry of the line position prevents the line from moving. This may be adequate, for example, when going past a boulder which has a notch which holds the line in place.
A tie-off generally involves wrapping the line round a fixed object once or twice, and may be made more secure by adding a lock, which is made by looping the reel around the incoming line and taking up the slack, before continuing the lay. A lock also puts the incoming and continuing parts of the line in contact, which makes it much easier to follow by feel. [2]
The security of both placements and tie-offs depends on the detail of the place where they are made, and some may be disrupted by a pull on the line in the wrong direction. This makes the skill of following a line without dislodging it an important safety issue.
Placements and tie-offs take time to set up, and time to negotiate when following the line by feel, so they should be limited to those which are actually useful. [2] To be useful, a tie-off would limit the distance to the next tie-off to a reasonable distance which could be negotiated with a safety spool in case of a break, or which prevents a line trap. More frequent placements and tie-offs are likely to be used on a permanent line which does not have to be retrieved on the way back, and which must withstand use by many divers over a long period.
The position of the line can make a large difference to the ease with which divers may follow it. [2] The line would ideally allow divers to see or feel it while swimming comfortably without coming into contact with or being obstructed by, the bottom, sides or ceiling. This is not always possible. [8]
The bottom is often easy to follow by eye and often has suitable tie-off points, but sometimes swimming close to it may cause silting, and it may result in a higher inert gas loading and higher gas consumption than an alternative route. [8]
The sides have a problem in that they constrain divers to swim on one side of the line only. [2] [8]
The ceiling may be difficult to tie-off to, and is difficult to follow, as the divers will generally have to look upwards. Following a ceiling guide line by feel can be even more awkward and tiring, and an overhead line is both more likely to get snagged by a diver's equipment, and be more difficult to unsnag, as the snag is likely to be behind the diver where it cannot be seen or easily reached. [8]
If the lead diver is the one to lay line on entering the overhead environment, it is possible for other divers in the team to follow the guide line for their safety, and they can check the security of tie-offs and that the line is not moving into traps unnoticed. This order also reduces the risk that a diver will become separated from the team if the line-layer has to stop for any reason. [2]
The primary tie off is made in a place with direct vertical access to the surface, if possible, in a place where it is unlikely to be interfered with by outsiders. This tie-off should be secure. [2]
The secondary tie-off is made just inside the overhead, where the route to the exit is obvious even if visibility is lost. This is a backup in case the primary tie-off is compromised. [2]
The temporary entry guide line should be tied off to the permanent line and the reel locked. [2] A recommended method is to make two wraps around the permanent line and then clip the line end back to the line. Another method is to pass the reel or spool through a loop at the and of the line made for that purpose, the loop may be of stiffer and thicker line and may have a short extension to make it easier to undo on the return. This method cannot be accidentally released.
If the last diver out is the one to reel in the line, the lead divers can prepare the way by loosening tie-offs just ahead of the reel, and there is less risk of them becoming separated from the group without the reel operator noticing. [2] This can significantly reduce the risk of anyone getting lost. This order is even more safety critical if the exit is in poor visibility. In an emergency, the reel would be left at a tie-off and the divers would exit without recovering the line, as this would save time.
There is more to navigating by guide line than merely following the line.
Survey of line condition: A permanent guide line may have deteriorated since the latest reliable report on its condition. A complete check of line condition during the penetration will ensure that there are no unpleasant surprises like line breaks or line traps during the exit [3] [8]
Distance from the guide line: Good visibility may be compromised very quickly in some environments. If a diver is more than arm's reach from the line when visibility is lost, it will be necessary to find the line in possibly adverse circumstances. This can be avoided by remaining within reach of the line. [2] [8]
Guide lines are frequently used in areas with heavy silt, and the line may lie on the silt or be close above it. If silt is kicked up everyone following will have poor visibility, and the return along the line may be in low or zero visibility, which is at the very least inconvenient. The ability to fin without kicking up the silt relies on good level trim and appropriate finning techniques. [2] [8]
It can be useful to build up a mental model of the route, even to make notes and sketches indicating major landmarks and changes of direction. This helps to reduce disorientation on return along the line, when the surroundings may look very unfamiliar because they are observed from a different direction. For the same reason, occasional checks in the exit direction will make the route look more familiar on return. [8]
Use of a compass for occasional checks of direction has the advantage of providing a secondary input for sense of direction. This can be of great value when disorientated for any reason. [8]
It is important for safety to ensure that the gas supply for the return is sufficient for reasonable contingencies. It is more conservative gas management to do any work on the outward leg, and return directly, unless specifically planned otherwise. As the exit is approached, the gas stock and decompression obligations can be re-assessed, and plans adjusted accordingly. [8]
Although distance lines are considered to be safety equipment, there are hazards associated with their use.
In 1977, Sheck Exley published Basic Cave Diving: A Blueprint for Survival which pointed out that the lack of a continuous guide line was one of five main contributing factors in cave diving accidents. [1]
In underwater diving, open water is unrestricted water such as a sea, lake, river, or flooded quarry. It is a contradistinction to confined water where initial skills training takes place. Open water also means the diver has direct vertical access to the surface of the water in contact with the Earth's atmosphere. Open water diving implies that if a problem arises, the diver can directly ascend vertically to the atmosphere to breathe air. Penetration diving—involving entering caves or wrecks, or diving under ice—is therefore not "open water diving". In some contexts the lack of a decompression obligation is considered a necessary condition for classification of a dive as an open water dive, as a decompression obligation is a procedural and safety restriction on immediate ascent to the surface, but this does not affect the classification of the venue as open water.
Drift diving is a type of scuba diving where the diver is transported by the water movement caused by the tide, an ocean current or in a river. The choice whether to drift dive depends on the purpose of the dive, and whether there is an option. At some sites there is almost always a current running, and at others the strength and direction of water movement may vary with the tide, or other driving forces, like wind or recent rainfall. At some sites there may be considerable variation in visibility and underwater life activity based on the speed and direction of flow.
Wreck diving is recreational diving where the wreckage of ships, aircraft and other artificial structures are explored. The term is used mainly by recreational and technical divers. Professional divers, when diving on a shipwreck, generally refer to the specific task, such as salvage work, accident investigation or archaeological survey. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites. Diving to crashed aircraft can also be considered wreck diving. The recreation of wreck diving makes no distinction as to how the vessel ended up on the bottom.
Night diving is underwater diving done during the hours of darkness. It frequently refers specifically to recreational diving which takes place in darkness. The diver can experience a different underwater environment at night, because many marine animals are nocturnal.
Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave-diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression stops. A distinction is made by recreational diver training agencies between cave-diving and cavern-diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
A surface marker buoy, SMB, dive float or simply a blob is a buoy used by scuba divers, at the end of a line from the diver, intended to indicate the diver's position to people at the surface while the diver is underwater. Two kinds are used; one (SMB) is towed for the whole dive, and indicates the position of the dive group throughout the dive, and the other, a delayed surface marker buoy, DSMB or decompression buoy, is deployed towards the end of the dive as a signal to the surface that the divers have started to ascend, and where they are going to surface. Both types can also function as a depth reference for controlling speed of ascent and accurately maintaining depth at decompression stops. Surface marker buoys are also used by freedivers in open water, to indicate the approximate position of the diver when submerged. They may also be used to support a catch bag or fish stringer by underwater hunters and collectors. A DSMB is considered by recreational scuba divers and service providers to be a highly important item of safety equipment, yet its use is not part of the entry level recreational diver training for all training agencies, and there are significant hazards associated with incompetent use.
Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team. In professional diving, diver communication is usually between a single working diver and the diving supervisor at the surface control point. This is considered important both for managing the diving work, and as a safety measure for monitoring the condition of the diver. The traditional method of communication was by line signals, but this has been superseded by voice communication, and line signals are now used in emergencies when voice communications have failed. Surface supplied divers often carry a closed circuit video camera on the helmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can also be used to transmit hand signals to the surface if voice communications fails. Underwater slates may be used to write text messages which can be shown to other divers, and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through-water to other divers or surface personnel with compatible equipment.
A diving shot line, shot line, or diving shot, a type of downline or descending line, is an item of diving equipment consisting of a ballast weight, a line and a buoy. The weight is dropped on the dive site. The line connects the weight and the buoy and is used by divers to as a visual and tactile reference to move between the surface and the dive site more safely and more easily, and as a controlled position for in-water staged decompression stops. It may also be used to physically control rate of descent and ascent, particularly by surface-supplied divers.
A dive boat is a boat that recreational divers or professional scuba divers use to reach a dive site which they could not conveniently reach by swimming from the shore. Dive boats may be propelled by wind or muscle power, but are usually powered by internal combustion engines. Some features, like convenient access from the water, are common to all dive boats, while others depend on the specific application or region where they are used. The vessel may be extensively modified to make it fit for purpose, or may be used without much adaptation if it is already usable.
Diver navigation, termed "underwater navigation" by scuba divers, is a set of techniques—including observing natural features, the use of a compass, and surface observations—that divers use to navigate underwater. Free-divers do not spend enough time underwater for navigation to be important, and surface supplied divers are limited in the distance they can travel by the length of their umbilicals and are usually directed from the surface control point. On those occasions when they need to navigate they can use the same methods used by scuba divers.
In cave diving, line markers are used for orientation as a visual and tactile reference on a permanent guideline. Directional markers, are also known as line arrows or Dorff arrows, and point the way to an exit. Line arrows may mark the location of a "jump" location in a cave when two are placed adjacent to each other. Two adjacent arrows facing away from each other, mark a point in the cave where the diver is equidistant from two exits. Arrow direction can be identified by feel in low visibility.
A silt out or silt-out is a situation when underwater visibility is rapidly reduced to functional zero by disturbing fine particulate deposits on the bottom or other solid surfaces. This can happen in scuba and surface supplied diving, or in ROV and submersible operations, and is a more serious hazard for scuba diving in penetration situations where the route to the surface may be obscured.
Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
Underwater searches are procedures to find a known or suspected target object or objects in a specified search area under water. They may be carried out underwater by divers, manned submersibles, remotely operated underwater vehicles, or autonomous underwater vehicles, or from the surface by other agents, including surface vessels, aircraft and cadaver dogs.
Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as a scuba set. Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many also apply to surface-supplied diving. Some scuba skills, which are critical to divers' safety, may require more practice than standard recreational training provides to achieve reliable competence.
There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures.
Diving procedures are standardised methods of doing things that are commonly useful while diving that are known to work effectively and acceptably safely. Due to the inherent risks of the environment and the necessity to operate the equipment correctly, both under normal conditions and during incidents where failure to respond appropriately and quickly can have fatal consequences, a set of standard procedures are used in preparation of the equipment, preparation to dive, during the dive if all goes according to plan, after the dive, and in the event of a reasonably foreseeable contingency. Standard procedures are not necessarily the only courses of action that produce a satisfactory outcome, but they are generally those procedures that experiment and experience show to work well and reliably in response to given circumstances. All formal diver training is based on the learning of standard skills and procedures, and in many cases the over-learning of the skills until the procedures can be performed without hesitation even when distracting circumstances exist. Where reasonably practicable, checklists may be used to ensure that preparatory and maintenance procedures are carried out in the correct sequence and that no steps are inadvertently omitted.
In underwater diving, a downline is a piece of substantial cordage running from a point at the surface to the underwater workplace, and kept under some tension. It can be used as a guideline for divers descending or ascending, for depth control in blue-water diving, and as a guide for transfer of tools and equipment between surface and diver by sliding them along the downline at the end of a messenger line. A shotline is a special case of downline which uses a heavy weight at the bottom and a float at the top. A jackstay is a more lateral equivalent, that commonly follows a surface, and will not usually allow materials transfer without a messenger line from the destination end.
Human factors in diving equipment design are the influences of the interactions between the user and equipment in the design of diving equipment and diving support equipment. The underwater diver relies on various items of diving and support equipment to stay alive, healthy and reasonably comfortable and to perform planned tasks during a dive.