Diving in Currents

Going with the flow

Of all the obstacles a diver can encounter, currents can be one of the most underestimated and physically demanding. Even experienced divers sometimes seem unable to assess accurately the speed and impact of a current. Currents can accelerate your air use and exhaust you; they can even make it impossible for you to return to your dive boat.

Water is 800 times denser than air, so it creates resistance magnitudes stronger than the resistance caused by even a storm-level wind. At one-half knot, divers hanging on an ascent line will feel their bodies moving into a horizontal position, much like a flag in a 10-mile-per-hour breeze. At currents approaching 1 knot, turning your head to the side can result in a dislodged, flooded mask; letting go of an ascent line in a 2-knot current for even a brief instant can mean being swept away.
Understanding Currents
Before you consider diving in a current, it's important to have a basic understanding of how they work, especially as currents can vary in intensity as you descend through the water column. As a general rule, currents closer to the surface and in midwater will be stronger than the currents on the bottom. Just as you can stand behind a building to block a cold wind, the contour of objects on the bottom slows the flow of water. If a structure is big enough, like a shipwreck, moving behind it can completely stop the effects of the current; however, even small reef structures can significantly slow the water's speed.

Divers should be aware that currents do not necessarily travel in the same direction from top to bottom. Some currents, such as tidal currents, can reverse direction during the dive. It is not unusual to have surface currents change speed or direction midwater.

A detailed dive briefing should always precede a dive involving currents; it will orient you to the possibilities you'll encounter and provide the protocols for dealing with them. Before you go too far into your dive, stop and use a visual or physical reference, like an anchor line, during the descent to help you judge the strength of the current and how it will affect your dive.

Diving in a current requires one of two strategies: You can either choose to work with (or fight) the stream or go with the flow.

Go with the Flow
Going with the flow, or drift diving, is an extremely relaxing way to dive. You should plan to stay in a group, and the group will have a dive flag floating on the surface and tethered to a diver below; this allows the boat captain to follow the group's underwater progress. In lieu of a dive flag, you can also use safety sausages or similar signal devices; deploying them to the surface while keeping the line with you underwater makes it much easier for the "bubblewatchers" to track you. Regardless, you should have at least a visual and audible signaling device with you on every drift dive to aid in surface recovery. In addition, the boat crew should provide you with a detailed protocol that includes your dive profile and pick-up instructions for exiting the water.

Once your plan is established, your surface crew is in place and your signaling devices are set, simply fall into the water, get neutral and relax; from there you literally go where the water carries you. Swimming should be limited to depth and minor course changes. At the end of the dive, ascend slowly, do your safety stop, surface and wait for the boat to approach you, and execute the pick-up plan.

If you're doing a drift dive from the shore, the protocols are similar. You'll still prepare a plan, and you'll still carry signaling equipment. However, instead of a boat captain, you'll need to arrange some shore support, such as a car to pick you up at a prearranged rendezvous point. You'll also have to plan to exit the water on your own, or with only the help of your buddy.

Working with the Flow
If your dive boat anchors in a current, or if you plan to dive a site where you know you'll encounter a current, the dive can be a bit more stressful. Wrecks are good examples of this: You need to stay on the wreck for the duration of the dive, but the current can make it difficult. For these dives you must be able to move your body and equipment against the current; this requires some advanced preparation.

Swimming against even a mild current is physically taxing; it depletes your air supply more quickly and can even accelerate gas loading, which is a concern as it relates to the risk of decompression illness (DCI). When descending in a current, hold onto a line and descend hand over hand; it's much less demanding than using the muscles in your legs. Carrying accessories, like a camera, can make the hand-over-hand approach a challenge, so you may wish to clip accessories to a lanyard to keep your hands free.

In strong currents, dive boats frequently use current lines. Holding a "tag line" behind the boat provides an effortless wait for a buddy or for waiting your turn to reboard after your dive. A current, or "granny," line is one that attaches the tag line to the anchor line; granny lines help to decrease the effort of reaching the descent line. Once you are on the bottom, get neutral and begin your dive by swimming into the current. Effective current swimming requires three steps:

  • Gear preparation. Your dive gear should be streamlined with no dangling items. Even an extended regulator hose or a dangling console can create a lot of physically taxing drag. Cave divers have a good rule of thumb: Prep your gear so you can take a piece of twine, extend it across your mask, and drag it all the way to your fin tips without catching it on anything while in a face-down position. Of course the task is impossible, but a properly streamlined setup will get you close.

  • Proper weighting. Divers have a tendency to overweight, especially in strong currents. Although it accomplishes the goal of helping you descend more quickly, once you reach the bottom and attempt to get neutrally buoyant, the added weight will make it difficult, if not impossible, for you to achieve a streamlined swimming attitude in the water. Divers who are properly weighted and trimmed can easily swim in a position that aligns their fins directly behind their head. This attitude allows for movement through the water, opening the smallest hole possible in the force of resistance the water creates against your body.

  • Position. Both the position of your body and your position in the water column are important. Stay as close to the bottom as possible without making contact with objects, especially delicate ecosystems. Position your body in a streamlined manner; for example, dangling arms create drag, so tuck them in close to your sides or behind your back.

At the beginning of your dive you should swim into the current, as the energy you'll expend will deplete your gas and physical reserves more quickly. When you reach the turn point, usually after one-third of your gas supply is gone, simply drift back toward the ascent line. Be cautious not to pass it. You should use much less air and energy on the return trip, giving you time to explore the route and the area immediately around the anchor line (provided you still have enough gas and time). Just remember to keep the ascent point in view and stay close.

When it's time to ascend, maintain physical contact with the ascent line. On crowded boats, using a "jon line" to hang well away from the anchor line can make your safety stop a lot less crowded without forcing you to swim against the current. After the safety stop, slowly ascend to the surface, using the granny line if there's one available, and allow the current to push your body to the stern. Always maintain contact with the line. If necessary, use your fins to adjust your position in relation to the boat, and if there are other divers on the platform when you arrive, grab onto the tag line and hang well back from the ladders until it is your turn to exit the water.
Missing the Boat
If you make the mistake of getting down-current of the boat, and the current is too strong to swim against, don't fight it. Get positively buoyant, dumping weight if necessary, and inflate your safety sausage as soon as possible. If you have to make a safety stop during your ascent, inflate your safety sausage from below the surface; in a heavy current, even a 5-minute safety stop can take you far from the boat. By alerting the crew to your location from underwater, they can track you while you offgas, relieving you of the decision of whether it's better to be lost or risk DCI.

The closer you are to the boat when the safety sausage is inflated, the more likely the crew will see it. Complement the visual signal with an audible one; continue to signal the crew until you are sure they have seen you. Remember that the crew may have other divers to pick up before they can come to you, so stay calm, keep your mask and snorkel in place, and try to maintain eye contact with the boat. If you are with your buddy, stay together.

Knowing how to dive in a current exponentially expands the number of sites you can dive; confidence in your skills makes each dive a safer, more enjoyable adventure. Before you jump into the current, get some training in the skills you'll need, practice them in a controlled environment, and expand your experiences slowly as your comfort level grows.

© Alert Diver — Fall 2010