Drift Diving Basics: Entries, Staying Together and Surface Signals

What is a drift dive?

It is a dive where you let the current move you instead of swimming against it. PADI's definition: divers enter at one point and the current guides them along the site, which lets them cover large reef systems or drop-offs with little effort. There is no swim back to an anchor line. The boat follows the group and picks everyone up where they surface.

The speed is whatever the water is doing. PADI puts typical drift speeds at 1-3 knots (1.85-5.56 km/h), while DAN advises that divers should not dive in currents stronger than 1 knot without proper training and experience. A knot is about half a metre per second; DAN's field check is to throw something buoyant in and time it over a known distance, since it will cover 1.68 ft (0.51 m) per second in a 1-knot current.

Most of the skill is ordinary diving done more precisely: buoyancy, staying close to a buddy and sending up a marker. PADI's Drift Diver course practises exactly those, plus the floats, lines and reels used to mark a group. Our training guides cover how specialty courses fit with the other certification levels.

How to do a negative entry

A negative entry means going in with little or no air in your BC and descending straight away, then pairing up with your buddy below the surface. DAN describes it as a technique some drift dives need, depending on the current. The reason is the surface: if the group waits there, the current spreads it out before anyone has descended.

The descent is fast, so your ears set the pace. DAN's ear guidance applies directly: equalize gently before you descend, go down feet first if possible, and equalize every few feet for the first 3-4.5 m (10-15 ft). Pain means you have gone down without equalizing enough, so ascend a little until it stops. Our guide to equalizing covers the techniques. What operators brief varies by site, so the steps below are a pattern, not a rule:

• Be fully kitted, with mask on and regulator in, before the first diver goes in. Diving writer Charles Davis advises being ready to dive before the first diver enters the water, so the group lands close together.
• Pre-equalize on the boat, then roll or step in on the signal with the BC empty.
• Exhale and keep descending. Extra lead is not the way to get down; Davis points out that most divers don't need more weight for these entries.
• Level off, become neutral at the depth given in the briefing, and find your buddy and the guide before moving on.
• If your ears will not clear, stop and ascend a little. Davis's rule: if an entry is not comfortable without current, don't do it in current.

How to stay with the group in current

Stay behind the guide and close to your buddy. A Cozumel operator's drift briefing puts it simply: stay behind your dive guide, keep your buddy close, stay close to the wall and shelter behind rocks or sponges. DAN's version is to stay with your group or, at a minimum, a buddy, and to follow the boat crew's procedures closely to avoid entanglement and propeller strikes.

Buoyancy does most of the work. A PADI article on drift diving says neutral buoyancy lets you drift without collisions, that you should secure dangling gauges and alternate air sources to cut drag, and that the current is weakest close to the reef or the bottom. It also suggests watching soft corals: when they are blown over like trees in the wind, the current is picking up.

Expect one marker for the whole group. In a DAN case where drift divers were left behind, DAN's comment was that a float line with a surface marker is a more dependable way for the boat to monitor drift divers. On most guided drift dives that marker is the guide's, which is one more reason to stay behind it.

How to use a reef hook

A reef hook is a metal hook on a line that clips to your BC, used to stop and hang in one spot while the current runs past. It suits sites where the action is at a fixed point, such as a channel mouth or the edge of a plateau. PADI's description of Palau's Blue Corner is typical: drift towards the corner, hook in on the plateau out of the current, and hang there. Dive operator Emperor Divers describes the method this way:

• Clip the line to a D-ring on your BC, ideally at the waist and in the centre.
• Hook only into a hole in the seabed or a dead rock. Never onto anything colourful, and never onto live coral.
• Add air to the BC until the current lifts you off the bottom and holds you in place without tugging on the hook.
• Deflate the BC before you unhook, or you will leave the reef on an uncontrolled ascent.

Which surface signalling devices to carry

An SMB and a reel at the very least, according to DAN's advice on current dives, and many divers add a whistle and a signal mirror. The table shows what each device does well and where DAN's case reports found it wanting. Carry more than one type: a device that works in one situation can fail in the next.

What to do if you get separated on a drift dive

Look for no more than one minute, then ascend safely. That is PADI's advice for losing your buddy, and in current it matters more, because every minute of searching puts more distance between you. Send up your DSMB before you surface or as soon as you arrive, so the boat has something to see.

At the surface, stay together and stay visible. Inflate your BC, keep the SMB up, and use the other signals when a boat is in sight. In one DAN account, four divers spent more than four hours in the water and ended up 3-4 miles (about 5-6 km) offshore; their whistle failed to reach an upwind boat, and a search boat finally spotted their safety sausage. The guide kept the group together by having everyone join hands.

Boats lose divers too. In another DAN case, a crew member was freeing a line from the propeller when five drift divers surfaced, and the one sausage they raised went unseen. The group swam for 45 minutes to a deserted island and was collected about an hour after reaching shore. DAN's lessons: bright, large visual signals, more than one type of device, and consider a GPS-based distress device.

Gas planning for a drift dive

Plan an ascent pressure, not a turn pressure. DAN's rule-of-thirds advice is for current dives other than drift dives, where you start into the current and ride it back; swimming against it costs effort and gas on the way out. A drift dive has no way back, so the number that matters is the pressure at which you start up with enough left for the ascent, the safety stop and a problem on the way.

Here is a worked example with our gas planner, which uses gas = SAC × time × (average depth ÷ 10 + 1) and rounds pressure up to the next 5 bar. The dive: a 12 L cylinder filled to 200 bar, 40 minutes at an average of 15 m, maximum 20 m.

The second case is the one to plan for. A drift dive that involves finning to hold position behind the guide, or a hard kick into a hook-in point, is working time, and you don't know in advance how much of it there will be. If your SAC might rise to 20 L/min, cut the planned time to 28 minutes, or agree with the guide that you will start up at 80 bar. Our rock bottom guide explains the reserve calculation step by step.

• At a SAC of 15 L/min: 15 × 40 × 2.5 = 1,500 L, which is 125 bar. Rock bottom for 20 m, with the planner's default stressed rate of 30 L/min (twice the planning SAC), is 717 L, or 60 bar. Total 185 bar: the dive fits with 15 bar to spare.
• At a SAC of 20 L/min: the 40 minutes need 2,000 L (170 bar) and rock bottom rises to 956 L (80 bar). Total 250 bar, far more than the cylinder holds.
• At 20 L/min, the time that fits is 28 minutes: 20 × 28 × 2.5 = 1,400 L (120 bar), plus 80 bar of rock bottom, is exactly 200 bar.

Where drift diving is common

Wherever tides or ocean currents run along reefs, walls and channels. The four below are well-known examples, each described in its source's own words. Local rules vary as much as the currents: Cozumel's national park authority, CONANP, tells visitors to keep 1.5 m from the reef, not to touch it, not to wear gloves, and to dive only with boats and guides it has authorised.