Part 1: Checking Conditions
Diving in strong currents can be daunting and can be dangerous, if not done with the right precautions, preparation, and gear.
Here are a few tips (divided into 3 posts) to minimise the risk of mishaps and maximise fun and safety.
Part 1: Checking conditions
Part 2: Being prepared
Part 3: Essential gear
Dive site and topography
The first thing to think about is: 'is the site long enough and to an extent flat enough to drift along?'. If you have a short labyrinthine reef that then takes out to deep sea, it is perhaps not the best site for strong current drift diving. Ideally, you want a wall or a sloping reef, the occasional formation to hide behind is nice too, but you don't want vastly varying depths with fragile outcrops. You need to have a good idea about where the current will go (usually, of course - always expect the unexpected). Is there a split, a pull out to sea, upwellings, down currents, etc? Will it take you into a busy harbour / passage spot or fishing area?...
Assess your dive site and do a good few runs with a team of good divers. Also crucial is to have an alert captain and a surface team.
Tides
Tides are the single biggest influence on the strength of the current, Divers usually like to go out at slack high which is just the time before the tide reaches peak high tide. There is the least water movement, the water is stilling at high. Since it iss high tide, the visibility is better since it's clear water coming from the high sea rather than water coming in from the shore and inlets at slack low tide. If you miss it even by 20 minutes, the water can suddenly start moving very fast again, almost without warning, and can also change direction unexpectedly. But this is a rule of thumb and might not apply to the area you are in.
Find out what is the best time according to tides in the area you are in. Whatever you plan, and however well you have planned your dive, when scuba diving in current the rule is ALWAYS: « expect the unexpected ».
Moon phase
The moon influences the tides so logically influences the currents. At certain points in the month, the gravitational pull of the sun is added too, making for even bigger tides. The bigger the tide coefficient (the difference between the low tide and the high tide levels), the stronger the currents. The bigger the difference between the two, the more water will be moving. This often corresponds with the new moon or full moon. You might want to check if planning a trip to a strong current area during or just after these phases. It may be depending on whether you are a current junky and want your fix or would rather have some calmer dives. The neap tide or lesser current tides usually take place in the 1st and 3rd quarter moon, where it appears 'half full'.
Winds
Winds don't necessarily have an impact on the currents per se but combined with underwater topography can create swell. This can create a pull and push movement underwater which can be confusing to evolve in if you're not used to it. The key is don't fight it, use the push movement to advance, just resist gently on the pullback.
The issue with wind, however, concerning dive sites with strong currents is that it can create waves, which may impede the boat's ability to see you. You'll want to check weather conditions beforehand because if you drift far on a choppy sea even with a long fully extended DSMB it may be hard for the boat to spot you.
Weather and time of day
The same goes for anything else that might make finding you more difficult for the boat, such as heavy rain, mist, or dusk. Choose to dive on strong current sites on clear days, if in doubt make sure you have the right gear if you still decide it is ok to dive (we'll get back to that in part 3). Plan your dive early enough in the day so that the boat is not looking for you when the sun is setting, or, if they can't find you, are sending a search party out at night. Remember currents are unpredictable and you may end up somewhere unexpected; put all the chances on your side of being picked up easily and rapidly by having good surface conditions.
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