Useful Information from CPA
The information expressed herein should be treated as opinion. No guarantee is given or implied that any advice on the CPA website is necessarily correct. Nor might it best suit other divers and clubs due to regional and personal differences. Diving is a risk sport. All advice herein should be validated with advice from your own diving club, governing body, or approved published material before being adopted.
Control ascent problems
Biggest problem of buoyancy is the vicious circle. Ascend a bit – air in BCD expands a bit. Expanded air is more buoyant, so you ascend faster. As you do, air expands even more, so you ascend faster still, and so on. So, the later you leave it to correct positive buoyancy, the harder it is to get it back to normal – until point where it’s expanding faster than you can dump, then you can’t avoid going to surface. Often ends in a bend. Only avoidance is early correction. Keep buoyancy neutral at all times. Never forget fastest way of dumping – breathe fully out. Gets rid of 2 litres at least and often nearer 4, and works at any angle of swim. Like getting 4 Kg extra weight in one second flat. The instant you spot you’re going up a bit too much, make it a reflex to exhale fast as first immediate response & hold it out, at the same time go for the dumps. While dumping, can slowly begin to inhale as buoyancy control regained.
Dive safely in a dry suit
Dry suits are dangerous – risk of uncontrolled ascent. Worse problem if inverted, as no way for air to get out. Best avoidance is dive semi-dry! Seriously. Ask if your kind of diving really needs a dry suit. If it honestly does, ok. Next best thing is to keep buoyancy correct every second of dive. Small corrections early are easy. Large ones after probs start are impossible. Next most important thing is not to dive too heavily weighted. Makes you put too much air in suit or BCD. Example: go up just from 10m to 3m and air expands over 50%. If weighted well with only, say, 10 litres of air in suit/BCD, then that adds only 5 litres more air to get rid of. With 2Kg too much weight at surface, need 4 litres more air at 10m to be neutral. Same ascent 10m to 3m will then add 50% of 14 litres, or 7 litres more air – an extra 2 litres to lose. Shows how being over-weighted makes the ascent spiral problem worse. If get into ascent spiral anyway, do emergency air mega-dump by pulling neck seal open. Will get wet and cold but not bent. If inverted – you’ve blown it. Even more dangerous to be too light of course. Remember you can lose over 3Kg weight of air breathed from single cylinder by end of dive. Without shot line or reef to hold onto, can’t avoid missed stops and maybe get a bend. So, get weighting exactly right in dry suit. Test fully kitted in target type of water (sea or fresh – weighting’s different) with 50 bar in cylinder so you can just float at eye-level and sink if you breathe out.
Control buoyancy in a dry suit
Two schools of thought. Method one says use suit just to get rid of squeeze, then use BCD to control buoyancy. Reason here is BCD dumps faster than some dry-suit dumps. Method two says use dry suit for buoyancy too and leave BCD empty during dive. Use BCD only after surfacing for floatation. Reason here is only have one buoyancy control to think about. Less chance of confusion in panic situation. Your choice. My personal recommendation is method two: do it all on dry suit. First, like the “single way of dumping” argument. Second, modern dry suit dumps are as fast as BCDs, and have the neck-seal option in extremis. Third, a good test of being correctly weighted in dry suit is that just removing squeeze should get you neutral anyway – if you need BCD too, you’re too heavily weighted. So, get your weight right and you’ll find yourself automatically using method two in practice even if you prefer method one in theory.
Safely reduce air consumption
Don’t skip breathe. You’ll risk a burst lung, build up CO2 and get a headache. CO2 triggers panting too – only makes air usage worse. Worse still, CO2 increases blood flow to slow tissues during dive and thus increases risk of decompression illness. Only safe way to use less air is to breathe normally but use less energy. Relax. Less effort not only safer, but makes dive more enjoyable too. To use less energy (biggest savings first):
- Slow down. Energy use increases massively (to the third power) with speed through water. Take it easy. See more by looking harder not swimming harder. Stop and look around a lot.
- Get buoyancy dead neutral all the time. If not you’ll fin to stay level without realising. Finning head-up or head-down means you’re not neutral (watch novices to see this). Wastes energy finning needlessly but angle also increases drag through water wasting even more. To check buoyancy, stop finning frequently – if sinking or rising at all, adjust buoyancy.
- Use buoyancy control to go up or down (e.g. shot line), not finning.
- Use currents when going with you, cheat them when against you – swim nearer seabed for less current, keep to shelter of rocks/wrecks where possible. Use a surge by floating with current and locking on as it reverses.
- Keep drag down. As well as swim angle, carrying bulky items, being over weighted (thus over inflated), using big diameter cylinders, dragging goody bags etc. all use energy.
- Gently pull yourself along on rocks or wrecks (with care) if possible – more efficient than finning.
- Get the most efficient fins you can afford.
- Stay warm – use appropriate suit for dive.
Avoid being lost at sea
You’re more likely to be lost than drowned. Incredibly hard to see a diver on surfacing – small black head only. Impossible in big seas or poor air viz. Increase your visibility. Coastguard recommend collapsible flag. Carry in elastic cords round cylinder. Deploy if boat can’t see you. Cheap. Highly effective. Big delayed SMB almost as good. Brightly coloured hood also recommended. If you have black hood, stitch cyclists reflective plastic strips to it, or buy special Day-Glo over-hood. More expensive option is EPIRB – Emergency Position Indicating Radio Beacon in small watertight box. Emits international distress frequency radio signal. Can be picked up by helicopters, boats, planes, and (more powerful ones) satellites. Warns of problem and guides help to you. Works in fog, darkness, high seas. Almost ideal.
Dive safely as a threesome
Main thing is to all agree how it will work before diving. Safest approach is for each diver to look out for both the others equally. If either goes missing for any reason – pair with remaining diver and follow lost buddy procedure, both surfacing after one minute to check where third diver is and raise alarm if not surfaced. More common “buddy pair with one tagging along” approach is not as safe. Worst situation is not to have agreed how the threesome will operate before the dive. Very common here for one diver to go missing then other two are tempted to continue dive on assumption third went off solo deliberately or “can look after himself”. Often turns out ok, but only luck that it does. Can be fatal.
Know when to use a Surface Marker Buoy
SMBs let boat cover keep track of you (stops loss at sea) and mark where you’re surfacing (stops being hit). Use one always – especially on drift dives – unless:
- Wreck diving – will get tangled, never go far, and can come up on shot anyway.
- Lake diving with buddies & surface cover, and no boats on lake
- Diving anywhere else that tangling a problem: under pier legs through arches etc.
- If not using SMB for any reason, must have Delayed SMB with you instead.
Deploy a Delayed SMB properly
Have strong strap or cord and clip attached to reel housing. At least 2 mins before end of Bottom Time, find strong tie-off point (wreck or big rock). Tie off locked DSMB reel to it. Unroll DSMB & secure to reel. Using auxiliary air (octopus, pony, air gun etc.) fill bag according to depth. Aim to have bag just full by time at surface, so at 10m approx half fill it, 20m third fill, 30m quarter fill, 40m fifth fill and so on (Boyle’s law). Only then, release reel lock and let bag go up. Don’t deploy DSMB with unanchored standard reel. Reel may jam then either you lose surface cover/tracking or get pulled up and miss stops. For unavoidable mid-water DSMB, use twin reels so if one jams can release whole DSMB rig to go up on second reel (and hope that doesn’t jam). Safer method is to go to first stop depth and drop full length of line from simple bobbin. Make sure unwinds all the way (watch it – may be hard to be sure in poor viz). Attach bag to unwound line & fill as before. Let line run through fist as bag ascends. Can’t snag this way. Be careful to watch your depth control while fiddling though – easy to lose it and surface inadvertently.
Keep together on drift dives
Easy to lose buddy on fast drift. Poor viz, or buddy clinging on to look at something gets pair parted in a split second. Buddy line one approach. Another is to use SMB line. Should always have SMB on drift anyway, so feed out more line and let buddy (or buddies), using gloves, hang on a few metres away.
Get safely back to a wreck shot line
Should always take DSMB on wreck dive. If all divers have them, skipper may plan to lift shot as soon as all down. Find out! If not, may want to come back up shot anyway. In very good viz, small wreck and easy navigation points, free-swimming no problem. Poor viz needs a pathfinder. Attach end of line from second reel (keep DSMB reel in case have to cut loose and ascend without pathfinder reel) to wreck near shot (never to shot line itself in case skipper does lift it!). Pay out as dive progresses and reel it in to get back to shot.
Get the most from a Personal Diving Computer
Read the manual and play with it a lot. Get to know the meaning of every number and display icon without having to think about it. Use it as teaching aid – watch it and think during dives to learn how diving behaviour affects deco obligation. Change diving behaviour in future to lower it. If new to PDCs, read the PDCs Crammer doc in the download section. Summary points are:
- Use PDC to augment SAA Bühlmann System not replace it
- Get right type of PDC for your kind of diving
- Nitrox PDC setpoint for PPO2 must match the diving mix
- Always have backup
- Never dive with PDC out of step with diver tissue saturations
- Dive to the most conservative of a buddy pair’s decompression obligations
- Treat PDC as maximum allowable – don’t dive up to the line unless you have to
- Learn your PDC limitations and dive defensively where its assumptions wrong