Alex Griffin reveals how getting your weighting right is the most important aspect of mastering buoyancy when you are diving. (Text by Alex Griffin. Illustrations by John Grainger)
When you started diving you may have begun in a swimming pool somewhere, wearing a wetsuit that had spent most of its long and overworked existence doubling up as an adult nappy. Weight would have been generously supplied with the overall effect of gluing you to the pool floor like an electromagnet.
During your open water dives there’s a strong possibility that you wore your weight-belt lower than a hipster’s jeans and walked vertically through the water column with a fully inflated BCD worn as an attractive scarf.
Most divers will start out over-weighted to some degree. This is an inevitability caused by an initial lack of experience. Unfortunately many divers assume that they need more weight than they do and are scared of fast ascents and holding safety stops. This means they eventually learn to dive around the problem instead of fixing it.
GETTING YOUR WEIGHTING CORRECT
BUOYANCY CHECK: There is a tried and tested way to get your weighting correct. On the surface, you simply hold a normal breath and let the air out of your BCD and drysuit and you should float with the surface at about eye level. When you exhale you should slowly sink. This tends to work pretty well so don’t be scared to ask to do a weight check at the start of a dive trip if you’re not sure what you need.
I once saw a very slim lady wearing a shorty wetsuit wander over to the dive guide and ask for weight.
“How much do you want?” he said. Lady (very unsure); “Um, eight kilos?” The dive guide wordlessly handed it over.
So, take control of the situation and do a check. Remember it’s easier to add than to take away. Also remember that if your tank is aluminium that’s going to get over a kilo positive by the time it’s down to 50 bar so make sure that you compensate by adding one to two kilos at the start of the dive.
WORK ON YOUR BREATHING: If you’re on the surface hyperventilating from heat exhaustion caused by gearing up in the blazing sun (not a problem for me, I spend most of my time in cold, dark British quarries) then you’re going to struggle to empty your lungs sufficiently to sink. Wait until your breathing has calmed down, then exhale slowly and allow yourself to sink. The most important part is to ensure that you fully exhale and allow yourself to sink before you inhale again. If you do need to breathe, take a short, quick breath in and then completely expel it again. If you instantly take in another full lungful you’re just going to bob up and down on the surface whilst your buddy wads bricks into your BCD.
LOOKING GOOD UNDER THE WATER
Now we’ve got our weighting right, we need to get our trim sorted. Trim works on the basis that hovering in a roughly horizontal position is the most efficient way to dive. No-one glides through the water in a Buddha hover either, so you can knock that one on the head.
What can you do to try and get into a horizontal trim? It’s all about centre of gravity. Here are a few tips:
MOVE YOUR TANK: You know that thing instructors do where they lift up the BCD collar and show it in line with the top of the tank valve? It’s a good start point but it doesn’t always help. If you’re long and lanky like me then hovering horizontally in a wetsuit is pretty hard. Moving the tank higher up my back brings my centre of gravity forward and brings my legs up. If I lift my head I can feel the tank valve but it doesn’t bother me. The opposite is true if you’re lucky enough to have floaty feet. Simply move the tank down a bit.
MOVE YOUR WEIGHTS: Try moving your weight belt up your waist until it’s in line with your grandad’s trousers. You can do this once you’re horizontal so that it won’t slip back down. You can also use the integrated weight pockets on the BCD or trim pockets around the tank. All of that will pull your weight forward and bring your feet up. Getting your weighting and trim right is an ongoing process. Keep doing weight checks as your experience increases and your gear changes and you should find you’ll keep improving. Alternatively you can ignore all of this and go and roll about on the sand looking at the fish. It is supposed to be fun after all…