Weights and Wetsuits: Effectively Adjusting your Buoyancy
It’s that time of year again; the cold water upwelling is arriving to the reefs of the eastern Pacific Ocean. Suddenly our bath temperature water is dropping and could easily reach 16c in a cold year. We’re switching from our short 3mm shorties to our 7mm long suits followed by hoods, gloves and extra rash guards at some point along the way. With the changing of neoprene comes the changing of weights: more neoprene = more weights. The extra lead will off-set the buoyancy the extra neoprene holds and will enable a controlled descent but getting the balance right can be a challenge. The trick to good buoyancy is: how much extra weight do you need?
Why More Weight?
Your dive guide will no doubt ask you how much weight you think you need. If you’re using a rental suit this is often just out of courtesy to confirm what any experienced guide already knows by just sizing you up as soon as you step on the boat! If you have only dived in a 3mm shorty in the Red Sea in 85f, there’s no point insisting your log book states you need 8lbs when you’ve come to dive in the Pacific spring time in a 7mm long and 60f water temps. We want the group to have a comfortable dive, it makes life easier for all of us. With additional weights added for thicker suits you will be able to perform a controlled descent more easily. Please note the word CONTROLLED which is different to FAST! And don’t just pile on the lead. The CORRECT amount of weight ensures that you will make your air last longer, you don’t have to over-fill your BCD to stay neutrally buoyant underwater and most importantly you won’t be crashing into the reef destroying delicate aquatic life.
How to Establish the Correct Amount
“Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.” — Archimedes
Is a quote you don’t actually don’t need to learn to practice good buoyancy skills! But it’s the buoyancy concept and as a principle of physics we can apply some basic common equations to figure out how much weight you may need on your belt. Dive agencies provide basic guidelines that go something like this:
3mm shorty: 5% body weight
7mm long suit: 10% body weight
Aluminium tank: Add 2kg/ 4lbs
Steel tank: Subtract 2kg/ 4lbs
Boots or hood: Add 1kg/2lbs for each
Salt Water: Add 1kg/2lbs
Fresh Water: No extra weights.
These numbers are rigid and based on a person of normal build. Just as important is your BODY TYPE. If 2 people weigh 200lbs but one is a pro-athlete and the other a pro-eater we need to consider that muscle sinks and fat floats. In addition, if any of the neoprene you use is new then you need to add a couple more pounds.
Techniques to Use with Thicker Suits
The only way you are going to know for sure if you are correctly weighted is to do a buoyancy check in the water. Don’t be one of these divers who like to ‘be a bit heavy’. More weight means you will burn up air faster which brings your buddy out of the water sooner and you also risk getting too close to the reef. It’s a selfish diving practice. On my dive boat a weight check is mandatory on dive #1. How? You will need to have your mouth piece in as you deflate your BCD completely. Stop moving completely and exhale. Good weighting means you go down nice and slowly while staying very still and you don’t have to put much air in the BCD during the dive reducing drag and improving buoyancy.
Use the Buoyancy Compensator
Thick wetsuits are like a cork on the surface. That doesn’t mean you need to take the anchor with you to get to the bottom. Have patience, be completely still and a make a long, long, long, long exhale and you will make it down. Only after 10ft does the wetsuit suddenly compress making your descent quicker and quicker as air in the neoprene leaves the wetsuit. With the heavier weight system needed with the thick suit at the surface it is normal to feel quite heavy once at the bottom. Don’t be afraid of your inflate button! Add air slowly and steadily to the BCD. Let it do its job of keeping you nice and neutral. Guess what happens when you go up? Your 7mm wetsuit will suddenly ‘pop’ and become that cork again in a much more noticeable way than a 3mm. To avoid losing the group in an uncontrolled ascent and omitting a safety stop release any rapidly expanding air you put in the BCD at depth AS SOON AS you start your ascent.
Distributing weights evenly will help you to do a proper buoyancy check and control your position in the water during the more challenging ascents and descents thicker wetsuits cause.
The biggest mistakes people make when donning thick suits are; taking too much weight, omitting buoyancy checks and not properly compensating for extra weights suit during the dive with their BCD. If you have time take a buoyancy course. They don’t cost much more than a 2 tank dive, the training is extremely valuable and if nothing else it’s a good way to get your own instructor for the day!