The goal of every diver should be perfect buoyancy and trim throughout the dive as it has so many benefits for every dive site and situation but buoyancy control is one of those things that only practice and experience can perfect. To help we have put together some useful tips to give you some key aspects to focus on and get you moving in the right direction.
Being able to control your buoyancy makes diving so much easier, safer and more enjoyable. Beyond the need to be able to maintain a certain depth for safety stops some dive sites and destinations will require you to maintain a minimum distance from the sea floor to protect marine life such as delicate corals or prevent fine particulates like silt from being kicked up and making navigation very difficult and visibility very poor.
Getting the Right Weighting
A lot of problems start with incorrect weighting. As you change your kit and even dive site you'll need to check you have the right amount of ballast weight. If you are brand new to diving you might have just recorded the amount of weight given to you by your dive centre and assumed that was what you needed. Unfortunately some centres will over weight new students to save time and help reduce any weighting issues during dives and skill practising.
It is important to check you have the right weight every time you change a fundamental piece of your equipment. Different thickness wetsuits will have more or less buoyancy as well drysuits and their various undersuits. Don't forget that switching between fresh and salt water dives will also affect the amount of weight you'll need.
How to Perform a Weight Check
- Get yourself upright on the surface (ideally after a dive when your cylinder is at its most buoyant), put your mask on and regulator in your mouth.
- Empty all of the air out of your BCD and drysuit (if wearing one) and hold a normal breath.
- With the breath held you should float at eye level to the surface so that when you breathe out you should start to descend.
- Remember that your cylinder will become lighter during the dive as you consume the compressed air (yes it has weight), that is why it is best to at the end of the dive. If you are doing it at the beginning of the dive just add an extra 1 or 2kgs to compensate depending on whether it is a steel or aluminium cylinder (ali cylinders will become much lighter).
When adjusting the amount of air and therefore the buoyancy in your BCD it is always best to make small adjustments, allowing a few seconds for it to take effect before taking the decision to make another adjustment.
Adding air is simply done by pushing the inflate button as the pressure of the air in the low pressure hose will force it in but when it comes to deflating you'll need to take in consideration your orientation in the water compared to the highest point of the BCD.
If you are swimming horizontally and just push the deflate button on the BCD inflator assembly there is a good chance that nothing will happen. Air will naturally migrate to the highest point of the BCD so you'll either need to use the most appropriate dump valve on your BCD or rotate your body so that your preferred dump valve becomes the highest point. This could simply mean a slight upwards orientation and hold the inflator assembly above your head.
Be aware of your depth. It goes without saying that as you change depth you will need to either add or remove air to compensate but your buoyancy is affected to a much greater degree at shallower depths.
It is not a linear scale so as you descend you will lose half of your surface buoyancy in the first 10m of your descent and a third in the next 10m. That applies in reverse for ascending so you'll need to be even more aware of your ascent rates the shallower you get.
Whilst it is one of the fundamental rules of scuba diving that you should never hold your breath it doesn't stop you from using the range outside your normal lung breathing capacity to effect your buoyancy.
The huge air space within your lungs can mean that slight buoyancy changes could be achieved without even touching your BCD controls. Taking a larger breath in will make you more buoyant whilst breathing out will lower it.
The best place to practice this method is in the pool first before moving on to a safe open water dive but remember not to hold your breath, just change the range of your breathing.
Practice makes perfect. The more you dive the more experienced you will become and the more time you'll have to perfect your buoyancy.
Courses to help divers achieve good buoyancy skills are widely available. PADI, for instance, offer the Peak Performance Buoyancy.
Whilst you are perfecting your buoyancy it helps to keep a record of your weight in your dive log as well as any kit alterations you make for a particular dive. As time goes on it will help you to build up a history that you can gauge your perfect weighting against.