Buoyancy

[DaleC]

Just a point; a steel tank varies in buoyancy as much as an Al tank. Cold water divers use steel tanks because they are heavier and thus, less weight is needed on the belt. The buoyancy shift is simply the amount of gas you breath during the dive.

I do prefer St 72's for BC-less diving though, because the shift stays right around the neutral buoyancy mark. I am a touch buoyant myself, so only minimal weight is needed to make both myself and the rig neutral.

 

[elan]

Ditto to what DaleC said , it does not matter which tank it is the buoyancy swing is the same per cuf of same gas.
Many people are confused because they carry their weight on the belt so at the end of the dive the tank pulls forward as its buoyant while the weights still pull down this creating that confusing feeling of AL having more swing.
If one uses a BP or places the weight into the trim pockets on the tank this feeling is gone and you do not notice that difference

 

[Peter Guy]

Cold water divers use steel tanks because they are heavier and thus, less weight is needed on the belt.

A more accurate statement would be "because steel tanks tend to be more negative and thus" -- in fact, a steel 100 is lighter than an aluminum 100 -- but the steel tank is more negative which is what really matters to cold water divers.

 

[it_mike]

Just wait until you change your undergarments...

Warmer or colder water usually means thinner or thicker insulation. This leads to buoyancy changes.

 

[DaleC]

A more accurate statement would be "because steel tanks tend to be more negative and thus" -- in fact, a steel 100 is lighter than an aluminum 100 -- but the steel tank is more negative which is what really matters to cold water divers.

Yes, of course I was referring to weight in the water, or negative buoyancy. But a good clarification for accuracy sake.

 

[Diving Dubai]

I concur with all of the above. I started the year as and AoW with 22 dives over the preceding 4 years, I'm now knocking on the door of my first century (96 dives - 74 this year) Yes Buoyancy and air consumption does take time to master and improves with experience further training in this is always worth doing in case you're getting into bad habits. From my recent personal experience I thought I was pretty happy with my buoyancy - in a tropical set up with a wing and 5mm suit and 15l steel cylinder I was carrying 2lbs after a recent live aboard holiday being forced to use a 13L aluminium tank I started off with 6lbs and at the end of 2 weeks was down to 2lbs weight and a similar air consumption and time underwater to what I was before but with a smaller tank and lower pressure. As some point you'll realise you've made a huge leap when you realise you've not had to concentrate on buoyancy and you come up with more air..

You also get an inward sense of self satisfaction watching other divers flail along suing their hands while you glide about ...

 

[IanHussain]

HI there I have been researching similar tips lately. I passed OW last year and since followed up on 2 diving trips. Buoyancy did not seem to be a problem on the course and subsequent dives as the Dive Master had determined the correct weight that was required. The follow trips were always a struggle, and I largely believe that, while on holiday and on fun dives, the operators guess the weights that you require. I am now preparing for a liveaboard and been researching the subject, only to find out that weight you require is largely your responsibility and that there is a methodical approach to this.Here is the first tip...(I cannot recall this lesson as part of my OW)

Often proper weighting is determined through a process of trial-and-error experimentation. To start, you should complete a weight check by completing the following steps:


1 - Enter the water wearing all gear and an estimated amount of starting weight. This amount can be the weight you think you will need or the estimated number advised by a dive professional.
2 - With the regulator in your mouth, take and hold a normal to full breath.
Deflate your BCD – If you are “properly” weighted you should float at eye level and when you exhale you should descend.
Tip: remember to keep your legs still and do not kick! Any kicking motions will move you upward in the water obstructing your ability to determine the true amount of weight required.


3 - Add or subtract weight as necessary until you float eye level in the water; vertically at the surface.


It’s worthwhile for a diver to complete or repeat the steps above upon surfacing after a dive. The reason why it’s a good idea to complete a weight check after a dive is to make up for the buoyancy shift your cylinder may have during the dive. When a cylinder is full at the start of the dive, it may be heavier versus a near-empty cylinder at the end of a dive.