SIGNS THAT YOU MAY BE OVER-WEIGHTED * Bullet 1A sore back after diving
* Using more gas than usual
* Air escaping from the neck seal on your drysuit
* When you stop finning, you immediately sink to the bottom
* You are low in the water when at the surface
* A plummeting descent, ending in a rising cloud of silt on the bottom
* You find that you are continually finning in a near-vertical position in the water to maintain your position
* You find that you are constantly moving up and down and adding and dumping gas from BC or drysuit
* You have to use a BC as well as a drysuit for buoyancy
* Bouncing or dragging along the bottom underwater
* Over-exertion during the dive
* Finding it difficult to set off from the bottom at the start of the ascent
Salt and fresh water: You need to take off approximately 20 per cent of the weight you use in salt water when you move to fresh water and vice versa.
TOP TIPS1. Conduct a buoyancy check each time you change kit or after a long lay-off
2. Use near empty cylinders for the buoyancy check (approximately 50 bar)
3. Take weight off gradually
4. Adjust weighting to perfect your trim, so that when stopped, you lie horizontally in the water column, along both head-to-fins and
left-to-right axes
5. Ask your buddy to monitor your trim underwater
6. Take weight off when moving from salt to fresh water. However, bear in mind that salinities do vary around the world
7. Note down how much weight and equipment you are carrying, so that you know for next time
8. Keep trying to reduce weights carried
9. Ensure you can ditch your weight belt, or integrated weights, in the event of an emergency
10. Continually strive to perfect your buoyancy and trim
NINE STEPS TO CORRECT WEIGHTING
1. Find some sheltered water, accessible from either a jetty or boat.
2. Take half the weight off your weight belt and pass this to someone close to the water's edge.
3. If wearing a drysuit, crouch down to expel the air from the suit using a finger in the neck seal. Repeat if necessary until you feel as if
you have been 'shrink-wrapped'.
4. Once kitted up and buddy checks have been completed, enter the water. Keep the unused weights close to hand. Clip-on weights can
also be useful here. The task is made easier if someone close to the water's edge can pass weights to and fro.
5. Empty your drysuit of any remaining air and fully deflate your BC.
6. Breathe out. If your head drops below the surface easily, remove weight. If you are still high on the surface, add weights systematically
until your eyes drop below the surface and rise again on the basis of your breathing alone. Double-check that your BC is empty.
7. Adjust your trim. Ask your buddy to watch your position underwater, as you lie motionless. If your head tends to move up, experiment
by moving weight up the body. Try moving your cylinder higher on your back by adjusting the cam band, or replacing the equivalent lead
from ankle weights, if worn, onto the belt. If you are tending towards a head-down position, reposition the cylinder lower down.
8. Try remaining motionless for several minutes at 6m, or at the depth you normally conduct your shallowest decompression stops. Again,
do this with near-empty cylinders. Adjust weighting accordingly.
9. When equipment is changed, such as using a new heavy torch, or larger or more undergarments in winter, repeat the steps.
DIFFICULT DESCENTSIf you are correctly weighted but are having difficulties descending the first few metres, make sure all the air has been dumped from your suit and BC. Relax. Exhale slowly and completely and you should break the surface descending feet-first. Alternatively, make a duck-dive to break the surface. If you still can't get down, allow yourself to float up rather than continuing to fight your way down. Consider why you are unable to descend. Have you changed your kit? For instance, you could be wearing a bulkier undersuit. Are you certain that all the air is out of your BC? Finally, check that your buddies are not grinning broadly from the boat, waving your weight belt at you.
KIT BUOYANCY CHANGESWherever you dive, you are likely to require some form of thermal protection, be it a skin or wetsuit in the Tropics or semi-drysuit or drysuit in more temperate waters. Wearing an additional layer or moving to a thicker wetsuit will increase buoyancy. A thin wetsuit will trap less air than would be trapped between the layers of undergarments under a drysuit, or within the material of a neoprene drysuit. As drysuits and thick undersuits are more bulky, a larger volume of water is displaced, making the drysuit more buoyant than a wetsuit. The bulkier the undersuit, the more buoyant it will be. As depth and pressure increase during the descent, the air trapped within the suit compresses, taking up less volume and hence less buoyancy.
Neoprene drysuits can change volume significantly under water pressure - they may be buoyant at the surface, but during the descent will compress as pressure increases. The extent of compression varies from suit to suit and will depend on the material and manufacturing process used.
Adding an extra cylinder, or a heavy battery pack for an umbilical torch, will make a diver heavier in the water. A pony mounted on one side will increase the downward force on that side, sending the diver off-balance. Redistributing weight away from that side can solve this.
BODY MAKE-UPThere is no correct mathematical formula divers can follow to calculate how much weight they need, as body make-ups differ dramatically. The body is made up of different tissue types. The air in the lungs and fatty tissues elsewhere - being less dense than the surrounding water - together create an upward force or buoyancy. This is offset by the legs, which are made up of relatively dense bones and muscle that create a downward force in the water. The body is roughly neutrally buoyant in the water. However, buoyancy varies from person to person and between genders.
http://www.divemagazine.co.uk/news/article.asp?UAN=3937&v=4&sp=
