Which Weight System?
Brace Systems Ankle Weights To a degree, this is one of those "what suits you" answers, with a number of main options available, particularly for mounting lead on your waist. However care needs to be taken to carry the correct amount of lead and maintain your trim in the water These two points will be dealt with first since they should affect what you buy and whilst "Buoyancy Checks" are a feature most people are aware of to a greater or lesser degree, "Trim" is not something regularly covered.
The best way to find out how much lead you should be carrying is to carry out a buoyancy check by physically checking it in the water.
You simply go into some shallow water (2 metres?) with a buddy and a lot of loose lead blocks. You should only have:
You then gradually add lead to a belt around your waist until you are able to just sink and float in mid water. This should enable you to maintain a decompression/safety stop at 3 metres (9 feet)
Remember that your buoyancy needs to be checked in both fresh and salt water since more weight needs to be carried, in greater saline conditions. This also means that weighting can vary from ocean to ocean so you will need to check it every time you go to a new overseas destination or use different equipment (most notably when swapping between aluminium and steel tanks).
Typically there is a 2 Kg difference between salt and fresh water, but this will very much depend on the individual and equipment carried!
Trim refers to the position you naturally take when swimming in the water.
You frequently find that divers, particularly trainees, swim in a feet down position (Figure 1) stirring up the silt and fighting a lot of unnecessary drag. This is usually a symptom of one or more factors, namely inexperience, poor technique, over-weighting and/or poor buoyancy control.
Ideally a diver wants to be in a horizontal position (Figure 2). This relies on both getting the finning technique right and being properly weighted. (Finning will not be discussed here, but some of the video clips of finning techniques in the Links section will help.)
It helps to think of a diver as being a little like a see-saw, to review a little bit of basic physics, the downward force on each side of a see-saw is the same as the the weight multiplied by the distance from the centre point (fulcrum). So for example, if 1kg is 60 cm from the fulcrum, a 2kg weight on the opposite side would need to be 30cm from the fulcrum for it to balance equally. Needless to say a diver underwater is far more complicated than a simple seesaw, but the basic principles hold, since you can move weight arround to change the normal trim in the water rather than adding additional weight.
It is important that you initially need to know how much lead you should be carrying (above) and you can then distribute it across your body.
To get the proper trim in the water, a diver should be able to float neutrally buoyant in mid water in a horizontal position.To check it simply stop finning, make sure your buoyancy is right and keep completely still. If you go head down, you have too much weight on your upper torso (Figure 3) and need to move it downwards; foot down (Figure 1) and there is too much on your lower torso and need to move it up, this latter symptom is less likely unless over-weighted.
The centre of gravity (fulcrum) is indicated by the red triangle in Figures 2 and 3 and is around the waist/groin area, when checking your trim it may be best to start with all your weight on a belt and try moving it from there if necessary.With a lot of heavy equipment being carried on the upper torso, adding a V-Weight or P-Weight, whilst appearing beneficial due to the elimination of the traditional weight belt, may result in a loss of trim by moving weight upwards. This is a common cause of the head down position (Figure 3) shown above, particularly in twin set divers, if this is the case, a Tail Weight may be a better alternative since it moves some of the weight down; some people in this situation have also found that replacing the traditional (heavier) steel backplate with an aluminium one may help if they then keep all lead weight lower on their waist.
If you don't maintain a strictly horizontal position and you can't fully correct it by moving weight about then you can try to alter you natural body position, particularly if using a frog kick/modified flutter kick. Bending you knees more and keeping your head down will move the centre of gravity towards your head, likewise a straightened leg and head up posture will move it towards your feet.
Unfortunately as you may have now realised, there is no one way of getting your trim right and it depends very much on your height, build and equipment...all you can do is get in the water and experiment.
Equipment Types
The options available for carrying additional weight are quite varied and detailed below. There is no particular preferred option when "waist mounting" lead
These consist of a buckle threaded onto 2" webbing with blocks of 1, 2 and 3 Kg. This is the cheapest option, but some people find them uncomfortable, with the lead weights digging into the hips.
These are made up with a large pocket into which shot is poured, to the required weight. Most people who try this option don't go back to a lead block belt, largely due to the comfort-factor, but you need to be careful that it fits properly and will hold the shot securely. It will also leave a nice puddle on the floor of your car, not that that should be a problem if you are thinking of taking up diving… Some shot belts seem to stretch when they get wet, so you may need to re-tighten them at the start of the dive, when you reach the bottom.
It is relatively difficult to adjust the weight in a standard shot belt to allow for buoyancy changes over time or changes in other items of your equipment such as swapping cylinders between dives. To overcome this some shot belts have external pockets to take lead blocks.
When you buy new shot, please ensure you wash it out if you intend trying it out in the pool. Some shot can be filthy!
These are, as the name suggests, belts with a series of small pockets along their length. These pockets can take standard blocks of lead (cheap) or pre-weighed pouches of shot (comfortable). This may offer the best compromise between the easy adjustability of a standard belt and the comfort of a shot belt.
This is probably the most expensive option and uses a set of braces to support the lead weight (shot or block), which is often left on the hips and away from your back (shaded in red on left image, click for a larger image excluding shading).
They feature a quick release pouch system so that pockets of lead can be pulled out and dropped in an emergency. These systems are particularly useful if you suffer from back trouble or lack a waist line.
It is possible to make a "brace system" if you wish to try. Modular versions which can be fitted to harness/backplate systems are also available from Halcyon and some other suppliers but remember that this will increase the weight of your equipment particularly if someone else has to lift it into a boat etc.
If you are buying a twin-set, you can use a V-weight instead of a weight belt. A V-weight is a "Toblerone" shaped lump of lead that fits between the cylinders and the backplate. This weight cannot be dropped, so you need to ensure that you can release at least one other piece of heavy equipment in an emergency. It also removes the weight from your lower back, reducing the potential for lower back pain. These are normally 4 Kg or less.
V weights are available in 1 Kg blocks from Underwater Explorers and Aleutian Diving Products or for instructions on making your own, visit Jim Cobb's Trimix Site
These work in a similar way to V-weights but can be heavier and fit between the backplate and the diver. They have to be made individually due to differences in the size of the groove. The image on the left shows a wopping 8 Kg In place on an un-webbed backplate.
See the section on "Trim" above
For instructions on making your own P-weight, visit Jim Cobb's Trimix Site
These are similar to V-weights but are usually smaller and fit below the lower band on a twin set, rather than between the bands in the case of a V Weight. They have to have a tab with a hole in which fits over the lower bolt to keep it in place. They can be very useful in getting the weight lower down on a twinset when trying to balance your trim.
They can be used in conjuction with a V weight if necessary and are available from Aleutian Diving Products
Backplates are usually supplied in 3mm Stainless Steel (bottom left) which allows people to remove a little weight from their belt (none if made from aluminium). Thicker and heavier backplates are available, a 6mm backplate (top left) will allow you to remove a further 2kg compared to the 3mm versions.
Polished 6mm plates are available from Aleutian Diving Products, and you can also specify the exact placement of holes etc.
Ankle weights should not be needed by any diver. "Floaty" feet are due to only two causes - either having too much air in your drysuit or having buoyant fins. Either problem should be easily avoided, either by just using enough gas to offset suit squeeze or by putting the pennies you might spend on some ankle weights towards some solid rubber fins (See Which Fins?).
Whilst ankle weights may be of some limited benefit in helping you correct your trim, the benefit is minimal at best and the gain offered could be easily acquired through techniques described above.
A weight belt can also be worn beneath a crotch strap if you have one, this would theoretically catch the belt if it were released and the crotch strap were not already loose.
| Unfortunately there is no magic formula for weighting. It is a case of try it and see, but DO make sure you only carry as much lead as you really need to, divers commonly carry too much, and DOo try to get you trim right, your diving will be enhanced no end if you can hover in a horizontal position with no effort. |
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Diving can be a hazardous sport and the information contained within this site is not intended to replace formal training.
Furthermore no responsibility will be accepted for any accidents, injuries or financial disadvantage, howsoever caused.
Copyright © H Beasley 01 August 2001 All Rights Reserved
