I have recently been asked for my opinion and advice on
weighting and weighting systems. When it comes to deciding on the weight that
you need is falls into main areas: The Amount of Weight, needed to offset you
buoyancy, and The Distribution of Weight, for comfort, trim and emergency
procedures.
How Much Weight?
During a divers education they are taught how to calculate
and test their buoyancy to ensure they are properly weighted to maintain their
position in the water throughout a dive. For many divers this is where it stops
and only re-examine the issue if they make a kit change or dive in a new
environment, and sometimes not even then.
I think weighting is a much more on-going process than this
because many divers, especially to begin with, are constantly making subtle
changes and modifications to their kit configuration and the way they dive
until the find a system that they are comfortable with. With this in mind I
define weight into 2 categories: Useful Weight and Dead Weight. Useful weight
is any negative buoyancy that is offered to you through kit that you carry for
another diving purpose and is permanently attached throughout the dive. This
includes things like the empty weight of a cylinder (but not stage cylinders),
torches and battery canisters regulators and empty BCDs and wings. Dead weight
is any extra weight (lead) that we add to make our system neutrally buoyant,
this could be added to a weight belt, integrated pockets or similar.
To have the most
efficient system possible we want to maximise the useful weight and minimise
the dead weight. If we can do this we are then not just lifting and moving
extra weight that we don’t really other than to sink. To do this when you are
configuring your gear think about every item you are using, do you need it and
what benefit does it offer. So if for instance if you are diving in the UK with
a dry suit and you know you will need to carry more weight then why not take a
larger cylinder (which will also give you more gas for the dive) and make sure
it is made of steel. While doing this process don’t get too carried away by
just added more kit to your set up that you don’t really need as this just
becomes dead weight, and worse can lead to a greater chance of entanglement and
confusion. When configuring you kit you should still always be looking to
reduce waste and complexity while maintaining everything that you need to
complete the dive at hand. When working
the other way to a warm environment where you will typically be less buoyant,
and so need less weight, take an aluminium cylinder.
Finally when carrying out a buoyancy check, make sure you do
it with an almost empty cylinder and with only items that you always carry and
are not disposable. This will give you the minimum weight that you will need to
carry even at the end of your dive when you will be the most buoyant.
Weight Distribution: Trim, Comfort and Safety
At the early stages of diving getting down is the most
important thing and you have more to worry about than the specific location of
your weights. As you develop your diving this should be something that spend a
little more time considering.
First let’s look at trim and comfort. Improving your trim
allows you to move more easily in the water, reducing drag and therefore
reducing your physical exertion and so reducing your air consumption. The most efficient trim position is a flat body
with your knees up in line with your body and your feet above you. To begin
with this can be a strange position to be in as we are used to moving with our
feet at the lowest point and not above our head. To be able to maintain this
position comfortably we need to be in balance and this means having our centre
of mass and centre of buoyancy in the same location.
The natural centre of mass of a person is towards the centre
of the torso, for men this is slightly towards the shoulders and for women this
down towards the hips.This position is the point around which we can naturally
balance in equilibrium. For diving this is the point around which we want to
balance our buoyancy and weights. Firstly we position all of our standard kit (tanks,
Torches, BCD) around this point and should end up with relatively comfortable
set up. The easiest way to start positioning weight is to start close to the centre of mass with larger weights and as you move away the weights should be
smaller. This is due to the relationship of the moments around the centre.
For men typically using integrated weights or weights
attached to a cylinder dives a better trim position and comfort as it is closer
to his centre of mass. Women will typically find low integrated pockets and
weight belt s more comfortable for the same reason. Women have another added
advantage with weight belt comfort and that is their hips, or welt belt
retainers, which help to keep a belt from slipping down.
For added comfort splitting weights across multiple
locations (less on weight belts to reduce slipping) ensures that no one item is
too heavy during kit up, it also has added benefits when it comes to
emergencies which we will discuss later.
With regards to trim and comfort the last aspect is ankle
weights. Many people have strong views on this and at the end of the day it
comes down to personal choice. These are my thoughts on the issue. I personally
am not a big fan as I believe that they have the biggest effect on trim as they
provide a large moment away from the body centre which drops the feet.
I also think that they are working against you as, with a
dry suit especially, the buoyancy in your feet should naturally float your feet
to above your head and into a low drag position with no effort to the diver. If
you become comfortable and confident with you set up then feet high
orientations should not be an issue.
My final thoughts on weighting are to do with emergencies
and were touched on earlier. I strongly
believe that a diver should not have their weight all in one location as it
doesn’t provide many options in an emergency, you can either dump your weights
or not. If you distribute your weights across 2 or 3 locations it means that if
you did have a situation when you believed dumping your weights in the only
option then you can dump a small amount to make you slightly positively buoyant
and allow you to have a slightly more controlled ascent than just dumping all
of your weight. Also in terms of diver problems I think that many could be
solved before you dive by having proper weighting as it is surprising how many
divers dive with wrong weights, especially too many.
I hope that this blog helped and might have sparked some new
thoughts along the way. I would be happy to learn your views and opinions
because at the end of the day it all comes down to personal preference.
