Jump Training and Depth Testing

Do we sink like a stone or float like a butterfly?

This wasn’t our most scientific endeavour. However we did set out to determine if there was any
consistent factors which affect how deep we go when jumping from a 10 metre cliff. So having
gathered a group of unsuspecting instructors of varying shapes and sizes we set off to Plymouth
Life Centre, utilising their competition diving pool. This pool has a number of different height dive
platforms and a 5 metre deep pool, in which we suspended a marked rope so we could judge how
deep people would go.

Depth testing for coasteering

Different buoyancy aids were used and we deliberately haven’t named which performed best as obviously this would be commercially sensitive. But what we can say is, some performed better than others, and it wasn’t always the latest or most expensive that came out on top.
Each subject jumped a number of times, firstly with the different buoyancy aids which ranged from 50N to 70N and 100N. Then without a buoyancy aid and then finally some jumped without a buoyancy aid or wetsuit to look at how much resistance was gained from the buoyancy within its neoprene.
The first noticeable issue with our test was that because the subjects couldn’t wear shoes in the pool the impact on their feet was causing concern. It was apparent that this was making people retract their legs as they entered the water. Pictures taken in the pool illustrate the scooped landing that resulted from the involuntary self preservation.

The results from this first round of test are illustrated below. From these figures it was considered that the floatation provided by the buoyancy aid wasn’t having a great effect upon the depth reached. The major variation was related to the weight of the individual. Whilst this isn’t surprising, the change from using a 50N buoyancy aid to one with 100N was negligible.







2.3 3.5 3.5 4
2.5 3.5 3.5 3.5
3 4.5 4.5 4.5
2.5 4.5 3.5 3.5
2.5 3.5 3 4
3.5 3.5 3 3.5
3 3 4.5
4.5 4


2.79 3.95 3.5 3.94


When the buoyancy aids were taken off then the depths varied by just over half a metre. This illustrated that the buoyancy aid does make a difference, but not by an amount that was significant given the variables that need to be accounted for when guiding groups in this dynamic environment. A random experiment to see how much difference the wetsuit made saw Jon drop to 4.5 metres whilst wearing a 50N vest. This indicated to us that the buoyancy within the wetsuit
(particularly a winter thickness suit) may have a greater effect than what sort of buoyancy aid you wear.





5 4 4.5
4.5 4.5
4.5 4


4.67 4.17


Whilst the this non-scientific experiment doesn’t gives any real hard data about the factors which make some people go deeper than others, the general observations were :

underwater picture of landing

1. Body position as you enter the water greatly effects how deep you go. The straighter the legs remain in the water the deeper you go.
2. Body position in the water is greatly affected by the way you jump. If you step off and drop dead straight you tend to go deeper. If you make a positive leap forward where the legs are straight as you enter the water the forward momentum appears to bring your legs up in the water slowing your descent.
3. The wetsuit makes a big difference.

4. The buoyancy aid makes some difference but not a lot. Despite this the height that the individual floats in the water did vary greatly and this may make noticeable difference when working in swell.
5. The greatest factor in how deep you go is how big you are.

Straight landing after 10m jumpSo in conclusion what does this mean for us as we take out the public with their endless variations in sizes and shapes. If your working parameters dictate that you never jump from higher than 10 metres then you need a minimum of 5 metres of water below you. How you measure this is something that should be addressed in the operating procedures and must always be conducted at a know tide height against which it can be compared.
On a personal levels all the subjects commented about how much value it was to jump consistently from a know height and to be able to concentrate on their own position both in the air and the water. Oh! and above all it was FUN.


By Mick Burke – www.soggylemming.com