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Freediving Safety Lanyard Test Recommendation
AIDA International competition rules do not have a good basis for safety lanyard tests. Currently all the lanyard
tests in AIDA competitions are performed by the judges in subjective and varying ways. Therefore, I have created
this simple lanyard safety test/check recommendation. This test method is based on some physical facts
(calculations by Mikko Pöntinen):
1. Minimum sudden force and drop test
The force that the drop test creates on the lanyard depends completely on how much the lanyard stretches. The
more it stretches, the smaller the force against the lanyard. The reason for this is that when the lanyard cable
stretches more, the weight has more time to decelerate, so the impact is not as sharp. Some examples:
5-kilogram drop from 1 meter:
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Lanyard stretches 5 cm: Force = 980 N (approx. 100 kg)
Lanyard stretches 2 cm: Force = 2,450 N (approx. 250 kg)
Lanyard stretches 1 cm: Force = 4,900 N (approx. 500 kg)
Lanyard stretches 0.5 cm: Force = 9,800 N (approx. 1,000 kg)
Lanyard stretches 0.1 cm: Force = 49,000 N (approx. 5,000 kg)
20-kilogram drop from 0.3 meters:
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Lanyard stretches 5 cm: Force = 1,180 N (approx. 120 kg)
Lanyard stretches 2 cm: Force = 2,940 N (approx. 300 kg)
Lanyard stretches 1 cm: Force = 5,880 N (approx. 600 kg)
Lanyard stretches 0.5 cm: Force = 11,800 N (approx. 1,200 kg)
Lanyard stretches 0.1 cm: Force = 58,800 N (approx. 6,000 kg)
Drawing conclusions from those numbers, I would advise freedivers to construct lanyards that stretch somewhat,
because they are stronger and will not dislocate divers’ shoulders in worst scenarios.
2. Constant force
Calculating the drag force of diver when a counter-ballast system is pulling him or her up, we can use the drag
equation
where:
F is the force of drag,
ρ is the mass density of the fluid (1,000 kg/m^3 for water),
u is the velocity of the object relative to the fluid (1.5 m/s for a normal counter-ballast system),
A is the reference area (which depends on the position and the size of the diver, but let's say it varies between 0.1
m^2 and 1 m^2), and
C is the drag coefficient (0.7–1 for a diver)
D
D
Therefore, the maximum drag force is
F = 0.5 x 1,000 kg/m^3 x (1.5 m/s)^2 x 1 x 1 m^2 = 1,125 N = 115 kg.
D
We add to this the negative buoyancy of the diver, which at worst is 5 kg. This means we end up with 120 kg.
120 kg drag is a worst-case scenario where a very big diver is coming up sideways (the lanyard is attached to a
waist belt) at the speed of 1.5 m/s.
A more realistic drag would be:
F = 0.5 x 1,000 kg/m^3 x (1.5 m/s)^2 x 0.7 x 0.1 m^2 = 80 N = 8 kg
D
Again, we add the negative buoyancy to that force, and we get 13 kg. 13 kg of drag is a more realistic scenario,
where a diver is coming up one hand first in a somewhat streamlined position.
Conclusions and a suggestion for safety lanyard test for competition
judges
This lanyard test should be simple enough and easy to be conducted by every freediver, judge and competition
organizer. The purpose of this test is to make it possible to ensure that the competition lanyard has been properly
constructed, and that it is safe enough for competition conditions. The lanyard test should be also similar (that is,
standardized) for all athletes, judges and organizers.
My recommendation is that the lanyard test would consist of doing a 5 kilogram drop test from 1 meter, or else with
a 20 kilogram drop test from 0,3 meters (which is the minimum length of the lanyard, according to current
competition rules), while the wrist band is attached to a strong and stable bar that has about the same diameter as
a wrist. Five kilograms of weight is safer for the judges/testers to handle, and is easier to arrange. Both tests are
enough to reveal if a lanyard is not strong enough, but every well-made and safe lanyard should withstand either
test.
A constant drag force test should be performed on a wrist velcro attachment. As the figures indicate, the drag force
is much smaller than the sudden force, so I think every lanyard that can handle either of these drops test will
endure the constant force test as well. Therefore, my suggestion is to test constant drag for 1 minute with 75
kilograms (or with the diver’s weight—hanging on to it when lanyard is attached).
A lanyard should also be allowed to be elastic to increase its safety (based on the calculated facts above). Therefore,
in both of these lanyard tests, the length of the lanyard should be allowed to stretch a maximum of 25 % in
addition to its original length.