Effective umbilical management is a vital aspect of dive safety and is an integral part of Dive Supervision.

For passive (unmanned) tending the following constraints apply to the safe working distance for the working diver’s umbilical:

Cmax = D – 5 metres

OR

Cmax = A – 5 metres, depending which distance is shorter

AND

B is always less than C (This is to allow, in the event of an emergency, direct recovery of the diver to the deployment device.)

Where:

1. A  = distance from the deployment device to the nearest physical hazard
2. B  = distance from the deployment device to the in-water tending point
3. C  = distance from the in-water tending point to the diver
4. D = distance from the in-water tending point to the nearest physical hazard

Another useful Formula, used in Diving from DSV’s is:

FORMULA:         a²  +  b²         =       c²

a                                   =       diver’s depth

b                                   =       thruster distance

c                                   =       umbilical length

Example:

A DSV has a draught of 5 metres and its thrusters are 20 metres from the dive station. The diver is at a depth of 40 msw. What is the maximum permitted length  of his umbilical?

a           =       diver’s depth minus DSV draught.

             =       40 – 5 = 35 metres

b          =       20 metres.

   Therefore: –

35²  + 20²                       =  c²

1225 + 400                    =  c²

√1625                             =  c

c = 35 metres maximum umbilical length.

• IMCA D022. Guidance for Diving Supervisors Manual, section 8.22 (Umbilical Handling on DP Vessels)
• IMCA D010 Diving Operations from DP vessels, section 7, 10.3 (Diving Operations from Vessels Operating in Dynamically Positioned Mode)
• IMCA D015 . Mobile portable daughtercraft surface supplied systems
• IMCA D018 Code of Practice for The Initial and Periodic Examination, Testing and Certification of Diving Plant and Equipment.
• HSE ACoP 1997. Commercial diving projects offshore: Diving at Work Regulations 1997.
• IMCA D014 IMCA International COP. Section 7.3.20

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