[_yb2s]

They didn't really need an expensive and complex "umbilical cord" type of system, but a simple rope could pull the sub up in an emergency, and keep it from getting lost or separated from the ship.

This sub has 4 Innerspace 1002 thrusters that make for a max total of 342*4=1,368lb of thrust... I think a useful point of reference in deciding how much pull force would be needed for an emergency recovery tether.

I think it's reasonable that a 4mm dyneema line with a breaking strength of 4,000lbs would be sufficient for emergency surfacing, and safely provide much more thrust that it's own motors. The whole sub weighs 23k lbs and is approximately neutrally buoyant.

Total weight for 3 miles of 4mm dyneema is only about 120lbs, and for simple emergency use, in the spirit of OceanGates now infamous "scrappy thriftiness" could be pulled with the type of simple/cheap hydraulic winches used for pulling crab pots, anchors, or fishing nets. 3 miles of this line would have cost about $15,000.