Some of the Trans-Atlantic Cables head out from the west coast of Scotland.
As well as slightly reducing the lengths as Zarjaz has said, because of the nature of the coastlines and depth of sea-bed in those parts, gives some protection from shipping, anchors and fishing trawls.
If a cable gets damaged or broken, it is very costly for a highly--specialised cable ship to head to the general area of the break, locate it specifically, , dredge up the broken ends, cut back to a good section, not damaged by water ingress, splice the replacement cable in at one end, then move possibly a mile or a kilometre to the suitable point in the other part; going through the whole rigmarole at the other end.
In itself, depending on the sea depth; and the angles of dangles, there may be similar lengths of cable unsupported during the operations, thus liable to further damage.
The end result of that part is that the repaired cable is now longer than the original, straight-laid cable.
The structure and impedance of the replacement cable must be reasonable matches to the original cable, to avoid reflections and losses, as Zarjaz is aware of by his use of TDRs/JDSUs.
Such cable may not be available "off-the shelf" etc.
Once the initial physical repair has been carried out, the repaired cable has to be tested, end-to-end, to ensure that the necessary electrical parameters are met.
All on the stormy ocean and sea, with tidal surges etc.
Note the sizes of those ships.
Oil and gas under-sea pipelines have similar arrangements, along with the few Electricity Inter-Connetors.
Edited by eckiedoo (Fri 05-Jan-18 19:21:43)