On rigs and offshore vessels there are rope nets stretched on the helideck to reduce the risk of skidding after landing and before wheel chocks can be positioned.
In the situation I described the Floatel was a semi-submersible laybarge and the platform the Statfjord B in 1981:
The operation of shuttling was routine every time the gangway had to be removed due to weather. 150-200 persons transferred each way by 3 x S-61 choppers in 1-1.5 hrs.
In the case of Viking Sky there were no helideck, or designated winching zone (AFAIK), thus the procedure was decided on the fly.
PS> I posted about a storm on Statfjord B/ LB 200 here:
Pictures of 70+ foot seas