We use similar metal springs here in Agios Nikolaos on Crete because every winter we usually get three or four quite serious surges. The springs help take the shock loads off the boat cleats. Stainless steel is a mistake though in these kinds of spring. It stays looking nice and shiny (so SWMBO is happy) but it work hardens over time and snaps. When we used stainless springs we'd break at least one per winter. We now used galavanised mild steel and, although they rust and look awful, (SWMBO is not happy) they keep on doing the job...