Norway's Island Offshore is plotting more lay-ups during the winter months in an "unsustainable" market.

It already has four platform supply vessels (PSVs) and a subsea construction ship stacked, from its fleet of 25 units.

"We expect an additional minimum of four vessels to be put into seasonal lay-up during Q4 pending completion of current campaigns," the company said.

"Spot and term day rates for PSVs and AHTS are currently low and unsustainable following a period with some improvement.