I have chosen to use the Oil Mariner as an example of the typical Ysselwerf design of which about a dozen were built for UK shipowners between 1972 and 1976. This Dutch shipyard took on the task of producing ships for the increasingly large British offshore sector, when British yards did not seem to be capable of responding with either designs or actual construction as fast as the owners required. Where were the Norwegians you might ask, well believe it or not they were still feeling their way, although by now Tidewater had placed an order for two anchor-handlers with Ulsteins of which more later. And in the early 1970s Wilhelmsen Offshore were operating half a dozen ships built in America at the Mangone Shipyard, but although designated as anchor-handlers they were unable to deck the anchors then used by North Sea semi-submersibles. The designers at Ysselwerf had trouble sourcing engines of sufficient power which would fit into the engine rooms of these small vessels. Their solution was to use the prime movers originally designed for diesel locomotives and so some of these ships were powered by two Dormans, collectively producing 5600 bhp and later models with two English Electic engines producing about 3000 bhp each. They  had fixed pitch propellers and it took a heart stopping ten seconds to get from ahead to stop and another ten from stop to astern, resulting in a technique of always running one engine ahead and one astern when snatching at an offshore installation. They also had a Gill Jet forward, which was capable of providing thrust through 360 degrees, but which took an age to move from one of the fixed positions to another. It was possible to neutralise the sideways movement with the rudders and the water stream from the ahead engine, if that was necessary (further explanation of the technique in my book “Supply Ship Operations”). The ships were fitted with twin drum waterfall winches  controlled from a small house built above the main deck where the unfortunate engineer in charge would operate a large wheel to change direction and a lever to operate the motors. To get an anchor from the seabed to the deck in 200 metres of water took about 45 extremely boring minutes. A feature of this class of vessel was the large stern roller and wide gate over which they could haul the 30,000lb LWT anchors  and which would be secured on deck by using pelican hooks. This since after experimenting with a variety of wire securing means, the industry had settled on the pelican hook, traditionally used by the military to release anchors on old warships. Its main advantage was that it could be operated remotely from behind the crash barrier, by pulling a string. When changing from anchor-handling to towing it was necessary to close a gate over the roller, and then to loop the tow wire over it so that, on releasing the pelican hook, it would end up free to move around the stern.

Photographs: Oil Mariner on its way into Aberdeen by Gary Markham, and on its way down the River Dee by Victor Gibson.