Although concrete might at first seem to be a wholly impractical and rather cumbersome material to use in shipbuilding, in fact it makes a lot more sense than you might think. For boats over 25 feet long its often the cheapest and easiest material to employ. It doesn't need a weatherproof coating and it won't rust. Also a 30ft, 8 ton displacement vessel made of wood or concrete will weigh the same.
During ther First World War steel stocks were low. The British Admiralty ordered some support vessels to be made of concrete. Two were built at Whitehall Shipyard in Whitby, but by the time they were completed in 1919 the war was over.
...The wreck of The Creteblock on Whitby Scar is a familiar sight to anyone who has walked along the rocks to Saltwick Bay at low tide. In fact this vessel was not one of those from The Whitehall Shipyard. The Creteblock was built in Essex. She was too late to see active war service and was used as a tug before being sold to a Teesside shipyard.
Brought to Whitby in the 1930s she remained there, a decaying hulk until 1947. She was towed out to sea to be scuttled but abandoned before deep water could be reached. She now lies battered and broken, crewed only by barnacles, limpets and mussels in her final resting place beneath Whitby's imposing cliffs..