I’ve been puzzled by recent reports that Graythorp is the largest drydock in the world, as I’ve always thought H&W’s ship repair dock held that honour. Hard facts about dimensions and infrastructure are hard to get on the net though:(

If you look at the pictures, it’s clear that Graythorp is much bigger – 10 hectares, equivalent to 100×1000 metres. The gate is 122 metres. It’s a very different sort of dock, though: it’s not ship-shaped. It’s great for breaking up several ships at once (how it’s now used), but not so good for building a single large ship. I don’t know what it was originally built for, but it has been used for building offshore rigs.

http://www.ableuk.com/portfacilities-seaton.htm