St Mary Axe Boats

Lowry uses the phrase "St Mary Axe Boats" in his novel Ultramarine; "One of those bloody St Mary Axe Boats; the Leeway is knocking around here. Only its wings aren't clipped." (Pg. 33).

Lowry's seems to be using a slang/colloquial phrase perhaps used by sailors to refer to the Baltic Exchange which was located at 30 St Mary Axe in London.

The Baltic Exchange is the world's only independent source of maritime market information for the trading and settlement of physical and derivative contracts. Read more on Wikipedia. 

Lowry's reference may also have an ironic link in that the Leeway had been part owned by the St Mary's Steam Ship Co. Lowry's reference to the ship is probably due to members of the crew of Pyrrhus, on which Lowry sailed to the Far East, being familiar with South Wales where the Leeway had been based and the fact that the former owners St. Mary SS Co. were being investigated by the authorities for the loss of one of their ships the SS Eastway co-owned with Mr. Watkin James Williams. The case was reported in the Times and a full report can be read here.

Lowry's reference may refer to the idea that the Leeway maybe being set up to be "lost" as an insurance scam though this was not a conclusion of the inquiry into the loss of the Eastway. Lowry may have heard of  "death ships" - any boat so decrepit that it is worth more to its owners over-insured and sunk than it would be worth afloat. Lowry later would become familiar with B.Traven's novel The Death Ship, about such ships, originally published in 1926 but not translated into English until 1934 when Lowry probably read the novel as his German was poor.