After World War II, reduced budgets meant the Coast Guard continued to use its two existing wooden 52' MLBs, also known as the Type F lifeboats, Invincible and Triumph.
By the late 1950s, the wooden MLBs were starting to wear out and the Coast Guard built a set of steel 52' MLBs at Curtis Bay Yard to replace them, specifically designed for the high surf conditions encountered along the Pacific Northwest coast.
The steel 52' MLBs feature an aluminum superstructure and a hull divided into seven watertight compartments; because of their relatively high cost of US$250,000 (equivalent to $2,304,000 in 2018) each, only four were built.
After entering service, the steering/rudder system was modified by removing the rudder guard, shortening the bilge keels, installing twin rudders, and adding a hydraulic power assist to the steering.

The Coast Guard bills the 52-foot MLBs as "virtually unsinkable", with self-righting and self-bailing capabilities and the ability to tow vessels as large as 750 long tons (760 t) in 30-foot (9.1 m) seas.
In comparison, the next-largest 47' MLB has a towing capacity of 150 long tons (150 t).
To increase their endurance and capabilities, the 52' MLB is equipped with a complete galley and a fire/salvage pump with 250 US gal/min (16 l/s) capacity.
After World War II, reduced budgets meant the Coast Guard continued to use its two existing wooden 52' MLBs, also known as the Type F lifeboats, Invincible and Triumph. By the late 1950s, the wooden MLBs were starting to wear out and the Coast Guard built a set of steel 52' MLBs at Curtis Bay Yard to replace them, specifically designed for the high surf conditions encountered along the Pacific Northwest coast. The steel 52' MLBs feature an aluminum superstructure and a hull divided into seven watertight compartments; because of their relatively high cost of US$250,000 (equivalent to $2,304,000 in 2018) each, only four were built. After entering service, the steering/rudder system was modified by removing the rudder guard, shortening the bilge keels, installing twin rudders, and adding a hydraulic power assist to the steering.
The Coast Guard bills the 52-foot MLBs as "virtually unsinkable", with self-righting and self-bailing capabilities and the ability to tow vessels as large as 750 long tons (760 t) in 30-foot (9.1 m) seas. In comparison, the next-largest 47' MLB has a towing capacity of 150 long tons (150 t). To increase their endurance and capabilities, the 52' MLB is equipped with a complete galley and a fire/salvage pump with 250 US gal/min (16 l/s) capacity.
52-foot Motor Lifeboat