52' (foot)
In the mid-1930s the USCG ordered 2 52 foot rescue life boat for service where there was a high traffic of merchants ships and heavy seas that had a high capacity in the number of person that could be rescued of approximately 100 and could tow ten fully loaded standard life boats used by most merchant vessels.
Unlike the older 36' foot, the 52' foot had a diesel engine. One was built and stationed at Sandy Hook, New Jersey, the other in Oregon. IN time the Sandy Hook boat was transferred to the Pacific Northwest. http://www.uscg.mil/history/boats/docs/52FootWoodenHulledMLB.pdf
Read more about this topic: Lifeboat (rescue), Modern Lifeboats