Just an additional bit of info, I found my way to the RNLI "Lifeboat" magazine archive last night. There you can download PDFs of articles or editions and I found two articles of interest in the March 1948 and December 1937 editions, both of which have "Radio Telephony in Lifeboats" as the leader item.
Both the editions show the older Marconi equipment that had been fitted to some lifeboats pre-war and also shown is the new Coastal Radio installation which would be in place on almost all offshore boats "within two years". There are mentions of the problems of waterproofing the radio and ancillary equipment, the changes in aerials and the advantages of crystal control of the transmitter.
Two other Coastal Radio equipment owners who I have been in e-mail contact with have the "new" receivers as shown in the 1948 piece and their web sites were linked earlier in this thread.
The RNLI site also mentions publicity films and one I found (in two parts) on YouTube called "Gale Warning" has a brief shot of the new installations. Given the relatively small size of Coastal Radio they did well to land the RNLI contract against competition like Marconi and I wonder if Marconi bought-out Coastal in 1956 to re-secure their place in the lifeboat radio market?
The archive is here:-
https://lifeboatmagazinearchive.rnli.org/
Hope the above is of interest,
73
Roger/G3VKM