I can only go on what I have been told by by both engineers at the RNLI lifeboat stations that have Shannons and also by those at the AWL Centre at Poole when I have asked the question - it's always been 'anodised aluminium' and on one occasion 'duralumin'. I have asked this, as being an RNLI Educational Trainer for the South East [official staff - voluntary] I get asked this question frequently, by enthusiasts and modellers alike. This is especially when I give my illustrated talk on 'The launch and recovery of the Shannon Class lifeboat' - based on the Dungeness boat - up and down the country. My next one will be given in Eastbourne in March. Well before then, I will get the definitive answer from the 'top man' at the AWL Centre, Poole. It will posted here then.
Cheers to each.
Kim