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Difficult to be sure, there were very few steel hulled hireboats on the broads. The only steel boat builder of note was/is Braydon/Goodchild's.
These 5 "Sunhunters" may have started on the Beaver fleet one seems to have gone to Sutton staithe and one to Ripplecraft before they were taken over by Crown Cruisers under the management of Brian Gardener after he moved from Astons and it looks as if he acquired the others to go with it. Crown had interests on many waterways including Scotland and Ireland and I thought that Des Doolan did take on some "ironsides" for use in Ireland. More than that I do not know, Sorry