Hi Keith & steamboating friends
I thought I had better jump in here wearing my SBA Hon Sec Hat. Do have a look at this page Keith
(http://www.steamboat.org.uk/insurance.htm) as there are actually three sources. Blue Fin has served the SBA under various names (eg. Bishop Skinner) for many years and handle the Association's PL cover. So, they should know what they are talking about. Simon Winter is a smaller outfit, whose specialisation is yachts, but he has a proper handle on steam launches. It is rumoured that he is better for larger boats rather than smaller boats, but I have not been able to confirm that. IRCM also understand steam boats as they do (I believe) Alaska and Picket Boat 199.
Beware of using your house insurance or other less usual forms of cover as they may not be aware of the need to cover the damage from the explosive deconstruction of your boiler. Also if you are coming to SBA events (and I suspect IWA events) we do have a requirement that your insurance does cover that risk.
As for the logic of underwiters, I can offer no insights. However, I was informed by a fellow canoe club member that NFU mutual will happily cover your canoe as long as it is part of their houshold contents policy. They will not insure just the canoe...
Regards
Pete