I had a steamboat once.
I never had a BSC inspection done - no enclosed space, no gas, no electrics, no petrol, no diesel, only coal which took an hour to light.
The boiler, however, had a full inspection every year twice - when cold and in bits and then again when hot and hissing.
The Environment Agency though (who issues my river licence) still insisted I paid to have a BSS done to confirm the boat didn't need one!
To get round this I registered the ownership of the boat in Monrovia, Liberia at the cost of 50c per registered ton but the Liberian flag did cost me £26. The boat was then leased back to me by the 'owners' in Monrovia as the operator in UK waters. The only problem with this arrangement is that the Liberians could have demanded my boat in times of war.
This arrangement worked well for fifteen years I owned the boat, I still paid my full share of the river licence, but the EA never asked for another BSC certificate and I saved myslef £80 per year by not paying someone to say I didn't need an inspection!
The boat has been on the Thames and I was never challenged, the only questions I got was surrounding the strange flag on the stern.
Regards,
Gordon