I think the 'guard's regulations have changed in the past 10-15 years, going up in size. I think it used to be that boats of that size or larger were also required to have a licensed engineer. Most of those regulations are not enforced nowadays anyway unless you have paying passengers. I think we're all just an amusing oddity at the moment, as long as there are no accidents.
I am not against code boilers by any means, the current Kiwani boiler is a code piece. He is just stuck on it due to fear of liability and being near the general public.
The current boiler will fit fine, but is quite large compared to what a comparable watertube would be, even a package watertube like a Bryan (before finding this boiler my dad looked into getting a "naked" boiler from Bryan with no casings, and building his own more compact casing). More space is always a plus, as with the current boiler space for cleaning/maintenance and the head (with shower) is VERY tight and will make it quite difficult for the older, more portly, crowd. sqFT/HS per horsepower is generally less for watertubes than firetubes, so that will also aide in having a smaller package... I drew up a "Thornycroft" watertube with some 300sqft/hs in a 3.5'X5'X5' package with a 24" steam drum and a *i think* 12" mud drum(including casing). The grate area wasn't awesome, but it was MUCH better than the current boiler
Multi-fuel capability would be a benefit as the current boiler only has a 1ft diameter main flue, so liquid firing is a must. A watertube would have much more grate area for burning solid fuels if one so chose, or needed to.
Less weight would be nice as well. 4,800lbs + 280 gal/water as opposed to say, 3,000lbs and 175 gal/water? She will have plenty of ballast as it is, and the fact that she originally was a low-lying tugboat hull with a single diesel engine, we're not quite sure how much low-er she'll be with all of the steam machinery.
Faster steaming of a watertube and the ability to "force" is nice. Getting steam-up in an hour or so is much more enjoyable than waiting 2-3 hours.
Controlling is a mostly a non-issue. We're not talking a monotube or Lamont here, more like a Roberts, B&W, Yarrow, or maybe a Simpson Strickland "Thornycroft" style boiler with large steam and mud drums.
Building or buying would he a hurdle as it would not be free in the money or time departments and he bought the current boiler for a song.
The firetube would have much more reserve capacity if one found themselves in some sort of fuel shortage predicament as long as it wasn't 10 miles from the nearest liquid fuel with cords of unusable firewood lining the shore.
I am pretty good at telling him how to spend his money