Jon,
Steam is like anything else, it is safe as it is handled. Most everyone drives around with 20+ gallons of volatile fuel under vehicles, some have Propane tanks in their yards that hold 3-400 gallons of compressed LP and 250 psi working pressure, 5 gallon propane cylinders right outside our doors, almost all have water heaters with 150 psi working pressure in our homes that operate at higher pressures than some steamboats (water heaters are not constructed anywhere near as well as a power boiler) (my steamboat with a twin will operate on 40 psi, quite happily). These are safe because they are handled in a such a manner that makes them safe. Safe practice backed by codes and sound engineering is the key. Any boiler explosion on a hobby steamboat should be avoided obviously, regardless of the boiler type.
Hobby steamboaters are virtually self governed in regard to building and or operating their boilers due to state laws, and all do a commendable job at that. To my knowledge there has not been one incident of a hobby steamboat experiencing catastrophic failure of the boiler in recent (last 100) years, not from my research anyways. I've read of pipes leaking/fracturing from over-stress but no injuries were recorded in text or discussions.
Boiler explosions were common before the turn of the last century here in the US. The reasons are many, most notably, Poor material quality of steels and Iron, Poor craftsmanship, lack of codes and sound engineering for the design process and most importantly lack of training and understanding on the part of the owners and operators. It was common to allow water levels to run low dockside so the steamer could take off quickly (The steamline owners encouraged this to give the impression to those on shore that steamboat transit was very fast), then add water underway, this is where most of the explosions took place, feedwater flashboiling. That coupled with safety valves that were tampered with so they would not operate was a recipe for disaster. Hollywood has capitalized on the notion as it makes for great sensationalism in their movies. I've been asked several times about my boat "Aren't you afraid that thing is gonna blow up?" If I had any inclination that there was considerable potential for mishap, I wouldn't be running it. What I did do initially though, was educate myself by reading as much as I could and asking questions here and elsewhere. I'm still learning about it, but I understand enough of it to feel comfortable operating my boat now.
Incidentally, Laws governing Steamboat operation is the first time the US government passed laws and regulations regarding private commerce.
Here is a great paper on the subject:
http://leda.law.harvard.edu/leda/data/5 ... dacted.pdf
For someone just getting in to this and wanting to put a boat together, it may be a better move to find one already constructed as used boats do come up for sale on Ebay and elsewhere. Some of the prices they have been going for it's doubtful someone could buy all the components and construct it themselves and save any money. The old saying "The devil is in the details" definitely applies, once the hull is built or bought, boiler and engine is acquired there is still much to purchase. Piping, whistles, pumps, running gear, etc. can add up to sizable sum on it's own.
-Ron
and that it is better to design the boiler larger than needed if possible. I was thinking that perhaps I could "over build" the boiler and be able to run a larger engine in the future, or run a nice shirt pressing operation from my garage...
