Yes, I am aware of that situation, I had a 30 steam launch of steel construction that I had built, it has a water tube boiler, burning wood and oil it was a single chine with counter stern, the water level gages were on the center line of the boiler. the engine was of my own design, all built with castings, I think about 17 of them were built by myself and others, cylinder dimensions were 3&5-1/4 X 3 3/4, was counterbalanced and ran at 430 RPM with 150# steam with a 24 X 28P 3 bladed prop.that's kind of a basic drawing showing the wall tubes,, the boat plans place the site glass and try-cocks piping coming off the boiler at 40 degrees aft of the beam center line (if it was further aft it would conflict with the engine piping and space),, letting the engineman keep an eye on the level,,(the pressure gauge is also in the area) and also keeping the space for movement clear on that side of the boiler.. also being a water-tube boiler and not a fire-tube the level is a little more less effected by rolling,, boats are always rolling or pitching a experienced operator would know when to trust the level..
Here is the only pic that we could easily find of the boat when it had the steam plant in it, I later replaced it with a 11 hp Hicks gasoline marine engine, the guy I sold the boat to has now found and bought the steam engine and boiler and plans to put it back in. We also have a video that we could post of the engine running if folks would like to see it.great to here this info(any photos?) I'm in communication with several full scale steamboat folks that are giving me lots of advice and information.