..pv that generates <7kW out of 35m² and wind turbines <500W you have saved money on the wrong parts...

Interesting discussion - and relevant to off-grid/tiny-house/eco-friendly SH3D designs too. I must be missing something, because I still do not get the maths. My understanding is that max performance the very best photovoltaic panels is still <23%, which I believe roughly translates to max 230W/m² at optimal angle and perfect conditions. A couple of years back we did some tests on a 42' monohull sailing yacht during a long haul. Owner was an electrical engineer friend who had lived on board. Components tested were best quality, albeit with a smaller diameter wind turbine. We measured the turbine - if I remember correctly - to a dismal < 1/3 of rated output @ 8-9 m/s. The turbine you mention is 190 cm diameter rated 1500W @ 13 m/s, however, curve indicates 100W @ 4 m/s, 200W @ 6 m/s and 500W @ 8 m/s. But how often do you get stable > 6 m/s wind on inland waterways? So I still do not see how pv / wind can supply enough power to propel the boat. Certainly, you are right in saying that a good multihull could get pretty good general energy mileage. Do you have an estimate of energy consumption at cruising speed, i.e. stipulated range nm/kWh for your construction?

..never need 80hp...

You are right, at least for normal cruising and on lakes. My worry is based on gut-feeling: what if you go river upstream against a 3+ knot current and you hit a narrowing passage with increased currents, unpredictable winds and lots of vessel windage? A 50' 10+ tonnes boat is way beyond what I have ever considered for outboard power, but again, it should be interesting to see the estimations for waterline/speed and power/shaft speed and prop dimensions.

Maybe it is different for inland waterway navigation, but I have helmed boats of various sizes in narrow straits with tidal currents. No later than Sunday, in fact. True, I fear underpowered boats, based on some experience. While max power should not mean much on the overall energy usage, and rarely used, it is still crucial for maneuverability in critical situations - but then - my coast can be pretty rough, so maybe it does not compare.

..computed by the manufacturer, so they will lift the realy heavy House... ..hot dip galvanized...

Sorry, I did not mean to imply that it is impossible to fit pontoons to a pair of freight containers in terms of buoyancy. A lot of unnecessary weight, but possible. My primary concern would be the centre of gravity on a boat with little or no ballast. Again, I know very little about pontoon cats, but from the not-so-serious experiment in thread 6956, I seem to remember that the rule of thumb was that to avoid the pontoon effect, each of two lateral pontoons should have enough buoyancy to bear the load of the entire vessel (+ 13 m/s side-wind [:)]). Guess that means you will use bigger pontoons than I considered for the smaller sketch. The DIY part would certainly be easier with wood than welding steel - and maybe not that much more expensive? Except for the rusty containers I have seen in the dock, I know nothing about the steels used in freight containers, so I should probably keep my mouth shut, but what happens when you start welding?

Looking at your pontoon choice, I just found the 'KIRA' project linked. Not quite as big as yours, of course, but useful in the detailed description of the process with lots of tips and drawings that could have been made with SH3D. Also a very nice design. Recommended for anyone dreaming of a houseboat. Did not read the details, but looked at EIN ERSTER SCHRECK - interestingly he used the same two manufacturers mentioned previously and it confirms that your guys have bigger pontoons. Kira appears to be some 11m×4m (36') < 5 tons. Size of the pontoons quite large, engine looks like a Yamaha mid-range 30/40 with a low pitch alu prop. If the full specs for Kira were (are?) available, that should provide a good basis for other pontoon calculation (same hull constant and play with the other variables).

ok