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Comment: Nice idea, but... (Score 4, Interesting) 190

by pete314159 (#16127416) Attached to: Solar Boat To Cross the Atlantic
From the web-page: "Much of the expanding long-distance goods traffic on our oceans as well as many leisure boats could be powered by ecological solar energy. Solar energy will be the future of navigation techniques. But it needs more publicity and more confidence."

It sounds nice, but the practical application for the actual transportation of goods is something else.

The great things about ships is that the volume increases as a cubic function (roughly) of the length, but the drag only increases as the square. The area available to solar energy is more like a direct linear relationship to length what with ships being kind of long and skinny. That means that you can eventually build a ship big enough to carry it's own fuel to cross an ocean, and if you go bigger it can carry cargo even. Bigger still means more cargo with less fuel per cargo needed (generally). This is why we now have 1000 foot long container ships and 300,000 DWT ULCCs (Ultra Large Crude Carriers). But these ships that require less energy per volume still require a *lot* of energy, and not just energy, put power too (they need that energy fast). For example, the ship I work on (600 feet long by 75 feet wide, about 20,000 GRT--small by today's standards) requires about 14,000 horsepower to travel at about 17 knots when fully loaded. Just using a crude area approximation for the ship's dimensions and, say, 33% efficiency for solar cells you would get about 1630 kW of power, or about 2180 horsepower. 2180 horsepower won't even move a ship that size fast enough to maintain steerage. This isn't even mentioning the other auxiliary electrical loads associated with a ship (pumps, motors, air conditioning, sewage processing, etc.). Factoring average load for my ship in to that, you get about 1000 kW (1350 HP) available for propulsion. This is like trying to row a canoe with a spoon. Of course, if you don't put anything in the ship power consumption goes way down and you eventually get to the point where you have a boat like what they're using. But what business that makes money by moving lots of goods from A to B on a schedule is going to build a fleet of boats that can't carry anything and go very slowly? Maybe recreational boaters, but I don't see it so much for the commercial shipping industry.

I do wish them fair winds and following seas for their crossing, and hope that they are indeed correct that "Solar energy will be the future of navigation techniques" if for no other reason than we need to, as a society, start reducing out carbon footprint. As an engineer (a marine engineer, at that), though, I see a very long a tortuous path ahead.

You can observe a lot just by watching. -- Yogi Berra

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