From the ‘obvious when pointed out’ department comes this idea for powering ships. I’ve thought about this myself for ages, and wondered why sails were not put on ships as a matter of course. I presume they wouldn’t add a lot of power, but surely modest sails would pay for their capital cost and maintenance? A passenger liner has sails (I’ve seen the ads) but I presume that’s mainly PR. Why are they so rare?
Well now maybe we’ll see some wind power supplementation for freighters – and I was thinking about sails – not kites, which seem like a much smarter less obtrusive exercise. Click on the pickie and go to the story. Then again – why bother – the story is two paragraphs and is over the fold.
SkySails’ system consists of an enormous towing kite and navigation software that can map the best route between two points for maximum wind efficiency. In development for more than four years, the system costs from roughly $380,000 to $3.2 million, depending on the size of the ship it’s pulling. SkySails claims it will save one third of fuel costs. It recently signed its first contract with Beluga Shipping of Bremen, Germany, for one kite, but says it expects to sell 300 more within five years. Beluga says that the giant kite will help the company meet environmental regulations as well as cut fuel costs.
The sail systems are meant as a retrofit technology that can work with any cargo ship as well as yachts of more than 79 feet. Ships can use their engines to begin and end voyages and use sail power in lieu of engines for the middle portion. Use both, and you go even faster.
As the ships scale up, the sails and the countervailing keel (to point upwind) have to be disproportionately large. To generate enough power for a full sized modern ship you’d need big masts and rigging (which would radically reduce your cargo space) and a very deep keel (a problem docking). The beauty of the kite is that you can only let it out when the wind’s right.
As you say, it’s the sort of idea that, once pointed out, people say “d’oh – why didn’t I think of that!”.
Yes, but I wasn’t thinking of going the full deal. Just some arrangements for picking up the wind when it suits. After all a spinnaker is just a poor man’s version of the kite illustrated – and called a ‘kite’ by yachtsmen I think.
Check this for the history!
http://www.clubtroppo.com.au/2005/12/18/the-windjammers/
As sailors know, the problem with sails is the level of management required to get them up and down and keep them working. It’s generally more efficient to have more sails than bigger sails – or more exactly, to have more leading edge rather than more sail area. Hence the high aspect ratio on modern racing yachts.
To drag a cargo ship through the water I expect you’d want multiple large sails (kites) or the individual forces might start tearing things up. An computer-controlled system with a multi-kite launch and retrival system and an array of sensors is no doubt possible but it would be an engineering feat. You’d need a bigger, better-trained crew. I wonder how the economics work.
Of course, the big problem with the sea in general, and sails in particular, is sudden unexpected weather changes, especially towards extreme conditions. Clearly you’d want everything safely stowed and be cruising under engine power at these times but the weather continues to undo the best and wisest sailors on an on-going basis. Loose your rig – or your ship – only occasionally and the whole thing might loose it shine.