Sky Sails

[Iain]

Hi
A few months ago we had a ship called the Theseus in Plymouth. It has a telescopic arm on the fwd deck of the ship and we couldn't work out what it was for. We asked the skipper and he explained it was for a Sky Sail. They are on their second generation sail and he said he has had 12 kts out of the ship fully loaded with the engine shut down.(Sky Sail only) Apparently for the same "pull" they are more efficient than an engine as they tend to lift the bow as they pull the ship. There are a number that have now been built so actually seem to work. He generally uses his on the long runs, deep sea and apparently are quite easy to control. Ships are already an economical way of carrying heavy cargo long distances so this can only keep the costs and fuel usage even lower. There are obviously limitations of where and when they can be used but at least some companies are looking ahead and putting green energies in the mix
http://www.skysails.info/english/media/photos-and-graphics/mv-theseus/

Iain

[rondurrans]

Crikey I thought you were joking - sky hooks and all that - until I saw the pictures.....

"The SkySails system tows the ship using large, dynamically flying towing kites, which generate up to 25 times more energy per square meter than conventional sails propulsion systems. This equals up to 2,000 kW of propulsion power in good wind conditions.

Experience has proven, one kilowatt hour of SkySails power costs just 6 USD Cent, or only about half as much as one kilowatt hour from the main engine"

[biff]

looking at the pics,its quite incredible,a fantastic idea,perhaps borrows from mad max.yet it makes perfect sense to eat the miles across the oceans in such a way.all credit is due to the people responsible and the ship owners who employ this brilliant idea.modern weather charts and computer control make this possible and dependable.hats off to them.
                                                          biff

[Dave1]

Don't be to surprised if you see some on the Navy's ship's

Dave

[charlieb]

Good to see this happening as it's been talked about for some time.    I kitesurf, so I can vouch for the fact that a dynamic kite is massively more effective per m2 than a static sail.

Here's an equally funky idea with some parallels:   http://www.minesto.com/   

[Ivan]

skysails seems like a good idea, but the pictures show sails which in my view are far too small to make much of a difference to fuel consumption or top speed.

[Iain]

Hi Ivan
As in the first post the Captain was getting 12kts at times (ideal conditions during trials) and that is the rated top speed of the ship (without the main engine on) That appears to be just about 100%fuel saving! They save between 10% and 35% fuel saving annually, so that is "Tons" of fuel /day. Most people even with the small amount of fuel used in a car would be over the moon with this percentage of saving!
They are just about to use a 320m3 sail on a larger ship. This page links to some other info, quite interesting.
http://www.skysails.info/english/media/documents/
Iain

[Ivan]

I don't disagree with the principle, but I do wonder whether the stats quoted are very over-optimistic....at least for the sails in the picture. Maybe they've quoted the savings of the biggest sails and shown pictures of the smallest ones? I estimate that the DSM sail is only 20m2 - so if they're talking about 320m2 sails, that would make sense.

The close-up of the DSM sail looks only marginally bigger than a parachute. When I was younger, my Dad gave me an old parachute to play around with. We took it to a park and flew it like a kite on a windy day. It was obviously too powerful to anchor with just bodyweight, so my brother and I tied it to the towbar of a friend's car. The parachute did not exert enough force to pull the car along (we tried!), and we probably had it flying at 100m or so.

[M]

Allowing for perspective there's no way that is only 20m2.

Have a look at page 17 of their brochure, assuming that's the same sail it's got to be at least 50m2.

Also they mention a 320m sail and have products with references of 160 and 320 in their names, so I think it's pretty big.

The press kit states  "With a good wind the SkySails SKS
C 320 can produce a pulling force in the towing rope of more than 320 kilonewton (kN) – a force
greater than the thrust of both engines on an Airbus A321."

Are there any kite surfers out there game for a go?

Martyn.

[Iain]

Hi
Video of the first one, 160m2 on their trial ship in 2007. I think the one fitted on the Theseus was 320m2(second generation). They are talking of progressivly doubling the area of the sail each time as the technology improves.

http://www.youtube.com/watch?v=qyLjISR6XQQ
Iain

[qeipl]

I don't disagree with the principle, but I do wonder whether the stats quoted are very over-optimistic....at least for the sails in the picture. Maybe they've quoted the savings of the biggest sails and shown pictures of the smallest ones? I estimate that the DSM sail is only 20m2 - so if they're talking about 320m2 sails, that would make sense.

Look at the size of the people on the foredeck next to the DSM sail. Each panel of the sail must be at least 1.5m wide by maybe 9m long on average, and there are at least 20 panels, which gives an approximate area of 270m2. Could easily be the 320m2 sail tthat others are talking about.

[Ivan]

That's exactly what I was looking at (the person vs sail size)

I've just done some measurements from the 8th photo which shows people apparently close to the sail (although admittedly perspective may be misleading). The people are 0.7cm high on my laptop screen. Let's assume they are 1.7m height. The sail's width seems to be 20 segments ranging from 1.3 - 3.2cm long. The lowest 3 sections (ie the ones most perpendicular to the viewing angle) are 1.1cm.

So each segment is 0.9m wide. The apparent lengths range from 1.3 - 3.2cm, so let's assume an average apparent length of 2.25cm. That's equivalent to a real length of 5.46m. So the total area would be 20 x 0.9 x 5.46 = 98m2. More than my original assumption, but nothing like 270 or 320m2, unless of course they're counting both sides of the sail.

Don't get me wrong though, I think it's a great idea.

[MarkB]

According to: http://www.ship-efficiency.org/onTEAM/pdf/Brabeck.pdf

The Theseus was first fitted with a 160m2 sail - whether this is still the case or whether it has been upgraded is difficult to tell.

I have done a fair amount of kiting including very large single line kites and power kiting with sails up to 8.5m2. I also know the person who has designed and built the largest kites in the world (and have been *inside* one of them). Many years ago I put one of my friends, a keen parachuter at the controls of one of my meduium sized power kites. He was absolutely blown away by the power. There is no comparison between a well designed power kite moving in a figure of 8 pattern in the power zone and a parachute. These things will have immense power and I can probably believe the claims (although I think they are probably a little hyped).

The one issue with such a large sail is that it will be slow through the sky so won't generate quite as much power per m2 of area as a smaller, faster kite, but it will still pull like crazy, and given enough time could get a large ship up to the speeds claimed.

[charlieb]

Agreed.  I've definitely pulled a landrover with a foil kite smaller than a parachute. As MarkB says, kites get lots of their thrust from movement across the wind at several times the speed of the wind.  Boat kite wouldn't be able to do that I guess, but it would work as an assist to engines (which I assume it's designed for) - kiters call it 'apparent wind': once you're up and going it's easy to stay going.

[stannn]

It looks to me as though the problems, with this beautifully simple idea, revolve around deployment and recovery. The youtube video only shows the first stage of recovery. It must be difficult to collect the aerofoil without damage in serious wind.
Stan