usage of sails for large vessels

Same as any other sail, most efficient on a reach, perpendicular to the wind.
It's straight physics.
Low apparent wind going downwind and unfavorable thrust vector going straight upwind.

 

Using sails for commercial shipping is an economic question and must be seen in those terms. Steam, initially coal- then oil- fired, took over from sail and was in its turn replaced by diesel allowing smaller crews with less skill, ships could get larger and faster, so money was tied up in cargo for shorter periods, and the cost per ton to build and maintain became less as industrial progress replaced manual assembly and traditional skills. Once we called that progress . . .

In the meantime sailing technology has also advanced, better materials allow masts to be taller without standing rigging, sails use more durable material and can be deployed and furled remotely, wind conditions can be tracked by satellite and more accurate weather predictions used to optimize course using computers. There has been a dramatic reduction in crew size, construction costs and perhaps maintenance for a large sailing ship. Whether there would be a reduction in voyage duration - compared to the great clippers and windjammers of the past - is debatable, but improvements have taken place.

In addition, while all that has been taking place fuel costs have been rising and oil sources are, perhaps, becoming less dependable.

Assuming both these trends continue, a point should be reached when it is more economical to resume large-scale use of wind propulsion, at least on a part-time basis.

Has it been reached yet? Not even close IMHO. New exploration is finding fossil fuel sources at a greater rate than they are being exhausted and new methods of resource recovery are being introduced to increase extraction efficiency allowing existing resources to last longer and perhaps abandoned resources to be revisited.

There will always be greater uncertainty of the voyage duration for a sailing ship compared to a motor vessel and uncertainty translates to risk and expense, therefore the cost of sail will have to undercut the cost of power by a significant margin to justify its adoption, and it hasn’t reached break-even yet.

 

Big long discussion on Flettner effect ships here

http://www.boatdesign.net/forums/bo...again-flettner-rotor-ship-launched-24081.html

The latest commercial attempt seems to have failed.

 

wow...that was impressive..

 

Special routes could take advantage of sail assist

There are notable exceptions.

On some routes - sail; assist can be viable.

Popular Science January 1984

Article about a large motor vessel with a Flettner Rotor installed by Lloyd Bergeson (now deceased)

"Power Mode --- Ave. Wind (Knots) --- Ave. Boat Speed (knots) --- Ave Fuel Saving (%)

Rotor-Assist --- 16.1 --- 7.0 --- 44
Rotor-assist --- 12.9 --- 6.0 --- 27
Rotor Sailing --- 17.7 --- 5.3 --- 100

Under rotor power alone, the Tracker reached a maximum speed of 6.1 knots in an 18.4 knot wind and a true wind angle of 122 degrees.

Bergeson is demonstrating the Tracker to fishing-boat owners, talking to large shipping companies, and presenting scientific papers at maritime conferences. And interest is growing. He now has a Navy contract to study the conversion of a military sea-lift ship to rotor-assisted propulsion. He is also conducting similar studies for a number of independent shipping companies, including major oil and cruise-ship companies.

The economic potential certainly is there. Bergeson has calculated that the world’s shipping fleet consumes 730 million barrels of petroleum a year at a cost of $30 billion. If only 20 percent of the world’s fleet adopted sail assist, the savings would be on the order of 91 million barrels a year --- almost $3 billion.

The payback to an owner can be astonishingly quick. The entire rig for the Mini Lace cost $250,000. But the owner’s records show that the sailassit saves $48,000 worth of fuel a year. In addition, average speed is increased by 5 percent, which means that the ship can make more trips. Extra income from this source was $9200. At that rate, the rig would pay for itself in a little over 4 years. But there’s more. On the New Orleans-Jamaica route, where winds are usually unfavorable, the fuel savings was an incredible 36 percent, and the speed was up 18 percent. If the ship were used on similarly favorable routes, the payback would fall to an astonishing 1.7 years. "

 

pg 50 of this link has giant bat-wings on cargo ship.

http://books.google.com/books?id=NT...at wing sailing ship Government grant&f=false


The idea was they could quickly and securely be stored in their hangers.

One problem I see is the hangers take up so much deck. That might work for a tanker, but a bulk or container box freighter needs to use 90% of is deck for massive hatches over the holds or stacking the boxes.

That wouldn't be a issue with kite, or even too much of a problem with a Dyna-Rig.

Personally, I think Mr Dryden got a hold of some technically and reality challenged Govt Grant Hander-Outer and sold him(or her) a bunch of fantasy novel 'nature is better' fuzzy thinking. But his design might be workable as a better junk-rig. I remember they seemed to miss putting out any actual energy/wind flow data. Probably works, just everything else works better.

Greenpeace's new ship is supposed to have really good numbers as the result of extensive testing and reality based engineering.

 

As always, the price of oil goes up and interest in these wind ship technologies, new and old, increases.
In the 70s when fuel went through the roof and seemed like it would never come down, many people tried to figure out how to make a living and even a profit carrying things with sail, copying old ways, but none succeeded for long.
It seems the way of the future could be some sort of sail assist that is designed into the loading and unloading gear many ships have already.
If the cranes, booms, towers etc seen on many ships to assist in opening their huge hatches could be an active sail assist, this would be wonderful.
Don't ask me how, as I have no idea.

 

It costs less to burn fuel than to use sails. It cost less to drive a car than to walk (you wear out your shoes and use more food to walk more than fuel costs). It costs less to buy an airline ticket that to drive a car long distance.

None of that counts the time lost with slower transport. Take that into account smile and just use commercial fuel, and know that is the lowest cost way to move people or cargo.

 

- and that's why we do it!