Sail Ho As Energy Prices Go Up, Up and Up
by Capt. D.C. Anderson
Oil prices will continue to go up and down but the long-term price trend from this point forward will be upward. But even if the price of oil was not a problem we still need to be concerned about the emission of greenhouse gasses. The world’s merchant fleet is the sixth largest emitter of GHGs behind China, US, Russia, India and Japan. Merchant vessels don’t have many options when it comes to using fossil fuels. That leaves us with one question, Is it time for the maritime industry to consider auxiliary wind propulsion?
There are a number of ways to use wind power at sea today. Each method has both benefits and drawbacks but the important calculation is always the same; Benefits minus Cost:
Benefits of auxiliary wind propulsion:
• reduced engine ware,
• increased stability (not available with all systems)
• fuel savings
• reduced carbon footprint
Cost of auxiliary wind propulsion:
• the total installed cost of the system per square meter of sail area,
• extra operating costs, if any,
I cannot immediately put a value on all benefits, such as reduced engine wear and the impact sails will have on charter rates, but I can help you make a decision about which wind-assist system is most cost-effective from an operational point of view.
There are six different types of wind-assist systems considered here:
1. Semi-Rigid Air Foil
2. Combination Solar Panels and Wings
3. Flettner Rotor
4. Fixed Wing
5. Kites
6. Soft Sail With Roller Furling
Semi-Rigid Air Foil
The semi-rigid air foil was developed and promoted by the Japanese Small Machinery Development organization (JAMADA) in the early to mid 1980s. This system uses a fabric stretched over a fixed frame. This frame allows the air foil to maintain a better “wing” shape, and this in turn allows for a better lift coefficient. In addition it allows the sail, or wing, to be utilized when the apparent wind if further forward, i.e. closer to dead ahead. This allows for somewhat greater rate of utilization. Finally, the wing is adjusted to the optimum angle of attack by computer.
The drawbacks with semi-rigid air foil system are three fold: it is a) Extremely complex and very costly, b) It cannot be retrofit onto existing vessels and must be built as part of new construction, and c) when the sail is in the folded position it still has a very high wind drag coefficient.
Combination Solar Panels and Wings
The combination solar panel and wing is still in the design stage. This system also comes from a Japanese company called Eco Marine Power and uses the same fixed wing concept except the wing(s) will be covered with solar cells this time. The cells will presumably provide power to the ship.
Flettner Rotor
The Flettner Rotor was recently installed as part of new construction on a specially designed ship out of Germany. The company that was building the ship went bankrupt in 2009 and the vessel was towed to a different shipyard where construction may be completed. As of this writing the Flettner Rotor still has not been used in the past 85 years.
This type of ship will have two big problems, or in this case four big problems. I am referring to the Rotors. They are massive, they take up a huge amount of room, they will impact stability and they cannot be taken down in the event of adverse weather conditions.
Fixed Wing
The Fixed Wing is very much the same as the semi-rigid air foil developed by JAMADA (#1) with the exception that it does not fold in half. This system has never used on a ship for all the reasons previously mentioned: it is big, complex, takes up a lot of room and cannot be reduced in size when and if necessary.
Kites
Kites are a very new idea and the jury is still out on whether or not they will ever prove to be a practical solution. A company in Germany called SkySails has put large towing Kites on four ships with the help of a subsidy from the German Government. As a merchant seaman for over 45 years I would not be totally surprised if this technique did not encounter some operational problems. With 
that in mind, there are still some advantages to this kind of system. First is the fact that you do not need great deal of gear on the main deck – other than the large launching arm mounted on the bow. Secondly the Kite operates hundreds of feet above the ship where the air has fewer obstructions.
One big drawback has to do with the fact that the Kite can only pull the vessel and to that effect the wind has to be blowing significantly faster than the ship’s speed. This will cut down on the utilization rate. That is because the force is created by the wind being captured in the sail area and pulling the ship; for this reason the system cannot be used when the wind is forward of the beam. Going back to my argument about apparent wind, as long as the ship is steaming at “X” knots you will have a wind vector dead ahead of “X” knots. But, as I said before, the jury is still out on whether or not the Kite system will ever be effective for the merchant fleet.
Soft Sail with Roller Furling
The last wind-assist system is the more traditional Soft Sail with Roller Furling. Most of us already understand how the conventional soft sail works, but not all of us understand how soft sails can be used on modern merchant ships. As you can see from the picture, soft sails with automatic roller furling might just be the best of both worlds. You have both the ease of operation and a relatively low cost of installation. The soft sails can be used at any time when the wind is abaft the beam – like the Kites – and they can also be used when the vessel is headed into the wind – similar to the wing type sails – as long as the apparent wind is more than 15 degrees either side of dead ahead. Furthermore, as you will see in this video, the soft sails can be rolled up automatically when not in use and thereby offer reduced drag compared to any of the “wing” systems.
One of the biggest advantages of the soft sail – one that none of the other wind-assist system can offer – also happens to be one of the most difficult to document. At the same time this is a phenomenon that most yachtsmen are well aware of. I am referring here to the “slot” effect. This happens when two sails are placed close together with the space between the sails being further apart in the forward section, where the wind enters, and much closer together at the back end of the sail. This causes the wind to accelerate as it passes through the narrower opening – or slot – and, according to Mr. Bernoulli’s Principle, the faster a fluid moves the less the pressure. Less pressure on the lee side of the sail means more pressure on the windward side. More pressure on the windward side translates into more HP pushing the ship. More HP means more fuel saved.
The ship shown in this picture has two sails totaling about 4,500 sq ft of sail area (Note: 1.5 times dwt). When the apparent wind is blowing at least 15 knots and at least 15 degrees either side of the bow, each square meter of sail area can generate about 1 horse power. Because of the systems simplicity and the low cost of installation (about $365/sq m), the above system paid for itself in just under 100 days at sea. It should be noted that this ship also traveled on a trade route with very favorable winds and therefore had a very high utilization rate.
If you are considering doing something to help your vessels reduce fuel consumption while at the same time reducing your company’s carbon footprint, then there are five things to consider.
• installed cost of the wind-assist system
• ship’s speed
• route traveled
• days at sea
• configuration of the deck gear, if any
Cost of the wind-assist system: It is not just the cost of the hardware, it is also the cost and the ease of installation, how long does this ship need to be laid up, plus the cost of any extra crew, if necessary, weighed against the cost of fuel saved, the advantages of added stability, plus whatever advantages you think your company will realize in the charter market when you offer a ship for hire that has reduced fuel consumption and a smaller carbon footprint.
Ship’s Speed: When the ship moves through the water it creates wind. If the ship is operating in still air the wind would feel like it was coming from dead ahead and equal to the ship’s speed. But the wind is seldom completely calm so there are two vectors to consider. There is a vector equal to the speed of the ship, and another vector equal to the true wind speed and direction. This vector can come from any point on the compass and at any speed. The combination of the two vectors gives you what is called the apparent wind. When the ship is moving it is never impacted by the true wind; it is always impacted by the apparent wind.
There is no sail-assist system that can use the wind when it is coming straight at you and, at the same time, the second wind vector, the true wind, would have to be blowing quite hard if the combination of the two vectors was going to cause the apparent wind to be any use.
If, however, the ship was moving at 8 to 10 knots, even 12 knots, the true wind would not need to be blowing as hard, or as far off the bow, in order to be usable. Furthermore, NASA recently reported that the average wind speed at sea is increasing and will continue to do so as long as the planet continues to warm. Bottom Line: slower moving ships have the opportunity to get more energy from the wind.
Route Traveled: Some trade routes are better than others when it comes to optimizing the use of the wind. The operative word in this case is “optimizing.” The wind blows pretty much all the time in some places and far less in others, but that doesn’t matter with the soft sail system. It is inexpensive to install and therefore you can afford to use the wind when you can, and then roll up the sails when you can’t.
Days at Sea: This concept is pretty straight forward: the more days your ship is at sea 1) the more oil you will burn and 2) the more oil you will save using auxiliary wind propulsion.
Configuration of the deck: Container ships will obviously not be able to use most of the wind-assist systems mentioned here for the two reasons previously mentioned, their speed and the lack of open deck space. The best deck configuration is found on dry bulkers and most tankers. The soft sail system can also be used on general cargo vessels with cranes. In this case the ship’s cranes can be rigged to support the roller furling sails so the bi-pod masts will not be necessary. The Kite system can be used on vessels with any deck configuration because the kite system mounts on the ship’s bow deck.
Saving fuel at sea is no longer a purely economic question. Today, saving an irreplaceable resource, as well as reducing GHG emissions, is a matter of necessity for the simple fact that the future belongs to the efficient.
About the Author
Capt. D.C. Anderson holds a USCG Master's License, Oceans and an M.S. Degree in Marine Transportation from New York Maritime College at Fort Schuyler. His graduate thesis designed a computer based system to monitor a ship's speed/power performance curve as impacted by increased hull roughness and then relate this in terms of fuel lost. In 1985 he became the first person to successfully design, build and operate an auxiliary wind propulsion system for merchant ships. The Sail Freight system was the only one in the world to date that has ever proved to be completely cost-effective. Later he started a nonunion tug and barge company in New York harbor consisting of one tug, two barges and two small tankers. Today Capt. Anderson is offering to ship owners the Sail Freight system of propulsion combined with the hull roughness module.
Capt. Anderson can be contacted at [email protected]