Modern days sail technology

Not to mix the discussion on the merit of Ceiba Project with other (more realistic??) project involving using wind power to assist in the propulsion of ships across oceans and seas.

Here is a small scale project that is aiming at reducing fuel consumption by use of modern sail technology:


It is not particularly an improvement for the foreward view. I would like to see the radar screen and check the false echo’s. At certain ‘sail’ positions I suppose you also are bound to get massive return echoes.

Econowind BV is a Dutch company that started in December 2016 to develop auxiliary wind propulsion on modern seagoing vessels. A grant from the European Union was obtained through SNN.

Econowind BV designed foldable VentiFoils: wing shaped elements creating very high propelling force relative to its size. Boundary layer suction increases and controls the propulsion force. The goal of the unit is to reduce costs and CO2 emissions by reduction of used motor power.

On captains demand, the Ventifoils deploy. Further sailing is done automatically finding the optimal angles relative to the apparent wind. The generated force will be transferred right into the deck and thus helping with propulsion. To maintain the ships speed, the motor power can be reduced.

It is disappointing that not even some data etc about for instance possible fuel savings can be found on their website. This doesnot boost my confidence I must say.

Here we go again.

Note, incidentally, that the sail area of the ‘sails’ is counterbalanced by the sail area of the not-so-streamlined superstructure.

Another fantasy.

The “sails” were retrofitted to a 14 year old ship, presumably the superstructure was not rebuilt.

Obviously, this is dependant on the wind and the size of the vessel. Thus far in practice, the system saves 400 to 800 litres of fuel per day, but we believe the true potential lies around 1,000 litres. Depending on the size of the vessel that would translate into savings of 8 to 10%.”

. The expected fuel savings for the vessel should lead to a return of investment in approximately three years time.

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If it works, go for it. My gut feeling is that it won’t catch on and I strongly doubt the accuracy of such figures, designed as they are to sell a product with a glossy story.

As I see it the wind force developed by the ship’s propulsion is pointing backwards and as such opposes the foreword force developed by the sails making the system less effective.

The company doesn’t provide much technical data, but I think it works similar to winglets on an airplane.

The primary purpose of the winglet is to reduce the vortex and thus reduce induced drag. But as the diagram shows, the sail-like shape also provides forward propulsion.

Winglets reduce wing tip vortices but don’t directly produce significant forward lift. The leading edge slats (grey color) are more effective at doing so reducing leading edge vortices and lowering stall speed.

Note the green arrow in the diagram. The winglets do in fact generate forward motion. NASA’s Al Bowers is probably the leading scientist in the study of vortices. If you are further interested, you might be interested in the PRANDTL glider which may one day fly over Mars.

Edit: the keyword “significant”. Perhaps not a lot, but they are small.

AKA Cousteau Turbosail explained:
Turbosail - Wikipedia.

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Wrong. The green arrow is an over simplification. What the winglets do is reduce wing tip vortices. The reduction in induced drag results in improving the wing’s efficiency thereby lowering fuel burn. Enough to save the airlines some money given that they burn a lot. The same goal can be accomplished with proportionally longer tapered wings like on the high altitude U-2. The B777 reduces wing tip vortices using the same concept of an extended wing and more finely shaped tip.
The NASA article you quote is about something else i.e. using non elliptical wing shapes to reduce yaw when the wings are developing different amounts of lift…

“Winglets, which are airfoils operating just like
a sailboat tacking upwind, produce a forward thrust
inside the circulation field of the vortices and reduce
their strength. Weaker vortices mean less drag at
the wingtips and lift is restored. Improved wing
efficiency translates to more payload, reduced fuel
consumption, and a longer cruising range that can
allow an air carrier to expand routes and destinations.
To produce as much forward thrust as possible,
the winglet’s airfoil is designed with the same
attention as the airfoil of the wings themselves.
Performance improvements generated by winglets,
however, depend on factors such as the basic design
of the aircraft, engine efficiency, and even the
weather in which an aircraft is operating.”

89234main_TF-2004-15-DFRC (1).pdf (510.2 KB)

Al Bowers’ work on the PRANDTL is more than just yaw. The wing design was partially inspired by seagulls flying in formation wingtip to wingtip. Natural masters of vortex control.

You’ve just confirmed everything I just posted by cutting and pasting from what is in all likelyhood an article from the internet. The properties of non elliptical wings have been known for some time. The complexity is not so easy to replicate in aircraft.
Whether it can be replicated on vessels and whether it can provide rewards remains to be seen.

Wow. I think you mean NASA.

That’s your response? Once again you miss the point. The point is your post was plagiarized. The fact that it’s NASA at least shows you know where to look. Or was it from a book? Just curious.

Plagiarized? Did you miss the quotation marks? You did see the part about forward thrust? The gist of my theory to explain @Dutchie 's question about the effect of the forward motion of the ship?

The point is, winglets, just like sails, produce forward thrust. It’s sometimes referred to as “induced velocity”.

My original insight into how winglets work came from a talk given by Al Bowers.

Sails produce lift at an angle to the wind. The keel or daggerboard on a boat is necessary to minimize leeway. So do airplane wings. An AOC is necessary to create lift. If you can explain how foil provides useful forward thrust directly upwind, I’ll vote for you to be inducted to the board of directors at NASA so you can promote the ass hat who wrote that piece.

AOC?? I assume you mean AOA for Angle of Attack.

An angle of attack is only required if you don’t have a lifting airfoil. If you have a lifting airfoil like a flat-bottom or semi-symmetrical type airfoil, you achieve lift through the classic pressure differential. Gliders do it all the time. The modern foil type sails use similar physics. A lot of research has gone into the best airfoils for winglets, as well as the best angles for them. I don’t believe the symmetrical airfoil made the cut, but that is a deep subject and requires thorough and specific research.

The larger and more important point is that the ship moving through the water with its primary propulsion, can harness the relative wind and get some forward thrust out of the deal with an airfoil.

The sketch with the green arrow as ‘forward lift component’ seems to come from here >>>

They must have translated a drag reduction, hence a negative drag component, into a more positively looking ‘forward lift component’.

The Boeing 777 series have no winglets, but very fine wing tips (having the same effect).
For the larger 777X (the future 777-8 and 777-9) they needed more wing surface but could not extend the span, only few airports could have accepted this aircraft.

Now, on the tarmac, the 777-X looks like having winglets… before flying it unfolds these ‘winglets’ to make a larger span…

You nailed it. It’s press release hyperbole.