Frequently Asked Questions:


Q:  "Self Trimming" - Has it been used before. If so, is it a successful way of controlling a wingsail?

A: Yes, they date back to the 1940s when one was constructed in Norway by a man name Utne.
Later, the most notable use was in the Walker Wingsail series of luxury yachts, built in the 1990s some of which are still sailing today. (Click Here).

Another more recent use was on the "Greenbird" - a landsailing craft which is the current record holder for the fastest wind-powered vehicle on Earth at over 126mph (Click Here).

These examples indicate that the principle is a well-established and successful concept.

Q: How Do the "Windthrusters" with the automatic system work?

A: The tail is adjusted by the angle the whole rig makes to the boat. You can think of the wing and tail assembly working as a weathervane with the counterweight always facing the wind. The tail pivots a few degrees either way,  adjusting itself by the angle the "weathervane" makes with the boat, and thereby setting the main wing to provide thrust. This is what makes control automatic.

The idea came about as a result of the practical experiment you can see in the video below, not theory.
The present system is an improved version of this experimental system, you can see how effective it is.


In the video you can see that the boat is never blown downwind, even when head to wind, because the tail is making very small adjustments to the main wing, causing it to  provide enough thrust to keep the boat on station. The (patent applied for) windthruster system works the same as that shown in the video, but has the added option of being able to be adjusted at will, between the three positions, forward, neutral and reverse.

These tests, along with my full-size wingsail tests which you can find here prove the effectiveness of the system.

Q: How about reefing them if the wind gets up?

A: When the tail is a zero angle and perfectly aligned with the angle of the main wing. The rig presents a perfectly streamlined section to the wind and the drag is less even than a normal rig with "bare poles" - (with no sails up).

All builders of self-trimming wingsails like this have found that reefing or taking them down is not needed no matter what the conditions. They are perfectly safe to leave up when in "neutral" and will not drive the boat in any direction.

Q: How much would they cost?

A: Not much. There are a variety of ways of building wings, none of them very expensive, and they can be built lighter than aircraft wings, without such a large safety factor. There are no electronics or batteries to add to the cost. Simplicity is a keynote of the design. (Click here for further information about this.)

Q: Who would want one?

A: Due to their simple operation they could be attractive to the following groups:

  1. Motor-boaters who would like to be more green and have the option of using the wind, without all the complication of learning to sail, pulling on ropes, getting wet and cold, and would like to enjoy sailing from inside a cabin when the weather gets rough.

  2. Older people who like sailing,  but have been forced to give up because it is too physically demanding.

  3. The disabled, who cannot enjoy the experience of sailing for the same reason as above.

  4. Operators of electric boats, who would like to make use of the wind to extend their range, and as a failsafe way of getting home.

  5. Use on any boat as a fuel-saver as the units require no attention and they will give thrust to the boat whatever the heading or wind direction.

  6. Boats equipped with Windthruster Units, would be very suitable for hiring out to non-sailors who would like to enjoy sustainable boating but have no experience. Because of the single-lever operation there is no difference in use to hiring out a motor driven boat.
     "Hybrid" Windthruster/Electric boats would be a particularly suitable option.
  7.  Electric drive and Windthruster drive might be combined in a single power lever and speed switch, which would switch off electric power when the Windthruster unit brings boat speed up to a preset level.
    This way the boat would be using the most appropriate form of power. If enough wind, using windpower and saving battery. If not enough wind, using electric power for drive.
  8. Anyone who wants to have a sailing option that is easy to use single-handed. Conventional sail systems can be very difficult to handle in confined waters such as rivers or harbours without another crew member to deal with the sails. With Windthruster units, the lone sailor can concentrate upon manoeuvring, knowing that the automatic system will deal with all adjustments required due to wind-direction/heading changes, and also have the ability to stop and reverse when required.

  9. Not likely to be of interest to competition sailors who enjoy the challenge and difficulty of sailing. (Although self-trimming wingsails of this type do have the possibility of driving boats faster than conventional sailing rigs.)

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Construction Method Windthrusters Rotary Sailing



P. Worsley 2010