WINGSAILS AND LARINKA
John Walker designed the wingsail as we know it today. His first commercial
wingsail was for the Ashington . With no further interest from ship owners he produced the bi-plane wingsailed yacht, Blue Nova, and with requests for a smaller yacht he produced the monoplane wingsailed Zefyr. The demise of Walker Wingsail Systems was not due to any wingsail technical problem. And there are no wingsailed boats in production.
Wingsailed yachts could be produced, Ocean Foil has the wingsail technology. Some multihulls could be “re-engined” with wingsails. The occasional super yacht proposal has shown wingsail type wings, but nothing has happened. There is no technical reason to prevent wingsailed yacht production. Perhaps increasing fuel
costs will bring such boats into focus.
Wingsails and sails
, a comparison.
have as we know have been around for a few thousand years. Vertical wings have a recent history
. A sail is a single
surface aerofoil held in place by a mast
and in most cases standing rigging
. It is usually controlled by running rigging
and in the case of larger boats a considerable amount of deck gear
A wingsail pivots about a vertical axis and in the case of Larinka’s monoplane wingsail is controlled by a tail (aero rudder). The whole configuration is balanced by a weighted boom ahead of the wing. This prevents wing rotation due to boat heel and pitching. There is no additional rigging and deck gear
, although the bi-plane wingsail on blue nova did have classic bi-plane diagonal bracing wires.
A sail is controlled by sheets
and running rigging like out hauls to affect the shape of the sail, and sheets
to obtain the correct sail angle to the apparent wind
. Reefing is necessary to reduce area in increasing wind
Larinka’s wing has two major elements, the leading part and trailing part, there is a small flap pivoting from the leading part. This forms a wing section capable of increased lift
(thrust). The leading part can be rotated and the small flap allowed to overlap the trailing part to form a high lift
section, (maximum thrust). The leading part can be pivoted to align with the trailing part so that every element is in line, this is the feathered condition, generating minimum thrust with small angles of the tail, or with the tail at zero angle, the zero thrust geometry.
There is an interesting progressive comparison here, if we observe the development of hang gliders. Hang gliders started as single
surface wings (sails) and gradually developed to 100% double surface thick wings and lost
the rigging. This was done to improve the flying performance, all this on a wing that can be collapsed into a large bag and stored at home.
Sails / Wings performance.
A sail configuration like a main and Jib
will have a lift coefficient of about 1.3 a monoplane wingsail with high lift geometry has a lift coefficient of 2.7. These numbers are multiplied by wind speed squared, area and air density to give us the amount of thrust that can be generated. The Larinka wing generates about twice the thrust of a conventional main and jib
sail plan. This is a simplified comparison. A conventional sail plan has the most unfortunate aerodynamics, the main attached to a fixed mast
is not an efficient aerofoil, try placing a similar object (mast) on the leading edge of an aircraft wing, and I think the pilot would display radical behaviour. The exposed rigging develops aerodynamic drag; these features are detrimental to boats windward performance. The advantage of a conventional sail plan is the ability to dramatically increase the area to get more drive especially off the wind with enormous spinnakers. The other advantage of sails is the extremely light wind performance; here a single surface aerofoil can do well. The disadvantages are the method of control and necessary gear to do this, especially in increasing wind speeds. A hesitant decision to reef can create a difficult situation and even the basic method of sheeting requires frequent attention to optimise performance.
Controlling a wingsail is easy and can be done from a sheltered internal control station. On Larinka the helm
has two controls, one for the tail and one for the leading part angle. There is no computer control although that would be easy to install. The two controls are used to tack the wingsail and control the amount of thrust. If the electrics fail there is a manual override method that can be deployed from inside the boat. In all the weather
we have experienced on Larinka I never had to put on my weather
gear">foul weather gear, I could sit at the helm
, on watch, with a cup of tea in a dry environment
. We were not subject to the usual fatigue of an external cockpit
situation. Without a computer the fail safe mechanism is the concerned watch keeper when conditions become extreme and the boat speeds up, it is normal to reduce thrust. It is still a boat and in several instances we reduced boat speed through some challenging conditions. And this can be done from the internal helm position. Larinka recently experience 50 knots of wind, Joe the skipper
reduced the leading part to a zero angle (wing parts
in line) and put on just I degree of tail (the aero rudder). Larinka proceeded at 5 knots under complete control, I have been on board in extreme conditions and it is reassuring to have so much control. When all the wing parts
are in line the aero drag is much lower than masts and rigging. This is the zero thrust condition; the sail has been put away.
The Ashington and blue Nova had computer controlled wingsails and blue Nova did have a manual system if the computer system failed.
The only limit on a wingsail is the fixed area and this does become apparent in extremely light winds.
Durability and Maitainence.
So far Larinka’s wingsail has proved to be durable. It has had ten years of use and the only minor damage has occurred when the wingsail has been craned off the boat. This was done to allow boat maintenance
in a sheltered environment
. Wing maintenance
is easier than boat maitainence. in ten years of use how often are sails, rigging and the usual gear replaced. I do not have the numbers but I believe it is quite frequent. In a similar way the weight of a wingsail is not a great concern compared to the weight of a conventional rig. Larinka’s wingsail weighs about 1 tonne. And most of this weight is close to the base of the wing. The weight of a conventional rig should include every item required, like all the sails and all the deck gear. That analysis would be interesting.