The AWE+windmill sailboat


I want to share an idea for a sailboat. It is a variation of “a sailboat with a windmill” except I think the windmill maybe pulls better downwind, and also the moment of the windmill may be prohibitive for a boat.

So I was leaning towards some kind of TRPT AWE design but that is rather complicated to build. Then it occured to me that we could use the same principles as AWE [pitch control to stay airborne, less moment on the hull as the rig is tethered not on a mast], but make it solid like a windmill. A swashplate is a ready made component that could make this RC controllable in small scale (eg 1 meter diameter blades, 2 m long hull).

There are of course many variations:

  • power generation and electric propulsion using a propeller subsea
  • controlling the angle of the “tower” by servos or free floating
  • a hinge at the top of the tower, servo controlled or not
  • the «tower» may elongate during sailing

I guess as a starting point I would consider the “stupid” version where the tower rotates freely, maybe only with the option of changing the elevation angle now and then, maybe by a rope and cleat.

Maybe eventually put it on foils and give Vestas/Scirocco a run for their money as the fastest sailer ever

I do see some immediate concerning properties, namely cos^2 losses when taking the windmill blades at an angle to apparent winds…

The “rotary sail” boat (description reproduced below) includes both a rotor sail and an underwater propeller. That said your idea sounds different. So please can you point the main differences and the expected advantages compared to the design below, such like “pitch control to stay airborne”, “swashplate”, " controlling the angle of the “tower” by servos or free floating", “swivel”?

From DirectUpwind :

Video on

Ce bateau expérimental a été construit pour démontrer la possibilité et l’aspect pratique d’utiliser un vent de face direct pour propulser un bateau. Cela s’est avéré très facile et l’engin pouvait naviguer directement dans le vent venant en sens inverse.


This experimental boat was built to demonstrate the possibility and practicality of using a direct headwind to propel a boat. This proved very easy and the craft could sail directly into the oncoming wind.

Sure. I will try.

The first thing that is different is the windmill mast/tower is tiltable to any elevation angle and any yaw angle. The windmill blades form a plane normal to the mast/tower rather than being in a plane inline with the tower of a windmill [traditional VAWT setup].

This is the starting point which allows the force of the blades to be aligned mostly along the mast/tower rather than the cantilever structure of a traditional windmill. This could be a good idea because the large heeling moment that a traditional windmill would apply to the hull. This moment is mostly removed in this new design.

We will still have to grapple with a heeling moment in zero/low winds due to the weight of the mast/tower, swashplate and blades. So they must be lightweight and as small as possible, and they will limit the length of the mast/tower.

If we assume the mast/tower in the new design is attached by a ball joint at the base where it connects to the hull, we see that by using a swashplate we can steer the placement of the mast/tower freely, as long as the windmill is spinning.

The swashplate will enable us to provide more lift on the upper side of the swept area or the lower side, for vertical [elevation angle] control. Likewise the swashplate can provide more lift on the right or left side of the swept area to allow moving the rotating blades upwind or downwind, or from starboard to port side of the hull.

The control could be manual or automated, though anyhow it should be quite simple to implement as the swashplate is an off the shelf component that handles the most critical and hard to implement function (controlling pitch of the blades in their cycle).

Because it seems unlikely that this mechanism can support the weight of the mast/tower and blades in all wind conditions, I suggest that the mast/tower is supported by a wire that is attached to a more traditional sailboat mast. The rope can be used to change the elevation angle of the mast/tower by means of pulleys and fastened by a clamcleat.

If the mast/tower is supported in this way, the swashplate could be used to control the hull roll angle. Though I am not sure if this is very relevant.

I hope this detail provides a bit more clarity.

This sailboat should be able to do most things the other windmill powered boat can do. Still, because of the windmill pull acting at a point close to the hull rather than at the top of the tower, heeling moment should be less. Eg with a energy transfer from windmill blades to a propeller in the sea, it may be able in theory to sail directly upwind