Automatic Attack Angle and Immersion Depth Adjustment

The attack angles and depths of immersion of the hydrofoils can be  adjusted manually for attack angles between -12º and +12º and for immersion depths from totally retracted to fully immersed.  

An automatic option is also available as shown below.  This illustration does not show the entire hardware, but it does illustrate the basic concept.   A line is attached to the mast near the deck level.  As the mast rotates due to trimming the boom for various points of sail, the line winds and unwinds around the mast.  The other end of the line is attached to the hydrofoil attack angle adjustment apparatus.  This end is anchored on the hydrofoil holder and then extends to a spring which is then affixed to the hull of the boat.  As the mast rotates the from a close haul position to a running position, the spring extends, and the attack angle will change from positive to negative values.  Between the hydrofoil apparatus and the mast the line is equipped with an in-line strap tightener (engager).  Since the hydrofoils are free to move up and down, the depth of immersion of a hydrofoil is determined by the attack angle - fully immersed for negative angles and retracted for 0º or positive angles. 

The windward engager is disabled by the skipper when the boat tacks from starboard to port, or vice versa, so that the leeward foil takes a positive angle.  There are adjustment mechanisms on both sides of the boat.  Thus when tacking from starboard to port, the starboard mechanism's engager is deployed and the port engager is disabled, and vice versa when going from port to starboard.  This arrangement avoids the difficulty of manually unlocking the attack angles and setting immersion depths of both hydrofoils and then resetting them each time the boat tacks.  Merely engaging or opening each engager does the whole job, and the foil with the  engager implemented automatically sets the appropriate attack angle from -12º to +12º as the boom shifts position while the other foil is fixed at a default attack angle of +12º because the engager is disabled.  On a run both engagers can be disabled so the foils assist planing.  

It is also possible to employ a mechanism which automatically operates the engagers when tacking which makes the adjustment of the hydrofoils fully automatic.

  Starboard Tack, Reaching, zero attack angle.  only the starboard foil adjustment apparatus shown, 

Starboard Tack, Reaching, zero attack angle.  only the starboard foil adjustment apparatus shown, 

  Starboard view, -12º attack angle, engager implemented, starboard tack, beating

Starboard view, -12º attack angle, engager implemented, starboard tack, beating