Alternate views of the Canting Ballast Twin Foil™ System

Canting Ballast Twin Foil™ (CBTF™)

Canting Ballast Twin Foil(CBTF™) technology is an elegant yet practical and effective solution that incorporates the significant advantages of movable ballast into cruising and racing sailboat designs. A canting strut with a bulb of ballast at its tip provides righting moment quickly and easily. Because of the advantageous position of the ballast, a CBTF design needs only about half of the ballast required for a conventional keelboat and can be achieved at the touch of a button rather than the efforts of a large crew.

This results in a lighter and therefore faster boat. Maneuverability is simplified through CBTF’s two turning foils located forward and aft instead of the conventional rudder system. These CBTF developments significantly improve boat performance as evidenced by its growing popularity on racing (especially offshore racing) and cruising boats around the world. CBTF is the only moveable ballast system that provides safe, reliable and non-intrusive performance for everyday sailing.

The basic Canting Ballast Twin Foil™ Architecture

Maneuverability, Lift and Righting Moment

For all displacement sailboats there are three criteria that determine the effectiveness of an underwater appendage package. These are maneuverability, lift and righting moment. Over the decades and even centuries of evolution, the keel/rudder system or configuration has become the most common solution where the rudder is utilized for maneuverability and the keel is left to address the lift and righting moment. Unfortunately, in this configuration the effectiveness of the keel to do these two tasks is an inversely proportional relationship depending on heel angle. Enter the introduction of CBTF, a technology addressing the problem with a completely fresh and empirical solution.

CBTF starts by isolating the righting moment to an articulating/canting strut with a bulb of ballast secured at the tip. By canting the strut up to 55 degrees to weather, the necessary righting moment for a given hull and sail plan is comfortably achieved with 25-50% less ballast than required for a conventional keel. Net result: lighter overall displacement for a given hull and sail plan, hence higher power-to-weight ratio.

Twin Foils

The second part of CBTF is the use of the twin foil configuration, which addresses maneuverability and lift. Enhanced maneuverability over the conventional system is quickly attributed to the handling of the steering by two turning foils and lighter displacement as opposed to a conventional single rudder boat. For optimized lift efficiency (Cl/Cd) the foils are placed in the high-pressure zones created by the hull. Not only does this increase the underwater appendage package lift efficiency, but also reduces the boat’s overall wavemaking drag.

Another benefit of the twin foil system is the collective control.

This adjustment allows the boat to sail with virtually zero leeway upwind and superior directional stability downwind due to its ability to shift the CLR fore and aft, balancing the hydro and aero forces.

Misconceptions and Advantages

One of the most common misconceptions of CBTF technology is the belief that there is an increase in wetted surface area over the conventional rudder/keel geometry because of the addition of the forward foil. However, the reality is the wetted surface of a CBTF design is less than or equal to a conventional design for several reasons:

• The surface area of a canting strut is considerably smaller in chord since it is not required to generate the lift like a conventional keel.

• The surface area of the bulb is smaller due to righting moment efficiency (25-50% drop in the volume).

• The surface area of the hull is smaller due to its lighter displacement.

In conclusion, the CBTF appendage package outperforms the rudder/keel configuration:

1) Lighter hydro package (higher power to weight ratio = increased downwind performance)

2) Increased lift efficiency (lower induced drag = increased upwind performance)

3) Smaller wake signature (drop in wavemaking drag = increased up and downwind performance)

4) Superior handling, maneuverability and directional stability.

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©2005 CTBF Co.