KISS Complete's Mechanisms of Drag-Reduction

Historically, there are two accepted ways to reduce drag at the solid/fluid interface:

• The first, and most widely accepted means, is to modify the physical configuration of the surface. Ordinarily, the smoother the surface of the solid, the less turbulence there will be at the interface and therefore, better flow character may be expected. Most marine coatings promote themselves as drag-reducing because they reduce the amount of marine growth that remains on the hull. An anti-fouling paint that may have a relatively rough surface but has no barnacles or grass on it will give better performance than a smooth hull finish that has barnacles and other debris sticking to it. However, the way bottom paints work is by having the water dissolve out soluble salts (biocides) that kill the marine life, and then the surface of the paint sloughs, shedding its surface and the dead marine life along with it. This leaves a relatively porous and rough surface. Also, the biocides are toxic and hazardous to the environment.
• The second method of reducing drag is to treat the fluid component, by putting chemicals directly in the water to affect the fluid phase, or by having something exude out from the surface of the solid, again also ultimately modifying the fluid phase. This second method is not a normally accepted technique in boat racing and is not permitted by the Yacht Racing Union.
  

A third method of reducing drag has been developed in the last few years and is the basis for the riblets that were used on Stars & Stripes. The concept is to have precision cut grooves (similar to those on a record) following the path of fluid flow, acting in a fashion similar to flow directors on the wing of an airplane. They act by directing the turbulence of the flow. The current riblets are made by 3M®, being provided on a "wallpaper" that is glued to the surface. 3M® developed the material the film is made of, and not the riblets themselves. KISS-COTE® has been tested as an overcoating on the riblets by the Navy, and has shown as much as a 4% improvement in performance. Unfortunately, there are technical problems in applying the riblets, and the material they are made of becomes easily damaged. Once damaged, one loses the benefit of the directed turbulence. Instead, there is a rough surface which may actually detract from performance.

A final new method of improving the performance of a boat hull in water was developed by the Navy, and is based on the concept of having the boat traveling on a cushion of air. The hull has small perforations through which air is pumped to maintain the air layer around the hull. It has proven quite effective, although impractical for many circumstances.

We have taken a radically different approach to drag reduction. Rather than modify the physical configuration of the solid or the chemistry of the liquid, we modify the surface chemistry of the solid. KISS-COTE® provides a non-stick surface, so that fouling is not a problem as long as there is some shear force at the interface (literally, the turbulence of the water against the hull is sufficient to remove moderate accumulations of marine growth). KISS-COTE® is non-toxic and does not damage the environment. It does not prevent marine organisms from growing, it keeps them from sticking to a surface. Because of the contact angle we provide, the hull also sheds water from its surface, whereas most coatings actually hold water on their surface (making the hull have to drag water along with it). Allan Brown (Cigarette Racing Team, Inc.) has found that the water-shedding effect of KISS-COTE® eliminates chine walking by eliminating the hydrodynamic factors that usually cause it to occur, while permitting the boat to be trimmed higher for better performance. KISS-COTE's surface chemistry also causes any air in the fluid to aggregate along the hull, so that we provide a dry hull that is surrounded by a cushion of air. These properties are combined with the fact that we reduce the skin friction of the surface, whether it be a solid against a fluid or a solid against a solid.

Since KISS-COTE® has proven to improve performance in air as well as water (making aircraft go faster, using less fuel), we suggest KISS-COTE'ing the upper surfaces as well as the hull bottom. Because of its water-shedding character, we also suggest using KISS-COTE® on the sails.