Design Approach

In the post entitled ”Beyond 50“, Bob Imhoff shares his insight about “barriers” to high speed sailing. I’d like to discuss one of these barriers myself, drag.

In aeronautical engineering drag is a funny beast. The slightest bump, seam, or protuberance can cause seemingly disporoportionate amounts of associated drag. The goal, therefore, lies in designing and manufacturing aircraft that are mostly free of such characteristics. This is why the appropriately named sailplane is so effective at riding thermals. I say appropriately because gliding is analogouos to sailing. Two opposing forces, weight and lift, act together to “squeeze”–to use Bob’s analogy–the glider through the air. It’s best to think of a glider being kept in level flight by an updraft. Sailplanes minimize drag to the extreme, in addition to employing the use of high aspect ratio laminar flow wings, in order to achieve tremendously high (>50) lift to drag ratios.

I realized early on the connection between sailplanes and sailboats and decided, therefore, to focus my attention on reducing parasitic drag in my high speed sailboat design. I started by thinking of ways to modify existing designs, such as asymmetric multihulls and force-aligned boats, tinkering with novel ways of reducing supporting structures, streamlining existing structures, and using hydrofoils. Although I came up with what I thought at the time were novel configurations, the more I researched and hypothesized, the more problems and limitations I discovered.

For example, an inherent limitation of both Macquarie Innovation and Vestas Sailrocket is a need for “special” wind and sea state combinations. I say special because they are not natural and are not readily available at any one spot on this planet, except in the man made “French Trench” perhaps. And I guess I failed to mention my intent was to create a tackable and survivable craft to beat both outright and offshore records, negating the use of inherently restrictive designs. Another limitation of MI and VSR is the aerodynamic drag forces produced on their supporting structures, i.e. their “arms”, which substantially detracts from their top speeds.

So one day I had an epiphany. Why not put ballast on an actively balanced wingsail? In one fell swoop it removes ballast below the waterline, removes the requirement for supporting structure, and reduces the bending load on the mast step. It also allows for the use of high aspect ratio wings without a necessary increase in ballast weight or beam width, as would be required for a multihull. In other words, the opposing lift generated and ballast generated moments both scale linearly with wing span because both are produced on the same structure.

The downside, of course, is the need to actively balance an inherently unstable design, and this is where the fun begins. As I continue to analyze this concept I will update this site with my conclusions regarding its feasibility and practicality.