GPS and VMG

[wingsailor]

sailingdog,

A distinction needs to be made between wings/foils/sails in the air that are restricted in rotation (Rotating tear drop masts, rotating wing masts, aerorigs - the sort of rigs I think you are referring to) and freely rotating rigid wing sails (360 degree full rotation weather vain wings). My Ocean Cat has a (hydraulically controlled) aluminum tear drop rotating wing mast. The cord is a little over a foot. Most large ocean racing multihulls have "rotating" wing masts with a very large cord. They do make good storm "sails" but have standing rigging and "rotate" 45 degrees or so side to side. They also "hunt" when at anchor. Soft sails on these rigs would need to be reefed or taken down. All these rigs have excessive windage because of stays, halyards and foller furled sails. I am talking about the fully (360 degree) rotating wing sail such as the one developed/built by Walker Wing Sails (only a much simpler version). Walker crossed the North Atlantic and got a glancing blow from a hurricane, no problems, nothing fell down. The windage is less on a feathered wing than on a similar vessel with a stayed mast. Pictures of these wings are on my web site. The problem I am having is that most rigid wings are build for very high performance speed record attempt machines (that usually crash because water over a foil moving at 50K tends to vaporize and they loose traction, spin out or go airborn) and few cruising boats have been fitted with them. I feel like I am a guy looking at multihulls in the 1960s with all the lead mine "conventional wisdom" sailors saying they are dangerous, they won't work, they will flip and they will break up. The early multihulls had their share of problems but there are a lot of us sailing them now.
Aside from the "Little America's Cup" sailed by catamarans with restricted rotation wings there is not much action for these devices in racing. This is a racing thread so a discussion of wings should probably go to another Forum. Any suggestions regarding where to look (what forum) for help with this project?
Wingsailor

[sailingdog]

The Boatdesign forums would be a good starting place.

[llissenden]

Polars are great for target speeds in the absence of wind shifts and wind speed changes. GPS will tell you speed over ground and course made good taking into account wind and current and your boats' movement across the face of the earth - not just through the water. We always punch in the leward turning mark at the start (usually the pin, sometimes a separate mark just upwind) to look at VMG-to-the-mark coming back downwind. At the top mark, we punch in again if doing multiple laps. VMG readings tell you not just best angles but can tell you when to tack/jibe when the number starts to drop. It's a great racing tool! Covering competition must always be weighed, especially in onedesign or bigger multiple race regattas..but being on the right tack and at the right angle will get you around the course faster in most cases.

[sasbibic]

Small Software can give You helping hand with VMG, sailing speed towards target point, polar diagrams, speed diagrams and many more. Personal Sail Computer is FREE with statistic information for last 30 minutes.