Winged Keel Polar Diagrams

[Andy]

Has anyone got polar diagrams on 29.5 or similar vessel?Previous article response on PHRF complaint was "If you have the wing keel, don't sail it like you would a fin keel. It will not perform. Make the polar diagrams to get the most performance from your boat Follow your polar diagrams, not the fin keels."I was wondering if any of you polar bears could give a hint as to how high a wing keel should try to point?

 

[Robert Dean]

Wing keel

Andy,I to am curious as to what was meant by the phrase "don't sail a wing keel as you would a fin keel."Prehaps Don H of Houston will chime in and explain this caution in more detail.I have a wing keel on my HL 35. Having never sailed a fin keel HL 35 I am at a loss as to how to not "do it."As to the polar diagram, search the web. Seems to me I've seen a listing for polar diagrams that can be purchased.Sail on,Bob Dean

 

[Don H.]

Fin Keels, Wing Keels, and Polar Diagrams

To be accurate, I am referring to cruising shoal draft wing keels (like Hunter's, Beneteau's, Catalina's, etc.); not high performance wing keels like on America's Cup yachts.UPWIND PERFORMANCE: The fin keel is a more efficient hydrofoil and therefore provides better resistance to lateral motion (leeway) for a given speed. If you take a fin keel and sail it against a shoal draft wing keel on similar boats, the fin keel will point higher and faster. If you try to hold course with the fin keels, with the cruising wing keel, you lose on two counts. You don't point as high, and you don't go as fast. Note: Your compass heading may be the same, but your CMG is two or three degrees off the wind from the fin keels due to leeway. To reduce leeway, foot off. Don't follow the fin keels. Get back your speed and reduce your leeway at the same time. To find the optimum angle of attack for your boat and sail combination, you can use polar diagrams. Or you can use the "experience" approach. That is, try to catch up with the rest of the fleet by trying different combinations of course and sail trim while racing. Of course, while you are experimenting, the guys who have figured it out before the race are blowing your doors off.The construction of polar diagrams for specific boats (and sail combinations) is too complex to cover on a bulletin board. I would recommend a good textbook on the subject, Wallace Ross, SAIL POWER. It explains how to make and use polar diagrams for your boat. By the way, polar diagrams work for all points of sail, not just upwind.Good luck!

 

[Bryan C.]

What is a "polar diagram"?

That's a new one on me. Thanks.

 

[Bill Howitt]

Get info from US Sailing

You can purchase a "book" of performance material for your specific Hunter model whether you are a member or not. I think mine cost about $130. It has all the charts and polar diagrams for best performance under all points of sail. It's a good value.

 

[Don H.]

US Sailing Polar Diagrams

I was surprised by Bill Howitt's response in that I thought polar diagrams were only commercially available for serious racing one designs (through class associations, etc.). I logged onto www.ussailing.org/merchandise/Performance.asp and found that they will sell you a Performance Package for your boat including polar diagrams. There is a sample graphic display on their website.For $210, I would save my money and build my own polar diagrams. It would probably take a couple of months of data aquisition, but what you learn about the performance of your boat in the process will give you an edge over the person that just buys the theoretical polar diagrams for his boat. Besides, it a good excuse to go out sailing. I think that these polar diagrams are based on the assumption of perfect sail shape. In the real world, our sails are usually less than perfect. It is possible that the "perfect polars" you buy may not be the best performance solution for your boat (at least until you buy a new set of racing sails). Good luck!