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### Sail polar diagram

Posted: **Fri Jul 30, 2021 10:45 pm**

by **AlexQ23**

Do anybody know where polar diagram from a variety of sails could be found? For example square rig sails, bermudian and so on? I'm really looking to have a real diagram where the wind is coming from all direction. Thanks' in advance.

### Re: Sail polar diagram

Posted: **Sat Aug 07, 2021 4:32 pm**

by **Robert Biegler**

I expect you know Marchaj, and I attach another source, for oceanic sails.

This paper is for the Tornado, but has references that look useful:

https://link.springer.com/article/10.10 ... 007-4#Bib1
Then there is Fujiwara et al. (2003) On aerodynamic characteristics of a hybrid-sail with square soft sail

https://onepetro.org/ISOPEIOPEC/proceed ... 3-379/8731
Leloup et al (2014) Kite and classical rig sailing performance comparison on a one design keel boat

https://www.sciencedirect.com/science/a ... 1814002625
Cella et al (2021) VPP Coupling High-Fidelity Analyses and Analytical Formulations for Multihulls Sails and Appendages Optimization

https://www.mdpi.com/2077-1312/9/6/607
It looks like there is some more stuff in a special issue of Ocean Engineering on the topic of yacht engineering:

https://www.sciencedirect.com/science/a ... 1814003497

### Re: Sail polar diagram

Posted: **Thu Aug 12, 2021 11:25 pm**

by **AlexQ23**

Thanks' Robert!

I was more looking to something more pragmatic like the one we could found on a real boat. In those data, the speed factor could be adapted with a ratio according to boat length. A sail in a real life with influence of hull and a proper mast and so on, is quite different than the curve we could extract from a computer program. Lets keep an eye on it! Regards. Alex.

### Re: Sail polar diagram

Posted: **Sat Aug 14, 2021 12:56 pm**

by **Robert Biegler**

Those who are interested in a sail would want to separate the properties of the sail from those of the hull, so you get tests of a sail alone. That said, data including a hull are what you need for a Velocity Prediction Program, so the relevant data, or models, must exist. I don't know whether they exist in the public domain, or only as trade secrets of the big design teams.

If you have access to the boats that interest you, and especially if they are not large, then Edmund Bruce's approach, as described in "Design for Fast Sailing" appeals to me. In case you haven't read a book that old, you drop an anchor, ideally in water shallow enough to walk in, and attach the line to a bridle to the boat's bow and stern. There must not be any current. Measure wind direction far enough from the boat to get an undistorted reading. The anchor might be a good spot. Adjust the bridle and sheet in. The boat will swing around the anchor. The angle between the wind and anchor line will be 90 degrees + drag angle. If you measure wind speed and force on the anchor line as well, you should get all the numbers you need.

I suppose you could measure drag angles and forces for the underwater parts of a boat if you can find a suitable spot with a current where you can tie the boat to a fixed point with a line that remains above the water. If the current is predictably variable, you can get measurements for a range of speeds through the water.

### Re: Sail polar diagram

Posted: **Tue Aug 31, 2021 12:31 am**

by **Robert Biegler**

A few more papers