Sail Coefficients

[DAVID C]

Hello I am working on my first design: a 14 ft skiff. So far I’ve been using Hazen’s Model, from Larsson’s Yacht Design, to size the rig. Would it be better to use something like the IMS model to get sail coefficients? Where could I get a copy of their formulas and data? Is either of these models accurate enough to design the rig and top mast with the proper elastic behavior and yield point?

Also, I’m interested in learning what other sources designers use to size the rig and calculate performance. Any thoughts or suggestions would be appreciated.

Thank you.

[tspeer]

I believe the IMS originally started with the Hazen model, and it has been modified since then. Handicap systems like IMS specifically keep their models secret to inhibit designers from taking advantage of weaknesses in the model (the key to a winning is not to create a fast boat, but to have a boat that's not as slow as the handicap rule says it is), so you're not going to find out what they use. Even US Sailing wind tunnel tests and other technical efforts are often not released publically because they want the handicap system to stay ahead of the designers - even though their tests are paid for by we US Sailing members.

SNAME has recently relesed a CD of small craft papers. You may find a suitable sail force model in there.

[bhnautika]

You may won’t to look at
“Sailing Yacht Design-Theory” Chapter seven, Velocity Prediction Programs by A Claughton

“High Performance sailing” by Frank Bethwaite