# SA/D calculation for cutter; staysail included?

Discussion in 'Sailboats' started by hiracer, Jul 19, 2006.

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### hiracerSenior Member

In the case of a cutter, is the sail area for the staysail included in the calculation for sail-area-to-displacement ratio?

Same question for ketch as to mizzen sail?

I understand that only the 100% jib area is included.

TIA.

2. Joined: Aug 2004
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### MikeJohnsSenior Member

Yes you use 100% of the foretriangle and the main as you would with a sloop.

With a ketch use 100% of the mizzen , in addition you want to add the free projected area of a mizzen staysail as the SAD is a light air performance measure.
Keep in mind that SAD is just a crude way of comparing boat light air performance. Once the wind rises the sails drop in size very quickly since the energy is prop. to the wind vel squared and then its the powewr of the hull to carry sail that is everything and SAD becomes meaningless.

Hope this helps

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### hiracerSenior Member

Yes, that helps a lot. Thanks.

4. Joined: Jun 2006
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### hiracerSenior Member

Hey MikeJohns, I appreciate your help but I need to clarify your answer, just to make sure I'm not confused.

With respect to a cutter, one uses the area of (1) the main, (2) the 100% jib, and (2) the stay sail, correct? It's not just the Main and 100% jib. All three sails are used, right?

The staysail makes a big difference in the calculations for cutters. Moves a boat from motorsailer range to cruiser status, typically, so the inclusion/exclusion of staysail is pretty critical from a mathematical standpoint.

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### MikeJohnsSenior Member

hiracer

No for a cutter it is the 100% fore triangle and the main, Not the staysail as well.

For a ketch it is as above with the Mizzen and the mizzen staysail free projected area, ie the area not blanketed in the side view by the other sails, some alos add an allowance for other light air sails but I think this is better left out.

cheers

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### hiracerSenior Member

MikeJohns,

Many thanks. If you look in my light airs thread, you will see that you have been a major help to me.

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