# Sail area calculations?

Discussion in 'Sailboats' started by Howlandwoodworks, Nov 25, 2020.

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### HowlandwoodworksMember

Good Evening,
Kind of late in finding this out but.
Does the Total Sail Area calculation just use a 100% jib only? (I and J) I have just been using a 100% jib in my boats calculations so far just to keep it simple stupid.

Cheers!

Last edited: Nov 27, 2020
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### jehardimanSenior Member

Depends on what you want it for. In many measurement rules, it is defined as main and 100% of the fore triangle, in others it is defined in other ways. In stability measurements, you calculate all the situations. <shrug> Generally, for SA/D calculation, it is with a "standard suit of sail", which (for a typical knockabout) would mean main and the jib closest to 100% the vessel was designed/delivered with.

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### HowlandwoodworksMember

jehardiman,
That makes senses.
Thanks
John

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### gonzoSenior Member

Is this for a racing rule or for stability calculations? For the first, use whatever minimum the rules allow. For stability, use the actual total area.

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### HowlandwoodworksMember

I am going to add some options for a cutter rigging design to my sail plan with a staysail option to both the sloop rigged and gaffed rigged versions.
Is it the total sail area for stability or is there some ratio for the jib sail section that overlaps the foresail and there is a staysail overlapping the jib sail also?
I am unsure about a masthead vs a fragmented sloop rigging, nor do I know the advantages of one to the other. Other than the total sail area and the top of the main sail behave more like a jib on the fragmented sloop rigged boat because there is no jib to compress the air up there.
"Oh what a tangled web we we weave." (Sir Walter Scott, 1808) I don't think this is what he was talking about but it seems to fit my particular predicament.
John

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### gonzoSenior Member

Large overlaps are used in racing because there is sail area that isn't measured under some handicap rules. For stability, use the real sail area.

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### HowlandwoodworksMember

Oh, that makes senses.
I have a friend who is sailing a 155% jib and a gennaker or a Tartan 27'.

Last edited: Dec 4, 2020
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### gggGuest...

I believe its decades since any active measurement rule used that calculation. To my (limited) knowledge the IOR, which expired at the end of the 90s was the last major rule that indulged in such eccentricity. These days if you do see overlapping jibs on a modern racing boat its more likely because that gives the most sail area on a given set of spars.

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### gonzoSenior Member

Howlandwoodworks likes this.
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### BobBillSenior Member

Sir Scott, circa 1608

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### HowlandwoodworksMember

Thanks, PHRF Fleet Rules are a good set of parameters for me to shot for.
The Sail Plans as are all of plans still in limbo. This Gaff rig Sail Plan will have those pesky adjustable back stays.
I have a long ways to go before deciding on Gaff or Sloop, Masthead or Fractional , with or without Cutter rigging, and the percentage of the fore sails overlap, maximum camber, Foot round, Leech round -+, Broad seams cambers, etc... Finding the basic centers are the easy part. A spreadsheet keeps me from doing the math over and over as I add to a posteriori knowledge of my design but the options seem to go into ∞.

Sometimes I see the sail plans call for a cut of 32% max camber and others 50%. What's up with the cut of max camber on new sails?
So much for keeping it simple.

Last edited: Dec 17, 2020
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### HowlandwoodworksMember

What a tangled web you weave?

This quote is sometimes attributed to William Shakespeare’s Macbeth "toil and trouble"

Last edited: Dec 13, 2020

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### BobBillSenior Member

Love it and learning...
Simple is usually best in the beginning and always later. My way of life...I keep trying to handle a sheet of paper only once, but never quite do it often enough plus, I dare say neither Wm. of Occam, Sir Raleigh or Shake sailed IMO.

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