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Old 6th July 2010, 10:41 PM   #1
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Default How to calculate the sail size

Hi everybody,

I have a sail that I wish to sell, and I'd like to provide the size of the sail ( which I don't know and it's not indicated).

I originally searched online for the methods, which I did not find, so I guessed it was similar to calculate the area of a triangle.

So here is what I came up with:
My sail is 13.5 feet tall, 7 feet at the boom. I converted that to meters which gave me 4.11 meter tall and 2.13 meters at the boom.

After doing the calculation : (4.11*2.13)/2, it comes down to 4.3 square meters.

so I thought my sail was of size 4.3. But someone came and compared what is supposedly a 4.5 sail, and it's half the size of mine.

So therefore, how do I calculate the size of the sail, since apparently it's not what I thought.

Many thanks in advance.
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Old 6th July 2010, 11:54 PM   #2
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Well if the 4.5 is half the size of yours that would make it a 9 meter! But with a 411cm mast that's pretty doubtful I'm guessing that the shape of your sail and the 4.5 are quite different, so it's difficult to accurately compare their sizes.

This is probably a pretty old sail? Does it have any full battens; ones that go all the way from the leech (trailing edge) of the sail all the way to the mast?

One minor adjustment would probably be in the mast sleeve - it's probably curved so it's not quite a triangle.

If it's old enough, it might be marked with the area in square feet. Then you can convert using: sq ft x 1.1 = sq meters

You can always just sell it with a picture and the mast & boom measurements.

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Old 7th July 2010, 12:03 AM   #3
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Hi Chris, unless your sail is very old fashioned it has not a triangle shape and there is much surface outside. Based on my own sails collection I would suggest a x1.4 factor so ~6.2 m². This been said 4.11 sounds very compact for a 2.13 boom. I have a 7.3 m² sail with same boom length and 4.86 mast luff. What type of sail is yours?
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Old 7th July 2010, 03:46 AM   #4
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Thanks for the replies.

I think it's somewhat old. I am not the original buyer. And it's a NeilPryde (or something like that).
The battens are not full length (3 in total), and it's not far off from a triangular shape.
I looked everywhere on it, and it does not say anything about the size.

The measurements I took are approximate with a measuring tape, but I mean, in worst case it's an error margin of 1/2 feet.

As for the other 4.5, you could clearly see it had a lot less surface. It was approximately the same luff length, just half the width.

I'll try to post a picture to give a general idea.
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Old 7th July 2010, 06:32 AM   #5
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did an experiment since i have my sail specs in a spreadsheet

did reverse engineering and discovered luff * boom / 1.5 is REALLY close to sail size

so, in this case ...

4.11*2.13/1.5=5.836 sq meters
rounded up that's a 6.0 sail - make sense ??
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Old 7th July 2010, 08:47 PM   #6
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Sounds like a 25 year old regatta sail. Short mast and long boom with three short battens. Is the sail all Dacron (no plastic laminate on the sail), with a thick flexible window?

Given the mast and boom sizes, it my be around 5 - 5.5 meters. I still have my 1985 Superlight regatta sail and use it on the original board.

Are there any markings on the main body of the sail (numbers or a design)?

Any pulleys or just a grommet at the foot of the sail?
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Old 7th July 2010, 10:25 PM   #7
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Joe and Ken, thank you very much.

The sail is pretty much how you describe it, Ken: no laminate, small plastic window, no marking or number, and it's a grommet at the bottom.

Joe, I was dividing by 2, so your 1.5 is probably what I had wrong.

With a visual comparison (from memory) with the 4.5 sail, 5.5 or 6M would make sense.

I'll go with that.

Thanks for all the help, guys!

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Old 7th July 2010, 10:55 PM   #8
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There is an Application on iTunes that gives you the sail size depending on your weight and wind velocity.
The name is Sail Size.. Check it out. They also offer a windows excel program with the same things.

Last edited by nonopr; 7th July 2010 at 10:59 PM.
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Old 8th July 2010, 03:23 AM   #9
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Good Lord Sir !
By the sound of your sail, it is more likely you will be paying somebody to take it away !
I recently saw some wallets in Tarifa made from "old sail cloth".
You might do better to "recycle" it some other way.........
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Old 8th July 2010, 04:01 AM   #10
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Its a little off topic but a technique I use to compare my sails (from different manufacturers/ranges) is boom length x mast length (in cm) divide by 1000.

A 7 metre comes out around 100. A 5 metre around 70. Its sort of a power index which I find better for comparing sail "sizes" than quoted areas.

See where yours comes out and then work backwards to size.
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