How do I calculate the area of my spinnaker?

[Seven Spades]

I have measured the luff length at 14.9m and it measures 8.12m at its widest point and 7.9m across the bottom of the sail but if you measure the material at the bottom it measures 8m.

Any clues I have tried to Google it but cannot seem to find anywhere that helps.

 

[sarabande]

cloth area can vary quite bit with the type of spi, e.g. radial, tri-radial, floater, asymmetric.

If you want a precise figure, you need to measure panel by panel.


This is an approximation:-
http://www.ukhalsey.com/LearningCenter/encyclopedia/encyclopedia4c.asp

 

[snowleopard]

You can use a method called Simpson's rule. Measure the length from head to mid-foot then divide the height into an even number of of equal intervals and measure across at those heights. Let's say you divided it into 4 intervals giving 5 widths, the top one being near to zero.

Multiply your measurements by 1,4,2,4,1, add the results and divide the sum by 12 to get a weighted average width. Multiply by the height and there's your answer.

 

[bbg]

Measuring panel-by-panel might work, but it would take a LOT of measuring and calculating.

I wanted to know the area of my spinnakers, so I took them to a sailmaker. I expected to be told 70m2 and 55m2 (though I didn't tell him this). He told me they were 62m2 and 47m2.

I didn't believe him so asked him to re-measure. He said the measures he took were the same, but used a different program to calculate the area, and then he came up to 69 m2 and 52m2.

It can really depend how much fullness is built into the sail.

Edit - why do you want to know the area?

 

[sarabande]

thanks for that, SL, I have never come across Mr Simpson before

 

[mcframe]

You can use a method called Simpson's rule. Measure the length from head to mid-foot then divide the height into an even number of of equal intervals and measure across at those heights. Let's say you divided it into 4 intervals giving 5 widths, the top one being near to zero.

Multiply your measurements by 1,4,2,4,1, add the results and divide the sum by 12 to get a weighted average width. Multiply by the height and there's your answer.

Nice! I didn't know about that until now - I still think the _German Tank Problem_ is a pretty cool example of applied maths.

I was recently sailing with a more-geeky-than-me friend - when he spotted my house flag breaking 3/4 of the way along it's length - in the slot, on starboard tack - he then explained the _Reynolds Number_ when laminar flow becomes turbulent...

 

[Lady Campanula]

thanks for that, SL, I have never come across Mr Simpson before

It is also used to gain an approximation of the displaced volume from lines plans and, sometimes, from direct hull measurements.

 

[Csail]

You can use a method called Simpson's rule. Measure the length from head to mid-foot then divide the height into an even number of of equal intervals and measure across at those heights. Let's say you divided it into 4 intervals giving 5 widths, the top one being near to zero.

Multiply your measurements by 1,4,2,4,1, add the results and divide the sum by 12 to get a weighted average width. Multiply by the height and there's your answer.

Bloody hell....i would just get a sail maker to pop down to look.

 

[Seven Spades]

Its nuts. All I wanted was a web page where I could input some measurements and get an area

 

[flaming]

Its nuts. All I wanted was a web page where I could input some measurements and get an area

Ask and ye shall receive. (Sort of)

http://www.intersailsupply.com/about_spinnakers.html

http://www.ukhalsey.com/LearningCenter/encyclopedia/encyclopedia4c.asp