Fulmar spinnaker size

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jerryat

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Can anyone tell me the area of the radial head spinnaker for a Westerly Fulmar?

I'm looking for a secondhand spinnaker for my Fulmar and have seen one made for another make that has the same 'right' luff and foot dimensions, but what seems to be a completely different total area to that stated by Westerly for the same dimensions. /forums/images/graemlins/confused.gif

My maths is lousy so would appreciate help! /forums/images/graemlins/grin.gif
 
Hi Nightjar,

Yes, thanks for that, that's the area I have. The spi I'm looking at gives the same dimensions but an area of 380 SF, so I guess they've got it wrong, or there really is a huge difference in spi design!!
 
Thanks Vic, I had the dimensions and the area as I said.

The discrepancy is that the s/h spinnaker I'm looking at has virtually identical dimensions, but the details state an area of 380SF.

With the same dimensions, for a similar radial head spinnaker, Westerly reckon 760SF. Of course, the chap might simply have forgotten to multiply by two!!

I just wondered if anyone knew how to calculate the area of a spinnaker from its luff/foot lengths.
 
As I understand it, you calculate spinnaker area by dividing the area into two rightangle triangles by dropping a line vertically down from the head to the centre of the foot. A bit of basic trig will give you the length of the vertical line. You than assume that each triangle is a rightangle triangle and area is length times breadth divided by two. Once you've calculated the area of one triangle, multiplying by two gives the area of the spinnaker. Perhaps this is where the error was made?

I believe that the 'extra' area at the shoulders of the spinnaker is ignored in the same was that the roach of a mainsail is ignored for sail area calculations.

If my data is out of date please accept my apologies - I am not a sailmaker! Perhaps someone else will know better or confirm or deny my memory?
 
Yep, thanks for that John, that makes sense to me and was something I thought of when the advertised area was exactly half what it 'should' have been. I just wasn't sure how much 'extra' should be allowed for the 'bulge' if you see what I mean!

Come to think of it, every maker will have a slightly different design, so I suppose only that particular loft would know.

I think your method is as good as any and I think for the purposes I need, will do nicely.

Cheers Jerry
 
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