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Sail & Rigging - Maximum loads on spinnaker sheets and shackles.
20 January 2015 - 23:07
Join Date: 27 October 2013
Posts: 60

Maximum loads on spinnaker sheets and shackles.
I would like to know the design loads to be used for spinnaker sheets and shackles.

I have made a calculation as follow

Spinnaker area for Swan 44: 179m^2
Drag coefficient: 1.0
Dynamic factor: 2.0

I have divided the total drag force with three which imply that forces in halyards and the two sheets are equal. I don’t know if this is correct. It is of course more complex as we have guy and spinnaker pool etc.

I have applied a dynamic factor (spinnaker collapse and get full again)

It is few of us who would sail with spinnaker in 25 m/s (50kn) wind but the gear should be design for it.

My estimate point to something around 4500 kg. / sheet.
How far is that for common practice?

Lars Strom might have some “rules of thumb”

Best Regards,

22 January 2015 - 09:31
Join Date: 02 January 2008
Posts: 1547

Dear Bjorn
Interesting calculation, your estimated strength is about right provided you mean breaking load. You can find various estimators on the internet, and they suggest slightly lower numbers.
Kind regards

02 February 2015 - 17:06
Join Date: 02 February 2007
Posts: 202

On the internet one can find (on some rope manufacturer sites) the recommended BRAKING LOADS to be:
30 X surface for spinnaker sheets and halyards, which in your case means 5200 Kg.
For the mainsail they give 100 x surface (I am assuming that you have to divide this load by the number of sheets in you tackle),
and for a genoa they give 80 X surface.
I thought this could be of interest, especially for genoas where one can find all sorts of complicated formulas.
All the best.
Philippe 41/022

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