Storm jib size?

[mithril]

We have a Dufour 40 sailing boat and are thinking of adding a storm jib to our sail wardrobe. We plan a mini Atlantic circuit; Lagos Portugal - Maderia - Azores - Lagos, and while we dont plan on gales let alone storms it might be nice to have a storm jib, but what size do we buy?

If I was buying a new one I could ask the sailmaker but as it will be a second hand item I'm not sure of a size to go for.

Any suggestions?

 

[ytd]

When I bought a storm sail last year I asked lots of sailmakers what would be the best size for our Bav 44. I got lots of answers. They ranged from 8m2 because this is the biggest sail you can handle in a storm to 14m2 since this is the biggest the racing regulations would allow as a storm sail and then you can use the sail as part of your racing wardrobe.

I ended up with a 9m2 sail that zips around the furled genoa. It's a b..gger to fit (you have to furl the genoa sheets just so) but provides a surprising amount of drive when it's up. But we have never had it up in anything over 30 kts.

I'll be interested to see what others recommend.

 

[mithril]

Re: Storm jib size? an answer

I found this on the web: goog old google

Area determination - Method # 1

Choice A. Decide whether the sailing is done with a well experienced racing crew with ample manpower under all conditions. If so, then the area of the storm jib may be up to 5-1/2% of I².

Choice B. If the sailing is done with just a family where the crew consists of father, mother and children or similar light crew, then it is strongly recommended that the area of the storm jib be limited to 3% to 3.5% of I2.

EXAMPLE: If the I of the boat is 30’0, then I 2 will be 900. Therefore 3% of 900 equals a storm jib area of 27 square feet; 3.5% of 900 + 31.5 sq. feet; and 5.5% of 900=49.5 sq. ft. storm jib area.

So we need 67 sq ft or thereabouts.

 

[jb2006]

There is a difference between a heavy weather jib and a storm jib. The IRC heavy weather jib is up to 13.5% of I^2 in area - with our high aspect rig, that is approx 25 sqm and almost the same as a #3. The storm sail I have is around 5 sqm - just under 3% of I^2 so a little on the small side. If you are racing with roller furling declared you are always allowed a storm jib but you must declare a heavy weather jib if you wish to be able to change the headsail during a race (OR DURING A SERIES - the whole of Cowes week for instance)

 

[Guest]

Storm jibs are flat (or nearly) so make one out of three ropes in a triangle. Then try to sheet it back at the correct angle (bisecting the triangle) without fouling any rigging.

It is pointless to be in a storm and the rigging cuts through the sheet. Having sheets that put distortions in the rig is wrong also.

Just keep experimenting with the lengths of the 3 edges. The overall size should be determined by the wind you expect to still sail in. The force of the wind can be approximated by the squared rule. (There are lots of factors like wave height and surface turbulence). So for twice the wind speed you need a quarter of the area. So just halve all the dimensions of what you would have up in half the wind speed. The highest wind speed we have worked into is about 35knots (but never again as the distortion to the stainless fittings was terrible.). Down wind you can take more but then your boat speed is subtracted.
After a fixed point your intention should be to slow the boat by its stern and not try to speed up its bows.

Final point is that it should not block your view.

 

[pappaecho]

Solarneil is absolutely right, get the triangle right with its own sheets and blocks.
Make sure that the attachment system to the forestay is simple and quick to fit, because in a gale or more you wont have the time or the inclination to start mucking around with zips.
I have a storm jib which uses piston hanks and fits to the baby stay, so that it is further aft than the normal jib and can be rigged before it gets too rough, and so the only items required is to furl the genny and hoist the storm jib from the cockpit... hence the need to a second set of jibsheets, and cars set so that the triangle is right