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Old 10-02-2016, 15:44   #1
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What size gennaker for top-down furling?

I would like to get a gennaker soon and I'm wondering what would be the right size for my boat (32ft cruiser). The proposals I got from various sailmakers range between 58 and 86 sqm and most of the time they didn't give the luff length...

As I'm sailing single handed, the sail should be furled (Seldén GX10) and flown on a bow sprit. I can estimate the gennaker "forestay" length and from that the max AT-cable length. Then, what would be the maximum luff length of the sail? Does it need to be a bit shorter than the AT-cable for better furling results? A lot shorter so I can look under? Should it be the same? Should it be longer? I'm a bit lost - suggestions welcome
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Old 11-02-2016, 15:37   #2
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Re: What size gennaker for top-down furling?

I guess I shouldn't limit this question to the aspect of the furler. How big can a gennaker be in general? Do you have to be able to tighten the luff with the halyard/tack line?
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Old 11-02-2016, 16:52   #3
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Re: What size gennaker for top-down furling?

The luff needs to be very tight and the same length as the torsion line. If you are cruising I would make it a couple feet shorter than the max so you can see under it. On a reach you tighten the tack line, downwind you ease it.
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Old 11-02-2016, 17:38   #4
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Re: What size gennaker for top-down furling?

I will disagree.

I think a top-down furler may have its own furling "soft foil" and so the luffs can be much longer than the foil - the sail furls round this foil.

You do not want the extra length in a Zero but you may like it in a downwind sail.

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Old 11-02-2016, 17:39   #5
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Re: What size gennaker for top-down furling?

http://www.velasailingsupply.com/v/v...url-SPINEX.jpg

What do you say, gentlemen?

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Old 11-02-2016, 17:50   #6
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Re: What size gennaker for top-down furling?

Quote:
Originally Posted by Copprhead View Post

Then, what would be the maximum luff length of the sail?
You want a sail that can have its luff set tight for upwind and close reaching sails. You want a longer luff for broad reaching and running sails. You want an adjustment block below the drum to be able to play the tension unless you are happy with just playing the halyard.

Mind you still have to make the soft foil (at times it is just a length of non torsion line, at times it is a special gadget rope like with some Profurls and Bamars) relatively tight before you start furling. The luff of the sail does not have to be tight though.

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Old 14-02-2016, 02:32   #7
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Re: What size gennaker for top-down furling?

For top down furling Asymmetrical spinnakers they work best if the luff isn't more than 104% of the straight line length. Which is an all purpose asymmetrical, not a deep running sail. 58sqm sounds more realistic than 86sqm, but a proper sailmaker would look at your boat design, displacement and ballast ratio, the size of your working sails and take into account you are solo sailing and only cruising before drawing up a design. Find a sailmaker who isn't just a sales rep.
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Old 15-02-2016, 12:31   #8
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Re: What size gennaker for top-down furling?

Thank you all for the good advice. I see much clearer now

I would like to use the sail to its max upwind potential, so I need to be able to tighten the luff. Some room to look under the sail makes sense as well and I really don't need the max possible sail area for my cruising.
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Old 15-02-2016, 20:12   #9
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Re: What size gennaker for top-down furling?

If you want a sail that is capable of going upwind then you mite consider a straight luff sail that encapsulates the torsion rope with a regular bottom up furler.
The tack of the sail can finish any distance above the torsion rope so you see where you are going, this is common on cruising catamaran screechers.
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