Mainsail leech flutter

[rfriesen]

We have a 2007 B40 with a battened in mast furling (Neil Pryde) mainsail. In winds over 15 knots it is very hard to avoid significan leech flutter in a reach. I tighten the sail a lot using boom downhaul (main sheet and vang equal loads), but concerned about overloading stresses if I try to tighten much more.

I added an extension to the leech chord but it is difficult to add enough tension to help reduce flutter.

I have heard other in mast Beneteau battened mainsails have same problem.

Comments? Suggestions?

Rick

 

[Jackdaw]

It can be hard to maintain luff tension on most boats in a reach, and as you have found its much harder with a furling main. The V battens offer MUCH less support to the leech than traditional battens do, and the post 2006 NP furling mains have more roach than a typical in-mast furling sail. It helps performance but can add to the flutter. I'd try more vang. If the leech is not reasonably tight, all the leech line in the world will not stop the flutter.

As an aside, here's the NP tuning guide for your boat.

http://www.neilprydesails.com/pdfs/b40 tuning guide.pdf

 

[RichH]

If this is a developing or increasing problem, it could be that youve permanently stretched out the leech by constantly overtensioning the mainsheet. If so, two remedies: 1. apply small intermediate battens between the battens where the flutter is uncontrolled. 2. resew or add a very small amount of 'broadseaming' to the panel seams in the affected area.

As Jackdaw has stated ... more vang pressure is usually the first step.
Got a 'rigid vang'? If so, set up for 'vang sheeting' (less dependence on the traveler) to hold that leech pressure/tension more constant so that when the boom is outboard the leech is a bit more 'closed'/tight.

 

[bob_pattison]

Rick:
The other posts were good advice...I would just add that in reaching, the vang is what tensions the leech...boats with small travellers and certainly the newest boats with no traveller quickly run out of the ability to tension the leech with the mainsheet. So it is ALL about the boom vang. Depending on the wind strength and angle you are sailing, I would expect that you'll much more vang tension then mainsheet.

Also, you might find that reaching in breeze that once you get the leech trimmed correctly (tighter) that the boat will be overpowered and you need to reef, which will reduce the loads on the sail as well.

Bob Pattison