Mainsail leach flutter.

[Andy Dingle]

All.

I know this subject has been discussed before but I thought it time I addressed the problem of my main leach fluttering about in anything from an f3 upwards.
I think we have concluded the main problem stems from the fact that the CF gaff 'topmast' spar is flexing away when under pressure opening up the leach and causing it to flutter.
My first question is has any one done anything about strengthening the spar, or is the solution to replace it altogether with either a stronger CF spar or another one in different material - though there might be weight implications in this.

I took the opportunity yesterday to discuss the problem with my sail maker and we laid out the sail in his loft, his first comment was that there was little or no curvature cut into the leach and that, in itself would cause flutter, although he agrees that the main problem is caused by the flexing spar.
My initial thoughts were to fold a 'dart' into the leach to tighten it up and use this 'dart' to slip in a batten? However the sailmaker didn't think that would be effective and would put to much tension into the leach.

After some discussion we have agreed that he will recut and stitch up the leach with more curvature and make two batten pockets to try and control the flutter.

I am interested in hearing if any one else suffers from this problem and what they have done to control it?

I will be testing the main as soon as possible after I get it back so will update on my findings.

Incidentally, and I don't want to tread on anyone's toes, this is the second time my sailmaker has had the sail for alteration and he has twice now commented that the sail (Dolphin Sails) is poorly cut and he expressed surprise at that, saying it did not appear to be of the quality that normally comes out of the Dolphin loft.

Your comments would be greatly appreciated .. this is again just me blundering about in the dark trying to resolve problems that I don't know that much about.

Regards


Andy

[Graham W]

Andy,

Do you know the IMCS of your carbon spar?  Or failing that, and assuming it's an Amex one, which model it is?

I've replaced my original Dolphin sails with Hyde ones, which now come as standard on the latest BR's.  Harder wearing, better shape and better made.  Designed in the UK but made in the Philippines, apparently.

[Andy Dingle]

HI Graham ..
No I don't off the top of my head, but my BR is outside on the drive so will have a look when it stops raining. It's the original one that came with the boat back in 2009, or was it 2008, I forget.

Are you suggesting getting a stronger, stiffer yard?  I agree that would be the solution.

I didn't want to go the expense of replacing my main, if I did it would be to replace the whole rig for a 'traditional' gaff cutter rig - something else I have been toying with ..  and if the newly cut main isn't any better I will probably go down that route - could be fun and give me a lot to think about!

Andy

[Graham W]

Are you suggesting getting a stronger, stiffer yard?  I agree that would be the solution.

Possibly - it depends on the IMCS of your current yard. Mine originally came with an Amex Crosscut 75 with an IMCS of 30, which is reasonable.  If yours is softer than that (and I think some of them were) then replacing it would definitely be an option.  My current yard (a Point-7 C100+) has an IMCS of 36. These people supply Swallow Boats and keep a good range http://www.roho.co.uk/watersports/Windsurf_Masts.html

[Andy Dingle]

Thanks Graham.. I'll research that..

I will probably hunt the second hand market for a stiffer mast section, there must be loads laying around in garages throughout the country.

I would be interested in hearing from any others who have a fluttering leach and what they have done to cure the problem and if my plans to alter the cut of the sail and add battens will have any effect.. though fairly academic as the deed probably has been done by now.
Certainly adding battens was the traditional way of curing a fluttering leach.

[Graham W]

Silly question, but you've already tried tensioning the leech line?

[Andy Dingle]

Fair point but no leach line sewn in my main.
One of the reasons we were less than impressed with the quality of the sail.


Andy

[Graham W]

It sounds like you got a Friday mainsail.

[Simon Holden]

I recently changed my original Dolhpins for a set of Hydes and would certainly agree with Graham that they are of much higher quality both in terms of construction and shape

[Colin Lawson]

I too have an early Br20 that suffers from leech fluttering.  My sail does not have a leech line and so it would be useful to hear from owners of newer sails if a leech line or better sail shape solves the problem?

I could do with knowing if I should concentrate on buying a stiffer yard or a new sail with leech line included? (or both)?

Colin

[Graham W]

Colin,

I had a younger set of Dolphins (late 2010) and recently replaced them with Hydes.  Both the old and the new sets of sails have leech lines.  It took me a while and some help on this forum http://www.swallowyachtsassociation.org/smf/index.php/topic,427.msg2353.html#msg2353 to discover them on the Dolphins.  Once discovered, they got rid of an infuriating thrumming noise from the mainsail and jib leeches in strong winds.

A stiffer yard is always a help in strong winds (particularly if your yard is softer than my original Amex) but I'd say more in a racing context than for cruising.  It helps the mainsail peak to stand up to the wind rather than falling away to leeward. I changed to Hydes for racing reasons too, having been impressed in the 2012 Sail Caledonia raid with how well they performed on another BR20.

So if it is just the fluttering and/or thrumming (rather than sail trim) that is the problem, a leech line will probably solve this. I don't know whether this is something that can be retrofitted.  It says something for the Hydes that although all the sails have leech lines (even my new mizzen and flying jib), I very rarely have to use them and then only on the mainsail.

[Jonathan Stuart]

I've spent too much time looking at forum posts when moving and administering this site and I remembered some posts that might be relevant here. Just to prove to myself that they did exist I have found them and here are the links:

http://www.swallowyachtsassociation.org/smf/index.php/topic,326.msg1443.html#msg1443
http://www.swallowyachtsassociation.org/smf/index.php/topic,431.msg2399.html#msg2399

When ordering my boat, and before the BRe was changed to only have a one piece carbon mast, I noticed that a stiffer top mast is on the options list so presumably there is some benefit?

[Alistair L]

Andy

I too have a similar Friday sail not helped by a soft gaff. I have bought a couple of cheap old fibreglass windsurfer masts and I am planning on putting the top section of one inside the other to make a very stiff gaff - I don't really have any idea what the end result will be but worth a go.  I believe some of the earlier gaffs were more flexible being thinner at the top - like mine which is 30mm diameter.  I don't think the marginal weight increase of the gaff matters.

Adding batterns I think is a good idea, I hope you are successful.  A leech line can of course, if over tensioned, lead to a hooked sail which does not drive so well.

The opening leech I think comes not just from the gaff flexing in the stronger winds but also due to the boom lifting as there is no kicker or traveller and the sail foot does not hold the boom down that well.

BR32

[Colin Morley]

I have solved this problem by putting two battens into the sail. Cheaper than buying a new sail. Still not absolutely perfect but it is not a racing dinghy.

[Colin Lawson]

Colin, when you have a moment could you give us details of your battens. Did you fit them yourself or get a sail maker to do the job. Did you just guess the dimensions and positions?