The issue of flutter on the leach of the Bay Raider 20 main sail has been the subject of many discussions in the forum pages. As I have had the same problem on the main sail of my Bay Raider 20 “Kailani”, I thought that I would share how I have decided to go about tackling this issue. My main sail is cream coloured and was made by Dolphin Sails. The sail has a leach line.
A local sail maker here in Perth, Western Australia who specialises in gaff and gunter rigged boats, requested that we start the process by taking a series of photographs looking up the leach and luff of the sail as well as a couple of pictures from about mid-boom. All photographs were taken with the boat sailing reasonably close hauled in about 12-14 knots of wind.
The first issue clearly seen on the photographs was the softness of the gunter. I received advice from Andrew Denman at Denman Marine in Tasmania on how to stiffen the spar, he put me in touch with the carbon specialists at Soller Composites in the USA
http://www.sollercomposites.com/composites/carbon%20fiber%20sleeves.htmlThe guys at Soller Composites were extremely helpful as I am no expert with composites, they confirmed Andrew’s recommendations.
I ordered one layer of Uni Sleeve (1” to 2.75”) and one length of biaxial sleeve (2.5”). In each case I ordered enough to cover the gunter from around 300mm below the halyard host (full mainsail, no reefing) to the mast tip. This cost around US$150.00 including air-freight.
The carbon fibre arrived 10 days later in a small box. I had spoken to the guys at Soller and they recommended that I buy several sets of rubber gloves and wet out the carbon with my bare hands. I was somewhat sceptical of this advice; it did however prove to be the best method.
I carefully measured and photographs all the fittings on the gunter before removing them. The wooden block at the halyard hoist was left in place, as it proved extremely hard to remove. This was mistake, as it caused some distortion to the carbon sleeving. In retrospect I should have removed it even if it meant destroying it.
I slung the yard from my garage roof at a comfortable working height above the floor, with the tip held by a thin rope threaded through the hole in the wooded plug at the tip and a simple loop of rope around the gaff jaws. It is important to make an arrangement that allows the yard to rotate as you work the resin into the carbon.
I had a moment’s dilemma as to whether I should wet out both sleeves of carbon together or separately. The guys at Soller recommended a one shot approach. The Uni presents as an expandable tube of unidirectional carbon strips. It is quite sticky and needed to be very carefully placed over and then pulled down the mast. The Uni is made with elasticated transverse material that allows the tube of Uni to expand while at the same time holding the Uni-directional carbon fibres in place. The sleeve can expand from 1’ to a maximum of 2.75”. It is important that all the fibres are kept straight as the tube of Uni is slowly pulled over the mast.
The tube of biaxial was then carefully slipped over the mast tip. This material was more robust, and can be pulled over the mast quite easily. The biaxial looks like the outer sheaf of a braided rope.
Once the two layers of carbon were in place I mixed the epoxy resin and proceeded to wet out the carbon. As expected a lot of resin ended up on the garage floor. The whole process took me around 1 hour. I had some problems in finishing the ends of the carbon, and in hindsight should have ordered around 0.5 metres of additional biaxial so that the unidirectional material was completely covered by the biaxial. The Uni-directional stretched during the wetting out process and ended up protruding from the biaxial, not a big issue, more cosmetic than a problem.
After the resin had cured I lightly sanded the ends of the carbon to remove any stray filaments, reattached the fittings and re-lashed the mainsail to the gunter. This requires additional rope as the diameter of the gunter was slightly larger. I estimated that I added about 1.5kg to the weight of the gunter, though I should have checked the weight more carefully before and after. Also in my enthusiasm to get started I forgot to conduct my own before and after stiffness check of the yard.
A subsequent set of photographs taken while sailing showed that the yard was now much stiffer and did not bend off to leeward in a gust. The leach of the main sail still fluttered, so the next move was to re-cut the shape of the main sail.
The sail maker chose to re-cut the sail, by altering the shape at the luff. Instead of having a straight luff line from downhaul to mast tip the luff was angled back into the body of the sail from the point where the gaff jaws are located. This shortened the sail height by about 120mm, but tightens the leach when the gunter is hoisted and pulled up tight to the mast. In addition more eyelets were added to the sail so that the sail is lashed to the gunter in around double the number of places compared to the previously arrangement. We also had three short battens added to the leach. See photograph and drawing.
This work has almost completely removed the leach flutter, the sail sets well and the additional lashing points on the gunter gives the sail a far better shape near the top.
I would recommend this path to anyone wanting to find a method by which leach flutter can be reduced to a more acceptable level, but is not ready to buy a new mainsail.
