Tuesday, 3 September 2013

Contemporary Construction Types in Sailmaking


It is fair to say that sailmaking has probably changed more in the last 15 years or so than at any time in the past. Buying new sails can be something of a bewildering experience; speak to 3 or 4 different sailmakers and you could easily end up with what appears to be literally dozens of different options to choose from. However, a little knowledge can simplify the process considerably. The aim of this article is to provide a brief account of the three generic construction types that most sailmakers would currently offer.

Cross-Cut. In most instances cross-cut sails, where the panels run roughly horizontally across the sail would be made from woven Polyester, commonly known as Dacron. These are traditionally associated with cruising boats but are also commonplace on many smaller race boats and of course on dinghies.
  
Dacron sails are woven in the age old way on a special loom and have fibres running in a ‘warp’ and a ‘weft’ (fill) direction. The warp fibres run in a continuous length along the roll whilst the fill fibres run perpendicular to the warp, i.e. directly across the roll. It is possible to vary the quality and size of the fibres as well as the density of the weave and this in turn results in Dacron’s with different properties. In fact all of the cloth manufacturers offer many different styles of Dacron, each of which is suited to a different end use or budget. This is covered in more detail in a separate article.

Dacron fabrics tend to be much stronger in the ‘fill’ direction than the ‘warp’ direction which is why they are used in cross-cut applications; the fill fibres are lined up so that they correspond with the chord between head and clew which is roughly the direction of maximum load in the sail (see the red line in the picture above right). However, this depiction of the loads in the sail is rather simplistic as there are additional loads running in many other directions that are not particularly well catered for by simple woven fabrics.

Radial Cut. In order to cater for the myriad of loads present in a sail, the sailcloth manufacturers developed cloths that were stronger in the warp direction than the fill direction (opposite to Dacron) and which also had better properties in the ‘bias’ (45 degree) direction. By using these cloths in a tri-radial panel orientation more of the loads in the sail could be supported. The resulting improvement to shape stability means better performance. It is important to note that this is as important to the cruising sailor as the racing sailor as better shape retention equates to less heeling, less flogging and better handling. In the graphic on the right it is easy to see how the loads in the sail (red and blue lines) are more effectively taken up by the radial panel orientation than the cross cut one.

The cloths themselves are usually laminates featuring load bearing fibres sandwiched between clear Mylar films. There are a variety of fibre types used including Polyester, Pentex, Twaron, Technora, Dyneema and Carbon, each of which would be more or less suited to a particular size of boat, budget and end use. Adding a single or double sided taffeta backing to the fabric makes them more durable (though heavier) and therefore better suited to cruising.

Membrane constructions. This effectively refers to sails that are made from their base components upwards rather than cut from cloth that is on a roll. They are completely custom products in that typically each panel of the sail is laminated individually with a custom complex fibre map that is designed with the particular boat and end use in mind. The panels are then joined together to create one homogenous structure. The resulting fibre arrays more closely mimic the anticipated sailing loads than even the tri radial sails offering further improvements to shape stability and hence performance. Although these membrane sails were initially used solely on race boats, they are now increasingly commonplace on cruising boats of all shapes and sizes as improvements to technology and construction methods have reduced costs and added to their durability making them very cost effective alternatives to their radial cut counterparts. The photo above shows a membrane panel part-way through its lamination process, note the complex fibre array.

Broadly speaking, whatever it is that you are looking to buy (or whatever it is that your sailmaker is trying to sell you) will fall into one of these three construction types, regardless of whatever name the sailmaker has given it. There are of course some exceptions; some laminates are suited to cross cut constructions and it is possible to produce some woven cloths that are suited to radial cut applications. Similarly, many sailmakers will have their own slightly different methodology for constructing their membrane sails though essentially the principles remain the same. It wasn’t that long ago that laminate sails were the exclusive domain of the racing sailor but nowadays laminates including membranes featuring high tech fibres such as Carbon Fibre are routinely found on cruising boats. Next time you are looking to buy new sails don’t be afraid to explore the various options to find out what really is best for you….


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