A scrim is the open grid of load-bearing yarns laminated inside a sailcloth – the reinforcement layer that gives a film-based laminate its strength and low stretch. Instead of being woven over and under one another, the yarns of a scrim are laid straight, in the warp direction, across it in the fill direction and often diagonally on the bias, and then bonded to a Mylar® film with adhesive under heat and pressure. Beginners rarely see a scrim because it is buried inside the cloth; sailmakers judge a laminate largely by it, because the fibre type, yarn count and orientation of the scrim decide how the finished sail will stretch and how long it will hold its shape.
What a Scrim Is Made Of
A scrim is defined by three things: the fibre, the yarn weight and spacing, and the orientation. Fibres range from polyester and Pentex for economy, through aramids such as Kevlar® and Technora®, to Vectran®, Dyneema® and carbon for the highest modulus. Yarn count is quoted in denier and ends per inch, and a light scrim for a spinnaker staysail may have only a few sparse yarns while a heavy genoa scrim is dense enough to look almost woven. Orientation is the designer’s tool: a warp-insertion scrim concentrates yarn along the roll for radial panel layouts, a balanced scrim carries similar yarn both ways for cross-cut sails, and tri-axial or ×-ply scrims add diagonal yarns to resist bias stretch.
Why the Scrim Matters
Woven cloth stretches partly because its yarns are crimped – bent over and under one another – and straighten under load, and partly because the weave can scissor on the bias. A scrim removes the first problem entirely: straight yarns take load immediately, so a laminate with a given weight of fibre is far stiffer than a woven cloth with the same weight. The film handles the second problem, carrying the off-axis shear loads that the open grid cannot. The combination lets a sailmaker put a light, low-stretch sail on the boat that holds its designed draft position from the bottom of its wind range to the top, which is exactly what a racing sail or a performance cruising sail needs.
The scrim also lets the designer match fibre to load. A radial genoa built from warp-insertion scrim cloth puts its dense yarns along the leech and foot where the loads run, and lighter material in the body of the sail. The logical conclusion of that thinking is load-path construction: UK Sailmakers’ Tape-Drive® laid discrete high-modulus tapes over a light base laminate along the computed load lines, and today’s Titanium™ and X-Drive® sails apply continuous fibre to a film-and-scrim membrane or a woven base for the same reason.
Care of Scrim Laminates
The weaknesses of a scrim laminate are the adhesive bond and the film rather than the yarns. Repeated flogging and hard creasing break the bond and craze the film, so roll laminate sails rather than folding them, and never let them flap. Water trapped between the layers breeds mildew that stains the film and cannot be washed out, so dry the sail before stowing it. Aramid scrims lose strength in sunlight, which is why aramid laminates are usually built with taffetas or a UV-inhibited film, and why sail covers matter more on a laminate than on Dacron. Look for a milky or cloudy appearance in the film, or small bubbles between the layers, as the first sign of delamination.
Cruising Versus Racing
Racers accept the shorter life of a light scrim laminate in exchange for shape that does not move as the wind builds, and they choose aramid or carbon scrims for the leech and foot loads of a heavy jib. Cruisers who want laminate performance choose polyester or Dyneema scrims with taffetas on both faces – the so-called cruise laminates – that give up a little weight for a great deal of durability. For many cruising boats a good woven polyester remains the right answer, and an honest sailmaker will say so.
Frequently Asked Questions about Scrim
Is a scrim the same as woven sailcloth?
No. A scrim’s yarns are laid straight and bonded to a film rather than woven over and under one another, which is why a scrim laminate stretches much less than a woven cloth of the same weight.
Why do scrim laminates delaminate?
The adhesive bond between film and yarns is broken down by repeated flexing, hard creases, heat and trapped moisture. Rolling the sail, keeping it dry and never letting it flog are the preventive measures.
What fibre is best for a scrim?
Polyester or Dyneema for durability in cruising laminates; aramid or carbon for the lowest stretch in racing sails. Each trades lifespan, UV resistance and cost against modulus, and the sailmaker matches the fibre to the sail’s loads and the owner’s expectations.
The scrim is the skeleton of a laminated sail. Understand what fibre it carries and how it is oriented and you understand why one laminate holds its shape for years and another goes soft in a season – and why sailmakers spend so much time choosing it.