The Laser is an international one-design class. This means that all lasers built and raced around the world should be equal in weight, size, components and potential. Made of fibreglass with a gel coat finish, the hull is strong and durable. My own laser was built in 1976. Here the generalities of dinghy sailing are presented, as well as some of the more specific qualities of the Laser class.
Sailing vessels have been used throughout history, in all manners of construction and sizes. A dinghy is a special case, and defined in the Chambers dictionary as 'a small open boat' [CHAMBERS]. In the world of leisure dinghy sailing, a boat consists of a hull, a set of foils, spars, sails and rigging.
Below, are described the components of a generic dinghy. This is an overview, which should give the uninitiated reader grounding in some of the terminology.
The hull is 'the frame or body of a ship' [CHAMBERS]. The shape and composition of the hull can have a huge affect on the maximum speed of a boat; this in itself is a large area of research within marine architecture.
A general term for any of the surfaces acted upon by the water, with the exception of the hull, the term includes the rudder and centre / dagger board. Each foil can be described as possessing a leading edge and a trailing edge. The leading edge is the edge such that: as the foil moves forwards through the water, the flow of water separates at the leading edge before flowing over both sides of the foil, to merge after passing the trailing edge.
The rudder is usually positioned at the rear of the vessel, mounted on a vertical pivot. When rotated from alignment with the length of the boat, water flowing past the rudder exerts a force on the rudder, creating a moment that acts to turn the boat from its current course. Simple put, as the rudder makes a 'curve' with the rest of the hull, the boat moves along an extrapolation of that curve. However, this is not an entirely accurate description, since the rudder is not 100% effective. Usually a horizontal lever attached to its top controls the rudder. This lever is called a tiller and is the principle piece of equipment used to steer the dinghy. Generally, it is only larger craft such as yachts that use wheels to control the rudder, due to complexity.
The centre or dagger board is positioned toward the middle of the hull (front to back) and is positioned and aligned with the centre line of the hull (side to side). The centre / dagger board may only move in the vertical plane, to alter resistance to sideways movement. There are two names for this centre-aligned foil, due to separate methods of altering its active surface area under the water. The first is the centreboard, which is mounted on a pivot whose axis runs from side to side. The centreboard can be swung from the vertical position (maximal active area) toward the horizontal, which achieves minimal active area (hence least resistance to sideways motion). This method of mounting is most commonly used in older design racing dinghies, though still extremely common. The dagger board is usually implemented in simpler dinghies. As the name suggests, this system uses a foil, which slots through the hull and slides vertically to alter the effective area. Chosen for its simplicity with respect to removal and replacement, the dagger board is used in the Laser design, along with many other modern one-design craft.
A set of sails usually comprises of a main sail, a jib and some sort of spinnaker. While a dinghy may possess a different set of sails for different weather conditions, only one set is used at a time.
The main sail (commonly referred to as the main) is attached along its vertical edge to the mast, while the horizontal edge is attached to the boom either at each end or along its entire length. Providing most of the power, until a spinnaker is used, the main hangs aft of the mast and may be the only sail used on some classes of boat. The jib is has a smaller area than the main. It is positioned forward of the mast, usually attached to a tensioned line running from the bow to a point near the head (top) of the mast.
The jib is used to increase directional control, as well as increase the power available to the boat.
Finally, the spinnaker is a large sail that is able to provide a huge amount of drive, though only when moving down wind. Symmetrical spinnakers used to be the norm, suspended from a sheet running from near the head of the mast, and controlled by lines running from each of the bottom corners of the sail. Asymmetrical spinnakers work in much the same way a jib, though are a great deal larger and made of lighter material.
The spars include the mast, boom, spinnaker pole and jib stick. The spinnaker pole and jib stick are optional and depend upon the class of boat. Each of these is used when the boat moves down wind, to hold the respective sail open and full or in the correct position. The mast is the main spar, and is normally positioned forward of the centre of the boat. Held vertically (sometimes with a forward or backward rake) by shrouds or simply by a deep well in which it sits, the mast supports (directly or otherwise) all the sail area on the boat. The boom is attached to a pivoting joint on the mast called the gooseneck. The clew of the main sail is attached to the booms free end (see Figure 1: Parts of a Laser Dinghy).
Included in the rigging are items that help control, define and maintain the dinghy's structure. Controls are used to manipulate and restrain working parts of the boat. The main sheet is attached to either the centre or free end of the boom and runs through some form of purchase system, to the hull. Essentially a piece of rope, which limits the rotation of the boom about the mast, the main sheet resists further rotation of the boom, thereby the boat is forced to move. The jib also has a controlling sheet (rope), strangely enough called the jib sheet. While the main sheet often makes use of purchase systems, the jib leads directly from the free corner of the jib, through a fairlead and into the boat where it is gripped by a crewmember and / or a cleat. Other control lines exist, usually used to control form and position of the sails. The cunningham tensions the luff of the sail. The kicker or vang limits the gradient of the boom in the vertical plane, keeping the boom in a more or less horizontal plane. The outhaul and downhaul are used to pull the sail tight along the boom and mast respectively. Finally, there are the shrouds fore and aft stays. These lines support the mast and other spars in their positions, and maintain tension in the rig. Complex racing dinghies often have more control lines, to fine-tune and maximise performance, while simpler boats make do with even less controls or rigging.
A crew is required to control the dinghy, make tactical decisions and maintain balance. Depending on class rules, size of boat and weather conditions, the crew will vary from a single child to multiple heavy adults. Firstly, every dinghy will have a helm. The helms responsibility is to steer the boat. Usually in a small dinghy, the helm will make decisions on where to go as well as how to get there. In a dinghy with more than one crew, the second crewmember has responsibility for the jib sheet, maintaining the drive from the associated sail. Each member of the crew must work together as a team to control and balance the boat effectively.
Propulsion is generated by the interaction between the sails and wind, also between the foils and the water. On a simple level, this pair of interactions can be likened to a bar of soap being propelled sideways as a force is exerted on top and bottom. The wind exerts a force on the sails in one direction, while an opposite (though smaller) force is exerted on the foils by the water. Unlike the soap example, the forces are not applied along the same axis. This leads to a problem of moments, where the boat becomes unbalanced. This unbalancing effect is countered by weight within the boat. In a keelboat, this weight consists of the some dense material at the base of the main foil (the keel), and the crew. As the boat begins to rotate from the upright position, the weight exerts a force its self. This force works against the largest of the unbalancing forces, attempting to return the boat to its upright state. The weight in a smaller dinghy (centre board or dagger board boat) is provided solely by the crew, who must counter balance the force of the wind, to keep the boat upright. See Figure 3 for an illustration.
Direction is controlled by the rudder. This foil works as the hull moves through the water, exerting a force and causing the hull to pivot about its centre foil (be that a keel, centreboard or dagger board). The orientation of the rudder is controlled directly by the tiller, which is a lever attached to the top of the rudder. Lying in the same plane as the rudder blade, the tiller points in the same direction. The rudder is mounted on the transom of the dinghy, by means of a pair of pintles and gudgeons that allow the rudder to pivot (about an axis parallel to the mast) with respect to the hull.
The laser has only one sail, the mainsail that is rigged on a two-part alloy mast.The upper mast section slots into the hollow end of the lower section, which in turn is seated in the mast step; a well in the deck of the hull. This unsupported design allows fast rigging and de-rigging times, and overall simplicity in design.
The rig is held in place by the cunningham control line which is made fast to the mast. This is then passed through the cunningham gromet at the tack of the sail and down through a cleat on the deck of the hull. The cunningham is used to control the tightness of the sail luff.
Unlike traditional dinghies, the Laser has a flat deck over the complete hull with the exception of a small cockpit that appears more of a foot-well. This design allows the laser hull to be completely enclosed and increases the buoyancy potential of the boat.
The crew of a laser dinghy always consists solely of the helm. With three different sizes of main sail, the laser can be competitively sailed by anyone from 55Kg upward in weight. To obtain leverage against the heeling forces applied to the dinghy, the helm uses a toe-strap. The toe-strap is attached centrally to the front and rear of the cockpit. This allows the crew to lean out over the water, with only the lower legs within the boat, increasing the effectiveness of their weight.
Able to point as close as approximately 40° to the true wind, the lasers fastest point of sail is when on a reach, at an angle of approximately 90° to 150° to the true wind direction. Once the wind strength reaches a force 3 to 4 or greater, a laser will begin to plane when the sail is set and the boat is on a reach. At higher speeds, the laser will plane on a run, which is an extremely fast but unstable activity.
Tips and techniques for sailing the laser dinghy competitively can be found in [BAIRD82]. Rigging details can be seen in Figure 1: Parts of a Laser Dinghy, along with names for parts of the dinghy. Class rules and other details can be found in [ILCA96].
The principle aim when racing is complete the specified course ahead of your opponents. The course is composed of a number of waypoints. Each of these waypoints is represented by a buoy. The course is chosen by the race committee and set before the competitors take to the water. Each race consists of one or more laps of the specified course.