Impulse (dinghy)

History

The Impulse 4.0m Sports Sailing Dinghy is a restricted one-design class of single handed sport sailing dinghy. The dinghy was originally designed by Arthur Caldwell in Melbourne Australia during the mid-1970s as a home built plywood sports sailing dinghy that could be sailed on his local waters of Port Philip Bay. Because of the Bay's large size and reliable fresh winds, swells of one metre and more are common and provide a challenging environment for the bay's dinghy sailors. With the help of some of those local dinghy sailors, early Impulses were developed into sailing dinghies well suited to Melbourne's local waters. They were also found to plane very well on calmer waters which made them popular at various sailing locations throughout Australia and over the following three decades the Impulse's design has been further refined so that along with a process of fine tuning the class rules,^[1] a stable and forgiving yet fast dinghy has evolved.

Today Impulses are sailed and raced in many off-the-beach sailing clubs in all states of Australia. South Australia, Victoria, New South Wales and Queensland hold yearly Impulse state championships and once a year Impulse sailors from around Australia meet in one of these four states to race at the Impulse 4.0 Metre Sports Dinghy nationals.

Design

The dimensions, performance and yardstick ^[2] of an Impulse Sports Dinghy are similar to the popular Laser dinghy and you can often see both classes of dinghy involved in close club racing. Although they have their similarities, the Impulse has some significant differences to the Laser including:

• A new Impulse can be constructed at home by an amateur boat builder,^[3][4] while a new Laser must only be purchased from one of the sanctioned Laser manufacturers. This means that the initial cost of a new Laser can be more than double the cost of building a new Impulse.
• The Impulse's minimum hull weight of 47 kg is lower than the Laser's at 56 kg.
• The Impulse has much harder chines than the Laser, which gives the Impulse a gently V keeled and flatter wetted surface than the rounded Laser hull. This hull shape gives the Impulse more heeling stability on the water than the Laser making it more stable in rough and windy conditions.
• Due to the lower weight and improved stability described in the two previous points, an Impulse is less physically demanding to sail than a Laser and it is more common to see older sailors racing competitively in Impulses than you usually see sailing in Lasers due to the athletic ability needed to sail a Laser well.
• The Impulse's triangular sail shape and boom length were originally very similar to the Laser's, but a more modern sail shape was developed and ratified during the 1980s which saw the Impulse's sail given a broader head than a Laser's sail and consequently the Impulse's boom could be shortened. A shorter boom has meant that the Impulse can heal much more than a Laser before the boom touches the water. As well as slowing the boat down, a boom touching the water can lead to a capsize.
• Impulses have four full length battens in their sails as opposed to the Laser's three partial battens and the stiffness of the Impulse's battens can be varied to suit the sailor's weight and the prevailing conditions.
• Because the Impulse class rules allow for variations in the rotating mast's bracing and rigging including variations in the rigging attachment points at both the mast and the hull, this allows the Impulse sailor the option of tailoring the rig to better suit their weight and common sailing conditions. Lasers have no mast stays nor any external mast bracing.
• The Impulse class rules allow the sailor to individualise the way they run the main sheet between the boom and deck, while Lasers have a fixed main sheet route which can't be varied.
• There are several sail trim adjustments that can be built into the Impulse's rigging and hull giving an Impulse sailor more options trim the sail on the water than those available to Laser sailors.

Construction

A competitive Impulse Dinghy's hull can be built at home with commonly available tools by an amateur boat builder or it can be purchased ready to sail from a professional boat builder. The most common home building techniques are either:

• Using the stitch and glue method of hull construction with boat building materials such as marine grade plywood, selected timber, fibreglass and epoxy.
• Making a fibreglass hull from a private or Impulse association mould and adding plywood and/or fibreglass bulkheads and deck.
• Purchasing a fibreglass hull at various stages of completion from a professional boat builder and finishing the boat at home.

Many Impulse sailors also assemble their own masts and rigging to suit their individual needs using components provided through their state Impulse association and commercial chandlers. It is a testament to the hull's design and construction techniques that Impulse dinghies built in the late 1970s and 1980s are still sailing competitively today, more than three decades after they were constructed.

The future

Impulse dinghies have experienced a slow but steady growth in popularity since they were first seen on Australian waters in the 1970s. As new building materials and methods have become available as well as new professional boat builders producing competitive Impulses during the mid to late 2000s, Impulse fleet numbers have been steadily increasing in every state and national event over recent years. In 2011 the smaller 6.6 m² (71 sq ft) (D2) sail has started to appear in Impulse fleets and this smaller sail should encourage younger and lighter sailors into the Impulse, especially when sailing under more challenging conditions. Once ratified at a national level, the 6.6 sail is expected to help in the expansion of Impulse fleets.

Notes

Class Associations

• Australian Impulse Association

Manufacturers

• Tim Wilson Yacht Design
• Formula Sailcraft