One of the first things a yacht designer learns when grappling with the design of racing yachts is that there are many compromises to be made.

Generally, what makes a boat fast downwind will in all likelihood make it slower upwind. The aspects that make a boat safe to sail will ultimately make it slower. The comfort-factor, considered in terms of accommodation, will add weight and size and slow the boat down. Racing class rules will inevitably place constraints on a design that will reduce potential speed and too much or too little stability will slow a boat around a racecourse.


Everything a yacht designer incorporates compromises speed to achieve some other design requirement.
Boats such as the eighteen-foot skiffs and the modern 49ers show very little compromise and every design element that departs from the skiff concept reduces the speed potential of any given design.
We often talk about sport boats being fun, fast and safe to sail. By safe a boat is assumed to be self righting and unsinkable. These requirements cost speed but are a necessary requirement of the modern sport boat. But the really big compromise is the addition of a lead bulb to make a boat self righting. This alone sets the sport boat apart form the modern skiff.

The single biggest change in concept enjoyed by modern sport boats is the fact that owners are willing to accept a 6-8 metre yacht without cruising accommodation. Because of the reduction in these facilities we can design lighter boats and reduce the structure to provide for hull strength, rigging and keel loads only. This in turn allows more ballast to be added to the lead bulb and stability increased.



Foil design has made a significant contribution to the progression of on modern sport boat designs. The most limiting factor of modern sport boat foils is the drag caused by the lead bulb. While it is a necessary evil as far as the designer is concerned, it represents a significant portion of the overall drag. It is important also to get the lead bulb as deep as is practical in the boat but this again has its drawbacks as the extra draft adds extra wetted surface. There is of course a balance as far as depth and drag is concerned. Modern materials such as carbon fibre are often used in keel foils to help reduce the overall size of the fin. Carbon fibre allows a designer to produce a narrow yet relatively stiff foil to support the lead bulb and often the lateral area requirement of the fin is exceeded because of its depth.

Rudders tend to be rather large for the size of the boat. This is generally due to the fact that oil design has made a significant contribution to the progression of on modern sport boat designs. The most limiting factor of modern sport boat foils is the drag caused by the lead bulb. While it is a necessary evil as far as the designer is concerned, it represents a significant portion of the overall drag. It is important also to get the lead bulb as deep as is practical in the boat but this again has its drawbacks as the extra draft adds extra wetted surface. There is of course a balance as far as depth and drag is concerned. Modern materials such as carbon fibre are often used in keel foils to help reduce the overall size of the fin. Carbon fibre allows a designer to produce a narrow yet relatively stiff foil to support the lead bulb and often the lateral area requirement of the fin is exceeded because of its depth.

Rudders tend to be rather large for the size of the boat. This is generally due to the fact that oil design has made a significant contribution to the progression of on modern sport boat designs. The most limiting factor of modern sport boat foils is the drag caused by the lead bulb. While it is a necessary evil as far as the designer is concerned, it represents a significant portion of the overall drag. It is important also to get the lead bulb as deep as is practical in the boat but this again has its drawbacks as the extra draft adds extra wetted surface. There is of course a balance as far as depth and drag is concerned. Modern materials such as carbon fibre are often used in keel foils to help reduce the overall size of the fin. Carbon fibre allows a designer to produce a narrow yet relatively stiff foil to support the lead bulb and often the lateral area requirement of the fin is exceeded because of its depth.

Rudders tend to be rather large for the size of the boat. This is generally due to the fact that very large asymmetric spinnakers tend to push the boat around in the puffs of wind. Once the boat is up on the plane the rudder size could probably be halved, as there is generally very little force on the rudder while the yacht is planing. Rudder sectional shape is therefore aimed at low drag rather than high lift, as there is ample area to provide the lift required.

In summary the modern sport boat design has evolved into a very sophisticated package. It includes a holistic approach that includes all of the design parameters of hull shape, foils, rig and sail design. Gone are the days where a boat can be put together without consideration for all of these elements and still remain competitive.

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Modern Sport Boat Shape

Easily driven boats with narrow waterlines allow a designer to add more sail area, in particular to asymmetric spinnakers. This is because, when a puff of wind hits a boat that is easily driven, it accelerates and the added energy is transposed into forward motion rather than healing moment.

Rig design has been simplified so that they automatically exhaust additional air from the sails in the puffs. This is a very important aspect of sport boat design as it is important to keep the boat easy to sail. Careful attention is paid to the topmast and mainsail roach profile so that they work together to power up when required and exhaust in heavy air. The use of carbon fibre in the mast has helped induce this effect. When the topmast bends in the wind puffs the leach of the mainsail opens up to exhaust the additional air not required.

A great deal of sail development has gone into providing sport boats with sails that maximise forward motion and minimise healing force. Part of the answer is in the shape of the mainsail that provides a sail shape that is deeper downwind when the mast is straighter and a lot flatter upwind as the mast bends under load. The sailmaker’s art of getting the luff curve to fit the mast is very important. Jibs often use full-length battens with a positive roach in the top of the sail to help with twisting off at the top to exhaust the wind puffs much like the mainsail. Forestay tension is gained from the effect of mainsheet tension and the rigging loads.

I mentioned that too much stability can reduce speed. In particular this will slow the boat downwind as stability is gained by increased weight or increased hull form stability that increases wetted surface. With this in mind, the hull drag is reduced by narrowing the waterlines and trading hull form stability for righting moment from an increased lead bulb weight.

The fact that crew weight is often carried outboard of the gunwale when the crew use hiking straps, further increases this trend.

Modern sport boats often have a ballast ratio greater than 150% when the crew weight is taken into consideration
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