The International 505 Sailing Boat

The International 505 is widely regarded by sailing purists and high-performance enthusiasts as the “Queen of Dinghies.” It is a high-performance, two-person monohull planing dinghy that strikes a rare balance: it is manageable enough to be sailed by a mixed club team yet technical enough to demand the absolute peak of athletic and engineering prowess from Olympic-level sailors. At 5.05 meters in length, the boat is significantly larger and more powerful than the collegiate 420 or the Olympic 470, offering a sailing experience that is characterized by raw power, stability in heavy air, and an exhilarating turn of speed that rivals modern skiffs.

For the American audience, particularly those frequenting the breezy venues of San Francisco Bay, Santa Cruz, or the choppy waters of the East Coast, the 505 represents the ultimate “adult” dinghy. It is a boat where the learning curve never truly flattens. Unlike restricted one-design classes where the boat is fixed, the 505 allows for an open layout in rigging. This means the boat is as much a machine of engineering as it is a vessel of sport. You are not just a pilot; you are a flight engineer, constantly adjusting rake, tension, and foil angles to optimize the hull’s interaction with the water.

Visually, the 505 is unmistakable. It features a wide, flared hull that creates a dry ride and massive righting moment. The most distinctive feature is its large, symmetrical spinnaker, which, when fully filled on a broad reach, transforms the boat into a freight train of momentum. It does not skitter nervously like a 49er; it ploughs through waves with a reassuring, thumping power, planing effortlessly at speeds exceeding 20 knots. It is a boat that rewards physical fitness—the crew hangs from a trapeze wire while the skipper hikes hard—but it places an equal premium on tactical intelligence and technical setup.

The Origins: The Coronet and the 1953 Trials

The genesis of the 505 lies in the search for the perfect two-person racing dinghy. In 1953, the International Yacht Racing Union (IYRU, now World Sailing) held trials at La Baule, France, to select a new two-person performance dinghy for the Olympic Games. The British naval architect John Westell entered a design called the “Coronet,” an 18-foot boat with a sleek hull and a large sail area.

The Coronet performed exceptionally well, dominating the competition in terms of speed and handling. However, the IYRU selection committee ultimately chose the Flying Dutchman (FD) as the new Olympic class, primarily because the Coronet was deemed too large and perhaps too advanced for widespread adoption at the time.

The Birth of the 505 (1954)

Undeterred, the French sailing association (Caneton) approached Westell with a proposition: could he scale the Coronet down to a slightly more manageable size without losing its performance characteristics? Westell agreed and reduced the length to exactly 5.05 meters. The new design was named the “505.”

The boat was an immediate sensation. It was officially recognized as an International Class in 1955. Its adoption was rapid, particularly in France, the UK, and the United States, where sailors appreciated a boat that could handle the big Pacific swells and Atlantic chops better than the lower-freeboard designs of the era.

Evolution of a Classic

Over the last 70 years, the 505 has evolved while remaining true to Westell’s original hull shape. The class organization (International 505 Class Association) has managed a brilliant “box rule” philosophy. While the hull shape and sail plan are strictly controlled one-design elements, the construction materials and rigging layouts have been allowed to modernize.

• 1950s-1970s: The era of wood. Cold-molded plywood hulls were the standard, beautiful but maintenance-heavy.

• 1980s-1990s: The transition to fiberglass (GRP) and polyester resins.

• 2000s-Present: The carbon revolution. Today’s competitive 505s are built using epoxy, carbon fiber, and honeycomb cores (baked in autoclaves). This makes the hulls incredibly stiff and light, ensuring that a 10-year-old boat can still be competitive at the World Championship level—a rarity in high-performance sailing.

Design

The design of the 505 is a masterclass in hydrodynamic efficiency and “flared” geometry.

The Hull Form

The 505 hull features a round bilge with a significant flare at the gunwales.

• Waterline vs. Beam: At the waterline, the boat is relatively narrow, reducing wetted surface area and drag in light winds. However, as the boat heels or as the crew moves weight outboard, the wide, flared gunwales (maximum beam of 1.88m) provide a massive lever arm for the crew on the trapeze.

• Planing Surface: The aft sections of the hull are flat and run straight, designed to support early planing. Unlike boats that dig their sterns in, the 505 lifts comfortably, allowing it to plane upwind in as little as 10-12 knots of wind.

Table 1: Physical Dimensions and Specifications

Specification	Metric Value	Imperial Approx.	Notes
Length Overall (LOA)	5.05 m	16 ft 7 in	Defining dimension of the class.
Beam (Width)	1.88 m	6 ft 2 in	Wide flare provides high righting moment.
Hull Weight (Stripped)	127.4 kg	280 lbs	Minimum sailing weight (hull + foils + spars).
Draft (Board Down)	1.45 m	4 ft 9 in	Deep high-aspect centerboard for pointing.
Draft (Board Up)	0.15 m	6 in	Easy launching/beaching.
Mast Length	6.90 m	22 ft 8 in	Typically aluminum or carbon (carbon now standard).
Ideal Crew Weight	140 – 180 kg	310 – 400 lbs	Wide competitive range due to adjustable rig.

The Centerboard

Unlike the daggerboards found in Lasers or 470s (which slide vertically), the 505 uses a high-aspect gybing centerboard. The board pivots on a bolt, but crucially, the trunk is wide enough to allow the board to angle slightly to windward/leeward. This “gybing” action changes the angle of attack of the foil, generating lift to windward and allowing the boat to point higher than a fixed-board equivalent.

The “Gate Start”

A unique design feature of 505 racing is not the boat itself, but how it starts. The class utilizes a “Gate Start” (or “Rabbit Start”) for large fleets. A “Pathfinder” boat sails across the fleet on port tack, and the rest of the fleet must pass behind its stern to start. This allows fleets of 150+ boats to start fairly without the chaos of a line start, and it is a hallmark of the 505 culture.

Propulsion

The 505 is powered by a fractional sloop rig that is arguably the most adjustable in the world of dinghy sailing. The propulsion system consists of a large mainsail, a jib, and a massive symmetrical spinnaker.

The Powerhouse: Sail Plan

The sail area is generous for a 16-foot boat. The mainsail is fully battened (often with a square top in modern iterations), and the spinnaker is a 27-square-meter parachute that dwarfs the hull.

Table 2: Sail Area Comparison (505 vs. 470)

Sail Component	International 505	International 470	% Difference
Mainsail Area	12.30 m²	9.12 m²	+35%
Jib Area	4.94 m²	3.58 m²	+38%
Spinnaker Area	27.00 m²	13.00 m²	+108%
Total Upwind Area	17.24 m²	12.70 m²	+36%
Total Downwind Area	44.24 m²	25.70 m²	+72%

Dynamic Rig Adjustment

The “secret weapon” of the 505 is its ability to change its shape while sailing. In most boats, the mast rake (the angle of the mast) is set on the dock. In a 505, the shrouds and forestay are attached to adjustable purchase systems led to the crew or skipper.

• On the Fly Rake: If the wind increases from 10 to 20 knots during a race, the 505 crew can pull a control line to ease the shrouds and tighten the forestay, or vice versa, literally raking the mast back toward the stern. This moves the Center of Effort aft and depowers the sail plan by flattening the mainsail and opening the leech.

• The Ram: A strut (the “ram”) pushes the mast at deck level to induce bend, further flattening the sail.

This adjustability means a light team can rake the mast back aggressively to survive in heavy air, while a heavy team can keep it powered up. This equalizes the field across a wide range of body weights.

Construction and Materials

The 505 class rules regarding construction are “open” compared to the strict one-design of the Laser, but the hull shape is strictly controlled. This has led to a technological arms race that has benefited the boat’s longevity.

The Carbon Era

Modern 505s are technological marvels. While early boats were wood and mid-era boats were glass-reinforced plastic (GRP), the current championship-winning boats are built using epoxy resin, carbon fiber, and Kevlar reinforcements.

• Honeycomb Cores: High-end hulls use a Nomex honeycomb core sandwiched between carbon skins. This creates a structure that is incredibly stiff (transferring all wind energy into speed) yet meets the minimum weight rule.

• Baked Hulls: Builders like Ovington (UK) and Rondar (UK) cure these hulls in high-temperature ovens (autoclaves) to maximize the resin properties.

Table 3: Construction Materials and Builders

Component	Standard Material	Key Builders (Current & Past)
Hull	Carbon/Epoxy/Honeycomb or GRP	Ovington, Rondar, Hamlin, Waterat
Mast	Carbon Fiber (High Modulus)	Selden, Super Spars, CST
Boom	Carbon Fiber	Waterat, Selden
Foils	Carbon Fiber	Tuttle, Milanes, Gybe Tech
Sails	Laminate (Mylar/Kevlar/Technora)	North Sails, Glaser, P&B, Doyle

Durability and Value

Because the class minimum weight (127.4 kg) is relatively high for a high-tech carbon hull, builders can put extra material into structural areas. The result is a “tank.” A 505 does not go soft after two seasons like some lightweight skiffs. A 15-year-old carbon 505 can—and often does—win regional championships. This high residual value makes the initial investment more palatable for US sailors.

Types and Comparisons

When discussing “Types” of 505s, one usually refers to the builder or the rigging philosophy (e.g., “American rig” vs. “German rig”). However, it is most useful to compare the 505 to its contemporaries to understand its place in the market.

505 vs. The Skiffs (49er)

The 49er is the Olympic skiff. It is faster than a 505 in flat water and light air due to its massive wings and light weight. However, the 505 is arguably faster and certainly more manageable in high-wind/high-wave conditions. The 505 punches through waves; the 49er flies over them (or crashes into them). The 505 is for the sailor who wants speed but values tactical racing over pure survival.

505 vs. The 470

The 470 is the Olympic stepping stone. It is smaller, slower, and restricts materials (no carbon hulls). The 505 is the “graduate” boat. Many Olympic 470 sailors move into the 505 class post-Olympics to enjoy the relaxed culture and higher performance.

Table 4: Performance Comparison (Portsmouth Yardstick)

Lower D-PN indicates a faster boat.

Boat Class	US Sailing D-PN	Speed Potential (Est)	Crew Trapeze?	Spinnaker Type
International 505	79.8	High	Single	Symmetrical (Large)
49er	68.2	Extreme	Double	Asymmetrical
International 470	86.3	Med-High	Single	Symmetrical
Flying Dutchman	80.0	High	Single	Genny + Sym
Club 420	97.6	Low-Med	Single	Symmetrical
Snipe	91.9	Low-Med	None (Hiking)	Whisker Pole

The “American” vs. “European” Rig

Within the 505 class, two main rigging styles exist:

1. The American Rig (E.g., Waterat): Often features a launcher tube for the spinnaker (the chute enters a tube in the bow) and emphasizes simplifying controls to keep the crew’s head out of the boat.

2. The European Rig (E.g., Rondar): Often features spinnaker bags and a slightly different purchase layout.

   However, modern boats are converging, with carbon masts and double-pole launcher systems becoming standard globally.

The USA Context: A Cult Following

In the United States, the 505 has a cult-like following. It attracts engineers, tech professionals, and lifelong sailors who are bored by slow keelboats but don’t want the instability of a foiling Moth.

• Key Hubs: The West Coast is the stronghold. St. Francis Yacht Club (San Francisco), Santa Cruz Yacht Club, and Alamitos Bay (Long Beach) host massive fleets. The East Coast has strong pockets in Annapolis (Severn Sailing Association) and Hampton, VA.

• The Culture: The US 505 fleet is known for its “open book” policy. Top professionals (like World Champions Mike Martin and Howard Hamlin) freely share their tuning numbers and rig settings with newcomers. This camaraderie drives the fleet’s high retention rate.

Table 5: Estimated Cost of Ownership (USA Market)

Condition	Price Range (USD)	What You Get
New (Race Ready)	$45,000 – $55,000	Brand new Ovington/Rondar, carbon rig, custom fit-out, new trailer.
Used (World Class)	$25,000 – $35,000	2-5 years old, competitive at World Championship level.
Used (Club Racer)	$8,000 – $15,000	10-20 years old, competitive regionally, fully carbon.
Entry Level	$3,000 – $6,000	Older GRP hull, aluminum rig. Great for learning.

Conclusion

The 505 Dinghy, designed by John Westell in 1954, remains a marvel of the sailing world. It has defied the typical lifecycle of racing classes, staying at the cutting edge of performance for over seven decades. By allowing its construction and rigging to evolve while keeping the hull shape constant, the class has created a boat that feels modern, fast, and aggressive, yet retains the tactical depth of traditional racing.

For the USA-based boat lover, the 505 offers a unique proposition: it is a boat that can be sailed by a couple on a Wednesday night or raced by Olympic medalists in a 150-boat World Championship. It is a “Tank” that flies, a 16-foot engineering project that delivers 20-knot thrills. In a world increasingly obsessed with foiling, the 505 stands its ground as the ultimate planing monohull—a testament to the fact that sometimes, the original design was just right. Whether you are blasting under the Golden Gate Bridge or navigating the shifts of the Chesapeake, the 505 delivers a sailing experience that is, simply put, unmatched.