The evolution of hulls
Vertical bows: optimum sailing
Initially, cruiser yachts had a hull inspired by merchant ships: the engine pushes the boat while displacing the water. This is always the case when the boat is heavy with a modest level of power. The best performance is obtained with a long waterline length and minimal width. This is the rationale behind vertical bows. However, each increase in speed requires a significant increase in power.
If we reduce the weight, the bow slices through the water and rises above the surface. The bow wave is pushed back. This is a semi-planing – or semi-displacement – hull and drags less and less water. Some “cruisers” have hulls like this. Around 1906, an 18m slim hull was powered by three 200hp V8 engines. But the on-board weight and deep hull did not make it possible to rise above the bow wave.
When it climbs up on to this wave, the hull becomes planing; it hydroplanes. The boat planes. It moves quickly, but it is uncomfortable in choppy waters.
The first hydroplanes with flat bottoms date back to 1898, but are considered to be uncontrollable unless they are fitted with centerboards and rudders. As flat hulls require less power than displacement hulls, light outboard engines became popular. A low-power DeDion outboard is launched in 1905 and, over the following years, between 1920 and 1940, the Lutetia, Goïot and Monet-Goyon outboard engines (derived from motorbikes) will become famous, before the arrival of the American and Japanese engines.
Three-pointer: Revolution in the 1950s
On very calm waters, special hulls are developed known as “three-pointers” (racers, prop-riders). Viewed from above, the hull is shaped like a “spade”, wide in the front and very narrow in the rear, with plunging decking. Two lateral runners around 15cm high stand out from the bottom and run from the front to the middle of the boat. The rear section no longer touches the water. The propeller is the third point of contact with the water. The hull is very unstable and, despite a small centerboard, slides a lot when cornering. Planning ahead is vital.
Several categories are created in the 1950s. The engines from the auto industry are sometimes very powerful and the pilot is sat in the rear of these very quick racers. With an outboard engine, the international category is the C 500. Pilots are laid down, with their head facing forward, behind a small windscreen.
To adapt an outboard engine for a canoe, a transom takes the place of the rear section with a pointed design. This is how we saw Colette Pétard, the daughter of the folding kayak manufacturer Lapon, do so well in the Paris 6 Hours race with a 25hp unit.
Canoe builders like Rocca, Jeanneau, Matonnat and Kirié will move on from round, wooden, unstable hulls to recreational boats that are wider with flat bottoms, molded using polyester. Oreste Rocca was the world speed champion in 1953, 55 and 56.
High-speed catamarans
In the 1960s, Prince Michel of Bourbon-Parma and Count Adrien Balny d’Avricourt will use Zodiacs with raised bottoms for racing, and these are the first power catamarans. The competition is between Zodiac and Aérazur. Around 1963, the bottoms are raised by a further 10 to 25cm. Elements like rubber deflector runners enable them to reach speeds of nearly 90 km/h with 50hp (850cc).
The catamaran’s central section serves as a wing, which lifts the boat above a certain speed: around 40 km/h. The boat accelerates and tends to take off when sailing into the wind. Pilots are constantly adjusting and moving the top of their body to keep the balance with their weight. The piloting is all about finesse, depending on the wind and water conditions.
In 1966-70, on Lake Como, the builder Renato Mollinari draws inspiration from the three-point hulls to lift the boat out of the water and achieve less drag. Two runners are created with a V-shape in the front and almost flat in the rear, and strakes and steps are added in front of the engine. This raises the bottom by at least 25cm. The wind flows between the runners and, thanks to this sort of elevating wing, the boat rises, rises… above a certain speed. The more it rises, the less contact it has with the water, and the quicker it goes. Depending on the engine capacity, speeds reach 150 to over 200 km/h. Pilots have a trim button on the wheel to modify the angle of their engine depending on their position upwind or downwind. Any lapse of concentration can be costly, with the boat taking off and flipping over. Doing a full flip is less of an issue, but if you land upside down, the boat, with its lightweight build, might break up and sink. That is why today, racing catamarans are fitted with reinforced survival cells, with breathing equipment.
Specific features and appendices
Scandinavian clinker hulls are very old. The hull’s longitudinal boards are fitted to overlap one another. Like strakes, this gives lift and more stability on the sea with hulls that are slightly too round.
The chine is a sharp angle between the boards and the bottom. This is common for plywood hulls. A hull may have several chines. This gives stability, a bit like the edges on skis, and the boat presses on them.
Strakes are narrow flat sections of the hull, running from the front to the middle section; a bit like accentuated flat strakes, to reduce the spray, improve the passage through the waves and support the planing.
The steps are sometimes called strakes, but do not have the same benefits. These are steps in the bottoms, which break up the water flow and reduce the wet surface area. A bit like if the boat was shorter. A three-point hull is a stepped hull. The step may concern just the chine or the whole central section of the hull. We can use this step to guide air beneath the central hull. This is becoming quite common on cabin cruisers, which have one or more steps. The engines are often balanced in the rear, as if the hull was shortened; this step reduces the drag.
The strakes are little flat offshoots along the hull which reinforce the bottoms, channel the water flows and increase the lift. They help with planing. To improve their passage through heavy seas, they are sometimes V-shaped rather than L-shaped.
All of these subtle features provide essential stability for V-shaped hulls, which often tend to list too much to the side.
Extreme racing: Power on the sea
In 1906, in Monaco, races could reach 100 or 200 km on the sea. The legendary Calais-Dover, Miami-Nassau (1956), Cowes-Torquay-Cowes (1961) and Viaregio-Bastia-Viaregio (1962) events recognized the leading pilots: Don Aronow (founder of Formula, Donzi, Magnum, Cigarette), Richard Bertram, Jim Wynne and architects like: Ray Hunt, Don Shead and Renato “Sonny” Levi. These three architects are behind the Delta hulls (a slim front and wide rear) with a deep V, which makes it possible to dampen the waves when at sea. Summarizing, a lake boat has an open V, with one of the sides at 10° (or less) from the horizontal; it is quick, but is uncomfortable at sea because it jumps from wave to wave. To get a hull for racing on the sea, you need to look at 23° to 25°. It goes less quickly on calm water and absorbs more energy because it sits lower in the water. But when it climbs up onto its V, it performs wonders at sea, supported by its chine and strakes. The transmission uses movable shafts (up / down), with independent rudders and semi-aerial propellers.
After 1990, we see the arrival of catamarans with an engine on each hull, a two-person crew and speeds of over 250 km/h. The boats are heavy and are less at risk of taking off.
We have seen a rapid increase in the power of in-board engines, sometimes up to 4000hp, leading the international union (UIM) to review the regulations for the various classes, strongly in favor of the United States. Class 1: 12 to 14m hulls, 2x 1100hp Mercury Racing engines (a total of 2200hp!).
There is a certain analogy with the evolution of sailing and motor hulls, but we must not take it too far: – The waterline length is not relevant for planing or semi-planing hulls – if we keep below 40 km/h, a catamaran goes slower than a monohull because there is more wet surface area – a round and flat hull is an aberration on an offshore boat. Today, foils are very in fashion on sailing yachts. However, the first patent submitted in France was for motorboats in 1869, and the first “hydrofoil” was tested in 1898. There are hydrofoils everywhere around the world for passenger transport and in certain navies.
But we are closer to aeronautics than the sea.