Hydronamic designs, water jets and stronger steel are constantly increasing the speed of ferries. But for now, anyone who wants to cross the Atlantic in less than a day will still have to take a plane.
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“When the Irish Oak departed from Cork in 1949, we thought we would be in New York a week later”, reads the opening sentence of Frank McCourt’s novel about his emigration from Ireland to the US. If McCourt were to make his journey again today, he wouldn%t have nearly as much time for long conversations in a lazy deck chair. Modern ferries easily reach speeds twice as high as previously%up to sixty kilometers per hour.
Last Thursday our future shipbuilders convened at a symposium on High Speed Craft organized by the maritime engineering society, William Froude, and they dreamed out loud about speeds of fifty knots or ninety kilometers per hour and more.
Speed and traveling comfort are two concepts that are difficult to combine. “In World War II high speed torpedo boat cruisers were designed. Their crew stood on crates, that were supposed to absorb the first shock of any particularly hard impacts with waves”, says Dr. Alexander Keuning, of the department of Boat Hydromechanics of the faculty of Design, Construction and Production. As recently as several years ago Keuning suspected that maritime designers unjustly assumed the length of a boat to determine the price, causing them to restrain it to a minimum. According to him, a fast ship with the same load capacity, speed and functions on board, but with a greater length proportional to its width, will perform better.
Bathtub
To prove his statement the hydrodynamics engineer from Delft redesigned a Hong Kong patrol boat and made the hull more than half again as long. As expected, this caused the water resistance to decrease, making it possible for the ship to reach the same speed using considerably less motor power. What’s more, this adjustment did not negatively affect the crew: the vertical acceleration of the bridge caused by the waves decreased. This promotes the comfort of living on board when using high speeds at sea. The long ship did bounce on the waves a lot at the bow, but Keuning solved this disadvantage by altering the form of the bow. This resulted in a new ship that was six percent more costly, but cheaper in use and with the added ability to venture out of the harbor in bad weather, unlike it’s shorter predecessor.
Keunings elongated ship concept so appealed to a shipyard that it applied it in the construction of three patrol boats for the Dutch marines. This breed of ship, christened ‘The Panther’, is currently racing around in the Caribbean Sea. No matter how long and slender the hull, without thrust any boat is as fast as a bathtub. For slower ships a screw is sufficient propulsion, but at higher speeds nowadays the water jet is employed. The principle of this propulsion system has been known for more than two centuries, but wasn’t commercially applied until its use in fast catamarans and yachts in the course of the twentieth century enabled them to reach a speed of50 knots (93 kph).
Midget
According to Norbert Bulten, designer for the ship propulsion manufacturer John Crane-Lips, a speed of 75 knots is attainable using waterjets. A ship moving at that speed does need an athletic heart though, because a speed that’s twice as high requires a quadrupling of the pump capability. Bulten illustrates the consequences of this rule with a picture of his colleague standing upright in the pump of a water jet for a fast marine frigate. To make it clearer: “My colleague is no midget.”
Whether or not a water jet attains the required power depends on the design of the water inlet. It has to be adjusted to the form of the hull for each boat. Bulten tries to determine the optimal form with the aid of computer models. The inlet has to lead to the pump as steeply as possible. This decreases the weight of the water that the ship takes aboard. “Water doesn’t pay for its passage,” Bulten explains. “And every cubic meter of water is taking the place of a carload of passengers.”
“Now back to planet earth”, says the last speaker, M. van der Schaaf of Van der Giessen-de Noord shipyard. Van der Schaaf spoke of a project for the design of a passenger ship with a length of 200 meters and a required speed of 50 knots. This should be possible by constructing a much lighter hull of very strong steel.
The high speed required an unconventionally slim hull. This converted the placement of the engineering rooms, car decks and passengers quarters to a complex puzzle. More problematic, though, is the fact that a high speed inevitably causes harder collisions with the waves. According to Van der Schaaf it’s still uncertain whether the thin ship wall will be able to withstand this slamming. And will the passengers be able to withstand it? The ship architect personally experienced that the frequency of the collisions with the waves was an exact match with the inherent vibration of the ship itself during a test run. “I was jolted up and down on the bridge.” Van der Schaaf believes that presently the high-speed passenger ship is only able to travel across the drawing table.
Translation by: Katy Gerstner
Hydronamic designs, water jets and stronger steel are constantly increasing the speed of ferries. But for now, anyone who wants to cross the Atlantic in less than a day will still have to take a plane.
“When the Irish Oak departed from Cork in 1949, we thought we would be in New York a week later”, reads the opening sentence of Frank McCourt’s novel about his emigration from Ireland to the US. If McCourt were to make his journey again today, he wouldn%t have nearly as much time for long conversations in a lazy deck chair. Modern ferries easily reach speeds twice as high as previously%up to sixty kilometers per hour.
Last Thursday our future shipbuilders convened at a symposium on High Speed Craft organized by the maritime engineering society, William Froude, and they dreamed out loud about speeds of fifty knots or ninety kilometers per hour and more.
Speed and traveling comfort are two concepts that are difficult to combine. “In World War II high speed torpedo boat cruisers were designed. Their crew stood on crates, that were supposed to absorb the first shock of any particularly hard impacts with waves”, says Dr. Alexander Keuning, of the department of Boat Hydromechanics of the faculty of Design, Construction and Production. As recently as several years ago Keuning suspected that maritime designers unjustly assumed the length of a boat to determine the price, causing them to restrain it to a minimum. According to him, a fast ship with the same load capacity, speed and functions on board, but with a greater length proportional to its width, will perform better.
Bathtub
To prove his statement the hydrodynamics engineer from Delft redesigned a Hong Kong patrol boat and made the hull more than half again as long. As expected, this caused the water resistance to decrease, making it possible for the ship to reach the same speed using considerably less motor power. What’s more, this adjustment did not negatively affect the crew: the vertical acceleration of the bridge caused by the waves decreased. This promotes the comfort of living on board when using high speeds at sea. The long ship did bounce on the waves a lot at the bow, but Keuning solved this disadvantage by altering the form of the bow. This resulted in a new ship that was six percent more costly, but cheaper in use and with the added ability to venture out of the harbor in bad weather, unlike it’s shorter predecessor.
Keunings elongated ship concept so appealed to a shipyard that it applied it in the construction of three patrol boats for the Dutch marines. This breed of ship, christened ‘The Panther’, is currently racing around in the Caribbean Sea. No matter how long and slender the hull, without thrust any boat is as fast as a bathtub. For slower ships a screw is sufficient propulsion, but at higher speeds nowadays the water jet is employed. The principle of this propulsion system has been known for more than two centuries, but wasn’t commercially applied until its use in fast catamarans and yachts in the course of the twentieth century enabled them to reach a speed of50 knots (93 kph).
Midget
According to Norbert Bulten, designer for the ship propulsion manufacturer John Crane-Lips, a speed of 75 knots is attainable using waterjets. A ship moving at that speed does need an athletic heart though, because a speed that’s twice as high requires a quadrupling of the pump capability. Bulten illustrates the consequences of this rule with a picture of his colleague standing upright in the pump of a water jet for a fast marine frigate. To make it clearer: “My colleague is no midget.”
Whether or not a water jet attains the required power depends on the design of the water inlet. It has to be adjusted to the form of the hull for each boat. Bulten tries to determine the optimal form with the aid of computer models. The inlet has to lead to the pump as steeply as possible. This decreases the weight of the water that the ship takes aboard. “Water doesn’t pay for its passage,” Bulten explains. “And every cubic meter of water is taking the place of a carload of passengers.”
“Now back to planet earth”, says the last speaker, M. van der Schaaf of Van der Giessen-de Noord shipyard. Van der Schaaf spoke of a project for the design of a passenger ship with a length of 200 meters and a required speed of 50 knots. This should be possible by constructing a much lighter hull of very strong steel.
The high speed required an unconventionally slim hull. This converted the placement of the engineering rooms, car decks and passengers quarters to a complex puzzle. More problematic, though, is the fact that a high speed inevitably causes harder collisions with the waves. According to Van der Schaaf it’s still uncertain whether the thin ship wall will be able to withstand this slamming. And will the passengers be able to withstand it? The ship architect personally experienced that the frequency of the collisions with the waves was an exact match with the inherent vibration of the ship itself during a test run. “I was jolted up and down on the bridge.” Van der Schaaf believes that presently the high-speed passenger ship is only able to travel across the drawing table.
Translation by: Katy Gerstner
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