Ships work by supporting their payload through reaction forces. In the case of a displacement ship this is given by the mass of the displaced water, Archamidies principal etc. This has the disadvantage that the hull movement is resisted as it attempts through the water.
This resistance takes two forms pressure resistance and frictional resistance. Pressure resistance is the component of resistance which forms the waves where as viscous resistance is what is due to the friction effects of the hull passing through the water. As stated in the two articles the resistance changes depending on the vessels speed/length ratio or Froude number. This ratio is a none dimensional term used in fluids mechanics similar to the Reynolds number.
If Froude no. is plotted against speed the curve obtained has a series of peaks and troughs, low and high resistance's. for conventional displacement vessels you get a big trough at about 23 kts then a large peak. If you want to get over this peek you need to put a massive amount of power into the vessel. The problem is that as the speed increases, the frictional resistance increases by a power of 2 or something along those lines.
If you want to go fast you've got to reduce frictional resistance and the best war to do this is to get the hull out of the water. The 3 methods used by naval arch's are hovering, hydro foils and planing. A good book that goes through the principles involved is Mechanics of Marine Vehicles.
The planing hull work by the reaction force created by the passage of water along the underneath of the hull. The simple analogy is of an angled plate in a jet of water. As the plate moves through the water it gives rise to two forces, one horizontal (drag) and another vertical (lift). In the case of the fast ship the vertical force will lift at least part of the body out of the water therefore reducing the friction.
The disadvantage is that this will use a much larger amount of energy than a displacement ship, but it will provide an effective solution for a transportation system that is between a plane and conventional ship. Military application are limited by the noise it would produce, passive sonar seeing it from the other side of the Atlantic (a guess), and the fact none of there other ships would be able to keep up, so the worlds big navy's probably won't be placing orders just yet.
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Tim
This resistance takes two forms pressure resistance and frictional resistance. Pressure resistance is the component of resistance which forms the waves where as viscous resistance is what is due to the friction effects of the hull passing through the water. As stated in the two articles the resistance changes depending on the vessels speed/length ratio or Froude number. This ratio is a none dimensional term used in fluids mechanics similar to the Reynolds number.
If Froude no. is plotted against speed the curve obtained has a series of peaks and troughs, low and high resistance's. for conventional displacement vessels you get a big trough at about 23 kts then a large peak. If you want to get over this peek you need to put a massive amount of power into the vessel. The problem is that as the speed increases, the frictional resistance increases by a power of 2 or something along those lines.
If you want to go fast you've got to reduce frictional resistance and the best war to do this is to get the hull out of the water. The 3 methods used by naval arch's are hovering, hydro foils and planing. A good book that goes through the principles involved is Mechanics of Marine Vehicles.
The planing hull work by the reaction force created by the passage of water along the underneath of the hull. The simple analogy is of an angled plate in a jet of water. As the plate moves through the water it gives rise to two forces, one horizontal (drag) and another vertical (lift). In the case of the fast ship the vertical force will lift at least part of the body out of the water therefore reducing the friction.
The disadvantage is that this will use a much larger amount of energy than a displacement ship, but it will provide an effective solution for a transportation system that is between a plane and conventional ship. Military application are limited by the noise it would produce, passive sonar seeing it from the other side of the Atlantic (a guess), and the fact none of there other ships would be able to keep up, so the worlds big navy's probably won't be placing orders just yet.
Tim