c
Tulin two-dimensional supercavitating section - TMB 1954 Posdunine supercavitating section 1945 5-term Johnson J 3-term Johnson 2-term Circular arc Comparison of 2-term and TMB modified sections Comparison of 2-term and TMB modified sections Hydronautics, 1961 Fig. 15.26 b Examples of supercavitating blade sections. Johnson 5 term section Johnson 3 term section Newton Rader section Tulin section Sulzer-Hydro ventilated partially submerged propeller installed on Mekat SES Fig. 15.26 b cont....
Cushion pressure ratio Hq Euler number
In order to correctly simulate air leakage from an air cushion and external aerodynamics of full-scale craft, as well as the spray caused by the cushion acting on the water surface, the scaling criteria of cushion pressure ratio Hq, the Euler number, can be written as where pc is the cushion pressure N m2 , a the air density Ns2 m4 and Fa the velocity of air leakage, m s . According to Table 9.1, V.d can be written as If Fa denotes the velocity of the craft model, then expression 9.2 is similar...
Design loads for craft structure overall bending and torsion
The loads acting on the craft structure during the calculation of overall bending and torsion can be determined using the maximum inertial load coefficient measured at the craft's CG. The inertial load coefficient operating in waves can be obtained from prototype or experimental results of models in various operation modes and various modes of overall deformations. The loads acting on locations other than the CG can be determined as follows tj 1 px O, - xg x - xg p2 yx y lp2 p2 x2 - xg x - xg...
Open loop and segment Fig 713d
This skirt is used on smaller craft, generally below 5 t. The loop is at pc and so this is the most efficient skirt form. The geometry of the loop can be varied to give the right combination of responsiveness for a seaway and skirt shift mechanisms can be used to enhance manoeuvring. Tapered geometry is possible, though not normally used. A swept-back bow skirt is necessary, as it is not practical to design a stable bulbous bow geometry as for a responsive bag and finger skirt. This is not a...
Air cushion adiabatic stiffness coefficient Cb
The coefficient which characterizes the adiabatic stiffness of air cushion can be expressed by where Vc is the cushion volume m , pa the atmospheric pressure N m , pc the cushion pressure N m and y the adiabatic constant for air m2 N . This coefficient characterizes the adiabatic change of cushion air in compression due to the heaving, pitch and roll motion of hovercraft running at high speed, which affects heaving stiffness and damping. The cushion pressure denotes the excess pressure of...
Nondimensional characteristic curves of fans and air ducts
The Reynolds number for model air ducts is rather small because the dimensions of the model decrease with the dimensional ratio A. This will influence the air duct friction drag. However the air friction drag losses are usually small the main losses of air pressure in air ducts are due to the curved or sharp bends in the ducts and sudden expansion of air flow into the cushion. Thus the air pressure loss in ducts can be considered independent of Re. Calculation of losses is similar to analysis...
45 Factors affecting ACV transverse stability
Based on the equations mentioned above, one can discuss the effect of the various parameters on the static transverse stability of an ACV. However, the errors of calculation are rather large since no account is taken of the deformation of skirts caused by the Fig. 4.33 Typical static transverse stability curve for ACV. Fig. 4.33 Typical static transverse stability curve for ACV. change of cushion pressure of the craft in heeling and the effectiveness of the air cushion blown from the nozzle of...
Platforming analysis
The first mode is platforming, i.e. the cushion pressure and the vertical position of the wet deck remain constant, then the vertical acceleration will also be constant. This is the ideal operating attitude of craft and what the designer requires. However, one has to regulate the lift power and lift inflow rate to keep the cushion pressure constant. This condition is also the one which will absorb the greatest volume of air therefore we will make an analysis of this case. When the craft moves...
Sidewall hovercraft or SES
This concept Figs 1.4 and 1.5 reduces the flexible skirt to a seal at the bow and stern of a marine non-amphibious craft, using walls or hulls like a catamaran at the sides. The walls or hulls at both sides of the craft, and the bow stern seal installation, are designed to minimize the lift power. Due to the lack of air leakage at the craft sides, lift power can be reduced significantly compared with an ACV. Also, it is possible to install conventional water propellers or waterjet propulsion,...
Winginground effect WIG and power augmented ram wing PARWIG craft
These craft are rather different from the ACV or SES. They are more like low flying aircraft, and use ground proximity to increase lift on the specially shaped wing. The craft are supported by dynamic lift rather than a static cushion. The WIG Fig. 1.6 initially floats on the water and its take-off is similar to a seaplane. An aeroplane wing operated close to the ground generates lift at the pressurized surface of the wings which is increased significantly due to the surface effect. The...
Concept development from the early 60s to the early 70s
The results of research trials with SR.N1 indicated that a truly competitive commercial hover ferry would probably need to be 125 to 150 tons in weight and some four times the length and breadth of the SR.N1 manned model, in order to cope with 4 to 6 feet seas. A jump from 4 to 125 tons represented such a major engineering step that it was decided by Saunders-Roe to approach this in three stages over a 7 years programme. 207 The first stage was implemented with the 27 ton SR.N2, which was used...
Deck area and cabin volume
The ACV and SES both give spacious deck area and cabin volume. These vessels need to be large relative to their displacement, to keep cushion pressure realistic. They are therefore suited to applications where volume is the most important parameter Table 1.7 The footprint pressure of various forms of transport Table 1.7 The footprint pressure of various forms of transport The configuration of transport forms passenger and car ferries, fast military logistics vessels, utility vehicles and, at...
Market development from the beginning of the 80s to the present
Although air cushion technology had advanced significantly by the end of the 70s, there were still difficulties to overcome in order for hovercraft to compete fully with Fig. 1.18 Hovermarine HM-221 SES fireboat on trials before delivery to port of Tacoma. Fig. 1.18 Hovermarine HM-221 SES fireboat on trials before delivery to port of Tacoma. other transport systems such as hydrofoils, high-speed monohull passenger craft, high speed catamarans and long range buses and trains where appropriate....