Gas turbine-waterjet propulsion offers significant advantages in many high-speed or special purpose ships, which generally have speed capability above 30 knots and installed power-toweight ratios above 10 hp per full-load ton. Included are destroyers of the destroyer (DD) type and some smaller destroyer leaders (DL), hydrofoils above 40 knots, surface effect ships, and planing craft. Optimization of gas turbine-water jet installations for maximum net thrust (system thrust less drag associated with propulsion system) depends primarily on the L/D ratio of the basic hull, design speed, ship length, and component efficiencies. The major components are the inlet, pump, gearbox, gas turbine, and associated required auxiliaries. For high-speed ships, propulsive coefficients of 60-65% are possible with conservative component-loss assumptions.Ib g = gravitational constant, ft/sec 2 h = inlet lip height, ft H = head, ft/H 2 O H S i = head, static inlet, ft Hsx = head, static hull, ft H io = head, total, freestream, ft Hti = head, total inlet, ft H i2 = head, total, diffuser exit, ft L = waterline length, ft L/D = lift/drag ratio N = shaft speed, rpm NPSH = net positive suction head (total head above the vapor pressure at waterjet inlet), ft N 8 = specific speed, JV(gal 'min) 1/2 /Afi r3/4 PC = propulsive coefficient, TV/shp X 550 Q = flow rate, gal/min R = radius, in. £ = suction specific speed, N(Q) 1/2 /NPSH 3 / 4 sfc = specific fuel consumption, Ib/hp-hr shp = shaft horsepower T = thrust, Ibf v = local velocity, fps Vim = mean inlet velocity, fps Vj = jet velocity, fps Vk = velocity of vehicle, knots V 0 = freestream velocity, fps FI = inlet velocity, fps w = flow rate, Ib/sec W = weight, Ib x = distance from bow to inlet, ft y = distance perpendicular to hull or flow boundary layer, ft 5 = boundary-layer thickness, ft A = displacement, long tons (2240 Ib) rj p = pump efficiency, % 0 = momentum thickness A# = pump total head rise, ft 0GB = gearbox efficiency, shp 0 ut/shp in , %