Table 11.4 Principal dimensions and features of available and planned ACV [81] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28a 28b 28c 28d Name SR.N4 Mk 3 N500 Aist SR.N4 Mk 2 SR.N4 Mk 1 JEFF (A) JEFF (B) VT-2 Lebed BH.7 Mk5A Bell AL30 BH.7 MV.PP15 Voyageur AP1-88 N300 Gus Vosper 18m ACV MV.PPSMkll Viking 7505 SR.N4 Mk 6 MV.PP5 Viking 7501 SR.N6 SR.N5 SH2-4 SH2 Skima 12 (12) Skima 12(9) Skima 12 (6) Skima 12(3) Country UK France Russia UK UK USA USA UK Russia UK USA UK Japan Canada UK France Russia UK Japan Canada UK Japan Canada UK UK UK UK UK UK UK UK Weight (t) 300 265 260 200 180 157 150 100 90 55 52 50 50 35 29 27 27 25 19.3 19 17 16.3 14.7 10 6.7 3.1 1.8 1.9 1.675 1.45 1.225 Length (m) 56.4 50.0 47.8 39.7 39.7 28.0 24.2 30.2 23.3 23.1 23.0 23.1 25.1 20.0 21.5 24.0 21.3 18.4 17.6 16.5 17.1 15.4 13.2 14.8 11.8 8.0 5.9 7.2 7.2 7.2 7.2 Beam (m) 23.2 23.0 17.5 23.2 23.2 13.4 13.1 13.3 10.2 11.2 10.0 11.3 11.1 10.0 10.1 10.5 7.3 9.3 7.6 6.7 6.6 7.6 6.7 6.6 6.6 4.4 4.4 2.8 2.8 2.8 2.8 LIB 2.43 2.17 2.73 1.71 1.71 2.09 1.86 2.27 2.27 2.04 2.30 2.04 2.26 2.00 2.13 2.29 2.92 1.98 2.32 2.16 2.59 2.03 1.97 2.47 1.97 1.82 1.34 2.57 2.57 2.57 2.57 PC (kg/m-) 257 315 360 257 230 469 484 305 390 268 267 244 217 213 200 169 193 185 186 193 155 185 193 128 129 110 90 101 89 77 65 pJL (kg/m 3 ) 4.56 6.3 7.53 6.47 5.79 16.75 19.84 10.10 16.81 11.60 11.61 10.56 8.65 10.65 9.30 7.04 9.06 10.05 10.60 11.70 9.06 12.10 14.62 8.65 10.93 13.75 15.25 14.03 12.36 10.69 9.03 (m 2 ) 1168 840 725 780 780 335 310 328 230 205 195 205 230 166 145 160 140 135 104 90 110 88 76.3 78 52 28.3 20 18.8 18.8 18.8 18.8 '•'* 0.272 0.257 0.225 0.315 0.351 0.127 0.131 0.229 0.128 0.208 0.155 0.244 0.322 0.171 0.250 0.367 0.214 0.322 0.240 0.220 0.267 0.270 0.214 0.350 0.462 0.265 0.372 0.120 0.164 0.225 0.363 Power (shp) 18000 17000 26000 17000 17000 22500 22500 7600 7200 3800 3600 3800 4400 2600 1 500 3000 2340 2500 1050 1 700 1 125 1 050 1 700 900 900 200 200 250 250 250 260 Speed M, = WVIP (knots) 65 70 70 70 70 60 62 63 55 58 50 60 65 47 55 62 50 60 52 50 50 55 50 52 60 42 45 27 30 32 38 7.43 7.48 4.80 5.65 5.08 2.87 2.84 5.87 4.72 5.76 4.95 5.42 5.07 4.39 7.29 3.83 3.95 4.12 6.56 3.89 5.18 5.86 2.97 3.96 3.06 4.46 2.80 1.41 1.37 1.29 1.27 Table 11.4 (continued) 29a 29b 29c 29d 30a 30b Name Skima 4 (4) Skima 4 (3) Skima 4 (2) Skima 4(1) Skima 4 Mk 2 Skima 4 Mk 3 Country UK UK UK UK UK UK Weight (t) 0.475 0.40 0.325 0.250 0.550 0.330 Length (m) 4.0 4.0 4.0 4.0 5.03 5.03 Beam (m) 2.0 2.0 2.0 2.0 2.08 2.08 LIB 2.0 2.0 2.0 2.0 2.42 2.42 PC (kg/m-) 95 80 65 50 78 47 pJL (kg/m) 23.75 20.00 16.25 12.50 15.51 9.24 S c (m 2 ) 5.0 5.0 5.0 5.0 7.0 7.0 q v /p c 0.081 0.150 0.224 0.292 0.085 0.310 Power (shp) 25 25 25 25 40 40 Speed (knots) 22 27 30 30 20 30 M { = 2.82 2.96 2.65 2.04 1.89 1.68 WVIP Notes: 1. M, is a non-dimensional coefficient, therefore the physical units in this expression are: IV m N; v in m/s; P in Nm/s. 2. q = 0.5 p., V~ has units of m/s. Determination of principal dimensions of ACV/SES Table 11.5 Weight distribution of a Chinese ACV and SES Craft version Type Date completed Manufacturer Hull structure Outfit Power plant Electric system Skirts Empty weight Passengers and crew (including luggage) Liquid load (water, oil, etc.) Fuel All-up weight Key W\ Wl m W4 W5 W W6J m w% AUW 7313 Design weights (kg) SES September 1969 Wu Dong shipyard 7796 2605 8540 735 Included in 'Hull' 19676 6400 Included in 'Hull' 800 26876 % %W 39.6 13.3 43.4 3.7 % AUW 73.2 23.8 3.0 100 7202 Final weights (kg) ACV October 1980 MARIC 641 289 734 117 270 2051 520 32 20 2623 % %W 31.2 14.1 35.8 5.7 13.2 % AUW 78.2 19.8 1.2 0.8 100 guide. Remember that this is simply an initial step, all the data will need to be refined at a later stage. With this as a starting point, it is useful to determine a number of the basic dimen- sions for the craft such as / c , B c , S c , p c , Q', // sk , /f sw and 5 SVV as in section 11.4 and Table 11.6. Start with: then where then where K p = 50 kg/m 2 (low-density craft) 100 kg/m" (high-density craft) S c = Wlp, =( pjl c - \0~\5 (low-density craft) 15-20 (high-density craft) B c = 1 C BJI C BJl c 2.0-2.8 (amphibious ACV) 3.0-3.5 (SES) (11.7) (11.8) (11.9) First approximation of ACV displacement 389 Table 11.6 Determination of principal dimensions and weight of ACV (taking the given engine type as the constraint, as this is the normal situation) Item Dimensioning value Calculation method Remarks 1 W 2 B W L c = BJ(BJL C ) p c = WI(L C B c ) // = (HB The various weights can be calculated as follows: I. Hull weight 1. Metalic structure 2. Deck equipment and paint 3. Ship equipment 4. Life-saving equipment 5. Other items in hull group II. Power plant W s = K s S c W2-2 = K2-2 W W2-4 = K2-4 W° IV2-5 = K2-5 5 n According to prototype W3 = A3 . N N = designer choice III. Fuel weight m IV. Electric equipment weight W4 = q e Z N Rl V, K& = K4 W V. Skirt weight VI. Provision weight VII. Passenger weight W5 = K5B c h,p c W5 = K5 (L c + B c ) /? sk p c W\Q = A"10 W W6 = K6 P n K6 =140 kg passenger only 200 kg with luggage Calculation of craft weight W c = Z Calculation of speed I. Wave-making drag II. Air momentum drag III. Air profile drag IV. Skirt drag V. Trim drag V. V = f (LJB C , P C IL C , W,F t ) m = f(Q, Fr, IV ) a = / (S a , Fr, . . .) sk = / (Q, Fr, . . .) v =/( ) Initial starting estimate L C /B C ratio andpJL c initially chosen from Table 11.4 According to given LJB Z ratio chosen from Table 11.4 According to given L C /B C ratio chosen from Table 11.4 According to given H^IB Q from Chapter 10 (requirements for stability) Coefficient in weight calculation from this chapter S n - passenger numbers determined by role Lift and propulsion engines can be obtained according to the AUW of craft in the first approximation, craft speed and some coefficients. Then designers can select the type of lift and propulsion engines and thus determine the power plant weight 5 n is number of passengers or seats. K6 will vary a little in different parts of the world If this relation does not hold, then the process should be iterated until the difference is small enough to be ignored (say less than 5% at estimating stage) Iteration. See Chapters 10 and 3, Fig. 12.5 Use method in Chapter 3 S, is frontal area of craft 390 Determination of principal dimensions of ACV/SES Table 11.6 (continued) Item Dimensioning value Calculation method Remarks Estimation of lift power 10 Estimation of engine power propulsion power Total power 11 Estimation of transverse stability 12 Estimation of speed of craft in wind and waves 1. ** w max (drag peak in calm water) II. J? m III. R a V. R ¥ VI. Thrust reserve 13 Seaworthiness I. Maximum vertical acceleration at CG, II. Maximum vertical acceleration at bow 14 Area of passenger cabin S,,, N t = Q Hl(r, f r,u) where Q = Q'S c (2p c /p a f H = A/C h ,A =P l p c /?, = bag/cushion pressure ratio N = F s I R, l\ N< + N n nj h 0 IB c = R ¥ = T = where T = = f(L e IB e ,p c IL c , Fr. ) (r-/?' wmax )//?' w f(N,[V w where A w = wave height L w = wavelength k , LJL C H is fan overall pressure head Ch is the coefficient due to loss of head in ducts, obtained from prototype tj p is efficiency of air propeller If this expression is not satisfied it has to be revised and repeated until it is Determined as in Chapter 5. During this initial estimate, skirt responsiveness is not considered Note: head wind and oncoming waves Use Chapters 3 and 8 The wind speed has to be taken into account for calculation of II-V then . . . R' vm . M = I/? F w is wind speed For Passenger craft, the main check targets are the vertical acceleration in a wave, which can be calculated by the method in Chapter 8 and according to the seaworthiness requirements for craft given in Chapter 10 L c . d and 5 Cil denote cabin length and width respectively, which are related to L c , B c and the relation between them can be determined It is also helpful to estimate the installed power at this point, which can be found from N=K n W 7/8 kW (11.10) where K n = 135 W = AUW in tonnes This expression is representative of efficient craft of all sizes through the late 1980s assuming speed and size follow existing norms. High-speed craft would require addi- tional power, low-speed craft less. This also applies to SES as well as ACVs. First approximation of ACV displacement 391 Table 11.7 Weight Estimate Checklist Item Sub-items Check comments W\ Hull weight including: Main hull structure, including basic raft or hull structure plate, frames, stringers and other scantling,decks, sandwich panels Superstructure Bow/stern ramp structure Doors and hatches Landing pads Air propeller ducts and mountings Engine mountings and their strengthened structure Bearings and mountings, etc. Integral tankage Fins (vertical or angled stabilizers) Horizontal fixed aerodynamic stabilizers W2a Basic Outfit weight including: Rudder and their handling equipment Mast Ladders Windows and doors Retractable equipment for ramp Floors and coverings Isolation, insulation, sound proofing, trim, partitions, etc. Painting Flight crew seats Flight crew emergency equipment Passenger seats Fire precautions in payload areas Marine equipment, including anchoring Life-saving and fire-fighting system Life-rafts and containers stowage Life-jackets and stowage W2b Customer-specified equipment which may be considered optional, including: Passenger tables, lockers and other furnishings and cabin equipment Heating, ventilating and air conditioning Toilet and washing facilities Galley facilities Domestic water supply (in toilet) Long-range tankage and system W3 Power plant including: Main engine(s) Machinery equipment such as: Main reduction gear boxes of main engine Reduction gearbox(es) for lift fan(s) Radiator(s) for lubrication oil system Air filters Hydraulic and propeller pitch controlling system Transmission shaft system Remote control systems W3a Lift and propulsion equipment and auxiliaries, including: Propellers Lift fans Fuel supply tanks (if not integral with hull) Pipelines The hull includes the primary structure (buoyancy tank area for ACV, sidehulls and central buoyant connecting structure for SES) superstructure and all main secondary structures The items included here will be very dependent on the craft mission and safety regulations for the area of operation These items should be checked individually, since most of them will not normally be installed Do not assume they are included in the historical reference data, unless clearly identified 392 Determination of principal dimensions of ACV/SES Table 11.7 (continued) Item Sub-items Check comments W4& Basic Electric system including: Batteries Electric generators Electric transmission and distribution system Engine starting system Illumination system Voltage rectification equipment Cabling and cable trays Navigation equipment, inc. radio, radar, Navaids W4b Cockpit communications equipment Intercommunication and internal broadcasting Electronic enclosures and racking Signalling equipment Environmental equipment W5 Weight of skirt and joints including Loop or bag Bag stabilizer diaphragms Segments or fingers or jupes Rear double segments or anti scoop flap Rear multi loop skirt (SES) Longitudinal stabilizer skirt Athwartships stabilizer skirt Skirt shift mechanism Segment ties Loop attachments W6 Weight of payload including: Weapons, passengers and luggage, vehicles, freight Wl Weight of crew and luggage, Provisions Bonded stores and sales stores Fresh water supplies Boarding parties and their equipment Spares carried on board m Weight of fuel, Main fuel, reserve fuel, long-range fuel Lubrication oil W9 Liquid load on the craft such as: Bilge, water in the pipelines and engines WIO Reserve displacement This item should include : Project weight estimating reserve These items should be checked individually, since most of them will not normally be installed. Do not assume they are included in the historical reference data, unless clearly identified Estimate loop surface area Estimate one finger and total number off Estimate loop surface area Estimate loop surface and individual cones X number Define as unit weights, number and distribution Do not start with less than 15% An alternative to this expression is to use installed power/tonne knot: N = K W V 1 *e -* v n '' ' s where F s is the design craft service speed, W the weight (t) and K n = 0.7 (light large craft) 0.9 (light small craft > 5 t) (11.11) First approximation of ACV displacement 393 2.0 (dense large craft) 3.0 (recreational and small utility craft) We can now move on to develop further estimates for the craft weight components and begin to refine the parameters. Weight of hull structure According to ref. 4, the weight of the hull structure for an ACV, W s can be written as W w or W — = 0.6/p c W™ + 0.015 ^° 33 (11.12b) W where W & is the weight of the hull stucture (t), W the weight of craft (t) and p c the cushion pressure (lb/ft 2 ). (Note: 1 Pa — 0.02 lb/ft 2 = 1 N/m 2 .) This expression can be seen plotted in Fig. 11.1 and the structural weight of some hovercraft is shown in Fig. 11.2. Based on data from some SES designed and built in China, the weight of the hull structure can be estimated by the following equation [11]: W. = 8.8 K[\ + 0.045(K S /L)° 666 ] [L (H + 5 C )/100] 125 (11.13) where W s is the weight of the hull structure (kg), L the length of the hull structure (m), F s the design speed (knots), £ s the cushion beam (m), H the cushion depth (m) and K a coefficient, which can be taken as K = 750-800 for welded aluminium alloy structure = 900-950 for GRP structure = 830-860 for the combined structure of GRP and aluminium (GRP sidewalls) = 1100-1500 for combined structure of steel and aluminium (aluminium superstructure) = 1200 for whole steel structure Weight of metallic structure for an ACV, l/l/ s (or I/V1) (11.14) where S c is the cushion area (m") and K\ a coefficient (taken from the prototype or reference craft, see Tables 11.1 and 1 1.4). Weight of deck equipment and painting 1/1/2-1 Wl-\ = WKl-\ (11.15) 394 Determination of principal dimensions of ACV/SES _ 60 £ 50 '53 * 40 <tt rt I 30 % 20 i a 10 SES-100A BH? -100B/ 0nnUla<1L2) SRN4/J LowpMc 'HighpA Formula (14-3) 10 100 1000 Displacement (t) 10000 Fig. 11.1 Weight trends for ACV/SES structures with displacement. 60 £ 50 SP '53 * 40 <£H (S 1 30 ^ 20 3 a 10 719 tBH7 o Modern hovercraft 7 Tanker X Cargo ship 7202 10 100 1000 Displacement (t) 10000 Fig. 11.2 Hovercraft and ships' structure weight statistics with displacement. where Wis the craft weight (t) and K2-\ a coefficient. Typical values are 0.12 for an ACV and 0.1 for an SES. Weight of ship's equipment 1/1/2-2 (rudders, anchors, mooring, towing, lifting equipment, etc.) .0.666 ^-2 = ^2-2 W"™° (11.16) where K2-2 is a coefficient. Typical values are 0.08 for an ACV and 0.1 for an SES. First approximation of ACV displacement 395 Life-saving equipment 1/1/2-3 In the case where the weight of the craft is similar to that of a prototype, then W2-3 is W2-3 = K2-3S n (11-17) where S n is the number of passenger seats (should also be the same as the number of passengers) and K2-3 a coefficient. Typical values are 3.0 (kg) for an ACV or an SES, covering life vest and weight component of life-raft and fittings installed. Weight of ship's systems 1/1/2-4 K2-4W (11.18) where K2-4 is a coefficient. Typical values are 0.05 for small ACV (AUW < 2000 kg) 0.05 for medium ACV (AUW < 20 000 kg) 0.02 for large ACV 0.02 for small SES (AUW < 20 000 kg) 0.01 for large SES Weight of power plant 1/1/3 m = K'K3ZN (11.19) where K3 is a coefficient according to the specific weight of the given power plant. Typical values, in kg/kW, are 0.5 Gas turbine engines 2.5 High speed diesels 5.0 Medium speed diesels and X N is the total installed power (lift, thrust and auxiliaries) (kW). For engine weight, with respect to the total weight of the power plant, the coefficient K' has to be found in this equation; for example for gas turbines K' = 2-3, while for high-speed diesels K' = 1.5-2.5. This is to account for gearbox weights, etc. Note: Cooling systems additional outfit weights (in addition to K'} 0 for air cooled (though maybe there will be an oil cooling system) 0. 1 for water cooled diesels 0.2 for recirculated cooling water It should be noted at this point that it may be best to check the available power plants to provide the power. A number of design choices may have to be taken at this point, since if it is decided to use separate power systems for lift and propulsion, an estimate of the required cushion system power is needed. This will mean making a preliminary cushion system design (Chapters 2, 6 and 12) and then revisit the engine selection, before going on. Power system selection has a strong influence on the whole craft layout, so it is worth while spending some time on this aspect. Since engines are [...]... aspects: Determination of air flow rate 1 the determination of cushion parameters concerned with the performance of the craft, e.g the relative flow rate Q, the bag cushion pressure ratio p{/pc and the cushion pressure/length ratio pc/lc', 2 design of air inlet and outlet, as these seriously affect the loss of total pressure head; 3 air duct design; 4 air fan design 12.2 Determination of air flow rate, pressure... reserve of craft in waves respectively It is suggested to select the alternative which gives the maximum craft speed or minimum displacement and also meets these restrictions The method expressed by Table 11. 6 can also be illustrated by a block diagram as shown in Fig 11. 5 12 Lift system design 12.1 Introduction In Chapter 2 we introduced air cushion theory and its development to date Modern air cushion. .. calculation can be undergone as in Table 11. 6 In this example, we take the general condition of design into account, namely the role stipulates not only the number of passengers, range, speed of craft, requirement Fig 11. 4 Optimization plots of craft leading particulars selection prior to design Determination of hovercraft principal dimensions 403 Initial data Weight of craft known components Wh Installed... the air feed holes of via the air feed holes of via the air feed holes of via air feed holes of the the bow and fore side bag into the cushion; the stern and rear side bag into the cushion; the longitudinal stability skirt bag into the cushion; transverse stability skirt bag into the cushion According to the Bernoulli equation and knowing the cross-section area of the duct sections, the flow rate in air. .. (H} = fan pressure, Pt = bag pressure): (1) air from bow and fore bag, via its bow into cushion; (2) air from stern and rear bag, via its hole into cushion; (3) air from longitudinal stability skirt bag and via its holes into cushion; (4) air from transverse stability bag and via its holes into cushion In order to reduce the work, during the preliminary design, the overall fan pressure on an ACV can... pressure at the air inlet increases in square proportion to the inflow velocity, thus increases inversely in (a) Fig 12.9 (a) Influence of inclination angle of air inlet on ram air pressure recovery: (a) dimension and variations of air inlet geometry Fig 12.9 (b) ram air pressure recovery coefficient vs air inlet configuration 1: standard air inlet plus A; 2: standard air inlet plus B; 3: standard air inlet... give high air duct efficiency due to the low air velocities Design of fan air inlet/outlet systems 419 Horizontal arrangement of fan with part volute (or guide plate) Often due to various requiremnts for craft layout, the air streamline in the horizontal arrangement of fans cannot provide free diffusion, but needs to be diffused smoothly via a part volute or flow-guide plates In this case particular... concerning the fan Design of fan air inlet/outlet systems (a) (b) Fig 12.5 A typical equivalent air duct system for SES: (a) air duct configuration; (b) equivalent parallel air network for calculations recovery pressure coefficient and pressure loss at inlet, etc can be calculated as detailed above 123 Design of fan air inlet/outlet systems Inlet system From Figure 12.4, it can be seen that the air inlet pressure... lip radius; 2: air inlet fairings; 3: centre body for smooth flow; 4: close fitting inlet to fan; 5: height of air inlet duct; 6: influence of air propeller/pylon I 30 • 25 a* I 20 I- MOD4 b MOD 1/0 r / Fairing / body MODl 10 /MOD3 £ famng >© body MOD2 'MOD2 V type fairing body 4J 15 e MODS Un-faired body 1000 2000 3000 4000 5000 6000 7000 Q (ft3/s) Fig 12.7 Influence of gearbox shape on air inlet systems... 93]: HJlc = 0.05/H^ 5 (12.2a) Table 12.2 Flow coefficient for various Hovercraft Craft Country Type Cushion length 4(m) Cushion area 5 c (m 2 ) Craft Cushion weight ^(t) pressure /> c (N/m 2 ) Flow rate Q (mVs) Q bar HM.216 HM.218 HM.221 713 711- IIA SR.N6 SR.N4 JEFF (A) UK UK UK China China UK UK USA SES SES SES SES ACV ACV ACV ACV 11. 95 14.39 17.44 17.5 10.09 14.8 39.7 28.0 58.29 70.19 85.07 87.30 52.32 . (high-density craft) S c = Wlp, =( pjl c - ~5 (low-density craft) 15-20 (high-density craft) B c = 1 C BJI C BJl c 2.0-2.8 (amphibious ACV) 3.0-3.5 (SES) (11. 7) (11. 8) (11. 9) First . '' ' s where F s is the design craft service speed, W the weight (t) and K n = 0.7 (light large craft) 0.9 (light small craft > 5 t) (11. 11) First approximation of ACV . loss. It is important to remember that cushion air thrusters for ACVs, and cushion vent- ing systems in the case of SES, absorb part of the cushion air flow or lift power if sep- arate