1..ab.
y.
Scheep..sbouwjunCk
''COR E(GEN GEE:U EÍÀRCHEt
STUDiE ÜQELEI:Ery.
Scheepsbouwkun
Technische Hogeschool
0F SE VERAL HYBRID
Deift
S URFA CE SHIP CONCEPTS
THE AUTHOR
received his Bachelors and Masters degrees in Aeronautical Engineering from Rensselaer Polytechnic institute. Prior to
his current employment with the Systems Development
Departmentofthe David W. Taylor Naval Ship Research and
Development Center, he held several research and
develop-ment. long range planning, and engineering management
positions with Boeing-Vertol. Tran-Sonics. Air Force Cam-bridge Research Center. and the Aero-Elaszic Laboratory at
Mi. T. Mr. Meyer is a memberofA/AA. SNAME, Sigma Xi.
and serves on the A/AA Marine Systems and Technologies
Technical Committee.
ABSTRACT
In this paper several hybrid surface ship concepts are
described and their estimated speed-power and range per-formance compared under calm and rough water conditions.
The concepts analyzed are the Small Waterplane Area Single Hull (SWASH) Ship, Hydrofoil Small Waterplane Area Ship (HYSWAS), Large Hydrofoil Hybrid Ship (LAHHS), Hydro-foil Air Cushion Ship (HYACS), and Small Waterplane Area Air Cushion Ship (SWAACS). All concepts investigated are of
2,000-ton (2,032m ton) displacement ha'ing various
combi-D
R. MEYER, JR.
A COMPARISON
nations of buoyancy, foil lift, or powered static lift from an aIr cushion.
Analysis showed that HYSWAS and LAHHS with about 70% buoyant lift and 30% dynamic lift are expected to have generally favorable characteristics in both calm and rough
water over a broad speed spectrum leading to relatively good
speed and range performance. These concepts, therefore,
appear to be promising configurations for future
considera-tion. However, for special purpose missions where, for
instance, only a segment of speed spectrum ¡s dominant or
rough water operations are not anticipated, other hybrid
forms may show potential and might be pursued further. INTRODUCTION
EVERAL NEW HYBRID FORMS OF ADVANCED SHIP
concepts were examined to obtain initial indications if
vehicles with combinations of at least two sustention
systems could provide better platform capabilities than prime vehicles
[lJ. These concepts in the 2,000-ton
(2.032m ton) size category. where all references to tons
are long tons, with speeds up to 50 knots, were the
Hydrofoil Small Waterplane Area Ship (HYSWAS),Large Hydrofoil Hybrid Ship (LAHHS), Hydrofoil Air
Naval Engineers Journal, April 1977 183 TABLE I
HYBRID SURFACE SHIP FORMS
HYBRID TYPE SOURCES OF SUSTENTION
SMALL WATERPLANE AREA SINGLE HULL
(SWASH) SHIP
BUOYANCY (85%) FROM SINGLE SUBMERGED SLENDER
HULL AND STRUT AND DYNAMIC LIFT (15%) FROM
______________
W. L.
SURFACE-PIERCING FOIL SYSTEM.
I
.
HYDROFOIL SMALLWATERPLANE AREA SHIP (HYSWAS)
BUOYANCY (70%) FROM SINGLE SUBMERGED HULL AND SINGLE STRUT AND DYNAMIC LIFT (30%) FROM FUlLY-SUBMERGED FOILS.
LARGE HYDROFOIL HYBRID SHIP
(LA}D1S)
BUOYANCY (70%) FROM SINGLE SUBMERGED HULL AND DYNAMIC LIFT (30%) FROM FULLY-SUBMERGED
FOILS (MULTIPLE STRUTS ARE EMPLOYED TO JOIN UPPER AND LOWER HULLS).
HYDROFOIL AIR CUSHION SHIP (HYACS)
POWERED STATIC LIFT (70%) FRON HIGH LENGTH-TO-BEAN AiR CUSHION/RIGID SIDEHULL SYSTEM
W.L. AND DYNAMIC LIFT (30%) FROM A FULLY SUBMERGED
FOIL SYSTEM.
SMALL WATERPLA[
AREA AIR CUSHION SHIP (SWAACS)
POWERED STATIC LIFT (70%) FROM HIGH LENGTH-TO-BEAM AIR CUSHION/RIGID SIDEHULL SYSTEM AND BUOYANT LIFT (30%) FROM A SINGLE SUBMERGED SLENDER HULL AND SINGLE STRUT
Cushion Ship (HYACS). and Small Waterplane Area Air Cushion Ship (SWAACS),
It was found that calm water speed-power
perform-ance of these hybrids generally fell between that of
hydrofoils and high length-to-beam surface effect ships. Specific hybrid configurations exhibited relatively eco-nomical calm water powering over wide speed ranges as well as attenuation of hump drag.
Another hybrid surface ship concept, the Small
Waterplanc Area Single Hull (SWASH) Ship. has been investigated by GERSTEN [21. and was included in a study comparing speed/range performance of the above mentioned hybrids in calm and rough water
131-The several hybrid forms are shown in TABLE I with a sectional sketch, a brief description of the combina-tions of lift, and the percent support provided by each. The study was organized by established plausible hull configurations for each of the hybrids based ori a
2,000-ton (2.032m ton) size. Data on the speed-drag
properties of each of the support systems is used to
estimate the total speed-drag features of each
con-figuration. Propulsive efficiency for each of the credible propulsion systems is estimated from separately
deter-SMALL WATERPLANE AREA AIR CUSHION sHIP (SWAACS)
POWERED STATIC LIFT
184 Naval Engineers Journal. April 1977
BUOYANCY
HYDROFOIL AIR CUSHION
SHIP (HYACS)
mined data. Added drag effects of sea state are also
estimated, extrapolating from data on related
con-figurations. Each of the selected combinations is then
conipared for speed, power, and range in calm water
and rough seas using the same prime mover (installed
SHP). where range is determined from the amount of fuel that can be carried and the power requirements.
Speed and range degradation in waves is based on
power available as the only constraint; no consideration is given to vertical accelerations as a speed constraint at
this time.
The intent of this study was to obtain comparisons of the merits of different hybrid configurations relative to
each other. Subsequent analyses will compare these
configurations with so called "prime" vehicles, i.e.,
monohulls, hydrofoils, air cushion vehicles, et cetera.
DESCRIPTION
The types of hybrid vehicle concepts considered in
this paper are shown in Figure 1 and briefly described
below. All ships are 2,000 tons, and each obtains the
total lift required from various combinations of
SMALL WATE RPLANE AREA SINGLE HULL (SWASH) SHIP
HYDROFOIL SMALL WATERPLANE AREA SHIP (HYSWAS)
Figure 1. Sustention Triangle with Hybrid Concepts.
'ç
LARGE HYDROFOIL HYBRID SHIP (LAHHS(
MEYER HYBRID SURFACE SHIP CONCEPTS buoyant, foil, or powered static systems. Such hybrid
vehicles were conveniently represented by JEWELL [4J in
terms of three values: x, y, and z, whose integer values
represent
the tenths of total
weight supported bybuoyancy (unpowered static lift), dynamic lift, and powered aerostatic lift, respectively. The hybrids
dis-cussed here have designators with one zero,
e.g.,HYSWAS is a hybrid concept represented by (x,y,0). Displacement ships, hydrofoils, and cushion-borne craft
are usually located at or close to the x, y, z vertices
respectively of the sustention triangle shown in Figure 1.
and are considered to be "prime" vehicles.
Small Waterplane Area Single Hull (S WASH) Ship
in this concept the submerged hull and centerline
surface-piercing strut (small waterplane area hull)
provide about 85 percent of the total buoyant force. The
configuration is characterized by the constant chord,
passive, surface-piercing V-foils mounted to the
above-water platform, outboard and fore and aft. At zero
speed, the remaining buoyancy is obtained from sidehulls with sufficient waterplane area to provide trans-verse as well as longitudinal stability. The side hulls are integral parts of the above-water platform. At operating
speeds, sufficient lift is generated by the
surface-piercing hydrofoils to lift the side hulls clear of the
water. In this mode of operation, the hydrofoils support about 15 percent of the weight. In addition to lifting the
side hulls out of the water, the hydrofoils have the
important function of providing roll, pitch, and heavestability to the craft.
Hvdro/bil Small Waterplane-A rea Ship (HYS WAS)
This hybrid vehicle concept consists of a single sub-merged hull with a fully-subsub-merged foil system and an upper hull structure supported above the water surface
by a single, thin, longitudinal strut. In the low-speed
(huliborne) mode, sustention is provided by buoyancy of
the submerged hull, the strut, and a small segment of the upper hull. As speed increases, the dynamic lift of
the foil system raises the upper hull above the water and
the waterplane area on the strut becomes small. This
transition can occur gradually at speeds below about 23
knots depending on foil loading (or waterline level)
selected
by the operator. A design
foil loading ofl,2001b/ft2 (5.859Kg/rn2) was adopted for a
fully-loaded ship to provide a bare foil maximum lift-to-drag ratio of about 26 (based on aspect ratios of 6 to 8) at 40
knots. A secondary control surface is provided aft to
maintain appropriate trim and satisfactory pitch stability.
Large Th'dro/òil H brid Ship (LAHHS)
lt is characteristic of hydrofoil craft in general that
larger displacements are associated with ever increasing ratios of main foil-span-to-hull-beam. Existing hydro-foils have span-to-beam ratios that vary from about 1 .0
to 1.7, whereas designs for larger ships are ir' the
neighborhood of L8 to
2.3. The LAHHS hybridconcept, with a slender submerged hull and foil system
connected to the upper hull by three struts, attenuates
this trend and can offer span-to-beam ratios for multi-thousand ton ships no greater than current hydrofoils of
several hundred tons. The underwater hull of the
LAHHS configuration considered in this paper has a
circular cross-section, a length-to-diameter ratio (2/d) of 20. and a prismatic coefficient (CpH) of 0.80. A foil
loading of 1,200lb/ft2 (5,859Kg/rn2) was selected with a forward and aft distribution of load of 30 percent and
70 percent respectively. Foil and strut thickness ratios of 0.10 were assumed.
Hydrofoil Air-Cushion Ship (HYACS)
This hybrid concept consists
of an
air cushioncaptured by a rigid sidehull extending downward from each side of the upper hull, with flexible seals for and aft, augmented by a fully submerged aft foil connected to the sidehull by Struts, and a forward foil supported
by a strut
on the
centerline of the upper hull.Calculations were made for a (0, 3, 7) hybrid with the following basic parameters held constant (Other combi-nations of dynamic and powered static lift were investi-gated in Reference [1]):
Cushion length-to-beam ratios (2/b)
- 4.0 and 6.5.
Cushion pressure-to-length ratios
- (p/i):
1.02 and 0.681b/ft3.
(16.4 and 10.9Kg/rn3).
Foil loading - l,2001b/ft2 (5,859Kg/rn2).
Foil aspect ratios - 6.0 forward; 8.0 aft. Foil draft-to-chord ratios - 1.0.
Forward and aft foil load distribution - 0.30/0.70. S,nall Waterplane Area Air Cushion Ship (S WAA CS)
The major features of this hybrid concept are an
air-cushion captured by a rigid sidehull extending down
from each side of the upper hull with flexible seals fore and aft augmented by a single slender underwater hull connected to the main upper hull structure by a single,
thin, longitudinal strut. Calculations were made for a
(3, 0. 7) hybrid with the following basic parameters held constant (Other combinations of buoyant and powered static lift were investigated in Reference [1]):
Cushion length-to-beam ratios - 4.0 to 6.5.
Cushion pressu retolength ratios
-1.02 and 0.681b/ft3. (16.4 and l0.9Kg/m).
Underwater hull length-to-diameter ratio - 20.
Underwater hull prismatic coefficient - 080. Strut length-to-underwater hull length ratio - 0.6. Strut prismatic coefficient - 0.83.
Strut/hull draft-to-diameter ratio - 1.5.
DISCUSSION
General Approach
Comparison of the various hybrid concepts is based
upon power. useful load, and range characteristics. Calm and rough water power characteristics through
Mid-Sea State S (significant wave height of lOft; 3-1m)
have been estimated. Drag of the hybrid forms was
derived from elements of model and full scale test data of the parent forms. For example, HYSWAS drag was obtained by adding the drag of a demi-hull plus strut of SWATH and a foil system of a fully-submerged
hydro-foil. Although interference drag between major lift
systems was neglected, resistance and propulsion system margins have been included in performance estimates.
Useful load is defined as payload plus fuel. A weight breakdown analysis has provided a basis for determin-ing available fuel, which, when combined with power requirements, determined range capability. Range has been estimated for calm and rough water through Sea
State 5 (Hi,,3 = lOft: 3.lm). These characteristics will
be discussed under the following assumptions:
I) Ships in the 2,000-ton size category examined have about 158 tons (160m tons) military payload. Groups 3
(Electric Plant), 4 (Communications and Control), 5 Conventional Portion of Auxiliary Systems), 6
(Out-fitting and Furnishings), and 7 (Weapon Systems) were held constant for all ships. A 60,000 horsepower power-plant and a Group 2 (Propulsion Machinery) weight of
200 tons was used for all ships. Note that air cushion
ship (ACS) seals are included in Group 2 weights; foil weights have been added to the conventional portion of
Group 5. LAHHS, as currently configured, requires
superconducting machinery; alternate foil/strut
combi-nations could provide for either waterjet or a Z-drive propeller system with some impact on weight and or
performance capability. Weight margin is assumed to
be 15% of lightship weight. Group I (Hull Structure)
weight calcuJated for each ship, when combined with all the above weights and a variable load of 50 tons (51m tons), provided an estimate of fuel available for range
calculations.
Rough water power degradation information
available
on SWATH ships,
hydrofoils, and highlength-to-beam ratio ACS is applicable proportionally. component-wise. to hybrid surface ship forms.
Power degradation, i.e.. (EHP)/(EHP)0. in given Sea States is the same over a speed range from 25 knots
to calm water maximum speed. Here subscript "r" is the Sea State. and "o" is calm water; EHP is effective horsepower.
Propulsive coefficient is not affected by Sea State. Propulsion on SWASH, HYSWAS, and LAHHS is obtained from subcavitating propellers on the stern end of the submerged hull.
Propulsion on HYACS and SWAACS is obtained from partially submerged propellers at the stern of the sidehulls. (It is realized that if a 60.000HP transmission system could be developed to fit within the relatively
1 86 Naval Engineers Journal, April 1977
limited strut/lower hull structure of SWAACS a
sub-cavitating propeller with improved efficiency could be
employed.) Power
Power characteristics have been treated in
consider-able detail in Reference [1]. However,
data from
Reference fil and more recent results are shown in
Figure 2. These hybrids are 2,000 tons and EHP is for
bare hulls in calm water. Drag in the speed regime
below about 15 knots has not been estimated. Although a wide variety of hybrids have been examined in terms of percentages of buoyancy, dynamic lift, and powered static lift, the 30-70 percent combinations represented in Figure 2 appear to be dimensionally feasible and at the same time have relatively reasonable power require-ments. Note that the LAHHS and HYACS (which both have strut/foil systems) are characterized by relatively
high power in the low end of the speed range. There
would undoubtedly be a power hump (or large bump)
between 10 and 25 knots in the transition from hull-borne to full foil loading for LAHHS and HYACS.
HYSWAS and SWAACS power characteristics show a marked improvement over LAHHS and HYACS in the
low speed range (from 15 to 27 knots). The SWASH
Ship shows a higher power requirement over the entire speed range primarily because of the inferior lift-to-drag ratio (L/D) of the surface-piercing foil system. Cushion
length-to-beam ratios of 4.0 to 6.5 are shown for the cushionborne hybrids. The reason for considering a
ratio of 4.0
is to reduce structural weight, therebyincreasing fuel load and range as discussed later.
I.
71
Figure 2. Hybrid Calm Water Power Comparison - Effec-tive Horsepower.
Variations of propulsive coefficient (P.C.) with speed
assumed for the various ships studied are shown in
Figure 3. It can be seen that the curves peak at speeds
between 30 and 35 knots. HYACS and SWAACS
propulsive coefficients were realistically taken somewhatlower than SWASH. HYSWAS, and LAHHS because of the relatively poor flow conditions expected at the stern of the sidehulls of' HYACS and SWAACS. lt should he
MEYER
noted that recent tests on SWATH (Small Waterplane
Area Twin Hull) VIl showed propulsive coefficients
even greater than the values assumed here for SWASH,
HYSWAS, and LAHHS [51. Also given in Figure 3 are
the power margins assumed in the conversion of EHP
(see Figure 2) to shaft horsepower for the calm water
condition shown in Figure 4.
1.0
HYSWAS. SWASH, 1. LAHUS
20 W
$01 L 0/0 NOTO
Figure 4. Hybrid Calm Water Power Comparison.
Although calm water has traditionally provided a
baseline for performance comparisons, it must be rec-ognized, according to Birmingham [6], that rough water in terms of SS-4 (H l/ 5.Sft; 1 7m) and above occurs
about 70 percent of the time in
the North Atlantic(above 300 latitude, or Jacksonville, Florida) (See
Figure 5).
/
OVOSGO iT3. 0- 13i0 toe 1200 flI lolL LOADING
/ 1/'//
However, SWATH Ships and fully-submerged
hydro-foils appear to have relatively low power increases of 2% to 8% in head seas through Sea State 5 (Hi,,3 = lOft;
31m). The results of the analyses are shown in Figure 6 where it can be seen that HYSWAS and LAHHS have
much less power degradation
than HYACS and
SWAACS as rough head seas
are encountered. Itshould be noted that power to provide a heave allevia-tion (comfort control) system for hybrids with an
aero-Naval Engineers Journal. April 1977 187
HYBRID SURFACE SHIP CONCEPTS
40 z I-1 30 u z O 20 o u z 10 O 0 SSS £5.6 OS-7 z o .5 >
-
0 3 53 7.5 125 20 425 1.911 1161.12.31 3.8) 1611 1131SIGNIFICANT CREST TO-TROUGH WAVE HEIGHT/FEET METERSI
Figure 5. Annual Distribution of Wave Heights in North
Atlantic Above 30°N Latitude.
&SWAACS
O
O Data on power degradation of various vehicles in
.3 FO W E A
rough head seas were collected and applied to the
SHIP
MARGIN I%T hybrid ship forms previously described. lt was found HYSWA 10 that high length-to-beam SES predictions correspond
LAUTES
UVA OS 5 to power increases of approximately 15 percent in SS-3 SWAACS
SWASII 10 (H i,'3 4.Sft; l.4m) and about 35% to 50% in SS-5
(H,'3 lOft; 31m) depending on length-to-beam ratio.
O IT) 4 8 2) $ SI 18 LIGNIFICONT WAVE HEIGOTIFT IMOTEMSI
- 3 -- -L-. - 'T-.--
-SIA STATE
Figure 6. Estimated Power Degredation of Hybrid Ships
with Sea State.
10 2V 30 40 50
SPEED/KNOTS
Figure 3. Assumed Propulsive Coefficients and Appendage Allowance for Various 2,000 Ton Hybrids.
SOSAcS 3.8 71.II 20 /
II,IS . LO.,,', I03Ib/fl3 OIfl$II31-/
OTAC IO. ¡TI
LO. PA,. ¶.LTNTT3- ILL
J".
'L.
/1/
Sn. 0100011
Figure 7. Hybrid Power Comparison in Sea State 5.
static lift
component was not
included essentiallybecause, at the time the computations were made,
reliable values were not available. As mentioned pre-viouslv under General Approach, power degradationinformation on parent forms is applicable proportion-ally component-wise to the various hybrid ships.
Power ratios in Figure 6 were then used to modify the
calm water power estimates and to provide a
com-parison of shaft horsepower in Sea StateS (H½ = lOft; 3.Im) (See Figure 7). Note that a comparison of Figures
4 and 7 for hybrids in calm water and SS-5, (Hi,'3 =
lOft; 3.lm) respectively, shows a widening of the curve separations in favor of foilborne hybrids over
cushion-188 Naval Engineers Journal, April 1977
£00 STATE
Figure 8. Speed Degred.ation of Various Hybrids in a
Seaway Based on Power LimiL Only.
borne hybrids. Maximum speed degradation was esti-mated assuming that 60,000 horsepower was installed in
each ship, and as mentioned earlier, propulsive
coefficients were not affected by sea state. The results of these speed degradation analyses are shown in Figure 8. As expected. the slopes of all curves for cushionborne
hybrids are considerably greater than those for other
hybrids examined. Although the cushionborne hybrids analysed have a higher speed capability in calm water, rough water quickly negates this advantage and speed
drops relatively rapidly.
TABLE lI
WEIGHT BREAKDOWN 0F VARIOUS HYBRID SHIPS
WSSWAS tJ3124S MYACS SWAACS HSACS SSJ&ACS sasw
(0.3.7) (3.0.1) (0,3.7) (3,0,7) (8.5,L3.0)
(7,3.0) (3.3.0) 6.5 o'l.1-6.5 L0/b0 - 4.0; $ib- 4.1);
CROuP p/f,- o.o. tii. 17.7.0
-v/I0- 1.02 I'f4- 1.02 WE)0741 (2. Toss) Z 1JEICNT (I. TOMS) W610M1 (L TOWS) 2 vCC$T
(L TONS) Z (L TOIlS)%l'tC$T Z OJE1CWT
(L TOUS) z OJ2IC)4T (L TONS) z 1. 111 Strocture 475 23.7 620 21.0 575 28.7 642 33.1 480 2'..O 567 28.4 523 2b.2 2. .p.ulVion ILIC6. 200 10.0 200 20.0 200 10.0 201 10.0 200 10.0 200 10.0 71)0 10.0 6.0 3. 1trctrie P1151St 220 6.0 120 6.0 120 6.0 120 6.0 120 6.0 120 6.0 110 4. Con.', 6 Cc'ntrol4 80 6.0 80 4.0 80 4.0 80 4.0 60 4.0 80 4.0 80 4.0 5. A.x. 5LC*' 140 1.0 140 7.0 140 7.0 140 7.0 140 1.0 140 7.0 140 7.0 5.0 rail/soils 40 2.0 118 5.9 80/" 4.0 S - 80/° 4.0 -/ - 200 6. 0.tuitt1n 6 lorn. 76 3.7 74 3.7 74 37 74 37 74 3.7 14 3.7 74 3.7 7. wc.ssos Syste*s 26 1.3 26 1.3 26 5.3 26 1.3 26 1.3 26 1.3, 26 1.3
totol Li0ht Ship 1135 38.0 1178 09.0 1295 65.0 1302 65.0 1200 60.0 1207 60.4 12(.' 63.2
)6..lrt.c (135 L.S.) 1/3 8.6 177 8.9 2.8'. 9,0 1°.I5 9.7 so 9.0 18L 9.0 190 9.3 nip FocI. 570 28.5 51.0 27.0 410 20.5 400 20.0 520 26.0 510 25.5 445 22.2 lisio roJ5 20 1.0 20 1.0 20 1.0 20 1.0 20 1.0 20 1.0 20 1.0 Viciut.1 L.odi 50 2.5 50 2.5 50 2.0 50 2.) 0 2.5 50 2.5 10 2.5 Ship Aa.,w 57 .85 17 85 17 .85 2,7 .1) i7 .85 17 .85 17 .55 6ICLOC 13 .61 1) .65 13 .65 13 .15 13 .45 13 .65 13 .65 Sparos 0 2 .1 2 .1 2 .1 2 .3. 2 .2. 2 .2. 2 .2. Tat1 F1 Lood 2000 .0 1997 00.0 200L .100.0 1999 100.0 2002 100.0 2000 101.0 2002 100.0 jodjc..tcs itC','p in 158 7.9 158 1,9 158 7.9 158 7.9 PUiltary P.ylond 158 7.9 { 158 7.9 138 7.9
$000310 included La Croip #2 (.tit propulsion)
Hote: Weights in most of the Groups are based on a 2)9O-toro SWs.TH; Reference[7).
't I?SCO0 4 C /1 .4Ø R. 4024021V', IW&SIIIII 0 .11d II. 044 o4,_3 *444117 OlI 4' 7041 1L104__ -0 4
7/
¡aSACO li 0, C A 20 .4 LøA ' 30 - loi_j_o, 7/r
IIYOWAS IT. 3.01 44 lthoe lnnp tust ¡,i.,3j 7041 10*01*01 '0
MEYER HYBRID SURFACE SHIP CONCEPTS Usefuul Load and Range
A weight breakdown analysis of the various hybrids
was performed to provide values of useful load - here
defined as
the sum of Group 4 (Command and
Control). Group 7 (Weapon System), ship ammunition.
other items such as helicopters, helicopter fuel, and
spares. The weight breakdowns for HYSWAS, LAHHS,
HYACS, SWASH. AND SWAACS are shown in
TABLE II. Payload was held constant and was based on a SWATH small escort design [7J of 2,092 tons (2,l2Oni
tons). Ship fuel was then adjusted to within S tons to
yield a full load of about 2,000 tons. Note that most of the group weights were held constant across the table; margin was taken as 15 percent of light ship through-out. Weights that changed because of configuration are hull structure and foil/seal systems.
It was found that hull structure plus foil systems of
HYSWAS and LAHHS were about the saine. The
SWASH foil system is relatively heavy because of the
larger foil
area and vertical struts of the
surface-piercing foil system. HYACS and SWAACS hull plus
foil/seal systems total weights were close in value. These estimates were based on the strut/foil system of large
hydrofoils with about the same size foil system as the HYACS; lower hull/strut combinations for SWAACS
were based on SWATH ship structural densities; seal
system weights are included in Group 2 (propulsion) in accordance with SES practice. As mentioned above, the
cushionborne hybrid concepts were examined at 1-wo
length-to-beam (Pc/bc) ratios, namely 4.0 and 6.5. The
Pc/'bc = 6.5 designs, with a pressure-to-length P2C
ratio of 0.681b/ft3 (10.9Kg/rn3), result in an inherently large volume with higher hull weight, and subsequently
about ISO tons less fuel available than the HYSWAS and LAHHS configurations. The Pc/bc = 4.0 at P/PC
= l.021b/ft3 (16.4Kg/rn3) configurations reduced hull weights sufficiently to provide about the same fuel load as the other hybrids.
Calm water range calculations were based on the shaft horsepower curves in Figure 4. Ship total fuel
rates were computed with a propulsion allowance of 10
percent and a "hotel load" fuel rate of 0.10 tons/hr.
Specific fuel consumption variations with actual turbine power output were taken into account and were based
on an up-rated LM2500 (or FT-9) performance. This was likewise done for a cruise engine installation. A
separate l0.000HP (l0,15OmHP) gas turbine is assumed for the cruise condition between 10 and 20 knots. Range computations were then also tempered with an unusable fuel factor of 5 percent. The results for hybrids in calm water are shown in Figure 9, where it can be seen that at a speed of 20 knots. HYSWAS has a range capability
about 1,000 nautical miles greater (even without a
cruise engine) than the other hybrids. Above 27 knots
LAHHS is superior until about 40 knots where the
range differences become relatively small (within severalhundred nautical miles) and probably within the
accuracy of the computations. The BREGUET Range
Formula was used for all cushionborne hybrids.
However, constant weight (replacing fuel with ballast)
has been used for SWASH, HYSWAS, and LAHHS to satisfy intact stability requirements in heavy beam seas and high winds.
Figure 9. Hybrid Range Comparison in Calm Water. The impact of rough water on range of the various
hybrids was assessed on the basis of the power degrada-tion values in Figure 6.
A comparison of RANGE versus SPEED for hybrids in Sea State 5 (Hy3 = lOft; 3.lm) is shown in Figure 10. Here HYS WAS and LAHHS maintain a superior range capability over most of the speed spectrum in Sea
State 5 (H½ loft; 31m). However, LAHHS range
drops off sharply below 27 knots.
33-* *lIßN3t T
\
3 .3 3 .A, 32 3V,.» 3
Figure 10. Hybrid Range Comparison in Sea State 5.
Operariotzal Profile/Rough Water
1f one visualizes a ship lifetime operational speed
profile where a large proportion of time is at speeds less
than about 30 knots and in the North Atlantic (or
equivalent) environment, then it appears that the
HYSWAS. and to a lesser extent, LAHHS
configura-tions offer significant speed-power performance
ad-vantages (See Figure 7). Also, if the speed spectrum is
expanded to about 18 to 40 knots, HYSWAS and
LA HHS still promise superior performance, although
HYSWAS is expected to have a lower take-off speed.
On the other hand, if ship lifetime operations are
predicted to be restricted to 30 to 50 knots (negligible
time at low speeds) in the real year-round ocean environment, then the LAHHS concept appears to be superior.
SUMMARY
It is evident from the work to date that certain
combi-nations of sustention systems and proportions thereof
can produce hybrid ships having a broad range of
characteristics. These may be either worse than, the same as, or better than the parent forms, dependingupon the performance characteristic, speed range, and size under consideration. Although a complex subject, and this paper could not treat every possible sustention
combination and ship performance requirement, the
results of hybrid ship investigations provide some
insight as to which hybrids should be promising with
regard to certain operational characteristics. At the
same time, analytical tools are being developed by
NAPPI [8], LEE [9], and KARAFIATH [10] to
accom-modate configurations encompassing buoyant, dynamic, and powered static lift for other hybrid forms that may
be conceived.
The Author realizes that a more detailed weight
analysis might change the group weight values
inTABLE I of this paper, as exemplified by 2,000-ton HYSWAS studies {l l}[12][13]. However, it is expected that all of the concepts considered would change in
about the same way, and that the relative fuel load (for a given payload) would be essentially unaffected. There-fore, the range performance trends shown in this paper
would still
hold. At the same time, the reader
iscautioned not to compare the results in
this paperdirectly with other ships of similar size, either existing or conceptual, since the intent of this investigation was
to obtain relative results amongst the hybrids
them-selves.
CONCLUSIONS
I) For a surface ship operational profile where a
large proportion of time is spent at speeds less than 30
knots and in higher sea states (such as experienced in
the North Atlantic on a year-round basis), the
HYSWAS and, to a lesser extent, LAHHS
configura-tions have superior performance over the other hybrids
investigated.
Likewise, for operational profiles where a large
proportion of time is in a speed spectrum of about 18 to
40 knots and in
higher sea states, the HYSWAS concepts and LAHHS have relatively better speed and range performance, although HYSWAS is expected to have a lower take-off speed.If operations are restricted to 30 to SO knots with negligible time at low speeds, and in a year-round North
Atlantic environment, the LAHHS configuration
ap-pears to be superior.
Although the cushionborne hybrids analysed have
a higher speed capability in calm water, rough water 190 Naval Engineers Journal, April1977
f'.
tends to negate this advantage and speed drops
relatively rapidly under such adverse conditions.
The buoyancy supported fully-submerged
foil-borne hybrids, because of their favorable speed-power
characteristics over a broad speed spectrum in both calm and rough water, should continue to be investi-gated with emphasis on stability analyses, structural
analyses, general arrangements, and model tests to
validate the utility of the concepts. However, for special purpose missions where, for instance, only a segment of the speed spectrum is important, or where rough water
operation is not anticipated, other hybrid forms may
show potential and might be pursued further.
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