The Hysucat (catamaran) development

The Hysucat Development

by

Prof. Dr.-Ing. K.-G. Hoppe

Mechanical Engineering Department University of Stellenbosch Stell enbosch/RSA

wwnur

mor. Meke!weg 2, 2628 CD Deift T 015.788873 Fa 015.751836

DEPARTMENT OF MECHANICAL ENGINEERING UNIVERSITY OF STELLENBOSCH

*

The RYSUCAT Development by

*

Dr. K.G. Hoppe SUMMARY

The Hydrofoil Supported Catamaran (Hysucat) is a hybrid of a

catamaran hull equipped with a hydrofoil system between the

demi-hulls which carries a part of the craft's weight at speed. The efficient load carrying capability of the

hydrofoil system in combination with the inhérént stability and pleasant seakeeping properties of the planing catamaran results in a most economical high-speed-surface craft with

excellent seakeeping behaviour.

Towing tank model tests and a 5.65 in seagoing model in the

rough seas off the Cape proved the new principle to be

efficient, stable and comfortable and allowed further design

optimisation. Several, sea going prototypes have been

developed from 5 in to 3, in pròving. the Hysucat advantage.

The development of a Hysucat 'design théory assisted by

towing tank experiments has been initiated and has already

produced well optimised Hysucat designs.

1. INTRODUCTION

The designation Hysucat stands for Hydrofoil-Supported

Catamaran and describes a high speed planing catamaran with a hydrofoil system between the two demi-hulls which carries

a part of the weight of the craft at speed resulting in a

considerably reduced overall resistance and propulsion power

reqtiirement with the pleasant rough water seakeeping

properties of.a catamaran.

The. use of a hydrofoil system consisting of _{a mainfoil near}

the longitudinal centre of gravity and a trim foil at the

stern, arranged to operate in the so called hydrofoil surface effect mode ensures a dynamic trim stability

automatically leading to a well functioning hydrofoil

Supported catamaran, see HOppe [1].

The tools for the Hysucat design were consequently developed and the new prindipie was first evaluated by extensive use

of model tank tests. _{A-seagoing model, as a first prototype}

proved the principle to be extremely effective _{and the}

ex-pected good handling and seakeeping characteristics could be

demonstrated i.n many open sea tests in various _{weather con} ditions from calm to extremely rough weather. Various

Hysucat's with sizes of 5 in to 36 in were built, all craft

proving the considerable improvements detected already in

the early model tests.

A 36

in Yacht with a hydrofoil

system,. a so called CAT4FOIL, is being built at _{present in}

Cape Town.

Dr. Hoppe is a Naval Architect and AsSociate professor at the Mechanical Engineering Department of the

The present report is intended to highlight the Hysucat

development and point out the considerable advantages to be

gained by the application of the Hysucat priñciple.

_The

present work also intends to determine the field of Hysucat

size- and speed range for whiòh the principle can be applied

with advantage. _{Using numerous tank tests the Hysucat}

principle was developed gradually to produce one of the most

hydrodynamic efficient highspeed small craft.

By more

systematic optimisation on specific craft further

improvement seems possible.

2. THE HYSUAT PRINCIPLE

The efficiency of a planing hull and a hydrofoil are best expressed by their drag-lift-ratios

£ = D/L

with resistance coefficient, D = dragf orce, L = liftforce. As indicated in Fig. 1, the high speed

planing catamaran has a resistance coefficient of _{0,25 to}

0,30, whereas the hydrofóil wing section in the high speed near surface mode has a resistance coefficient of 0,03 to

0,05 (depending strongly on the aspect Ratio). The

hydrofoil, even in the surface effect is considerably more

efficient to carry

load at speed than the hull. A

combination of the catamaran with hydrofoils, therefore, must improve the traf t considerably.

0.25 lo 0,30 Cf011 _{0,03 lo 0,05}

D

Fig. 1 Lift-Drag Ratios

To achieve a well functioning Hysucat the two elements. _must

be properly combined to reduce the overall resistance and to

produce sufficient. transverse and longitudinal and course

stability at all speeds. At low speeds the load is carried

mainly by buoyant forces whereas at high speed the _larger portion of the load is carried by dynamid forces, _which

means, at different speeds the lift proportions are built-up

of physically different forces This has a strong effect on

Further requirements in any practical boat design for sea

operation are for good seakeeping and handling

characteristics The seakeeping of the catamaran is further

improved by the hydrofoil, action, which is sketched in

Fig. 2, where a Hysucat is shown encountering a wave òrest.

Fig. 2 Hysucat in Wave Encounter

The demi-hulls with their strong reserve buoyancy and

planing area are rising abruptly in the wave encounter

carrying the hydrofoil with them and creating the vertical

velocity component Vv The relative inflow to the

hydrofoil, which is the vector sum of ship- and vertical speed,

is changing in the wave crest encounter and the

incidence angle OEr is reduced resulting in lower hydrofoil

lift forces. This means that the hulls have to carry more

load ornentariiy and follow the, wave slope less abruptly

with less vehement vertical motions The hydrofoil, this

way, improves the already good wave-running characteristics

of the catamaran by it's damping effect against vertical

accelerations in waves The damping effect is also present

when the Hysucat leaves the wave crest and re-enters the following t-roúgh.

The Hysucat design propoSal after Hoppe [1] is höwn in principle in Fig 3 and presents a hydrofoil arrangement with automatic trim stabilization at speed

dernI-hull Innir side wall

main foil

Al

Fige 3 Hysucat Principle eiern foil

Two hydrofoils are installed inside the straight tunnel of

the fully asymmetrical planing catamaran in tandem

arrangement The larger mainfoil is situated slightly in

front of the longitudinal centre of gravity (LCG) near the

keels and a smaller sernfoil (or two strut foils) in the vicinity of the stern òf the boat near the waterlevel at speed. Both foils approach the water surface with

increasing ship speed from beneath. They are designed to

operate in

the

so called hydrofoil surface effect mode which

means the liftforces reduce gradually by approaching the

water surface from beneath, see DuCane (2] and Schuster and

Schwanecke [7]. When disturbed in the steady state motion,

for example, when submerged deeper, the foil in Surface effect creates strongly rising iiftf orces which tend to

return the foil to the original level of submergence _This

way the hydrofoil's trim stabilization is less dependent on the angie of incidence a and trim angle T of the hulls but

strongly dependent on submergence. _{The hydrofoils have to}

be dimensioned to compensate for the reduction of lift in

the surface effect and must have relatively larger areas. The foils are arrangéd so, that the resultant liftforce of

ail hydrofoils is situated lengthwise near the best

longitudinal centre of pressure (LCP) position for the

investigated catamaran hull which can be determined in model

tests with a single foil arrangement. The intensity of the

hydrofoil surface éffect is expressed in dependence of the

ratio

k

_{= Hw/e}

with Hw = water height over foil, e chord ength of fOil.

The smaller the surface effect ratio k the stronger will be

the trim stabilization. However, in extreme surface effect

the foil drag to lift ratio is increased. For good performance the surface effect ratio k should not be much

smaller than

k= 0,2.

The height of the stern

foil over keel hk, in Fig. 3

influences the craft's trim angle

_r

_{at speed and can be} determined as follows:.

uk2 = hk1 AL (tan

r -

tan 8) ₊

k1.e1 - k2.e2 ...i.i

(12, hlc],

8, indices i and 2 defined by Fig. 3), 8 = the downwash angle of the mainfoil inside the tunnel, which

main foil

LCG position

f ish vtew

Fig. 4 Typical Hysucat Arrangement

A typical Hysucat arrangement is shown in Fig. 4. The

mainfoil has a slight sweep angle and very low dihèdral to allow for smoother penetration of the water surface in waves

at high speeds. _{The sternfoils consist of two strut foils}

with sweep and low dihedral angles _{Strut foils can be}

built stiffer for the small foil _{areas in request The foil}

system is designed to carry 40 % to. 60 % of the craft's total weight at design speed.

The determination of the hydrodynamic forces _{of the Hysucat}

presents a very complex problem and

_{is not possible by}

theory alone, especially not as long as the wave-making

resistance is of importance.

Model tank tests, are the most effective and _{economical tool}

to investigate the Hysucat resistance in _{dependence of the}

main parameters as speed, displacement, _{centre of 'gravity}

position, _{longitudinal centre of pressure' position of 'the} hydrofoils' and the hull form parameters.

3.

. HYSUCAT EVALUATION

3.1

Model Tests

To prove the weil functioning and 'the _{good hydrodynamic}

efficiency of this new principle, _{a series öf model tests}

with different planing catamaran hulls _{and various foil}

'arrangements were conducted. _{Initially small models of}

about 0,5 m length were tested in the

High-Spèed-Watercirculating Tunnel at the University of _{Stellenbosch.}

These qualitative tests proved the well functioning of the

Hysucat models 'when the hydrofoil system _{was well matched to} the catamaran hulls. _{By comparing the correlated results to}

the same hulls without hydrofoils the _{improvement due to the}

hydrofoil system could be determined and was in the order of level at rest

40 %. _{These tests also delivered the knowledge of the} hydrofoil, arrangement

_{in relation to the hulls and the}

longitudinal centré of gravity position of the _{craft to} achieve minimum resistance and sufficient dynamical

stability and course holding _{This way the influence of the}

main parameters in thé Hysucat design could be established

and applied to the later designs. _{The hydrofoil of the} model. was also, tested. in. separation of the hull to

investigate the interference effects between the demi-hulls

and the hydrofoils _{It was found that the pressure field of}

the derni-hulls at planing speed inôreasès the effective

aspect ratio of the hydrofoils spanning the tunnel and the

bridging main hydrofoil also increases the _{planing hull} aspect. ratio. _{Both these interference effects are positive} and improve. the. total resistance of the Hysucát considerably. _{The interference effects were always strong}

and play an important role for the good performance, _which

first was noted with disbelieve _{The body plan of a typical} half meter-model Hysucat is shown in Fig. 5. .

-model deck

CWL

Keel 5' $o CWL

Fig.. 5 Model 'of Hysucat 5

Sea Keeping and Handling .

'The watercirculating tank. 'tests were ',not only conducted for resistance determinations but also to investigate and

improve on the models'' handling and _{seakeeping 'behaviour.}

The model tow rope is attached near the centre of gravity to allow relatively undisturbed heave, pitch and sway motions

This way, the dynamic directional stability and course

holding ability, the tendency to porpois'e and _{the trim "at}

speed and softness of ride can be observed in the

circulating tank. - The watercirculating tank at the

University of Stellenbosch is equipped with a steerable

nozzle outlet flap which allows the creation _{of wavé-like}

water surface variations similar to a head-wave-of-encounter

for the model at speed. _{Tests were conducted by running a}

typical Deep-V-Planing mo,el after [5] simultanéously _{with a}

Hysucat model and recording the behaviour in various _wave

arrangements were varied to determine.best positions. The

catamaran hull without hydrofoils was also tested in

comparison. These tests proved that the Hysucat behaves well at speed with no tendency to porpoising whereas this was not the case for the catamaran and the Deep-V-Planing hull which showed strong porpoising. for LCG positions astern

of 0'34Chin

Course stability was excellent

of the

Hysucat and slight directional problems were observed only

when the LCG position was too far ahead, in, front of

O42LChine.

. . .

Behaviour in severe waves was better of the Hysucat than for

the. Monohull with softer. motions and less spraying. The so

called sea survival test, showed that the Hysucat could

withstand similar extreme head waves, when the wave length

of encounter is about equal to the ship length, as the

Deep-V-Planing hull but with softer motions.

In these tests deep dippings of the bows are observed on all

models. The reserve buoyancy in the bow region and reserve

planing area are important design requests to 'withstand these most severe conditiOns. The Hysucat modél showed best

behaviour for LCG positions' of

_O36Lchjne.

The qualitative tests in the Circulating Tank indicated that

the Hysucat would have reduced power requirement against a

catamaran and Deep-V-Planing hull in the order of 40 % and'

excellent seakeeping properties, superior to conventiónal

hulls. .Later tests with a 5,6 m seagoing Hysucat operated in the 'open sea of the Cape confirmed these observations.

More details about the qualitative Hysucat tests are given

in the reports [3] and [4].

Towing Tank Tests

The indication of the considerable improvements due to the hydrofoil system obtained in the qualitative tests enhanced

further research work and a number of different Hysucat designs were outlined and, models for the towing. tank tests

produced. The first models weredesigned for résearch work

only.. _{Later models were built to specified designs, a 12 m}

Police Patrol Craft, a 18 m Coastal Patrol Craft and a 27 m

high-speed Navy Patrol Craft. _{The later two weré tested at}

the Versuchsanstalt fur Wasserbau und Schiffbau, Berlin in

Germany under the supervision Of the author.

The. earlier research test series were used to. optimize _the

Hysucat by using different foil systems and arrangements _and

a steady progress was made in improving the Hysucat system. Designs for different sizes of prototypes were elaborated of

the various model results.

The Hysucat model 6 presented. a 20 rn, 65 t, 40 knot craft

with simplified hull shape for easier construction in

aluminium. It had 'Deep-V-Planing demi-hulls with prismatic

shape and high deadrise and a relatively narrow tunnel for _a

stiffer hydrofoil arrangernent. The maximum chine beam was

Bma* = 6,8 m. A typical result js shown in Fig. 6 where the

the. presented. Sea Craft Tendency Curvés. The hump

resistance at about half of the maximum speed is

. still

relatively high due to the lower foil width in relation to

the demi-hull chine beam.

The correlated results of the resistance coefficient L over

the Fronde-displacement number FflV are shown in Fig. 6 with

the ship. length and displacement indicated. _{All demi-hulls}

are of the Deep-V-Planing type with relatively high deadrise

angles and practical width's resulting in length-beam ratio's of between 2,5 and 3,0. For some of .the designs the

resistance coefficients without hydrofoils are incorporated to demonstrate the considerable resjstance improvement due

to the hydrofoil system.

The Hysucat resistance is improved with wider tunnels and larger. hydrofoi] span.

The so called hump resistance appears for Froude numbers of

1,4 and was still re]ative1y high for the early models. For. Diesel Engine propelled craft with fixed pitch

propellers a low hump.resistance is desirable..

By systematical demi-hull design improvement the hump

resistance, which is mainly dépendent on the demi-hull

shape, could also be reduced and ïs well below £ = 0,1 for

later models, seé Hysucat 27 in Fig 6. Cavitation and

hydrofoil . efficiency considerations result in relatively

large foil areas with wide tunnels for the slower and larger

Hysucat's, see Hysucat 7 in Fig. 6.

A number of further tests were conducted i.n the Towing Tank

at the University of Stelienbosch to investigate Hysucat design tendencies for larger hydrofoil areas, increased hydrofoil span width in broader tunnels, _{hydrofoils with} dihedral and penetrating beneath the keels of the demi-hulls, towing tank tests with force measurements _{on the}

hydrofoil in the Hysucat arrangement and tests to determine

the downwash angles behind the main hydrofoil _{The Hysucat}

model li has denu-hulls with reduced deadrise in the

stern-part of the demi-hulls _{(to better accommodate a waterjet}

propulsion System). _{The Hysucat 9' model has a prismatic}

hull with a deadrise angle of 25° from frame 6 to the stern

and increased deadrise in the foreship The denu-hull chine

beam is strongly reduced towards the stern and in a recent

retest the heel of the stern was equipped with a stern wedge. This craft has a high slenderness degree of the derni-hulls and a relatively large (but not impractical)

tunnelwidth with a wide. hydrofoil span. _{The towing. tark}

prediction shbws the lowest Hysúcat resistance coefficient

at top .speed so far reached in.. all the tests. _{The model} runS exceptionally well and the tank test simülating the design speed of about 40 knot is shown in Fig. 7.

lOo 2 O, I HYSUCAT 7 (30m: (got) 32 knot HYSUCAT 27 (no fell) (MT-Ca t amar an ((0m 6,5t) Supramor Hydrofoil r (4(t) HYSUCAT 27 127,n:lOBt) HYSUCAT 5 (løm;7 It) 0,3 ¡,0 2,0 4,0 5,0

Fig. 6 _{Resistance Displacement Ratios of Sea Craft.}

b --,

-i'°°-''° zf-,

__J11/IIIITIIT

Fig. 7 Hysucat Model 9 at simulated 40 knot.

Fig. _{8 presents a typical tank prediction for the Hysucat}

model 9 design as a ₁₇ m,

33,5

_{t Ferry Craft with a topspeed}

of 40 knot in form of the dimensionless resistance

coefficient L. _{The hump resistance coefficient is still}

relatively high with _{Ch =}

_0,115

_{but lower than for usual}

Deep-V-Craft _{The hydrofoil system, in this specific case,}

was designed to achieve the resistance minimum at design speed of 40 knots _{The resistance coefficient at this}

speed, indeed, presents the minimum resistance _{of the bare}

hull (without appendages for rudder and propeller

installation) and is very low with ₌

_0,073,

_{which présents}

only 34 _{% of the resistance of the same catamaran without}

the support-foils and, proves the basic logic of this

Io

o .25 0.20 0.15 0.10 0.05 0.0 0 / I I

/

-A A'

/

Mode I . L. -Catamaran without hydrotol Is Prototype _(17m;33,5t1 -'-_ Model Prototype HYSUCAT 1i7m;335t) 2 .3 4 5 Fnv V/'Ig.vI/3

Fig. 8 Hysucat 9 Tank-Prediction with. and without Hydrofoils

The hump resistance is mainly dependent on the demi-hull shape and loading (V/L3, V being the volumetric

displacement) as the foils carry less than 15 % of the

displacement weight at these lower speeds.

The tank results in Fig. 8 do not account for superstructure

air resistance and appendage drag which form part of the

propeller design calculations which resulted in a propulsion

power of 2 533 kW (including 10 % trial run addition) för

40 knot and 33,5 t displacement and the case in which the

craft is propelled by two high speed propellers driven by

V-type ZF-gears and inclined shafts.

The propulsive coefficient P.C. _{= eff'b (ref f}

power, _b = Diesel brake power) in such

arrangement is estimated to be conservatively

including a propeller efficiency of = 0,70.

elaborated própulsion systems better propulsive

seem possible. = effective a standard P.C. = 0,56 With more coefficients

The Hysucat model 27 was designed in collaboration with

Hysucat Engineering Germany (HEG) and the Lürssens Shipyard

in Bremen, Germany. Special emphasis was placed on low hump

resistance and low top speed resistance. À slight propeller

tunnel f ör inclined shaft drive was incorporated in the

demi-hull design. The hydrofoil system was optiniised for

the service speed of 40 knot.. Systematical test series with a three metér long modèl were conducted at thé Berlin Model

Basin, Germany.

The result of the Hysucat 27 in the design load condition is

shown in Fig. 6 as e over FnV together with the tendency

curves of sea craft and the other Hysucat data.

II

A very low hump resistance coefficient of Ch = 0,09 was

reached indeed with this design and a remarkably low service speed resistance coefficient of £ = 0,08 (so far e does not

include Superstructure-Air-Resistance!) which presents improvements of 46 % at 40 knot and 50 % at 45 knot against

the same hull without hydrofoils.

Further commercial Hysucat's have been tank-tested with

similar good results but most clients prefer to keep their test data confidential which prevents the data publication.

3.2 BXI - Hysucat Seamodel

General Design

In view of the promising Hysucat-model test results the Bureau for Mechanical Engineering at the University of

Stellenbosch (BMI) sponsored the design and construction of

a first Hysucat prototype to be used as a seagoing manned

model in a well finished-off form as a pleasure or ski-boat

for offshore operation. Carrying capacity was requested to

comprise four persons and 300 kg of payload. A small cabin

was included for save and dry storage of instrumentation for

the envisaged sea tests. The design elaboration resulted in

a 5,65 in long craft with a full load displacement of 1250 kg when built in GRP material.

The craft was named

BMI-Hysucat. The photograph in Fig. 9 shows the hull from

beneath exposing the hydrofoil system.

The hull was built by "Ton cup Yachts" of Cape Town and the craft finished off by BMI at the University of Stellénbosch.

Tests

Prior to the sea tests of the BMI-Hysucat the twO pairs of

outboard engines to be used were tested, a pair of

35HP-Johnson's and 4OHP-Suzuki's _{The power characteristics and}

consumption of these two-stroke engines were determined in

the Stability Basin of the University by use of a series of

torque propellers and by torque strain gauge measurements.

The engines, were then. used in the same tuning-stagà on the

BMI-Hysucat in the sea tests.

The typical laboratory tested outboard characteristics _are

shown in Fig. 10, from which it becomes clear that the

outboard power rating differs from the shaft _power,

- 100 50 t P0 :1.01 bar rei .humld.65Z 1000 2000 3000- 4000 5000 6000 7000 Nmef II/minI

Fig.. 10 Outboard Engine Characteristics

especially of the American ôutboard engines _{which have a} much lower shaft output.

The specific consumptions of the twO-stroke _{engines are} relatively high (nearly double!) when compared to

four-stroke gasoline engines or Diesel engines, especially in the

medium speed range, which effects-. the Craft's

sea-consumptión strongly and in a negative way. For more details see Hoppe [4].

0.6 0.5 f LO E e o. s-o Motor i rated: 401f Motor 2 rat Cd 351f Power / / / -/ -/,

,/

30 t - 20 lo

J 3

Smooth water tests with speed, resistance and consumption

measurements were conducted with thrust measurements on the

outboard engine pivots. The outboard engine underwater

drive system ("leg")

drag was also measured in the sea

trials by removing one propeller and giving the craft a

third engine. _{The high speed "leg" drag coefficient was as}

expected with a drag coefficient of C _{0,5, based upon} cross-sectional area of the submerged parts (lower than

transom!) and including the cavitation plates. _{However, at}

low speeds in the turbulent wake, when the transom is not

fully ventilated, the "leg" drag was

much higher than

expected and aggravated the already undesirable high planing

craft hump resistance. The "leg" resistances of both

outboard engines constituted about 30 % of the total

resistance at top speed.

Using the laboratory outboard engine tests and the

measurements of the fuel flow by two VDO-fuel flow _meters and engine revolutions the propulsion power and specific consumption of the craft at sea is shown in Fig. il.

60 X 50 e C C w 40 o -o I-e Q3 f 20 I0 o o Po w. r spec. ecrisump. 5 IO 15 20 25 30 V Lknot J 0.2

Fig. 11 _{BMI-Hysucat Consumption and Power in Sea Test} The fuel consumption tests were further elaborated to

achieve a general comparison method, _{which is given by the}

"Craft Specific Fuel Consumption Ratio C " in liter of fuel

per km travelled and per 1 t of displacement. The results

with both engine types are given in Fig. 12 as a diagram of

C* over the speed and the Froude-displacement _{number FnV.}

-C X -X E En C o 'J Io

f.

I-a 0.8 0.6 0.4

I.00

t'

vop

_.p

JSuzuki ?'

flowmeter tests on sea

.1 V :1170 kg, LCG: 341

fi

o Jàhnson 35'smeasured fuel weight over

o Suzuki 40's dIstance on seä,. i Suzuki 40's roùgh sea

Suzuki 40's at Zeekolvlel with mild chop and Wiñd 10-15 kn,SE

'4

io 15 25 30

V5 I knót I

Fig. 12 BM1-Hysúcat Specific Fuel Consumption in. Sea Tests

The specific coñsumption .ratio is nearly constant over

the whole planing speed range with añ average value of. about 0,58. At hump speed (vh = 8 knot.) it increases to about

0,68. This speed is uneconomical and should be. prevented as cruising speed.

The propulsion overall coefficient P.C., based on propeller

shaft power reached 0,53 in the planing speed range and dropped to 0,47 at hump. speed.. . The P.C. contains the

outboard leg resistance The open efficiencies of the

propellers are around.0,70. . . .

-These resülts are in general agreement with the design data.

The Hysucat specific consumption ratio C compares well with

similar ratios of Deep-V-Monohulls which often have a value

of over C = 0,9 when driven by outboard engines. Craft'

with inboard systems aI four-stroke enqnee or especially

with Diesel engines can have much lower C values because of

the much better specific consumption of the engines The

DMI-Hysucat sea tests prove that the general design logic

was right and highlights some design aspects where further

improvements are possible. The BMI-Hysucat was designed to

carry only about 50 % of the displacement weight on the

foils at design speed This choice was applied as not to

offset stability reserves at high speeds too much in this

pilot-project The sea tests have shown that there was no

indication of any stability defect in the whole speed range

and also not in rough seas Therefore, it was anticipated

to design future craft with higher hydrofoil loads which

will reduce the resistance further. A hydrofoil load of 65

% seents possible after the latest modeltest results which

would reduce the resistance coefficient C of the Hysucat to

L = 0,12, which had been for the sea model C = 0,16

I .5 3 y o V O V o

Sea trials were conducted in False Bay off Gordonsbay, in.

the Atlantic Ocean off Hout Bay and in the sea off Knysna including many test series to establish the practical

functioning of the craft over a test. period öf a year.

Fig. 13 shows the BMI-Hysucat at sea.

In the. early tests only the Johnson 35 outboard engines were

used and .a top speed of 25 knot achieved. Surprisingly,

even in 35 ]ot headwinds the BMI-Hysucat could maintain it's 25 knot top speed.. .Short choppy waves were negotiated

very smoothly and comfortable and even when. "jumping" the

crest of a large. swell the boat re-entered relatively smoothly - the "knee bending" landing impact of usual

planing craft was completely absent. . With the Suzuki 40

outboard engines speeds over 30 knot could be achieved.

In large

steep swell waves it was tried to broach the

Hysucat but no broaching tendency could be traced. _Sharp

turns could be performed in strong waves with approaching crests. The boat runs very dry and no "green water" was shipped, also not at low speeds when the Hysucat is properly

trimméd (trim angle 1° to 1,5° at rest!).

The seakeeping and handling tests gave fully satisfying results and sorne

conditions had been so severe that

_a similar test with a conventional mono-hull is unthinkable.

The BMI-Hysucat was operated f br about a. year in the sea

around the Cape at various weather conditions from calm to

extreme rough seas and proved extremely sea-friendly, economical and survived any severe condition without _the

slightest default. It proved the Hysucat principle to be

fully acceptàble with the promised advantages of low propulsion power, low consumption and improved.seakeepi.ng.

r -.

4. DESIGN APPLICATIONS

4.1 Hysucat DeSigns

A nuiber of Hysucat prototypes have been developed over the

last years The BMI-Hysucat was the first prototype and

presents about the smallest craft for which the Hysucat

principie can be applied with practical advantage. About 40

craft were built by use of the same mould.

Systematical design invstigations show that for practical

sea speeds of 30 to 40 knòt craft with sizes between 5 m and

35 m and 1.2 t to 150 t displacement are possible with

considerable advantage against conventional craft.

Many different Hysucat designs were, conducted and updated with improved design data becoming available from the research project, which is also concerned with the

theoretical development necessary for the design including a

series of towing tank tests on three different hydrofoil profile shapes with 0,15 in chord and 0,70 m span in the

towing tank to investigate the hydrofoil surface effect

HYSUCAT I I JET

Fig. 14 BMI-Hysucat 11 Waterjet Version

Fig. 14 shows the outline of one version of the BMI-Hysucat

11 with waterjet propulsion which will run 35 knot with a

displacement of

A= 9,5

[t] and two Dieselengines with

175 kW each The Hysucat 11 propeller version can carry a

higher load (11,5 t) f ör a continuous top speed of 32 knot

due to the higher

overall propulsion èfficiency of the

propellers at this speed Further improvements for a

slightly smaller Hysucat 10 can be achieved by use of the Volvo-Duo-Prop Z-drive system which has a 1Ö

% tO 15

%

increased overall propulsion efficiency against the usual

mono-propeller version. Fuel consumption will be improved

-Fig. 15 Hysucat 18 in initial Sea Trials

The german group "Hysucat Engineering Germany" (HEG),

licensee to BMI, concentrated on larger craft development. In collaboration with BMI and HEG the shipyard "Technautic

Inter Trading Company" in Bangkok, Thailand produced the

largest Hysucat yet in 1986, an offshore Patrol Boat [8],

shown in Fig. 15. With a displacement of 35,6

t and

propulsion by two MWM Diesel engines of 2*627 KW (10 % overload in tropical rating) the Hysucat 18 runs 36 to 38

knots continuous. A lighter version with a displacement of

32 t will achieve well over 40 knots.

In comparison to the Deep-V-Monohull "Precision

Offshore 17", referenced in [9), which had been elected top

Australian powerboat 1986, the Hysucat with the same MWN

Diesels TB234 12 cylinder and a total propulsion power of 2 *688 KW shows a 60 % improvement. Both ships run 38 knot but the Hysucat carries a total displacement mass of 35,6 t

against the 22 t of the "Precision Offshore 17".

The considerable improvement due to the Hysucat principle, which was elaborated above in many tank model tests is here demonstrated in similar proportions by the comparison of two

well sized prototypes.

T-Craft development

The Cape Town based company T-Craft (Ltd) developed a 10 in

Harbour Patrol Craft after the design by "Bob van Niekerk"

of "Liebenberg and Stander", Cape Town in 1989. On request, one of these craft which was varied to an off-shore game-f ishing-boat with game-flybridge was converted to a Hysucat. The

craft was tested prior to the fitting of the hydrofoil

system after [1) and reached 23,5 knot with a displacement

of 8,2 t. The propulsion system consisted of two 185 kW

ADE-Diesel engines (Mercedes Benz derived) and Castoldi waterj ets.

After fitting of the hydrofOil system the craft reached 33

knot. without any other change to the boat. Later the

Castoldi waterjets were adapted to the higher speed of the Hysucat by a gear-ratio change and the Craft was able to run

a maximum speed of 37 knot.. The Hysucat principle showed.

it's potential also on this conversion. . All T-Craft police

craft are converted to Hysucat's at the present.

A. larger version of a 12 rn yacht by T-Craft followed in.

1990.. The yacht is equipped with twin Caterpillar Diesel

engines developing 300 kW and Levi-Surface-Drive systems

(LSD) and has reached a maximum speed of 42 knot in calm sea

conditions, 39 knot jn average waves. A variation of the

12 in yacht is equipped with IVECO Diesel engines and Castoldi watérjets and will be on the water soon. These

craft are in series production now. Fig. 16 shows aT-Craft

game-fishing Hysucat with Hamilton waterjets and the first

12 in T-Craft..

T-Craft has altered it's production program and produces now

only craft of

the twin-hull type with hydrofoil-support

which are marketed as Foil-Assisted-Catainarans.

In October 1991 the T-Craft 22 in Patrol Craft with hydrofoil

support after

(11,

named Coastguard T22l2 for air/sea

rescue, offshore environmental protection and policing, was

launched in Cape Town. The T22 displaces about 23 t j-n the

light, load and 28 t in the fully laden condition. On the

initial trial runs the T22 achieved well over 40 knots with

the two 12 V MTU 183 T92 Diesel engines of 2 * 735 kW and

Católdi

07 waterjets, see Fig. 17. In the Overload

condition with 40 passengers aboard it runs comfortably a

continuous speed of 36 knots in moderate seas T-Craft has

apparently contracted seven T22 Patrol/Rescue craft already

änd is designing a 22 in Ferry-Version on the same basic hull

configuration. More details are reported in (10) and (il].. A 36 in Luxury Yacht with symmetrical demi-hulls designed by Nigel Gee and Associates (NGA), England and equipped with a

hydrofoil-system after [1]

has been built by T-Craft

International in Cape Town and was delivered to the ownet

Sir David BrOwn in Monaco in June this year. The Fig. 18

shows the "Chief Flying Sun" on the. initial trial runs off

cape Tówn. This

type of craft isdesignated CATAFOIL.

The hydrofoil system design including f..lát water towing tank tests for the optimisation was carried out by BMI at the

University of Stellenbosch. The Yacht will be propelled by

waterjets and MWM Diesel engines developing 2 * 2000 kW f or spéeds of over 40 knots with 110 t displacement.

Seakeeping tests have been conducted at. the Wolf ston Unit

Towing Tank in England.:

5. CONCLUSIONS

The. Hysucat was developed to improve the asymmetrical

planing catamaran with it's superior seakeeping behavioúr in comparison to seagoing Deep-V-Plan.ing-Monohulls in view of

required propulsion power This gaul was reached in the

19

first Hysucat design. After several years of theoretical

and experimental development work the Hysucat has a superior

seakeeping property and hydrodynamic efficiency than the

Deep-V-Planing-Monohull and competes well with

High-Technology- Craft as Hydrofoil craft and Surface-Effect-Ships (SES).

The Hysucat is without deeply or sideways penetrating foil

systems and can be handled as any conventional ship. In extreme rough weather at reduced speed it has superior seakeeping over Deep-V-Planing hulls, Hydrofoil Craft and SES. The hydrofoil spanning the tunnel between the two deiui-hulls stiffens and strengthens the structure.

The Hysucat is built up of solid and approved elements of

the Márine Industry and standard high speed craft shipyards

are well equipped for the construction.

/

j - -

w

-- --,s-- -'

Fig. 16 10 m and 12 m T-Craft

Future development work is mainly concerned with the further

reduction of, the so called "hump resistance" which is of

special importance to Hysucats propelled by Diesel engines and fixed pitch propellers and for general patrol cráft for

improved cruising speed capability. _{Hull shape development}

calls, for further systematical towing-tank work combined

with hydrofoil development and continued theoretical

research work. Further optimisation seems possible in

special design applications and if continuous prototype data

2

icr

Fig. 17 22 ni T-Craft Foil-Assisted Catamaran

__m----Fig. 18 T-Craft's "Chief Flying Sun" Catafoil on trial

6. LITERATURE

El]

Hoppe, K.G. (1982), "Boats, Hydrofoil Supported

Catamaran", SA Patent 82/3503 and corresponding oversea

patents

DuCane, P. (1972), "High Speed Small Craft", David +

Charles, Newton AbbOtt

Hoppe, K.G. (1980) "The Hydrofoil Support. Catamaran",

Internal Report 1980-2, Mechanical Engineering Department, University of Stellenbosch

Hoppe, K.G. (1989) "The HYSUcAT Development", Internal Report 1989, Mechanical Engineering Department, University of Stellenbosch

[5)

Bsch y.

Den, F.F. (1974), "Comparative Tests on Four

Fast Motorboat Models", TNO, Report N1965, Delft

Sakic, V. (1982) "Approximate Determination

of the

Propulsive Power of Small Hydrofoil Craft"., High Speed

Surface Cràft, March .

Schuster, S., Schwanecke, H, (1965), "On Hydrofoils

Running Near a . Free Surface", .3rd Symposium, Naval

Hydrodynamics, High Performanáe Ships, Office of Naval

Research, Department of the Navy ACR-65

[8) Lopez, R.. (1987), "Thailands Marine erprôbt neues

Internationale Wehrrevue 2/1987 .

- (1987), _{"Powerboat 86 in Australian mit}

Deutz-MWM-Motoren", Schiff und Hafen, Heft 5, Hamburg

Van Niekerk, Bob, (1991), "Daring Dart", Power and Ski,

Cape Town, Sept./Oct. 1991.

[li] Bezuidenhout, N. (1991), "New Coastguard Craft