Date Author
Address
December 2006 Keuning, lA.
Delft University of Technology Ship Hydromechanics Laboratory
Mekeiweg 2, 26282 CD Deift
TU Deift
Deift University of Technológy
"Grinding the bow!' or "HOw to ¡mprove the Operability of fast monohulls"
by Keuning, ).A.
Report No. 1501-P 2006
Publication: Interñatloflal Shipbuilding Progress, Völume 53, Number 4, 2006, ISSN 0020-868X
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International Shipbuilding Progress
Mariné Technology Quatierly Editor-un-Chief RHM. Huijsmans Ship Hydromechanics and Structures DelftUnivershy of Technology Mekelweg 2 2628CD Do/ft The Netherlands Fax: +31 152781836
E-maiL R:H.M.HLJIjsmans @túdelft.nI
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DeiftUniversity of Technology
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E-mail: P.Naaijen.@ wbmt.tudelft.nl
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The journal international Shipbuildiig Progress was founded in 1;954 and is published quarterly. From 2000 the journal has also been published electronically Pubiications submitted to Interna tional Shipbuilding Progress should describe scientific work of high iAternationai standards,
ad-vancing subjects related to the field of Marine Technology such as conceptual design struc
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Editorial Board
H. Boonstra
Delft Univrslty of Technology
The Netherlands
A. Francescutto
University of Trieste, Italy
J.J. Jensen
Technical University of Denmark Lyngby, Denmark
JO. deKat
Marin, Wagenin gen The Netherlands
J.A. Keuning
Deift University of Technology The Netherlands
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lOS Press
Editorial
Dear readérs of International ShipbuIlding Progress,
For those of you who do not know me yet, let me introduce myself: I am Rene
Huijsmans, professor at the Ship Hycfromechanics and Structuressection at the Deift
University ofTechno1ogy The current Editor, Jo Pinkster, is retiring as from 1 No-vember 2006; he will step down and I will take over his position .as Editor-in-Chief of the journal. I would like to thank him for his contribution to the journal.
Scope of the ISP Journal
Throughout the years, the ISP journal has gained a strong hydro mechanical and strucl:ural character. However, in the current scòp of the journal, shipbuilding and
design are also mentioned. Readers working in thearea of shipdesign and ship
build-ing are also encouragedtosubmit manuscripts for publication in the journal.
Rene Huijsmans Editór-in-Chjef Head Section Ship Hydromechanics and Structures
Tecimical University Deffi
Deift, The Netherlands
International Shipbuilding Progress 53 (2006) 28 1-310 281 TOS Press
"Grinding the bow" or "How to improve the operability
of fast monohulls"
J.A. Keuning
Department of Ship Hydromechanjcs, Delft University of Technology, Deift, The Netherlands E-mail: J.A.Keuning@ tudelftnl
1. Introduction
Achieving a good combination of a high forward speed and an acceptable level of the wave induced motions and, more in particular, accelerations on board of a
ship sailing in a seaway has been proven to- be very difficult. "Tearing around" at high speed in waves puts a tremendous burden on both the people on board and on
the structure of the ship. Ingeneral this leads to reduced comfort and sometimes
even serious injuries and structural failures. Although the term "fast" is not exactly
described in -general, in thecontext of this article it wifi be considered that ships are
fast with speeds above Froude numbers based on waterline length of 0.6 to O.7,-from
which speed onwards hydrôdynamic lift starts to play a significant role.
In the continuing search for this combination of higl speed and comfort all kinds of so-called "advanced" marine vehicle concepts have been designed, evaluated, build and used. Each of these concepts however proved to have its particular ben-efits and shortcomings. Among these are: the Hydrofoil Boat (RIB), the Air Cushion Vehicle (ACV), the Surface Effect Ship (SES), the Small Water Plane Area Twin
Hull ship (SWATH), the Catamaran (CAT), the Wave Piercing Catamaran, theWing
In Ground (WIG) and various "variations on these themes".
The design philosophy behind these new concepts is generally aimed at attaining - high forward speed by -reducing the resistance. In general this is achieved by mini-mizing actual volume of displacement or wetted area of the hull at speed or both. At the same time attempts are made to minimize the motions in waves under speed by reducing the wave exciting forces and/or by adding active control devices.
All these concepts have reached a certain stage of perfection over the last decades. Compared to the relative "simple" monohull however all these more advanced con-cepts tend to be considerably more complicated and vulnerable and therefore often more expensive in both their construction and operation. So in particular in various military and patrol applications ship owners and operators still tend to favor the well established and extensivelyproven fast monobull concept.
282 J.A. Keuning /"Grinding the bow" or "How to improve the operability offasr monohulls"
The behavior in a seaway of the fast monohull however certainly needed serious attention and should be improved upon as much as possible. This has been the aim of many research projects and design studies carried out since the 1970's, spme even earlier. Focus on this research increased when these fast monohulls were going to
be more and more employed in "exposed areas", such as coastal waters and even
the open sea. The emphasis in the design process before that time (i.e. 1970) was
generally put on obtaining a hull with the highest forward speed with the lowest
possible resistance.
From these research projects it became evident that the behavior of fast ships in waveswas strongly nonlinear by nature. This makes applying "normal" ship motion calculation routines and analysis procedures limited applicable. Also the limiting
criteria for establishing the operability of these fast craft were found to be vastly
different from those used for low speed displacement ships. From full scale
observa-tions it was evident the most of the speed reduction applied in fast craft operaobserva-tions in waves was voluntary.
From all this research it turned out that the characteristics, that influenced the
motions of a fast hull in a seaway most, were:
the development of the nonlinear hydrodynamic lift on the hull and
the nonlinear wave exciting forces in particular at the forward half of the hull. The parameters which control these aspects of a fast monohull to a large extend are:
the above and below water geometry of the hull, the length to beam ratio,
the length to displacement ratio,
the sinkage and the Ñnning trim of the craft at speed and the longitudinal radius of gyration.
It also appeared that there was a serious "trade-off" when choosing these parameters for optimal seakeeping behavior versus the calm water resistance of the hull. There-fore a detailed knowledge of the influence of these parameters on both resistance and seakeeping is necessary to be able to optimize any fast craft design.
is m to as st in )n ig 'y a-us e: rs e-ìe ce of es [Is ce ge m
J.A. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 283
water resistance, the motions and the vertical accelerations in waves. In the follow-ing years Keunfollow-ing [6,7] extended the mathematical model for the heave and pitch motions of planing craft in regular waves, as presented by Zarnick [8] to a full
non-linear mathematiòal simulation model for the heave and pitch motions of an arbitrary
planing hull in irregular head or following waves in order to be able to analyze the nònlinear behavior of a planing. ship in more detail and to asses the operability of
these craft in a. seaway.
All these results have been used to optimiie the stifi water performance and the behavior in waves (and so the operability) of a fast (planing) monohull. This has lead to the introduction of the Enlarged Ship Concept in 1995 [9] which was followed by the introduction of the AXE Bow Concept in 2001 [12]. Both concepts proved to be feasible design concepts for improved hydrodynamic performance of the fast monohull.
In the following the philosophy and rationale behind these concepts will be ex-plained and results of research carried out highlighted. Finally an short overview will be presented of their present and future applications.
2. Definition of the problem
The challenge is to improve the operability in a seaway of the fast monohull with-out loosing too much in the area of calm water resistance and buildingcost.
To meet this challenge first considerable effort is put in a proper determination of which wave induced behavior of the fast monohull exactly limits the operability of the craft in a seaway when it is being used in a naval- or patrol-boat application.
In the commonly used operability analyses carried ¿ut for surface ships the op-erability in a particular operating area is determined using results of linear theory approach, i.e.: the response amplitude operators (RAO) of the motions under con-sideration are calculated, these RAO's are combined with the wave spectra derived from scatter diagrams and this yields the response of the ship in all those particu-lar seastates. Applying a set of limiting criteria for motions and/or accelerations the operability of the craft in that particular operational area may be obtained. To be ap-.plicable in the "linear environment" used in this procedure most limiting criteria are
formulated as significant motion values not to be exceeded.
For fast craft this procedure is not really applicable however, in particular when the
vertical accelerations are concerned. This is due to the strong non linearities in the
response of the ship to the incoming waves. It was shown that the limitingcriteria for safe operations should-be based on the actual distribution of the peaks and troughs of
284 J.A. Keuning / "Grinding the bow" or "How to improve the operability qffast monohulls"
This is by far a more time consuming procedure then the "linear" operability analyses
carried out using the RAO's.
A significant implication for the assessment of the operability of a fast ship proved to be the finding that the standard limiting criteria, as often used for other naval ves-sels, are actually not applicable. To determine the most important limiting criterion
or criteria for the operation of a fast ship in irregular waves an extensive series of
full-scale experiments have been carried out by the ShiphydromechathcsDepartment on board fast patrol boats and SAR vessels on the North Sea. A number of these ships have been instrumented and tested while performing their tasks under real circum-stances at sea by their professional crews during a large number of runs. Besides the environmental conditions the ship motions and accelerations as well as the
"throt-tie control" and the voluntary speed reduction, as applied by the crew, have been recorded. During all tests a measurement team of the Shiphydromechanics Depart-ment was on board to get their own impression of the circumstances, the behavior of the ship and the reactions of the crews. The ships used for these tests ranged in size from 14 to 45 meters length overall and speeds ranges from a top speed of 35 to
30 knots. Ail measurements and visual observations during these tests were recorded
and analyzed afterwards, including interviews with the crews and commanders about their findings, reactions and comments. Also the impressions and observations of the experienced members of the measurement teams formed a consistent part of the analysis of the results.
An important conclusion drawn from these studies was that:
Generally spoken all crews imposed a voluntary speed reduction at roughly the same conditions. It also showed clearly that the real measure for imposing a volun-tary speed reduction was not the prevailing magnitude of the signflcant amplitude of the motions or vertical accelerations at that time, but the occurrence of the high
peaks in particular in the vertical acceleration. The occurrence of "one big skim"
provoked a speed reduction by the crew just to "prevent it from happening again"
In fact such a reaction is more or less in line with
a well known more general aspect of human behavior, namely that most people are inclined to react to "ex-tremes" rather than to "averages'These findings are supported by other researchers working in the area of operabil-ity of fast ships. However, in very few reports on the operabiloperabil-ity assessment of fast craft the peaks in the vertical accelerations are explicitly used for the limiting
crite-rion. Most criteria used in these operability analyses, and which are usually stipulated
and supplied by ship owners and alike, are based on the so called "significant val-ues" of motions and accelerations. This appears tobe a striking discrepancy between theory and the real world.
This discrepancy may be very well explained by the lack of reliable nonlinear
calculation models in use for ship motiOn calculations. Motion calculations for ships under speed are most frequently carried out with the aid of some kind of linear strip theory based computer program, which have reached a certain level of excellence and applicability. They combine great ease of handling with short computational
s-. )fl 1-'n )S :1-ie t-In to Lit ie le 'h I" ,, rd ar ip ai
J.A. Keuning / "Grinding the bow" or "How to improve the operability offasr monohulls" 285
ratio significant and maximum
values
8
vertical
acceleration 4
mIs2 6 2 o 12.5 25 30deadrise in degrees
Fig. 1. The ratio between the significant and the maximum amplitude of the verticai acceleration as fune-don of the deadrise angle of the planing bottom.
time requirements, which make them ideally suited for operability analyses, in which
quite a few calculations have to be made. The biggest underlying assumption of
these linear theories however is the linear behavior of the system "ship moving in waves".
So this implies that, if the occurrence of peaks in motions and accelerations was
considered in- the formulation of these criteria, a known relation between the
signifi-cant values and the occurrence ofpeaks is supposed to exist. If the generally accepted assumption is adapted that thewave heights in a sea wave spectrum are Rayleigh dis-tributed this implies that the wave induced response amplitudes of the ship are also Rayleigh distributed, if so then a known relation between the "significant" values and for instance the "1/1000 percentage of occurrence" peaks does exist. By formu-lating limiting threshold values for the motion amplitudes expressed as significant values then also the allowable peaks are embedded in the criteria.
For strongly nonlinear systems however suçh a straight forward relation does not exist. This is clearly demonstrated in Fig. 1 [4]. In this graph the significant values of the vertical acceleration and the maximum (close to 1/1000 chance of occurrence) values all measured during towing tank tests are presented. These tests were carried
out with three almost similar hulls except for the changing deadrise angle of the
planing bottom. The relation between these two values is clearly strongly dependent on the deadrise angle of the hull and it increases from some factor of 2.5 for the high deadrise hull to a factor of around 5.5 for the hull with the lowest deadrise,
A similar conclusioti may be derived from the results plotted in Fig. 2 [15]. This figure contains data obtained during full scale measurements with a SAR boat from the Royal Dutch Lifeboat Institution (KNRM). The relation between the Root Mean Square (RMS) value of the vertical acceleration during a run of 20 minutes duration and the maximum observed in the same time trace is displayed for both the positive
E:1 significant
286 JA. Keuning / "Grinding the bow" or "Wow to improve the operabilityoffast monohulls" 60 40 20 O -20 O
RMS value of vert, acceleration near bow (mis2)
Fig. 2. The relation between the RMS values of the vertical accelerations in a particular test run and the maximum measured value in the same run.
and the negative peaks. The straight line represents ,the relation if a linear response of
the system is assumed. From these results it is obvious that the nonlinear behavior,
i.e. the deviation from the straight line (the Rayleigh distribution) increases with
increasing RMS values of the signals.
In general this implies that the shape of the distribution of the peaks of the vertical accelerations measured in the working area of the vessel under consideration is the most prominent measure for the operability of the vessel under consideration. For optimum operability the high amplitude peaks in the vertical acceleration signals
with the low freqiiency of occurrenceare the ones to be avoided as much as possible.
In optimizing a design even higher "average" or "significant" values are acceptable if this leads to lower peak values. This is demonstrated in Fig.3, a typical example of a distribution curve, showing frequency of occurrence versus amplitude of the signal.
In such a distribution curve line "A" therefore results in an improved operability
when compared to line "B", even though the significant value is higher.
The goal of improving the operability of a fast craft in a seaway is achieved by establishing the distributions of the vertical accelerations at the places on board of prime interest and minimizing at those points the extreme values in the motions and
accelerations. This calls for extensive towing t2nkmeasurements or simulations with
a nonlinear mathematical model. The number of computer simulations andior tank tests necessary for a design optimization may be minimized by saving on the number of environmental conditions and headings used in theprocess.
j
- - - - III 000-th level fo
mean of 0.1% highest y mean of 0.1% higiest
O negatieve max dL D Positive max duri
I .
)f r, h il ie )r Is if a 1. y y )f d h k
J.A. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 287
25 c"l U) E Cl)
0) 15
o
I-10 CU U)o
oVertical acceleration levels
100 50
20 10 5
2 1 .5 .2 .1Probability of Exceedance [%]
Fig. 3. Distribution of peaks and troughs in the vertical accelerations of a (almost) linear and a nonlinear system.
So optimization of the seakeeping behavior (operability) of a fast monohull is actually achieved by reducing the nonlinear behavior of thesystem as far as
mo-tions and in particular vertical acceleramo-tions are concerned. This implies reducing
the hydrodynamic lift and nonlinearwave exciting forces in particular in the fore ship. This should be achieved however without reducing the benefits of the concept too much, i.e. with respect to the resistance characteristics etc.
The way this optimization is achieved in the ESC and ABC designs is described in the following paragraphs. First a short description of the physics involved is pre-sented, followed by the philosophy of how to reduce this nonlinear behavior. This is worked out in the design concepts, which are then subjected to calculations and measurements and finally compared.
3. The hydrodynamic forces on planing hulls
The first step in describing the hydrodynanilc behavior of fast (planing)monohulls
is made by an analysis of the influence of the main design parameters, such as length to beam ratio, deadrise angle, displacement and LCG, on the calm water resistance of the hull. Because the running trim is also important for the vertical accelerations in waves both the sinkage and the running trim of the craft at speedare analyzed too.
This research was carried out in a number of steps by Gemtsma and Keuning
[2,3]. They extended the original Series 62 experiments as, carried out by Clement and Blount [4], with a large number of similar models but now with 19, 25 and 30
288 JA. Keuning / "Grinding the bow" or "Hou' to improve the operability of fast monohulls" 0.2 0.18 0.16 C.) w 0.12 01
I
0.04 0.02 oResistance versus deadrise and weight UB=3.1
ApNol2/37.0 deadrise=25 -O ApNoI2/3=7.0 deadrise=1 2.5 £ ApNoI2/3=5.5 deadrise=25 X ApNoI2/3= 5.5 deadrise=1 2.5 O 1 2 3 4
Volumetric Froude number
Fig. 4. Resistance curves of planing hulls with LB = 3.1 and different weights and deadrise angle of the planing bottom at the midship section.
degrees of deacirise of the planing bottom respectively. This extension became known
as the Deift Systematic Deadrise Series (DSDS) and the results have been used to derive an approximation method for the resistance, the sinkage and the trim ofan
arbitrary fast (planing) monohùll at forward speed.
A typical result from this method, of particular interest for the present study, is
presented in Figs 4, 5. Jiithis figüth
Vt6r resïtänce òftwò rñcidels with25 and 12.5 degrees of deadrise are compared for two different displacements and two different L/B ratios. From ti ese figures. it is obvious that the influence of the L/B ratio is strong and for the low L/B ratio (i.e. beamy) hulls the influence of the
deadrise angle and the displacement on the resistance is very pronounced, while for the high L/B ratio (i.e. slender) hulls this influence is very small. Also the high L/B ratio hulls show a substantially suppressed "hump" behavior, which is beneficial for
patrol boats, which mission profiles ask for operations in various speed regimes.
From the hump behavior of the LIB = 2 ship and its lower resistance at the highest speeds it may also be concluded that the hydrodynamic lift plays a much bigger role
with these ships when compared to the high(er) L/B ratio hulls. This is a known
phenomenon with planing hulls where the LIB ratio may be considered as inversely related to the aspect ratio of a wing analogue.
The formulations of the hydrodynamic forces acting on fast craft sailing inwaves
used in the present report are largely based on the mathematical model as first
pre-sented by Zarnick 18] and later further extended by amongst others by Keuning [6,7]. In the present report the formulations wifi be restricted to a short summary. The
he 'n to m is th ie B Jr s. st le 'n [y 0.2 0.18 0.16 0.14 0.12 'ft 0.1 0.08 Q a 0.06 q) 0.04 0.02
JA. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 289
Resistance versus deadrise and weight LIB=7.O
ApNol2/3=7.0 deadrise=25 D ApNoI2/3=7.0 deadrise=1 2.5 £ ApNol2/3=5.5 deadrise=25 x ApNol2/3=5.5 deadrise=1 2.5 O O 1 2 3 4
Volumetric Froude number
Fig. 5. Resistance curves of planing hulls with L/B = 7.0 and different weights and deadrise angle of the planing bottom at the midship section.
The development of both the hydrostatic and hydrodynamic lift forces on a fast moving ship is described by making use of a sthp theory type approach. Dividing the ship in an arbitrary number of segments along its length (strips) the force on each of the segments may be considered to be constituted of a hydrostatic component related to the displaced water, a dynamic component related to the change of momentum of the incoming fluid and a viscous part, i.e.:
=
(mav) + Cdc pbv2 - abfpgA cos q,in which:
ma = added mass of the strip,
y = vertical velocity of the strip,
Cd = cross flow drag coefficient,
b = instantaneous half beam of the section,
abf buoyancy correction coefficient,
A = instantaneous submerged sectional area, p = specific density,
g = acceleration due to gravity,
and u and y are the velocity components along the length of the hull resulting from
the combination of the forward speed, the heave and pitch motion and the wave
orbital velocities, and me be expressed as:
290 J.A. Keuningl "Grinding the bow" oi "Howto improve the operability offasi monohulls' V = ±cgSfl8
(cg w)cos8
-in which: Xcg = forward speed, Zcg = vertical velocity, e = pitch velocity,Wz = vertical orbital velocity component.
Elaboration of these expressions yields for the vertical force on each of the sections: I dv dma dv dma
2
8F
=
ma
V dt + urna + UV d + Cd0bv cos 8 - abfpgA. From these expressions it may be seen that for the hydrodynamic lift component the added mass and its distribution over the length as well as the change in time playanimportant role.
For the determination of the hycirodynamic lift the change of the added mass of
the cross section in time is of prime importance.In the present approach the
determi-nation of the sectional added mass is carried out considering it to be directly related to the instantaneous maximum submerged maximum beam of the section under
conS-sideration, which is additionally corrected for the "pile-up" of the water in the dry chine sections. The expression for added mass following Wagner's approach then
reads:
ma = :p7rb2ka,
in which ka is a coefficient, which may be determined for each section and which is dependent on the beam to draft ratio and the deadrise angle. The magnitude of and ka are determined separately in the steady state equilibrium condition and considered constant also for the motions inwaves.
Due to the fact that in a nonlinear approach the relative motion of the ship with respect to the disturbed water surface is no longer considered to be small, the change
of shape of the actual submerged part of the cross section is taken into account. By doing so the change in added mass in time, needed in the formulation of the
hydrodynamic lift, is taken into account. In the present approach the added mass of each section of the fast ship is considered to bé frequency independent. On the
other hand the added mass is taken to be dependent on the actual momentaneous
J.A. Keuning / "Grinding the bow" or "How to improve the operabiliíy offast monohulls" 291
The cross flow drag term is determined using the instantaneous value of the normal
velocity component on each of the sections. The cross flow drag coefficient Cd0 is determined using the work of Shuford for V shaped sections and is:
Cd0 = 1.30 cos /3 in which: /3 = the deadrise angle of the sections.
In general it is found that this cross flow drag is of minor importance when compared
with the other forces involved.
Due to the dynamic lift and the flow separation over at least a part of the chine's and the entire transom the buoyancy force, which is determined supposing hydro-static pressure distribution, needs a correction. The buoyancy related lift therefore is corrected by a correction coefficient. This correction coefficient is abf and in the present approach this abf is assumed to be the same for all sections along the length of the ship were displacement of water is present.
In the computer code FASTSHIP developed by the Dem Shiphydromechanics
De-partment for the calculation of the heave and pitch motions of fast ships in irregular waves, see [7], the values of ka and abf are determined from the equilibrium con-dition of the craft at speed m calm water (no waves). For this particular concon-dition the running trim (pitch) and the sinkage (heave) of the ship are determined from the
results of the Dem Systematic DeàdÏie Series (DSDS), see [3]. Combining these
results with the forces calculated in the equations of motions the unknowns can be solved.
One other source for the nonlinear behavior of the fast monohull in waves may be found in the wave exciting forces. These originate from the large relative
mo-tions that these craft perform with respect to the incoming waves. From the research as reported by Keuning [7] it was revealed that the wave exciting forces on a fast monohull sailing in waves are dominated by the nonlinear Froude Kriloff
compo-nent. This is an important conclusion when these nonlinear wave-exciting forcesare to be calculated in a time domain solution, in which no frequency dependency can be
accounted for. This nonlinear Froude Kriloff force is calculated by integration of the dynamic pressure in the undisturbed incoming wave over the actual momentaneous submerged area of the hull whilst performing large amplitude relative motionswith respect to the disturbed water surface. For this calculation the full geometry of the hull from keel to deck is being used. The expression used yields:
FL = 2pgyç - pgkAç,
in which:FL = Froude Kriloff force on section, p = specific density of water,
Yw = momentaneous beam section on the waterline (time dependent),
ç wave height (time dependent), k = wave number,
292 l.A. Keuning / "Grinthng the bow" or "How to improve the operabilit- offast monohulls"
4. The philosophy behind the Enlarged Ship Concept
Resulting from all the above-mentioned data and considerations one possible way to improve the seakeeping behavior of a fast monohull is by applying what has be-come known as the "Enlarged Ship Concept" (ESC) [9].
The ESC is based on the observation that most vessels are too much restricted in length by the supposed linear relationship between length and building cost. This has in general a negative influence on the performance of the craft. Increasing the length has a beneficial effect on performance and more in particular with fast ships, all in line with the goal defined in the previous chapters of this report.
So in this ESC concept the original design (the "base" boat if applicable) is in-creased in length considerably, say by 2(1-50%, without making any change on the other main dimensions, such as beam, depth etc, and the also making no change in the functionality of the ship. This implies that a significant amount of "void space" will be introduced in the design. Also, since the functions or "payload" of the ship remains unchanged, the accommodation of the ship wifi stay the same in volume and dimensions (i.e. length). The "enlargement" or "lengthening" of the ship will take place in particular in the fore part of the hull. This results in a relatively more afterwards position of the prime working and living areas on board the ship, i.e. into the region along the length of the ship with normally -reduced vertical motions and accelerations. More in general it implies that by application of the ESC a more opti-mal position along the length of the ship of the prime functional areas on board may be found.
As a result of all this
the Length to Beam ratio of the ship wifi be increased, the Length to Displacement ratio wifi increase also, the Longitudinal radius of gyration Iyy (pitch) is reduced, and the Flare at the Bow is decreased.
All this is quite favorable for the hydrodynarnic behavior of the design. Another large
advantage of applying the ESC concept is that
the "void space" becomes available, in particular in the fore part of the ship, to modify the bow sections without inflicting any interior demand for space. This makes it possible to reshape these bow section purely from a hydrodynamic point of view, i.e. to
minimize the wave exciting forces and
minimize the hydmdynamic 4ft, in particular in the bow section of the ship.
This may be achieved by following the lines as described in the previous section regarding volume distribution and flare in these sections.
J.A. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 293
a marginal increment of the building cost of the ship or no increment at all,
because, in principle, only an empty part of the hull is added to the original
design.
S. The designs
For the study in the behavior of the ESC cooperation was sought with DAMEN
SHIPYARDS at Gorinchem, the Netherlands. They supplied us with all the necessary
data of their successful design the Stan Patrol 2600. From this design numerous ships have been built among others for the Hong Kong Police and the US Coast
Guard. This Stan Patrol 2600 design has now been used as the "base boat" design to demonstrate the the possible achievements with the application of the Enlarged Ship Concept.
Three alternative designs have been designed following the lines of the Enlarged Ship Concept:
s The first two alternatives are created by lengthening the original design by in-crçasing the station spacing This yields an enlargement of the overall length of the vessel with 35% and 58% respectively. The "new" designsare referred to as the "3500", with an overall length of 35meters., and the "4100", with an overall length of 41 meters.
s In addition an third design alternative has been developed using the "4100" as a starting point but now applying all other (hydrodynaniic) possibilities of the ESC, i.e. the bow modifications. This design with a highly different bow shape is further referred to as the "TUD 4100".
With regard to the engineering of these alternatives the expertise of DAMEN SHIP-YARDS has been used. The increase in structuralweight of thealternatives was com-puted via the weight data of the base boat design, adding additional hull plating and stiffeners and adjusting it to the change in hull dimensions. The new overall weight and the position of the structure's center of gravity as well as the radii of gyration have been recalculated. Using the calculation procedure as obtained from the Deift Systematic Deadrise Series (DSDS [3]) for each of the designs the optimal position of the center of gravity was calculated for obtaining minimalresistance and optimiz-ing the runnoptimiz-ing trim. The designs were adapted accordoptimiz-ingly for their machinery and tank layout to yield these positions.
Since the idea behind the ESC is equal payload for all alternatives it stands to
From the results obtained from extensive research on the nonlinear behavior of fast monohulls, [6,7], it became evident that the most important components con-tributiñg to the nonlinear behavior are the nonlinear wave exciting Froude Kriloff forces and the nonlinear hydrodyninnic lift. So minimizing these forces gliould lead to the desired reduction of the extreme peaks in the vertical accelerations.
The nonlinear Froude Kriloff force is found by integrating the hydrodynamic
pres-sure in the undisturbed wave over the actual momentaneous submerged volume of the hull whilst performing non small relative motions with respect to the wàves.
Using the Von Karman theory of the penetrating wedge for the assessment of the hydrodynamic lift it becomes obvious that minimizing this lift calls for minimizing the change in waterline beam of the section whilst thé ship is heaving and pitching.
Both reductions are most important mthe bow sections of the ship.
By comparing the body plans of the "3500" with the "TUD 4100" it is immediately obvious how the improvement in seakeeping behavior by these above mentioned bow
shape modification has been achieved:
Minimizing the nonlinear behaviour by minimizing the nonlinear
hydrody-nainic lift force and the nonlinear wave exciting force in the bow sections leads to minimizing the change (in time) of the added mass of the bow sections while performing large relative motions which sub- and emerge these sections and high forward speed due to the non small relative motions with respect to the in-coming waves. This implies small change in sectional (wetted) beam for these
sections.
The deck-submergence and bottom-emergence should be avoided as much as
possible. This leads to increasing the section depth and the sectional freeboard as much as feasible, while at the same time maintaining reserve buoyancy in the
bow.
The nonlinear Froude Kriloff component of the wave exciting forces is mini-mized by reducing the change in submerged volume of the sections whilst per-forming large relative motions with respect to the incoming waves.
d
C C
F 294 J.A. Keuning / 'Grinding the bow" or 'How to improve the operability offast monohulls"
Table i
Principal dimensions of the designs
DESIGN Base 2600 ESC 3500 ESC 4100 TUD 4100
f I f y y e d I-e LS
d
1-r-JA. Keuning / "Grinding the bow" or "How to improve the operability offasr monohulls" 295
1.00 L
1.58 L
1.58 L + Bow Shape
Fig. 6. General plans of the Base Boat, the EnlargedShips and the TTJD 4100.
All this leads to:
little flare in the bow sections,
narrowing the waterline in the bow sections, increasing the waterline length,
as little as possible change in volume in the bow so almost vertical sides both below and above the calm water waterline,
an increased sheer (reserve buoyancy and "spring" constànt) and
a deep forefoot.
The absolute magnitudes of the changes in sheer, volume and flair etc. have been determined using the nonlinear mathematical model for the heave and pitch motions of a fast monohull in waves as described by Keuning [7]. The magnitude of these changes was also restricted by some practical aspects as well as by "user imposed"
296 JA.Keuning / "Grinding the bow" or "How to improve the operabi1ix offast monohulls"
DEcL
j30
SPRAYk
Fig. 7. The lines plan of the "3500" and the TOD 4100 with modified bow.
6. The comparison between the designs
hi order to be able to compare the various designs on their respective (hydrody-narnic) merits a considerable amount of calculations and towing tank measurements have been carried out.
To establish the calm water resistance, the sinkage and the running trim of each
craft at speed use has been made of the approximation method derived from the results of the Deift Systematic Deadrise Series. The results of these calculations
have been validated with the results obtained from measurements in the towing tank of the Deift Shiphydromechanics Department obtained fromtests with models of the respective design variations.
An operability analysis following the traditional (linear) "route" has been carried
out for all designs in a typical North Sea environment using an "all year" wave scatter
diagram as presented in Ocean Wave Statistics. The operability of the designs has
been assessed by making use of the limiting criteria as formulated by the Dutch
National Authorities. The necessary heave- and pitch ResponseAmplitude Operators (RAO's) for this assessment have been obtained from ship motion calculations based on the so-called ordinary linear strip theory using the computer code SEAWAY, as described [16].
The nonlinear behavior of the designs in a number of different wave spectra
has been calculated using the nonlinear mathematical model as described by Keun-ing [4]. For these calculations use has been made of thecomputer code FASTSI{IP,
based on this nonlinear mathematical model, as developed by the Shiphydromechan-ics Department of the Dem University. The results of these calculations have been validated using the results of extensive towing tank measurements with the models
y-.ts ris ik er as rs as ra ri-p,
n-JA. Keuning / "Grinding the bow" or "How to improve the operabiliiy offast monohulls" 297
in a number. of different wave spectra. Four wave spectra have been selected repre-senting frequently met conditions at the NorthSea and in the water around the Dutch Caribbean and a more extreme condition, i.e.:
T = 5.3 sec.
and H113 = 1.25 m.T = 8.4 sec.
and H113 = 2.95 m.T=5.9sec.
andH113=1.29m.
T = 10.4 sec.
and E31/3 = 3.96 m.Special emphasis has been put on the distributions of peaks and troughs of the ver-tical acceleration signals. All the simulations have been carried out for a full-scale duration of half an hour.
Finally also an assessment of the building costs of the various designs has been
made with the aid of the data on this subject kindly provided to us by DAMEN
SHIPYARDS. For these assessments the real live data of the Stan Patrol 2600 were used as a starting point. The operational costs of all design alternatives have been considered for a scenario of a ten year economic life, sailing six hours a day at full
speed, seven days in a week for 48 weeks in a year and crewed by five persons (three
shifts per 24 hours).
7. The results
The results of these calculations and measurements wifi only be summarized here, a more detailed presentation may be found in the referencedreports.
The results of the weight and center of gravity calculations have already been pre-sented in Table 1. As may be concluded from these results the increase in overall
weight of such a craft as a patrol boat by application of the Enlarged Ship
Con-cept is only marginal, i.e. only 7% with an enlargement of 38% and 14.5% with an enlargement of 58%! The draught decreases and in particular the transverse stabil-ity increases due to the fact that the transverse moment of inertia of the waterline increases linear with length and the displaced water only increases with a fraction.
As a result of this some very important hull parameters have been changed for the
better, i.e. the Waterline length (and so the Froude numbers), the Length I Beam ratio
and the Loading factor: A/z2/3.
From the structural analysis it was found that the longitudinal radii of gyration of these fast patrol boats are considerably smaller than generally assumed. In addition the radius of the enlarged ships is even further reduced, which has been foreseen.
The effect of these changes in hull parameters is clearly demonstrated when con-sidering the results for the cairn water resistance, the sinkage and the running trim of the various designs. Both the calculated and the measured results are presented
in Figs 8, 9 and 10. In general the results ofthe calculations using the DSDS data
298 J.A. Keuning / "Grinding the bow" or "How to improve the operabi1i' offast monohulls" 0.8 0 -0.2 10 6 2 -2
Vessel rise of COG as a function of vessel speed
2600
-
--O + 3500 - 4100 TUD4100 2600 model results 3500 model results TUD4100 model results/
/
/
+---
-ò-
z -2600 3500--
4100 TUD4IOO 2800 model results 3500 model results TUD4loOmodetresutts --O + O 10 20 30 40Vessel speed (knots)
Fig. 8. Sin1age as function of speed for the four designs.
Vessel trim as a function of vessel speed
10 20 30 40
Vessel speed (knots)
Fig. 9. Trim as function of speed for the four designs.
lower compared to the base boat. The 58% enlarged ship has almost the same resis-tance at this speed. This behavior is probably due to the large increment iñ wetted surface of the hull (and so viscous resistance), which compensates for the reduction in wave making and induced resistance resulting from the high LIB. The enlarged
JA. Keuning / "Grinding the bow" or "How to improve the operabilüy offast monohulls" 299 20x105 15x105 10x10' 0. 5x105 0
Vessel resistance as a function of vessel speed
2600
7
-- 3500
-- . 4100 -- TUO4100 A 2600 model results 0 3500 model results i+ TUO4l0ømodelresults7
Ì'-y1-,/v
20 30 40- Vessel speed (knots)
Fig. 10. Calm water resistance of the four designs.
designs also show a considerable less pronounced "hump" in the resistance curve, which is a favorable aspect for patrol boat type designs often having quite signif-icantly separated top- and cruising-speeds. The development of hydrodynamic lift with the enlarged vessels is also less, as may be seen from the data on the sinkage and the running trim of these designs when compared to the base boat. The resis-tance, trim and sin.kage data for the "TU]) 4100" differ not significantly from the data obtained for the "4100".
The results of the towing tank measurements in these waves with the models
showed that the differences in heave motion between the various designs were only small. The differences in pitch are somewhat larger and favoring the enlarged de-signs. From these tests it is immediately obvious that the "TLTD 4100" has
signifi-cantly lower values for the peaks of the vertical accelerations in the wheelhouse in all
conditions tested, even though the differences between the significant values under the same conditions are much more marginal.
When the results of the various designs are compared using the fore mentioned criteria regarding the occurrence of high peaks in the vertical accelerations and the associated voluntary speed reduction is concerned the differences become more
pro-nounced.
For good operability in a seaway the high peaks should be avoided as much as
300 J.A. Keuning / "Grinding the bow' or "flow to improve the operabilit of frist monohulls"
25
4rn-- llJD4I
25 I ProbabWIV of ExosodonosI%I
Fig. 11. Comparison of distributions of the peaks and troughs in the vertical accelerations at the bow for the "2600", "3500" and "TTJD 4100".
line (i.e. the Rayleigh distribution) originates from the nonlinearity of the system.
Obviously the TUD 4100 has the least nonlinear behavior and in that respect the
modifications applied turn out to be successful.
From this plot it is obvious that, considering a given "threshold" value of allowable
peak values for the vertical acceleràtions, these are rather more frequently
encoun-tered in the case of the "3500".and even much more frequent so with the "2600"
when compared with the "TUD 4100". In particular the more pronounced nonlinear behavior of the "3500" and the "2600" is clearly demonstrated by these plots. From these figures the ratio between the magnitude of the significant value (at roughly 13.5% probability of exceedance) and the maximum measuredat say 0.3% probabil-ity of exceedance is shown to be strongly dependent on the nonlinear behavior and so on the particular design.
For all the designs also an economical analysis has been made. An estimate of the building costs of the different design alternatives has been made with the assistance of DAMEN SHIPYARDS. These estimates were made using the original building
cost of the Stan Patrol 2600 (the base boat) of which all the actualcosts involved
were known. These were corrected for the changes in the calculated steel weight, the extra stiffeners, the extra welding, the cleaning, preparation aridpainting of these
extra parts, additional installations costs, etc, etc. The final differences in the building
JA. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 301 Table 2
Comparison four designs on costs, efficiency and operability on North Sea.
1.8 1.6 1.4 1.2 I I 0.8 0.6 0.4 0.2 o 2600 3300 4000
From these results it may be concluded that there is a rather low increase in
build-mg costs of the vessels according to the Enlarged Ship Concept with a order of
magnitude of approximately 3% er 25% increase in vessel length. Considering the large gains made in actual operability withthe enlarged vessels compared to the base boat this increase in costs is highly justifiable.
8. The application of the ESC
The results of this initial study led the Royal Netherlands Navy to the adoption of this Enlarged Ship Concept for their new design of three Coast Guard Cutters for the Dutch Caribbean. They specifically asked in the tendering procedure for these ships for a "normal" design, following the "traditional" design path and for another design according to the "Enlarged Ship Concept". This challenge was taken on by DAMEN SHIPYARDS, who designed these two ships, applying in the design following the
ESC the knowledge and know how gained so far by the Shiphydromechanics
Depart-ment of the Deift University of Technology. In comparing the designs in that stage the benefits of the Enlarged version were so significant that the Royal Netherlands Navy choose the Enlarged design as the new Coast Guard Cutters to be build for the Dutch Caribbean.
The "traditional" design that sufficed the specifications was35 meters length
over-all and the Enlarged version was 41 meter length overover-all. The main dimensions are
presented in the Table 3. A general arrangement of the Enlarged version, which
be-came later known in the DAMEN SHIPYARDS product range as the "SPa 4207", is presented in Fig. 13.
As may be seen from this data the "enlargement" is about 25%. The suggested "Void Space" is not exactly accomplished as formulated in the design philosophy.
r
I
302 J.A. Keuning / "Grinding the bow" or "flow to improve the operbi1izy offasi monohulls'
Table 3
Main particulars of the "Stan Patrol 4207"
Beam 7.11 m Draft 2.52 m Depth 3.77 m Speed 27 kn Displacement ca 200 tons Power ca 4100 kW
Fig. 12. Tle Stan Pairol 4207 of the UK Customs the "VALIANT".
Fig. 13. General arrangement Stan Patrol 4207.
42.80 m
JA. Keuning I "Grinding the bow" or "How to improve the operability offcit monohulls" 303
The reason for this is that people feared that truly void spaces on board these ships
would in reality very soon be used for storage or other purposes and so disrupting the
idea behind the concept. Therefore itwas decided to use a slightly different approach
for these void spaces in which this extra and unused space was used to generate more
space for all other compartments, in particular engine room and auxiliary spaces. No
extra weight was put on board! In the end it turned out that this approach had a
favorable effeçt on the fitting out process of the ship (and so on the building costs) because now more room was ävailable to the engineers to carry out their jobs. The same wifi undoubtedly be true for the maintenance.
At the time of writing quite a few of these designs (about 18) have been sold for
various patrol tasks all over the world. A total of 16 ships at present are in full service already and so for a considerable period of time. Feed back from the users and owners
learns that they fully "live up to the expectations". The predicted improvements in behavior are fully achieved and both their crews and their owners are very satisfied with their performance.
9. Further improvements: The AXE Bow Còncept
The design philosophy behind the Enlarged Ship Concept is brought even further by the introduction of the AXE Bow Concept, Keuning e.a. [11,12].
Here the minimization of the nonlinear hydrodynamic lift in the fore body of the ship as well as a further reduction of the nonlinear wave exciting forces is further achieved by taking the modifications more to the extreme. So the design now
fea-tures:
an extremely sharp bow with no flare in the sections at all, a very small waterline beam in the bow sections,
an almost vertical sidewall in the fore ship, both above and below the waterline,
a considerably increased sheer towards the bow and
a downwards sloping bottom centerline forward of the midship, which increases the draft at the forward sections with the maximum at the forward perpendicular.
It should be strongly emphasized that this kind of shape is only possible when first applying the Enlarged Ship Concept design, i.e. creating thespace and length needed for this "thorough" shape modification.
The amount of increment of draft forward and the increase in sheer as well as the
amount of volume and it's vertical distribution in the bow sections needed to optimize
the behavior in waves is determined using an iterative procedure with the nonlinear motion calculation code FASTSHIP as described earlier. Special care has been taken
to achieve the same reserve buoyancy and pitch restoring moment as with the original
304 J.A. Keuning / "Grinding the bow" or "How to improve the operability offast nionohulls" -A
--p.- --'-------.---
-
-u
Fig. 14. Lines of the Enlarged design according to the AXE Bow Concept.
Fig. 15. Rendering of the hull accordingto the AXE Bow ConcepL
The shape of this AXE Bow Concept when applied on the TUD 4100 design is depicted in Fig. 15 and the lines in Fig. 14.
In order to be able to asses the merits of this new 'shape numerous calculations
have been carried out with the code FASTSHIP all of which showed considerable improvement of the behavior in head waves when compared to the ESC design. To check on these results it was decided to carry out a series of experiments in irregu-lar head seas in the towing tank of the Deffi Shiphydromechanics Laboratory. These tests have been carried out with the original ESC design without any bow modifica-tion, the TUD 4100 with bow modifications and the AXE 4100, featuring the AXE Bow. Similar conditions were used during the tests as in the previous ones. A typical result is presented in the Fig. 16.
Although not all results are presented here all showed the same trend: a consid-erable reduction in the extremes. Although the absolute values are smaller in the wheethouse the reduction in percentage is quite similarto those at the bow. It is obvi-ous thät a much more "linear" behavior of the AXE Bow Concept has been achieved when compared with the other two designs. The improvement over the TUD 4100 is
very significant not even to mention the improvement over the IESC with the
conven-tional bow!
J.A. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 305 140 120 loo 80 60 40 20 o 5° 20 10 Pe(X) (%)
Fig. 16. Comparison of the distribution of the peaks in the vertical accelerations at the bow of the "ESC 4100" (Conventional Bow), the "TTJD 4100" (Improved Bow) and the "AXE Bow".
Another aspect of the MOE Bow Concept had to be investigated because from the onset it caused concern; i.e. the possible extra sensitivity of the design with respect to broaching in stem quartering or followingwaves due to its bow shape.
First a extensive series of simulations have been carried out with the computer code FREDYN as developed by MARIN in Wageningen, The Netherlands and de-scribed [13,14]. The code is based on a nonlinear strip theory based mathematical model in which linear and nonlinear potential flow forces are combined with ma-neuvering and viscous drag forces. The non potential force contributions are of a nonlinear nature and bas. The force contributions taken into account are:
Froude Kriloff forces (nonlinear);
Wave radiation (linear);
Diffraction (linear);
Viscous and maneuvering forces (nonlinear); Propeller thrust and hull resistance;
Appendages, rudders, skegs; Wind forces (nonlinear).
In this model also the nonlinear Froude Kriloff forcesare the main contribution to the wave exciting forces. The viscous forces include roll damping due to hull and bilge keels, wave induced drag due to wave orbital velocities and nonlinear maneuvering derivatives with empirically determined coefficients.
From the simulations carried Out with FREDYN no significant differences
be-tween the designs with respect to their behavior in following, stern quartering and
5 2 1 05 .2
o
o
o
Negative vertical acceleration Bow
Seastate 5
ESC 411
TUD41a
306 J.A. Keuning / "Grinding the bow' or "How to improve the operabilityoffasrinonohulis 18 16 14 ' 12 0 lo o 8 6 U) 4 2 o 290 300 310 320 330 Wavedirection (deg) 340 --- AXE Bow ----TUD4lOO
Fig. 17. SignifIcant Double Amplitudes roll for TUD 4100 and the AXE Bow in stern quartering seas in H3 =2.5mandV5 =20knots.
beam waves was found and none of the designs performed anything like, a broach in the conditions investigated. It was found however that the roll and yaw motion of the AXE Bow Concept were somewhat larger than with the others, but no reason for
concern.
To investigate this following wave behavior further it was decided to carry out a series of comparative tests with a model according to the lines of the TLJD 4100and
a model according to the AXE Bow Concept. These tests were carried out in thenew
SMB of MARIN at Wageningen. These new designs were larger, i.e. 55 meter length
overall and had a significant larger speed range, i.e. orward speed ranged from 20
to50knots.
The models used in this experiment were equipped with two water jets and two skegs at the transom for directional stability. The skegs of the design according tó
the lines of the TUD 4100 had a skeg area of 2% of the lateral area and the skegs of the AXE Bow 3% (in total).
The tests have been carried out with 20, 35 and 50 knots forward speed, butmostly the results with 20 knots are presented here because this was the worst condition due to the low encounter frequency between the waves and the (moving) ship. The tests
were carried out in irregular waves characterized by a peak period of T
= 7.8
seconds and a significant wave height of H113 2.5 meters.
The significant values of the roll and yaw motions are presented first. From these
graphs it is obvious that this "average" roll angle in these conditions is not
dis-turbingly large and that more in particular there is no significant difference betweeñ the more conventional bow and the Axe bow. Also it should be noted that for both designs a marginal change in heading wifi lead to a very large reduction in roll,an
operational aspect to consider when assessing the performance of various designs in these conditions.
)
J.A. Keuning / "Grinding the bow" or "How to improve the operabiliiy offast monohulls" 307
o 290 300 310 320 330 45 40 35 9; 30 a 25 a >- 20 X a
2 15
10 5 Wavedirectlon (deg)Fig. 18. Maximum roll angle of the TUD 4100 and AXE Bow in stern quartering seas with H8 = 2.5 m
and V3 = 20 knots.
o
290 300 310 320 330 Wave direction (deg)
Fig. 19. Maximum yaw angle of the TUD 4100 and the AXE Bow in stern quartering seas with H3 = 2.5 m and V3 =20 knots.
dangerous roll angles have occurred during these experiments and once again the differences between the two designs are marginal.
Also the yaw angles occurring during these following sea tests have been com-pared. In the next figure the maximum yaw angles measured during the entire
ex-periment duration are presented as function of the wave direction for both designs.
The A) Bow design again has a larger maximum yaw angle the difference being largest at 300 degrees. Here the difference mounts to 10 degrees at most and for the other wave directions the differences between the two designs are again marginal.
308 JA. Keuning / "Grinding the bow r or "How to improve the operability offast mono hulls" 25 20 o 0 15 10 5 AXEBow liJO 4100 TIJD4IOO AXEBow L TUD 4100
Fig. 20. Maximum roll and Significant Double Amplitude for the TUD 4100 and the AXE Bow at V8 =50 knots and FI8 = 2.5 m.
Similar results were found for the forward speed óf 50 knots. For this condition only one typical result will be shown here in Fig. 20. In this figure both the values
of the maximum roll angle ¿and the significant double roll amplitudeare presented in the same wave conditions and the same headings.
So the overall conclusion from these experiments was that no serious tendency to broaching did exist and that the differences between the two designs were marginal.
10. Conclusions
From all research projects óf which thrltsaresurnrnarized here on the
op-timization of the seakeeping behavior of fast monohulls the following conclusions may be derived:
With respect to resistance, motions and acceleration levels on board fast ships much may be gained from proper hydrodynamic design.
Fast ships react strongly nonlinear to the incoming waves in particular when vertical accelerations are concerned.
Applying the correct limiting criteria for the safe and comfortable operation
of the fast ship is crucial in the optimization. These limiting criteria should be based on the extremes of motions and accelerations and not on their averages. Limiting these extremes wifi improve operability and limit voluntary speed re-duction by the crew.
In this respect it is of prime importance to reduce the dominating forces such as the nonlinear Froude Kriloff wave exciting forces and the hydrodynan-iic lift force in particular in the forward sections of the ship.
Application of the Enlarged Ship Concept improves the operability with 35 to 50 percent iii typical North Sea conditions when compared to a non optimized design.
.
AXE BOWh
o d
JA. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls" 309
Fig. 21. First build' ship according to AXE Bow Concept on trails.
Fig. 22. Artist impression of a new Patrol Boat design according to the AXE Bow Concept. Application of the AXE Bow Concept may improve the operability of a fast ship
in typical North Sea conditions with another 40 to 50 percent when compared with the ESC.
The A) Bow ship shows no significant higher tendency to broaching in stern
quartering and following seas then a comparable design i.e. with a similar size
and speed.
These results have lead to the actual design and building of a new ship according
310 J.A. Keuning / "Grinding the bow" or "How to improve the operability offast monohulls"
2006 has led to a verification of the results obtained from the model testing and
calculations. A photo of one of this new ship is depicted in Fig. 21.
Also, new designs in the range of patrol boats have been developed, an example of which is shown in the artist impression (Fig. 22).
References
J.J. van den Bosch, Tests with two planing boats in waves, TU Deift Laboratorium voor Scheeps-bouwkunde, Report 238, June 1969.
J.A. Keuning and J. Gerritsma, Resistance tests of a Series of Planing Hull Forms with 25 degrees
Deadrise Angle, International Shipbuilding Progress 29 (1982), 37.
J.A. Keuning, J. Gerritsma and P.F. van Terwisga, Resistance Tests of a Series of Planing Hull
Forrris with 30 degrees Deadrise Angle and a Calculation Method Based on this and Similar Series, International Shipbuilding Progress 40 (1993), 333-385.
E.P. Clement and D.L. Blount, Resistance Tests of a Series Qf Planing Hull F'or,ns, Transactions SNAME, 1953.
J.J. Blok and H.W. Roeloffs, The influence of the Forebody Deadrise on the performance ina
Sea-way, MARIN Report No 49207-l-HT, April 1989.
J.A. Keuning, Nonlinear Heave and Pitch Motions of Fast Ships in frregular Head Waves, ASNE
High Speed Marine Vehicles Conference, Washington, June 1992.
J.A. Keuning, The Non Linear Behavior of Fast Monohulls in Head Waves, PhD Thesis, Deift Uni-versity of Technology, September 1994.
E.E. Zarnick, A Non Linear Mathematical Model of Planing Boats in Regular Head Waves, David Taylor Naval Ship Research and Development Center Report '8-032, March 1982.
l.A. Keuning and J. Pinkster, Optimization of the Seakeeping Behavior of a Fast Monohull, FAST Conference Proceedings 1995.
J.A. Keuning and J. Pinkster, Further Design and Seakeeping Investigations into the Enlarged Ship Concept, FAST Conference Proceedings 1997, Sydney, Australia.
J.A. Keuning, J. Pinkster and F. van Walree, Further Investigation into the Hydrodynamic Perfor-mance of the AXE Bow Concept, Proceedings of the WEGEMT Conference on High PerforPerfor-mance Marine Vehicles, September Z002, Ischia, Italy.
J.A. Keuning, S. ToÁopeus and J Pinkster, The Effect of Bow Shape on the Seakeeping Performance
- of a Fast Monohull, FAST Conference Proceedings, Southampton, September 2001.
K. McTaggart and J.O. de Kat, Capsize Risk of Intact Frigates in Irregular Seas, Proceedings
SNAME Annual Meeting, Vancouver, October 2000.
1.0. de Kat, D.J. Pinkster and K. McTaggart, Random Waves and Capsize Probability based on Large
Amplitude Motion Analysis, Proceedings 21st OMAE Conference 2002.
J. Ooms and J.A. Keuning, Comparitive Full Scale Trials of Two Fast Rescue Vessels, International Conference SIIRV 4, 13&14 may 1997, Gothenburg.
d e s-Is a-id T ip 'r-ce ce gs ge L51
International Shipbuilding Progress 53 (2006) 311-312
TOS Press
Author Index Volume 53 (2006)
The issue number is given in front of the page numbers.
Dailinga, R.P., see Naaijen, P.
de Jong, P. andJ.A. Keuning, 6-DOF forced oscillation tests for the evalua-tion of nonlinearities in the superposievalua-tion of ship moevalua-tions
Ekman, P., A numerical model to simulate launching of evacuation capsules from a ship in beam seas- Simulations and validation using experimental tests
Hamanaka, S., see Naito, S.
Hoekstra, M., A RANS-based analysis tool for ducted propeller systems in open water condition
Huijsmans, R., Editorial
Iqbal, K.S. and A. Rahim, Mechanized country boats of Bangladesh: As-. sessing environmental impacts of hull form modification
Keuning, J.A., "Grinding the bow" or "How fast mdnohulls"
Keuning, J.A., see de Jong, P. Koster, V., see Naaijen, P.
Krishnankutty, R, see Varyani, K.S. Kuttenkeuler, J., see Stenius, I.
to improve the operability of
Lin, W.-M., see Liut, D.A
Liut, D.A. and W.-M. Lin, A Lagrangian vortex-lattice method for arbitrary bodies interacting with a linearized semi-Lagrangian free surface Ljutina, A.M., see Senjanovié, I.
Minoura, M., see Naito,S.
Motok, M.D. and T. Rodic, A case of unconventional use of finite element method in ship hydrostatic calculation
Munif, A. and N. Umeda, Numerical prediction on parametric roll
reso-nance for a ship having no significant wave-induced change in hydro-statically-obtained metacentric height
0020-868X/06/$17.00 © 2006 - Tos Press and the authors. All rights reserved
3 2 Author index Volume 53 (2006)
Naaijen, P., V. Koster and R.P. Dallinga, On the power savings by an auxil-iary kite propulsion system
Naito, S., M. Minoura, S. Hamanaka and T. Yamamoto, Long-term predic-tion method based on shipoperation criteria
Parunov, J., see Senjanoviá, I.
Rahiin, A., see lqbal, K.S. Rodic, T., see Motok, M.D. Rosén, A., see Stenius, 1.
Senjanovié, I., A.M. Ljutina and J. Parunov, Analytical procedurefor nat-ural vibration analysis oftensioned risers
Stenius, 1., A. Rosén and J. Kuttenkeuler, Explicit FE-modelling of fluid-structure interaction inhullwater impacts
Suzuki, K., see Tarafder, Md.S.
Tarafder, Md.S. and K. Suzuki, Computntion of free surface flow around a ship in shallow water using a potential based panel method
Umeda, N., see Munif, A.
Varyani, K.S. and P. KrishnankuttY, Influence-of mooring rope characteris-tics on the horizontal drift oscillation of a moored ship
Yamamoto, T., see Naito, S.
