THE USE OF A VERTICAL BOW FIN FOR THE COMBINED ROLL AND YAW

STABILIZATION OF A FAST PATROL BOAT

J Alexander Keuning, Shiphydromechanics Department, Delft University of Technology, Netherlands

Guido L Visch, Shiphydromechanics Department, Delft University of Technology, Netherlands

SUMMARY

From many research projects it is known that for fast patrol boats the motion behavior in large stern quartering and
following seas is often a limiting situation for its operability. The broaching tendency that may occur with most of the
relatively small (shorter then 50 meters) and fast (more then 25 knots) patrol boats often implied that a significant change
in forward speed or heading had to be made to prevent serious problems. The rudder action of the aft rudders in particular
in stern quartering seas, required to keep the boat more or less “on track”, significantly aggravates the rolling motion of
the ship and so the tendency towards a broach. A vertical fin at the bow however would have an opposite and thus
positive effect on the roll motions in those conditions. By using this forward vertical fin (or bow rudder) to control the
yaw motion of the ship in large waves, in addition to the rudders aft, due to the direction of the lift force and its phase the
rolling motion is reduced instead of increased, contributing significantly to the resistance against broaching. The
introduction of such a vertical fin on a conventional bow is difficult due to all kinds of practical reasons.
The very shape of the hull according to the AXE Bow Concept, introduced by the author in earlier publications since
2001, however makes it quite feasible to place such a vertical controllable fin at the foremost end of the ship.
In the paper the mechanism and the physics involved of such a vertical bow fin in stabilizing the yaw and roll motions in
waves will be described. In addition the results of an extensive series of experiments with an AXE Bow model fitted with
various realizations of such bow fins will be presented. Finally a series of tests with a free running model fitted with such
a bow fin has been carried out in the sea keeping tank of MARIN in stern quartering seas to check the principle behind
the idea.
A limited number of these results will be presented in the paper.

NOMENCLATURE board as well as to the ship itself could be experienced.

The emphasis was on the limitation of the vertical
Lwl Length waterline accelerations and in particular the big peaks, i.e. the
Bwl Breadth waterline slams. Typical improved hull forms have been developed
T Draft amidship and build, such as the Enlarged Ship Concept, Ref [1], [2]
V Displacement and the AXE Bow Concept, Ref [3] and [4]. Much has
Vmax Maximum Speed been achieved in this respect and the operability has been
GMt Transverse Metacentric Height increased significantly. In the present study emphasis is
k k-factor placed on other restricting phenomena when sailing with
Fy Side Force fast ships in a seaway.
Mz Yaw Moment One of these limiting phenomena is the tendency to
Mx Roll Moment broach when sailing at speed in following or stern
quartering seas.
1. INTRODUCTION
1.1 THE BROACHING PHENOMENON
The use of fast craft in a seaway has always posed many
challenges to the comfort of those on board and the Broaching is a well known phenomenon and may be best
safety of the ship. Partly this is due to the fact that most described as a coupled roll-yaw and pitch motion of the
applications of fast ships are restricted to the relatively ship. From full scale experience and systematic research
smaller vessels. If we consider ships with speeds in it is known that this broaching behavior is often
excess of 25 knots as “fast”, their typical length is introduced through a combination of a lack of transverse
generally restricted to 50 meters over all. This implies stability of the ship (at speed) and insufficient directional
that the waves they encounter tend to be relatively large stability.
compared to the ship size. Improvement of the sea What generally happens can, in physical terms, best be
keeping behavior of the ship may typically be found in described as follows: the ship is sailing at high speed in
increasing the pure size of the ship, but this comes at a stern quartering seas. Through the high speed the
cost. encounter frequency of the ship with the waves is low.
In the past decades considerable attention has been paid Let us now assume the waves come in from the port
to improving the operability of fast ships in head waves quarter. When a high wave reaches the stern of the ship
because in those conditions severe damage to people on the stern is lifted. Because more often then not the sterns

107
of these ships are broad and flat the ship is
simultaneously heeled to starboard. Through this
combined pitch and roll motion the bow is now more
deeply submerged in the wave crest just in front of the
boat. This deep submergence in combination with the roll
angle introduces an asymmetry and so a considerable
yawing moment on the ship to port. In addition the whole
sequence of events leads to a considerable loss of
directional stability. This is further aggravated by the fact
that these ships in most cases have two rudders each at
one of the ship of which the port (windward) rudder will
now most likely be partly lifted out of the water.
In order to keep the ship as much as possible on a
straight track considerable rudder action is e required.
The rudders are pulled over to starboard to correct for the
course change and the yawing moment. The rudders,
placed aft and underneath the hull, generate a lift force to
port and so a counter balancing yawing moment to
starboard. Simultaneously however they also generate a
considerable rolling moment and in the particular
situation under consideration to starboard, which leads to
an increase in the undesirable roll motion. If all goes well
control is maintained and the boat brought back to its
original course with the roll- and the pitch angle at
reasonable and manageable values. In the worst case the
yaw motion gets out of control and the ship ends up in
beam seas at excessive heel, sometimes even leading to a
capsize. The photos in Figure 1 show the two phases of a
moderate broach.

Figure 1. Phases of an AXE hull model without bow fin

broaching.

It is known that the phenomenon is most eminent in

waves in between 1.3 and 1.5 times the ship length and
so for a 40 meter vessel this implies that the encounter
frequency becomes almost zero with such waves (i.e.
wavelength of 60-70 meters) at or around 20 knots.
Solutions for preventing or reducing the broaching
tendency of a ship in typical environmental conditions,
such as the North Sea, can be found in:

• Increasing the length of the ship (design issue)

• Increasing or decreasing the speed of the ship
considerably (operational issue)
• Changing the heading of the ship with respect
to the waves (operational issue)

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 • Increasing the transverse stability of the ship The presumed advantages of a vertical bow fin for yaw
and so reduce the roll angle (Design and and roll motion control in stern quartering and following
operational) waves are:
• Increasing the directional stability by the
addition of skegs aft (design issue) • The rudder remains immersed on the most
• Appling an additional vertical bow fin (bow important moment, i.e. when the bow is pushed
rudder) fore. down and the stern is pushed up.
• It generates a large additional yaw moment
1.2 POSSIBLE DESIGN SOLUTION • It generates a considerable roll moment,
• In the coupled roll, yaw and pitch motion of a
The possible solution which will be evaluated further in ship in following and stern quartering waves it
this report, is the last one: i.e. an additional vertical fin at has a positive contribution to the roll
the bow. It is designed to reduce the tendency to broach. stabilization
The very shape of the AXE Bow hull and fore body
makes it possible to introduce such a vertical bow fin Possible disadvantages could be:
without much difficulty.
• Increased calm water resistance due to the
The philosophy behind this is that the vertical bow fin transition between rudder and hull
forwards effectively generates the desired yawing • Increased construction weight at the bow
moment to keep the ship on track because it is more
immersed than emerged as is the case with the rudders aft 2. VALIDATION OF THE PRINCIPLE IDEA
while at the same time it produces a roll moment that
reduces the prevailing roll angle. To check whether the principal idea works it was decided
to carry out a dedicated model experiment with a model
A typical vertical bow fin or bow rudder fitted on an of an AXE Bow in the new seakeeping basin of MARIN
AXE Bow could look like depicted in Figure 2. at Wageningen.
This test was carried out in conjunction with the FAST
Project described in previous publications, Ref [4] and
Ref [5]. The model used was the AXE Bow model of the
FAST project, a 55 meter long patrol boat capable of
speeds up to 50 knots.
Main Particulars of the ship are:

Length = 55.0 meter

Beam WL = 8.46 meter
Draft midship = 2.26 meter
Displacement = 517 tons
Speed max = 50 knots
GMt = 2.50 meter

Figure 2. Bow Fin fitted at an AXE hull model Figure 3. Linesplan of the used Aexebow model

109
The model was equipped with two water jets with over the entire track is some 0.5 degrees to starboard,
steerable nozzles. The maximum deflection angle of the which is understandable with the waves coming from the
nozzles was restricted to 23 degrees either side. At the aft port stern quarter.
end also two fixed skegs were fitted to the hull.
The tests were carried out with the free running model,
solely propelled by the two waterjets. The unique SMB Rayleigh Plots without bow fin
facility of MARIN allows the model to run completely 15
free of the towing carriage in irregular waves from any
crests
direction. The course of the model is controlled by an

R oll [deg]
autopilot. In the tests with the bow fin there was a direct
10 troughs
1:1 mechanical link between the steering adjustment of
the waterjets and the bow rudder. Only the direction of 5
the deflection of the bow fin was reversed with respect to
the aft “rudders” to yield a similar yaw moment resulting 0
from the bow fin as was established with the steering 100 50 20 10 5 2 1 1/5
nozzles aft. Probability of Exceedance [%]
The tests were carried out in one typical North Sea
spectrum, which, according to the available wave scatter 20
diagrams of that area, is only exceeded 5% of the time all

Yaw [deg]
year round. The main particulars of this spectrum are
:
10
• a significant wave height Hs equal to 2.50
meter,
• a peak period Tp equal to 6.75 sec and
• a energy distribution over the frequency range 0
according to the normalized Jonswap spectrum. 100 50 20 10 5 2 1 1/5
Probability of Exceedance [%]
Considering the wavelengths in the spectrum a forward 30
speed of around 20 knots was chosen because this posed
N ozzle [deg]

the largest likelihood of broaching in the situation chosen,

i.e. a wave incidence angle of 315 degrees (i.e. port stern 20
quartering). In the spectrum realization a considerable
number of tests was carried out to obtain a test run 10
duration of circa 2 hours at full scale.
The tests were carried out both with the AXE Bow model
without vertical bow fin and with the model fitted with 0
100 50 20 10 5 2 1 1/5
the vertical bow fin. The main particulars of the bow fin Probability of Exceedance [%]
used are those depicted in Figure 2.

The results are presented in the following figures: in

Figure 5 the results for the conventional AXE Bow and Signal unit Mean stdev Min Max
in Figure 6 the results for the AXE Bow fitted with the
vertical bow fin.
The results are presented as plots of the probability of Roll deg 0,38 2,21 -8,41 9,88
exceedance (in percentage of the total number in the Yaw deg 0,00 2,97 -10,66 16,40
entire time trace) of the peaks and the through of the time Aft-Rudder deg -4,06 11,88 -23,57 23,10
signal under consideration. The horizontal scale is sized
to fit the Rayleigh distribution, which comes out as a
straight line. The extremes of the peaks and troughs are Figure 4. Rayleigh Plots and Statistics without bow fin
found at the far right side of the plots, i.e. with the low
probability of exceedance.

As may be seen from these results the effect of the

application of the vertical bow fin in these conditions is
quite significant:
The significant roll amplitudes are reduced by some 30%
and the maximum roll amplitude encountered during the
2 hours even by some 40%. For the ship without bow fin
the maximum roll angle to starboard is slightly larger
than the maximum roll to port. The average roll angle

110
 case with the waterjet nozzles which are placed much
Rayleigh Plots with bow fin closer to the vertical center of gravity of the ship.
15 An autopilot which controls the combination of both, i.e.
controlling yaw and roll simultaneously, in a way similar
crests
to the already existing “rudder-roll” stabilizers, may
R oll [deg]

10 troughs possibly overcome this phenomenon. For the time being

the “average” between the distributions of the peaks and
5 the troughs could be considered for the sake of
comparison. The roll angle reduction in that situation
0 with the bow fin added increases then even further and
100 50 20 10 5 2 1 1/5 well to over 50%!
Probability of Exceedance [%] A similar trend may be seen with the yaw motion:with
the bow fin added the yaw motion is significantly smaller
20 than without. Here the reduction in both the significant
and the maximum amplitudes is also in the order of 50%.
Yaw [deg]

In particular the reduction in the extreme values of yaw

10 and roll are of interest because these may be the
introduction of a broach.
From the registration of the rudder angles during the tests
it may be seen that much less rudder action (i.e. smaller
0 angles) is necessary to keep the ship on track for the
100 50 20 10 5 2 1 1/5 model with bow fin. This is understandable because the
Probability of Exceedance [%] amount of control (surfaces) has been increased
significantly. In the situation without bow fin the
N ozzle & Bow F in

30
maximum nozzle angle is reached more often than not. In
the situation with bow fin this is hardly the case, which
20 leaves much more room to control the ship in those
[deg]

conditions.
10
The general conclusion that may be drawn from this
0 experiment is that the application of the vertical bow fin
100 50 20 10 5 2 1 1/5 in stern quartering seas is very effective indeed in
Probability of Exceedance [%] reducing both the roll and the yaw motion.

3. THE VARIOUS CONCEPTS OF THE BOW FIN

Signal unit Mean stdev Min Max
Now the validity of the concept has been demonstrated,
Roll deg 0,55 1,56 -4,08 6,82 the actual design of the fin and the design of a controller
had to be assessed.
Yaw deg 0,00 1,49 -5,39 6,55
The first step in this process was to establish the
Nozzle & effectiveness of various bow fin designs in generating
deg -2,79 8,00 -25,86 23,23 side force, yaw moment and rolling moment with respect
Bow Fin
to the one used during the tests at MARIN.
The aim of the series of experiments was to determine
Figure 6. Rayleigh Plots and Statistics with bow fin the minimum size rudder that is adequate for the job. The
reason behind this aim is found in some structural and
It is also of interest to note that with the application of interior layout limitations and the possible negative effect
the bow fin the reduction of the roll amplitudes to port is of the bow fin on the calm water resistance because the
considerable larger than the reduction to starboard. This fin will not be used for a certain amount of time and
may be partly explained by the fact that the autopilot should therefore generate as little disturbance as possible
used to keep the ship “on track” is controlling the nozzles in those conditions.
for the ship without bow fin and both the nozzles and the This aim was to be achieved by measuring a number of
fin for the model with bow fin. This autopilot has as only the hydrodynamic derivatives necessary for inclusion in
input signal the yaw angle (course of the ship) and not the mathematical model available at the Ship
the roll motion. The average offset in the course due to hydrodynamic Department (FASTSHIP) for all
the wave action from port quarters shows up as an configurations considered feasible as vertical bow fin on
average nozzle angle of circa 2.5 degrees. This yields the the AXE Bow.
differences in the distribution of peaks and troughs in roll The following six different configurations have been
for the model with vertical bow fin. Because the bow fin examined:
introduces a significant roll moment and this is not the

111
The first three are all vertical bow fins incorporated in
the bow profile of the AXE Bow model as presented
above. In principle it is a change the rudder area
established by keeping the height of the rudder as in the
original design used in the MARIN tests and reducing the
chord length in two steps yielding the original or large
rudder, the medium rudder and the small rudder. The
principal dimensions of these rudders are depicted in the
Figure 7a, 7b and 7c below.

Figure 7 Small bow fin

The reduction of the bow fin area by reducing the chord

length of the fins implies an effective increase in the
aspect ratio of the fins. This had the additional beneficial
effect that the beam of the cross section just after the
aperture in which the fin was fitted became smaller also.
This makes the transition or “blending” of the vertical
bow fin shape, with its typical foil type cross section,
into the hull more streamlined.
Figure 7a. Large bow fin Another possible realization of the bow fin is found in
the use of a so called Magnus Rotor in the most forward
part of the bow section. The other three configurations
investigated were all based on the use of a Magnus rotor.
The Magnus rotor works to the effect that a rotating
cylinder placed in a flow generates a lift force
perpendicular to the incoming flow. The lift force
generated is proportional to the velocity of the incoming
flow, which is the speed of the ship Vs in m/sec, the
rotation angular velocity or ω in rad/sec of the cylinder
and the radius of the cylinder in m squared. From earlier
tests it is known that the Magnus rotor is a very efficient
lift generating device.
The very shape of the AXE Bow with its rounded
sections lends itself very well for the application of such
a rotor. Without extruding from the hull shape as is a
rotor with a diameter of 0.35 meter can be placed at the
bow. The rotor is extended in length till the design water
line of the ship.
The biggest challenge lies in the incorporation of the
Figure 7b. Medium bow fin rotor in the hull shape and the design of the hull shape
just abaft and in the vicinity of the rotor. No results in the
literature were known about the effect of this on the lift
generating capabilities of the Magnus rotor. Three
different configurations have been tested:

• Configuration 1 with the hull of the ship

“faired” around the aft half of the rotor. This
configuration yields almost no deviation from
the original bow design

112
 • Configuration 2 with a gap just behind the rotor
in length equal to the diameter of the rotor,
which is then rotating in a sort of “gap”. This
gap will have some influence on the calm water
resistance when the rotor is not in use.
• Configuration 3 with a Magnus rotor extending
below the bow. In real life this would be a
retractable rotor. The shape of the AXE Bow
lends itself very well to such a set up. It yields
an unobstructed hull when not in use and a most
likely very effective rotor when used. In
addition the shape of the AXE Bow places this
rotor at a considerable distance below the center
of gravity generating large roll moment.

The principal dimensions of the three configurations are

depicted in the Figure 8a, 8b and 8c.
Figure 8c. Retractable Rotor

An extensive series of experiments have been carried out

using the same model of the AXE Bow as used in the
previous MARIN free sailing experiments described
above. In the present tests however the model was not
fitted with the waterjets but with two rudders aft. This
was done because for the sake of comparison the rudders
produced much more repeatable results than the waterjets,
with their flow dependent steering properties. The
dimensions of these conventional aft rudders are
presented in Figure 9.

Figure 8a. Faired in Rotor

Figure 9. Conventional rudders

All configurations of a vertical bow fin as mentioned

above have been fitted to the model and consequently
been tested in the tank.

The new series of tests have been carried out in the

towing tanks of the Delft University of Technology. The
tank is 142 meters long, 4.25 meters wide and has a
maximum water depth of 2.5 meters. The towing carriage
is capable of achieving speeds up to 8.0 meters per
second.
During the tests the model was rigidly connected to the
towing carriage by means of a six component
dynamometer and the six degrees of freedom oscillator
called “Hexamove” which was used in this measurement
setup as a model position and attitude manipulator.
Figure 8c. Free Rotor Forces and moments have only been measured on the

113
model as a whole, no forces on the rudders or rotors have the bow fins and in Figure 12e for the rotors. Here too,
been measured separately. The test layout is depicted in the results for the aft rudders are presented in the rudders
Figure 10. figure.
Finally in Figure 12c the roll moment is presented for the
bow fins and in Figure 12f the results for the rotors.

Direction Positive
Aft Trailing
Rudder Edge
Angle Starboard
Bow Trailing
Fin Edge
Angle Starboard
Bow Anticlockwise
Rotor From above

Figure 10. Hexamove setup

The tests have been carried out with the model in the
calm water trim and sinkage corresponding to the
forward speed under consideration. The following
parameters and all their possible combinations have been
varied during the tests:

• Forward speed of the model at 15, 25 and 35

knots full scale for the bow rudders and at 15 Figure 11. Defenitions
and 20 knots for the rotors, due to limitations FY Rudders
imposed by the available facilities at that time.
Fy [kN]

140
• The fin angle between minus 20 and plus 20 120
CONVENTIONAL
SMALL
degrees MEDIUM
• Three different yaw angles, i.e. 0 and plus and 100 LARGE
minus 5 degrees. 80
• In the case of the Magnus rotors different 60
relations between forward and rotational 40
velocity of the rotor expressed in the “k” factor,
i.e. k = . 20

0
The tests generated a large amount of results for use in -20
0 5 10 15 20

the mathematical model. In the context of the present Rudder Angle [deg]
paper only a limited amount of the results can be
presented. These results are primarily aimed at Figure 12a. Side Forces Rudders
facilitating the comparison between the various
MZ Rudders
configurations.
MZ [Kn*m]

3000
CONVENTIONAL
In Figure 12a and 12d the side force on the ship is 2000
SMALL
presented at 15 knots. This speed has been chosen MEDIUM
LARGE
because it makes a comparison between the 1000

configurations possible since it is used with all 0

configurations. In Figure 12a the results for the bow fins 0 5 10 15 20
are presented and in Figure 12d the results for the rotors. -1000
For the sake of comparison the same results for the
-2000
conventional rudders aft are presented in the rudders
figure. -3000

-4000
In Figure 12b and 12e the yaw moments of the various Rudder Angle [deg]
configurations is presented, once again in Figure 12b for Figure 12b. Yaw Moments Rudders

114
 MX Rudders
What may be concluded from these results is that the
small fin at the bow generates a maximum side force of
circa 10 kN, the medium fin a maximum of 30 kN and
MX [kN*m]

200
CONVENTIONAL
SMALL the large fin a maximum of 40 kN. So the larger size bow
150
MEDIUM fin is certainly the largest lift generator, although it is not
LARGE proportional to size. However they all compare relatively
100 low in efficiency with the conventional rudders, which
generates a maximum lift force of around 120 kN. It
50 should be noted however that this is generated by two
conventional rudders aft. The total area of the
0 conventional rudders aft added together is still almost
0 5 10 15 20 half the area of the large vertical bow fin fore. Because
-50 they operate underneath the hull there efficiency is
Rudder Angle [deg] greatly enhanced by the end plate effect of the hull. This
Figure 12c. Roll Moments Rudders reduced efficiency of the bow fins may, amongst others
be attributed to the rather complicated flow around the
FY Rotors
interception of the trailing edge of the fin with the hull
Fy [kN]

250
FAIRED IN geometry and also to ventilation effects. It was noted
200 FREE during the tests that serious ventilation could occur in the
RETRACTABLE more heavily loaded conditions of the foils. This could
150 be remedied by placing the top chord of the fins lower in
the water guaranteeing a larger distance to the free
100
surface or by the use of fences at the top. None of these
50
have in the present study been investigated.
In the “near to broaching” condition however this
0 difference in efficiency could be quite different because
0 1 2 3 4 5 at least one of the aft rudders may certainly be lifted
-50 partly out of the water as can be seen on the photographs
K-factor [-]
in Figure 1. This will yield a serious reduction in
Figure 12d. Side Forces Rotors efficiency due to loss of submerged rudder area and also
MZ Rotors
ventilation effects.
7000 When the yaw moments of the three bow fins are
MZ [KN*m]

FAIRED IN
6000 FREE
compared the similar trend may be observed: the large
RETRACTABLE
fin produces roughly 2100 kNm, the medium fin 1800
5000
kNm and the small fin 500 kNm. As may be observed in
4000
the generated side force as well the maximum moment is
3000 reached at 15 degrees fin angle and not at 20, except with
2000 the small fin.. The maximum yaw moment with the
1000
conventional rudders is 3100 kNm and also reached at a
15 degrees rudder angle. The difference in side force
0
0 1 2 3 4 5
production is larger between rudder and fins as the
-1000 differences in yaw moment.
-2000 The generated roll moments of the three bow fins are also
K-factor [-]
significantly smaller than those generated with the
Figure 12e. Yaw Moments Rotors conventional rudders, i.e maximum 14 kNm, 28 kNm
MX Rotors
and 60 kNm compared to some 186 kNm for the aft
MX [KN*m]

900 rudders.
FAIRED IN
800 Although not shown here all forces and moments are
FREE
700 strongly dependent on the forward speed. In most cases
RETRACTABLE
600 the increment with speed is rather more then quadratic.
500
400
The results for the rotor show in general that the “faired
300
in” rotor design is hardly more effective then the smallest
fin in all modes, ie. for side force, yaw moment and roll
200
moment. The rotor with “the gap” behind it, i.e. ( confi-
100
guration 2 ) is far more effective and approaches the
0
large bow fin in characteristics.
-100 0 1 2 3 4 5
By far the most effective is the (retractable) bow rotor in
K-factor [-]
configura-tion 3. Although the rotor used in the tests is
Figure 12f. Roll Moments Rotors only half the span of the other two rotors it out performs

115
all the others. This can of course be explained by the fact References
that it is completely undisturbed by any other part of the
structure. In addition combined with the AXE Bow hull [1] J A Keuning and J Pinkster
it is so deeply submerged that it is entirely free from “Optimization of the seakeeping behavior of a
ventilation effects in any of the conditions tested. fast monohull”
The biggest advantage may be however found in the FAST Conference Proceedings, Southampton UK
relatively enormous roll moment it generates when 1995
compared with all the others, fins and rotors and in [2] J A Keuning and J Pinkster
particular also with the conventional rudders aft. The “Further design and seakeeping investigations into the
retractable rotor outperforms the aft rudders in this Enlarged Ship Concept”
respect with a factor of around 4. FAST Conference Proceedings, Sydney Australia
For the rotor in configuration 3 it is also obvious that the 1997
maximum lift is achieved at lower values of k, implying [3] J A Keuning, J Pinkster and F van Walree
lower number of revolutions. “Further inverstigations in the hydrodynamic
The relative differences in calm water resistance of all performance of the AXE Bow Concept”
the configurations is compared in Figure 13. From these WEGEMT Conference on High Performance
results it is obvious that the “faired in” rotor has the least Vehicles September 2002, Ischia Italy
resistance increase [4] J A Keuning, S Toxopeus and J Pinkster
“The effect of the bow shape on the seakeeping
Performance of a fast monohull”
120
FAST Conference Proceedings Southampton
Induced Bowadd. Resistance [%]

September 2001
115
[5] FAST Project
110
Seakeeping Model tests for two patrol vessels
MARIN 19112-1-SMB
105

100

95

90

85

80
Small Medium Large Build In Free Telescope

Figure 13. Comparison Rudders and Rotors

The retractable rotor has the largest resistance increase

when deployed, which will obviously be the case in
beam seas to following seas, in which conditions the
resistance increase is less of an issue.

4. CONCLUSIONS

From the results of these experiments it may be

concluded that a vertical bow fin will have a beneficial
effect on the controllability of a fast ship in following
and stern quartering seas.
The configuration most suited, when combined with an
AXE Bow hull shape is the retractable rotor underneath
the bow. Second best is the medium to large bow fin.
There is a great opportunity for a combined yaw-roll
autopilot under these circumstances.

116