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Information on chine interceptors, as well as the whole topic of spray sheet deflection, is scarce and to the most extent dated. Therefore, a series of model tests have been conducted with a 19 m craft configured with chine interceptor arrangements (operating in a range of Froude numbers Fr = 0.77…1.35). The series is comprised of two benchmarks and two modifications for each of the benchmarks, altogether 6 models. Each model was tested at four displacements and speeds. The first benchmark, a bare hull, had the following two chine modifications: a 2x2mm rectangular rail attached along the outer edge of the chine and a 2x15mm chine inclination that covered the chine, resulting in a new chine surface angled down. The second benchmark, a hull equipped with spray rails with a rectangular 5x5mm profile, was tested with a rectangular 2x2mm and a triangular 5x5mm profile attached at the outer edge of the chine. Chine interceptors on reduced the total resistance of a planing craft by more than 3% both on a bare hull and hull equipped with spray rails.
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RESISTANCE TESTS OF A SERIES OF CHINE INTERCEPTORS ON A PLANING
CRAFT
M. Lakatos, T. Sahk H. Andreasson and K. Tabri, Tallinn University of Technology, Estonia
SUMMARY
Information on chine interceptors, as well as the whole topic of spray sheet deflection, is scarce and to the most extent
dated. Therefore, a series of model tests have been conducted with a 19 m craft configured with chine interceptor
arrangements (operating in a range of Froude numbers Fr = 0.77…1.35). The series is comprised of two benchmarks and
two modifications for each of the benchmarks, altogether 6 models. Each model was tested at four displacements and
speeds. The first benchmark, a bare hull, had the following two chine modifications: a 2x2mm rectangular rail attached
along the outer edge of the chine and a 2x15mm chine inclination that covered the chine, resulting in a new chine
surface angled down. The second benchmark, a hull equipped with spray rails with a rectangular 5x5mm profile, was
tested with a rectangular 2x2mm and a triangular 5x5mm profile attached at the outer edge of the chine. Chine
interceptors on reduced the total resistance of a planing craft by more than 3% both on a bare hull and hull equipped
with spray rails.
NOMENCLATURE
LOA Length overall (m)
LPP Length between perpendiculars (m)
LWL Length waterline (m)
BOA Beam overall (m)
BWL Beam waterline (m)
T Draught (m)
m Displacement mass (kg)
Displacement volume (m3)
LCG Longitudinal Centre of Gravity (m)
KG Vertical Centre of Gravity (m)
Fr Froude number (1)
Fr
Froude displacement number (1)
RTM Total resistance in model scale (N)
τ Dynamic trim (degrees)
zV,CG /
1/3
Non dimensional dynamic sinkage (1)
BH Bare hull
SR Hull with spray rails
CSR Chine spray rail
CSI Chine spray interceptor
C.INC Chine inclination
1. INTRODUCTION
Whisker spray is a phenomenon that occurs on high-
speed marine vehicles (semi-displacement craft, planing
craft and hydroplanes) when they operate at high speeds.
It is created from the stagnation line (a line that separates
the flow going under the hull into the pressure area from
the flow going into the spray area) and it forms a thin
sheet of fluid along the bottom surface above the
stagnation line, which under low-speed operation would
have been dry. This spray sheet of water causes frictional
resistance along its streamline over the hull surface. The
resistance of whisker spray has been shown to account
for 10% - 25% of total resistance (at high speed, when
Froude displacement number Fr
> 4) by inference from
a comparison of model test data with and without spray
rails installed on the hull bottom [1][4].
To reduce the whisker spray resistance, two to four
longitudinal stripes (also called rails, lifting strikes or
deflectors) are usually installed on the hull. The main
purpose of these appendages is to detach the spray from
the hull surface and deflect it towards the sides or
slightly down and aftward, thereby reducing the
frictional resistance by up to 18%. Deflection of the
spray also induces a lifting force that affects the running
trim of the craft. Depending on the position and shape of
the spray rail as well as the orientation of its deflecting
surface, it is possible to generate different amounts of lift
resulting from the whisker spray deflection [5]. Since the
running trim has a more significant effect on the total
resistance than a whisker spray, a spray rail will reduce
the resistance due to its lift producing qualities rather
than due to its spray detachment abilities.
An analytical model [6] that predicts the viscous drag in
the spray area as a function of deadrise angle, trim angle
and speed has been added to the Savitsky method [7],
which previously only included the viscous and pressure
drag components in the bottom area aft of the stagnation
line. In addition to whiskers spray, there is also a second
spray pattern called main spray [8], observed in planing
crafts. It is a discharge of water in the form of a cone
with its apex located near the intersection of the
stagnation line and the chine. The outboard trajectory of
the main spray is significantly elevated compared to that
of the whisker spray. Due to the large volume of water
and the high trajectory angle of the main spray, it can
impact the wings and propellers of seaplanes causing
structural damage. It can also impact the tunnel between
the hulls of a planing catamaran and thereby significantly
increase in resistance. Savitsky and Morabito [9]
developed and experimentally verified an analytical
model that predicts the geometry of the main spray as a
function of deadrise angle, trim angle and speed.
A few studies featuring spray rails on planing hulls have
been published within the last fifteen years. However, in
most of those studies, the focus is either on the validation
High Speed Vessels, 1-2 July 2020, London, UK
© 2020: The Royal Institution of Naval Architects
63
of numerical models of planing hulls in calm water [10]
and waves [11] or the evaluation of new hull form
concepts [12][14].
A recent study [15] showed that chine modifications can
reduce the total resistance of a planinig hull by up to
3.5%. However, the hull featured in that study had no
spray rails, which begged the question whether the effect
of the chine modifications would be the same on a hull
with spray rails. Therefore, this study investigates the
influence of the chine spray rails and interceptors on the
total resistance trim and sinkage of a planing craft
already equipped with spray rails.
2. EXPERIMENTAL TESTS
2.1 DESCRIPTION OF TESTED MODELS
A test case craft was designed and manufactured by the
Small Craft Competence Centre (SCC) in Kuressaare,
Estonia, to compare conventional and novel spray rail
configurations. The main particulars (Table 1) of the hull
design are common for a high-speed patrol, search and
rescue (SAR) craft or a larger pleasure craft. The craft
was designed to operate at a Fr = 1.354 and Fr
= 3.11,
equivalent to the displacement of 40 t and speed of 35
knots in full scale.
Table 1: Main dimensions of the naked hull.
Parameter
Model Scale
λ
10
Length overall
LOA
1.921 m
Length between perpendiculars
LPP
1.800 m
Length waterline
LWL
1.703 m
Beam overall
BOA
0.581 m
Beam waterline
BWL
0.581 m
Draught
T
0.108 m
Displacement mass
m
40 kg
Displacement volume
0.040 m3
Longitudinal Centre of Gravity
LCG
0.669 m
Vertical Centre of Gravity
KG
0.200 m
The series is comprised of two benchmarks and two
modifications for each of the benchmarks, altogether 6
models. The first benchmark, a bare hull (BH) (Fig. 1a),
had the following two chine modifications: a 2x2mm
rectangular interceptor (Fig. 1b) attached along the outer
edge of the chine (BH-CSI) and a 2x15mm chine
inclination (Fig. 1c) that covered the chine, resulting in a
new chine surface angled down (BH-C.INC). The second
benchmark (SR), a hull equipped with spray rails (Fig.
2a) with a rectangular 5x5mm profile (Fig. 2b), was
tested with a rectangular 2x2mm (Fig. 2c) chine spray
interceptor (SR-CSI) and a triangular 5x5mm (Fig. 2d)
chine spray rail attached at the outer edge of the chine
(SR-CSR). Each configuration was tested at four speeds
corresponding to full scale (20, 25, 30 and 35 knots) at
the model scale of 1:10 and four loading conditions (30
kg, 35 kg, 40 kg and 45 kg displacement).
Table 2: Test matrix of the spray rail series.
Fr
m
Description
[-]
[kg]
0.769
0.961
1.153
1.345
30
35
40
45
Bare hull
Bare hull with a rectangular
2x2 mm chine spray
interceptor
Bare hull with a triangular
2x15 mm chine inclination
Hull with rectangular 5x5mm
spray rails
Hull with 5x5mm rectangular
spray rails and a 2x2mm
rectangular chine spray
interceptor
Hull with 5x5mm rectangular
spray rails and a 5x5mm
triangular chine spray rail
Figure 1: a) bare hull (BH), b) rectangular chine spray
interceptor (CSI), c) chine inclination (C.INC).
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© 2020: The Royal Institution of Naval Architects
Figure 2: (a) hull with spray rails (SR), b) rectangular
5x5mm spray rail, c) rectangular 2x2mm chine spray
interceptor (SR-CSI), d) triangular 5x5mm chine spray
rail (SR-CSR).
2.2 LABORATORY INSTRUMENTATION
The calm water towing tests were conducted in the
towing tank of SCC following the ITTC guidelines 7.5-
02-02-01 [16]. The main dimensions of the basin are
length 60m, breadth 5m and depth 3m. The models were
tested in semi-captive condition (Fig. 3), i.e. the models
were free to sink and pitch. During the tests, resistance
and draught changes were measured.
The total resistance of the models was measured at 200
Hz sampling frequency, with 2-4 repeated runs at low
speeds (Fr = 0.769 & Fr = 0.961) and 3-5 repeated runs
at high speeds (Fr =1.153 & Fr = 1.354). The data
acquisition time was around 6 s to 9 s and 2.5 s to 4.3s
for low and high speeds respectively.
The uncertainty analysis was carried out following the
ITTC guidelines 7.5-02-02-02 and 7.5-02-02-02.1 [17],
[18]. Examples of the uncertainty of resistance, trim and
sinkage are given in Appendix A.
The bias of the force gauge (dynamometer) was 0.2% in
the range of 0 to 0.2 kN. The dynamometer was
calibrated before the model test according to the ITTC
Procedure 7.5-01-03-01 [19]. Five loads were
implemented by weights and randomly applied three
times each load. The fitting curve for predicting the force
was obtained by linear regression with a standard
deviation of SEE = 0.077N.
The trim of the craft was evaluated from the readings of
draught change in the aft and the bow. The draught
changes were measured with linear measuring wire and
draw-wire encoder the bias of which is 0.05% in a range
of ±1250mm.
The tachometer was calibrated at 1 m/s, 2 m/s, 3 m/s, 4,
m/s and 5 m/s, four runs for each speed except for the
speed 1m/s which was run 6 times. The fitting curve for
predicting the speed was obtained by linear regression
with a standard deviation of SEE=0.0011m/s.
The temperature of the water in the tank was measured
once a day with a K-type thermo-couple the bias of
which is 1 ºC in a range of -40 ºC to 1372 º.
3. RESULTS AND DISCUSSION
The two tested sets of chine modifications were
compared to their respective benchmarks in terms of total
resistance, trim and sinkage at the CG. Figures 4-6 show
the comparison in the design condition of the craft (m =
40 kg and Fr =1.354). In Figures 7-9, the test results are
presented as functions of Froude number, where the Fr is
based on the craft’s length between perpendiculars LPP =
1.8 m for better visualization.
Compared to the bare hull (BH), at the design speed of
Fr = 1.345, the chine spray interceptor (BH-CSI) and
chine inclination (BH-C.INC) reduced the total resistance
by 2.6% to 3.4% and 1.4% to 2.9% respectively. The
change of resistance was also dependent on the
displacement. The lighter the craft the greater the
reduction of total resistance.
The influence of the chine spray interceptors on the
performance of the boat equipped with spray rails was
rather similar to that of the bare hull. The chine spray
interceptors increased the total resistance by around 1%
in semi-displacement condition and decreased it by up to
3% in planing condition.
In semi-displacement regime, the rectangular 2x2 mm
chine spray interceptor (SR-CSI) increased the total
resistance in light and heavy loading conditions
respectively by 1.5% - 3.2% and 0.8% - 2%. In planing
regime the total resistance was increased by 0.4% - 1.1%
in light loading conditions and it was decreased by 0.8%
- 1.3% in heavy loading conditions.
In the semi-displacement regime, the triangular 5x5 mm
chine spray rail (SR-CSR) increased the total resistance
by up to 0.9% and 1.9% in light and heavy loading
conditions respectively. In planing regime, the total
resistance decreased by 2.1% - 2.6% and 2.5% -3% in
light and heavy loading conditions respectively.
Similarly, to the cases with the bare hull, both the chine
spray rail and chine interceptor increased the running
trim in semi-displacement and reduced it in planing
mode. The chine spray interceptors also reduced the
sinkage at the CG through the whole speed and
displacement range. However, the increase of the sinkage
at the CG was less than that in the case of the bare hull.
High Speed Vessels, 1-2 July 2020, London, UK
© 2020: The Royal Institution of Naval Architects
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Figure 3: Spray formation on the tested models in design condition Fr = 1.354 and ∆m = 40kg: a) BH, b) BH-C.INC,
C)BH- CSI, d) SR, e) SR-CSI, f) SR-CSR.
a)
b)
c)
d)
)
e)
f)
High Speed Vessels, 1-2 July 2020, London, UK
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© 2020: The Royal Institution of Naval Architects
Figure 4: Total resistance RTM with expanded uncertainty Up (RTM /Δ) of the tested configurations relative to their
benchmarks in design condition Fr = 1.354 and m = 40kg.
Figure 5: Dynamic trim τ with expanded uncertainty Up (τ) of the tested configurations relative to the bare hull in design
condition Fr = 01.354 and m = 40kg.
High Speed Vessels, 1-2 July 2020, London, UK
© 2020: The Royal Institution of Naval Architects
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Figure 6: Non-dimensional dynamic sinkage at the centre of gravity zV,CG /
1/3 with expanded uncertainty Up (zV,CG /
1/3) of the tested configurations relative to the bare hull in design condition Fr = 01.354 and m = 40kg.
Figure 7: Total resistance RTM of the tested
configurations.
Figure 8: Dynamic trim τ of the tested configurations.
High Speed Vessels, 1-2 July 2020, London, UK
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© 2020: The Royal Institution of Naval Architects
Figure 9. Non-dimensional dynamic sinkage zV, CG /
1/3
at the centre of gravity of the tested configurations.
4. CONCLUSIONS
The results of an experimental series comprising two
benchmarks and four chine modifications are presented
in this paper. Based on the results following conclusions
can be made:
The results show that it is possible to affect the
running position of planing craft with rather simple
chine modifications.
Both chine spray interceptor and chine inclination
reduced trim and total resistance of the craft,
particularly at high speed and in heavy loading
condition.
A simple rectangular interceptor on the chine
reduced the total resistance and trim nearly twice as
much as the chine inclination did.
A triangular chine spray rail reduces the resistance
and running trim more than a rectangular one does.
The main problem of this paper is that it remains unclear
whether the triangular 5x5mm chine spray rail performed
better than rectangular 2x2mm chine interceptor, due to
its size or angle with the chine surface. Therefore, future
studies should include a larger variety of tested chine
modifications to separate the influence of the angle of the
spray deflection surface from that of its size.
5. ACKNOWLEDGEMENTS
This research work was financed by the Estonian
Research Council via grant PRG83 (Numerical
simulation of the FSI for the dynamic loads and response
of ships) and by the European Regional Development
Fund via grant 2014-2020.5.04.19-0385 (Small Craft
Competence Centre analysis of the impact of external
construction elements on the performance of a vessel,
transfer of know-how and information). This help is
gratefully appreciated
6. REFERENCES
[1] E. P. Clement, “Effects of Longitudinal Bottom
Spray Strips on Planing Boat Resistance, Report
No.1818,” Washington, DC., 1964.
[2] E. P. Clement, “Reduction of Planing Boat
Resistance by Deflection of the Whisker Spray,
Report No.1929,” Washington, DC., 1964.
[3] G. Grigoropoulos and T. Loukakis, “Effect of
Spray Rails on the Resistance of Planing Hulls,”
in 3rd Intl. Symposium on Fast Sea
Transportation FAST’95, 1995, no. September.
[4] G. Grigoropoulos, “The use of Spray Rails and
Wedges in Fast Monohulls,” in IV High-Speed
Vehicles Intl. Conf. HSMV’97, 1997, no. March.
[5] W. J. Kapryan and G. M. Boyd, “The Effect of
Vertical Chine Strips on the Planing
Characteristics of V- Shaped Prismatic Surfaces
Having Angles of Dead Rise of 20 Degrees and
40 Degrees,” Langley Field, VA, 1953.
[6] D. Savitsky, M. F. DeLorme, and R. Datla,
“Inclusion of Whisker Spray Drag in
Performance Prediction Method for High-Speed
Planing Hulls,” Mar. Technol., vol. 44, no. 1, pp.
3556, 2007.
[7] D. Savitsky, “Hydrodynamic design of planing
hulls,” Marine Technology, vol. 1, no. 1. pp. 71
94, 1964.
[8] D. Savitsky and J. P. Breslin, “On the Main
Spray Generated by Planing Surfaces,” Hoboken,
New Jersey, 1958.
[9] D. Savitsky and M. Morabito, “Origin and
Characteristics of the Spray Patterns Generated
by Planing Hulls,” J. Sh. Prod. Des., vol. 27, no.
2, pp. 6383, 2011.
[10] T. C. Fu et al., “An Assessment of
Computational Fluid Dynamics Predictions of
the Hydrodynamics of High-Speed Planing Craft
in Calm Water and Waves,” in 30th Symposium
on Naval Hydrodynamics, 2014, no. November.
[11] J. Seo et al., “Model tests on resistance and
seakeeping performance of wave-piercing high-
speed vessel with spray rails,” Int. J. Nav. Archit.
Ocean Eng., vol. 8, no. 5, pp. 442455, 2016.
[12] D. J. Kim, S. Y. Kim, Y. J. You, K. P. Rhee, S.
H. Kim, and Y. G. Kim, “Design of high-speed
planing hulls for the improvement of resistance
and seakeeping performance,Int. J. Nav. Archit.
High Speed Vessels, 1-2 July 2020, London, UK
© 2020: The Royal Institution of Naval Architects
69
Ocean Eng., vol. 5, no. 1, pp. 161177, 2013.
[13] L. Olin, M. Altimira, J. Danielsson, and A.
Rosén, “Numerical modelling of spray sheet
deflection on planing hulls,” in Proceedings of
the Institution of Mechanical Engineers, Part M:
Journal of Engineering for the Maritime
Environment, 2016, vol. 231, no. 4, pp. 811817.
[14] B. Molchanov, S. Lundmark, M. Fürth, and M.
Green, “Experimental validation of spray
deflectors for high speed craft,” Ocean Eng., vol.
191, no. April, p. 106482, 2019.
[15] M. Lakatos, T. Sahk, R. Kaarma, K. Tabri, M.
Kõrgesaar, and H. Andreasson, “Experimental
testing of spray rails for the resistance reduction
of planing crafts,” in Trends in the Analysis and
Design of Marine Structures : Proceedings of the
7th International Conference on Marine
Structures, MARSTRUCT 2019, 2019, pp. 334
343.
[16] 28th ITTC, “7.5-02-02-01 Resistance Test,”
ITTC, 2017.
[17] 27th ITTC, “7.5-02-02-02 General Guideline for
Uncertainty Analysis in Resistance Tests,” 2014.
[18] 27th ITTC, “7.5-02-02-02.1 Example for
Uncertainty Analysis of Resistance Tests in
Towing Tank,” 2014.
[19] 28th ITTC, “7.5-01-03-01 Uncertainty Analysis,
Instrument Calibration,” 2017.
7. AUTHORS BIOGRAPHY
Mikloš Lakatoš holds the current position of early-stage
researcher at Tallinn University of Technology, Small
Craft Competence Centre. He is responsible for on
experimental testing and numerical modelling of spray
rails for improved resistance and seakeeping
performance of the fast medium-sized craft. His previous
experience includes work as a naval architect specialising
in marine hydrodynamics, hull design and propulsion
calculations in at Deltamarin Ltd.
Tarmo Sahk holds the current position of head of
laboratories at Small Craft Competence Centre of Tallinn
University of Technology. He is responsible for
conducting model testing and laboratory services for
commercial and research purposes. His previous
experience includes a BSc in Small Craft Building.
Henrik Andreasson holds the current position as Naval
Architect and owner of Flow Naval Architects. He has
been working with hydrodynamic design and
optimization since 1999. Until 2009 he worked as project
manager at the model test facility SSPA Sweden AB.
Since 2015 he has been Hydrodynamic mentor at Tallinn
University of technology, Small Craft Competence
Center, involved within the development and running of
the towing tank.
Kristjan Tabri holds the current position of senior
research scientist at Tallinn University of Technology.
He is responsible for developing a two-way coupled fluid
structure interaction model for dynamic impact problems.
His previous experience includes the simulation of
structural behaviour of marine structures under dynamic
loads.
High Speed Vessels, 1-2 July 2020, London, UK
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© 2020: The Royal Institution of Naval Architects
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The elemental hydrodynamic characteristics of prismatic planing surfaces are discussed and empirical planing equations are given which describe the lift, drag, wetted area, center of pressure, and porpoising stability limits of planing surfaces as a function of speed, trim angle, deadrise angle, and loading. These results are combined to formulate simple computational procedures to predict the horsepower requirements, running trim, draft, and porpoising stability of prismatic planing hulls. Illustrative examples are included to demonstrate the application of the computational procedures.
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A planing craft is a type of marine vehicle that is supported predominantly by hydrodynamic forces at high speeds. It has widespread applications in recreational and military use as well as for search and rescue operations. Although spray rails are a mature technology, there is limited experimental data illustrating their hydrodynamic effects. Furthermore, continuous efforts are being made to improve the efficiency, safety and performance of planning craft. In this paper, the efficiency of the spray resistance reduction technologies – spray rails and spray deflectors – are compared in model scale through towing tank testing in calm water and irregular waves. This study examines the influences of the technologies on the total resistance and running position of the hull in calm water and on impact accelerations experienced at the center of gravity and bow in irregular waves. The experimental results are discussed in connection with established semi-empirical methods for predicting the performance of planing craft and improvements for further testing of the spray deflection methods are proposed.
Conference Paper
Spray rails, as well as the whole topic of spray sheet deflection, have been generally disregarded since the 1960s. Therefore, a series of model tests has been conducted with a 19 m craft configured with different spray rail arrangements (operating in a range of Froude numbers Fr = 0.77…1.35). The model test series comprises five spray rail configurations: two chine modifications, two conventional spray rail configurations (with 2 × 2 mm and 5 × 5 mm rails) and a V-shaped spray rail arrangement. A number of significant findings are reported. A simple rectangular interceptor rail on the chine reduces the resistance of a planing craft by more than 3%. A V-shaped spray rail on the hull can reduce the resistance by up to 4%. Conventional spray rail set up reduces the resistance by nearly 2% at planing speeds. This publication sheds new light on well-known as well as recent concepts in planing craft design.
This paper considers the modelling of spray formation on planing hulls. The focus is on assessing the applicability of the prevailing theories and two-dimensional and three-dimensional Computational Fluid Dynamics (CFD) simulations in the investigation of different design factors for a novel spray deflection concept. The spray deflection concept is presented and its performance is evaluated by comparison with traditional spray rails. It is found that the prevailing theory where the spray field of a planing hull is represented by a two-dimensional flat planing plate will overestimate the spray thickness, whereas the theories that are based on wedge impact are correlating well with the results from the CFD simulations. Compared to a bare hull, adding spray deflectors reduces the viscous resistance by 28% for the studied cases. The spray deflectors further redirect the spray aftwards which reduce the total drag an additional 4%. The paper also discusses various aspects on CFD modelling of spray formation.
Article
Experiments were made to determine the effects on planing boat resistance of several configurations of longitudinal bottom spray strips. It was found that such strips extending aft from the bow about 70% of the hull length decreased the resistance somewhat at high speed but increased the resistance at low speed. The performance was noticeably improved by sharpening the edges of the spray strips. An experiment was also made with bottom spray strips extending only forward of the high-speed stagnation line. This arrangement gave a 6% reduction in resistance at high speed with no increase in resistance at low speed. (Author)