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1 INTRODUCTION
The design of ships and marine facilities is a complex
iterative process involving numerous trade-off
decisions. It is directly related to meeting client
requirements and the specified input data.
Commercial shipbuilding has shifted far to the East,
to countries like China, Korea, Japan, and others in
recent years. In Europe, only the construction of
specialized ships and marine structures has remained.
This necessitates a reorientation of the market niche for
European shipbuilding enterprises, primarily small
and medium-sized ones, which are the backbone of the
European economy.
European shipbuilding enterprises construct
passenger ships, dredging fleet vessels, auxiliary port
fleet vessels, floating docks, and more. Some European
countries rank among the leaders in the statistics for
building floating docks.
Small and medium-sized shipbuilding enterprises
often face limitations. These limitations can be divided
into two main groups: production-related and
geometric. These two groups of limitations affect the
characteristics and qualities of the designed and
constructed ships and marine equipment. For this
reason, a study was conducted on their impact on a
floating dock's operational and strength qualities
during the conceptual design stage.
Floating docks are subjected to various loads
caused by the environment and their operation. These
loads include hydrostatic, hydrodynamic, contact, and
mooring loads, with six degrees of freedom [7]. During
the simulation, the loads from mooring and docking
were taken into account. No significant changes in the
dock's structure were observed as a result of the loads.
A finite element model can adequately assess the
strength of ships and marine structures. Such an
assessment has been carried out in [3], where the
Impact Study of Shipyard Limitations to Designed
Floating Dock Construction
Y. Denev
Technical University of Varna, Varna, Bulgaria
ABSTRACT: The development of modern marine technology requires flexibility in design and high-quality
craftsmanship. To some extent, this necessitates considering the various limitations imposed by shipbuilding
enterprises. These limitations influence ships' and marine equipment's construction, characteristics, and
operational behavior. The article analyzes the impact of production constraints on a steel floating dock's design
and strength characteristics. The strength properties of the facility, determining its suitability for use, have been
analyzed using the MARS 2000 software. Two structural models of a floating dock have been developed—one
with imposed width constraints and the other without constraints, with the same lifting capacity. It turns out that
in the structure with constraints, the strength characteristics are close to those determined by the regulations. This
provides grounds to claim that the geometric constraints of small and medium sized enterprises(SME)s do not
always negatively impact the structural qualities of floating objects.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 19
Number 2
June 2025
DOI: 10.12716/1001.19.02.23
532
longitudinal and transverse strength of a floating dock
has been evaluated. Using a dock model in the finite
element environment, the current stresses have been
assessed and compared with those specified by the
rules of classification societies.
Floating docks are used not only for ship repair
activities but also in other branches of industry. An
analysis of a floating dock in the form of a platform is
presented in [4]. During the design, modeling, and
analysis, two groups of constraints were considered,
which can be divided into linear and nonlinear
categories. The linear constraints are related to the
geometry of the dock, while the nonlinear ones are
associated with its operation. Taking these constraints
into account, two geometries of the floating dock have
been developed.
Over time, the structure of floating docks loses
some of its operational capacity. This is caused by the
effects of corrosion. The behavior of a dock,
considering the effects of corrosion and modeling with
six degrees of freedom, is analyzed in [5]. It has been
found that after damage caused by corrosion—holes in
the ballast tanks of the dock—the inclination angles
increase, which can lead to a serious accident or
environmental disaster.
Modular floating docks find application in the
shipbuilding and ship repair industry. The connection
between individual modules is articulated. The
calculation of the load and strength analysis of this
type of floating structure was performed in [6]. The
analysis was carried out using the SESAME program.
The evaluation of the properties was conducted
through the modeling of a three-dimensional wave
flow. In the initial design, the stress values in the areas
of the connections were high, but after reinforcing the
structure, they decreased to permissible limits.
The structural strength of a floating dock during
ship docking was evaluated using the finite element
method in [8]. The evaluation employed the so-called
"load per linear meter" method. Constraints were
imposed on the main dimensions of the dock,
stemming from the specifics of its operation. The
developed procedure and model can be successfully
used to assess proper ballasting to reduce stresses in
the hull structure. The simplicity of the method makes
it easily adaptable to similar structures with different
main dimensions.
The conversion of a dock from a single-pontoon to
a multi-pontoon structure without significant
modification to its design is presented and analyzed in
[9]. Once again, the authors have used the finite
element method to assess the stress state. It was
determined that after the conversion, the stresses are
lower than the allowable limits, which provides
grounds to claim that the structure operates on the safe
side. An economic analysis of the activity has also been
conducted.
One possible and quick way to construct a floating
dock is by converting a ship that has been
decommissioned for various reasons. Such is the case
presented in [2], where an offshore barge is converted
into a floating dock. An assessment of the global and
local strength was conducted under two scenarios
using a 3D finite element model. The dock is
constrained in terms of width and length. During the
analysis, stress concentrations were identified in the
area of the main deck around the ballast tanks, but
these were eliminated after structural improvements.
A large part of the research related to marine
engineering, and more specifically to floating docks, is
based on strength assessment using the finite element
method. It would be beneficial for the evaluation to
also take into account the constraints from a
manufacturing perspective and to assess their impact
on the characteristics of the marine structure's design.
2 MODEL DEVELOPMENT
The development of a model for assessing the impact
of production constraints on the designed marine
structures was carried out using the specialized
software MARS 2000. The article examines and studies
the influence of the constraints of a small and medium-
sized shipbuilding enterprise on the characteristics of
the floating structure design.
The imposed constraints are geometric and directly
related to marine structures' design and operation. The
assessment applied a width limitation of 16.0 meters to
the floating structure. For comparison and evaluation,
a similar model without constraints was used while
maintaining the same load capacity. The main
dimensions of both models are shown in tabl.1 and
tabl.2
Table 1. Floating dock main dimension with restriction
L,m
B,m
D,m
t,m
LC,t
Disolacement, t
Double bottom height, m
Side tank depth, m
Table 2. Floating dock main dimension without restriction
L,m
B,m
D,m
t,m
LC,t
Displacement, t
Double bottom height, m
Side tank depth, m
The floating dock analyzed in the study is entirely
made of steel. It is designed for docking ships and
marine structures with a launching weight of up to
2000 tons. The design of the structure follows the rules
for floating docks set by the classification society
Bureau Veritas. The material used for construction is
ST 235, a standard shipbuilding steel. The ordinary
frame spacing is 600 mm, while the web frame spacing
is 1800 mm for both cases. The shear forces and
bending moments acting on the dock during operation
have been determined according to the classification
society's rules. The corrosion allowance for
determining the type of profiles and their geometry has
been established according to the procedure set in the
rules and is in the range of 1.5-2.0 mm.
The section modulus of the bottom and deck shall
not be less than that calculated by the following
formulas:[ 1]:
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for bottom
3
, =
ab
Iy
Zm
N
(1)
for deck
3
, =
ad
D
Iy
Zm
V
(2)
where:
Iy - moment of inertia of the hull transverse section
about its horizontal neutral axis, m
4
;
N is Z co-ordinate, in m, of the centre of gravity of the
hull transverse section, m
Z is Z coordinate, in m, of the calculation point of a
structural element., m;
VD- vertical distance, in m; in general:
DD
V Z N=−
(3)
ZD is a Z co-ordinate, in m, of strength deck with
respect to the reference co-ordinate system, m
Figures 1 and 2 show the models of the dock's
midship sections. They show that the structure has a
double bottom and double sides, with a height of 2200
mm and a width of 2200 mm.
A longitudinal framing system has been used,
incorporating bulb profiles. In both constructions, HP
160x8 profiles have been utilized for the framing in the
double bottom structure, the side construction, and the
deck. In the double bottom, a watertight stringer is
located at a distance of 25% of the dock's width for both
models. On the sides, two non-watertight platforms are
positioned at 25% of the side's depth.
Figure 1. Midsection of the floating dock with restricted
breadth, L= 80.00m, B=16.00m
Figure 2. Midsection of the floating dock without restrictions,
L=60.00m, B=20.00m
The designed structure is loaded with the weights
acting upon it. In this case, these are the weight of the
cargo, which represents the dock's lifting capacity, and
the pressure from the water in the ballast tanks. This is
achieved by dividing the structure into its constituent
ballast tanks and compartments.
3 CONSTRUCTION ANALYZE
The impact of geometric and manufacturing
constraints on the structure of the floating dock has
been evaluated in several aspects, which are part of the
classification societies' requirements for the strength of
ships and marine structures. The first aspect evaluates
bending moments concerning the bottom and the deck,
the second evaluates normal stresses, and the third
assesses global strength.
The evaluation of the actual section modulus is
presented in fig.3 and fig.4.
Figure 3. Section modulus at deck
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From the graph presented in Fig. 3, it can be
observed that the current section modulus has higher
values than those determined by the minimum
requirements of classification society rules (orange
line). The values of the current and minimum section
modulus have been determined using the specialized
software MARS 2000, in which the rules of the
classification society are implemented. With the dock
structure designed under the imposed constraint (1),
the value of the bending moment relative to the bottom
is close to the minimum value. In contrast, in the case
without the constraint, the current value is relatively
higher than the minimum. This indicates that the dock
designed with the constraint will have a comparatively
lower launching weight.
A similar situation is observed with the bending
moments relative to the bottom, as shown in the figure.
In both cases, the values are significantly higher than
those determined by the rules of the classification
society. The minimum values are represented by the
orange line, the dock with constraints is marked as 1,
and the other as 2. Although the bending moment
values significantly exceed the minimums, modifying
the structure would compromise local strength.
Figure 4. Section modulus at bottom
The normal stresses in the structure arise from
applied bending moments. Their distribution depends
on the position of the neutral line within the structure.
Figure 5 and 6 show the distribution of normal stresses
in the structures of both models under identical
loading conditions.
The hull girder normal stresses at any point of the
net hull girder transverse section, calculated with the
following condition [BV]:
11

AB
(4)
where:
1
AB
- allowable hull girder normal stress, N/mm
2
1
190
=
AB
k
for steel hull;
K - material factor, for shipbuilding steel ST 235, k=1;
Figure 5. Normal stress distribution with restricted breath
Figure 6. Normal stress distribution without restricted breath
The values of the normal stresses in both cases are
below the allowable limits for the structure. For the
constrained structure, the normal stresses have a value
of σ1r=166,77 N/mm
2
, while for the unconstrained
structure, they have a value of σ1=115,17 N/mm
2
. The
obtained values, compared to the allowable ones, are
lower. For the constrained structure, the values are
close to the allowable limit, around 90%.
Figures 7 and 8 present the overall strength results.
The stress distribution in the structure with the
constraint appears more vulnerable, i.e., the values are
closer to the nominal ones.
In the dock structure with imposed constraints, the
loads from overall strength are carried by all structural
elements. The elements farthest from the neutral axis
are particularly loaded, fig.7.
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Figure 7. Hull global strength with restricted breath
The overall strength is different in the structure
without imposed constraints. In this case, the areas
around the bottom and part of the double hull are not
intensively loaded. Loading is observed only in the
area of the last plate from the double bottom to the
double hull, but it is not significant.
Figure 8. Hull global strength without restriction
The approximate mass of the steel structure of the
dock, considering the constraints, is around 563.0 tons,
and without the constraints, it is around 484.0 tons. The
manufacturing cost of the steel structure is
approximately 366155.4$ for the constrained version
and 314293.59$ for the unconstrained version.
4 CONCLUSIONS
The article examines and analyzes the impact of the
limitations of small and medium-sized shipbuilding
enterprises on the floating dock design. The influence
of the limited width of the building and launching
facility on the behavior of the floating dock structure is
analyzed in the article.
Two variants of the floating dock structure have
been developed: with and without width limitations.
Using a model in the MARS 2000 program
environment, an assessment of the strength was
carried out with and without the imposed limitations.
The strength assessment was conducted in three
aspects: evaluation of the section modulus to the
bottom and the deck, distribution of normal stresses
from bending moments in calm water and waves, and
overall strength.
The obtained values of the section moduli to the
bottom and the deck are higher than those determined
according to the rules of the classification society. For
the structure with limited width, it is observed that the
section modulus value for the deck is close to the
allowable limit.
The normal stress values in both cases are within
the allowable limits for the structure. For the
constrained structure, the normal stresses are σ1r =
166.77 N/mm², while for the unconstrained structure,
they are σ1 = 115.17 N/mm². The obtained values of the
normal stresses for the constrained structure are close
to the allowable limits but do not exceed them.
In the dock structure with imposed constraints, the
overall strength loads are distributed across all
structural elements, with the elements furthest from
the neutral axis experiencing the greatest load. In
contrast, the overall strength behavior differs in the
structure without constraints. In this case, the regions
near the bottom and part of the double hull are not
heavily loaded. The loading is primarily concentrated
in the area of the last plate connecting the double
bottom to the double hull, but it remains minimal.
The designed structure of the floating dock,
considering production constraints, does not exhibit
inferior qualities compared to the one without
constraints. In the structure with limited width,
relatively lower values of the section moduls are
observed, which indicates the efficient use of material
rather than the excessive reserve.
ACKNOWLEDGMENT
The article was developed under the National Program
"Young Scientists and Postdoctoral Researchers - 2" at the
Technical University of Varna, within the Postdoctoral
Researchers section.
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