EP1350716A1

EP1350716A1 - Floating facility equipped with cranes

Info

Publication number: EP1350716A1
Application number: EP03007591A
Authority: EP
Inventors: Mario Terenzio
Original assignee: Coeclerici Logistics SpA
Current assignee: Coeclerici Logistics SpA
Priority date: 2002-04-05
Filing date: 2003-04-02
Publication date: 2003-10-08
Anticipated expiration: 2023-04-02
Also published as: ATE276916T1; DE60300052D1; ITTO20020297A0; ITTO20020297A1; EP1350716B1

Abstract

The facility (1), which basically amounts to a floating crane, has a relatoproductivity coefficient CRlter defined as: - CR1ter = (1/3) [ΣiQi·ΣiJpi·P(CB·B4L2/6T2- D/T)/I3]0.2

with the index of summation i ranging from 1 to n, where n is the number of cranes, and

Q_i is the maximum hoisting capacity of the i-th crane (t);

J_pi is the moment of inertia of a load equal to the hoisting capacity of the i-th crane with respect to the side of the facility (t·m²);

L is the length on the waterline of the facility (m) ;

B is the breadth of the facility at maximum draught (m) ;

T is the maximum draught (m);

C_B is the block coefficient of the facility at maximum draught;

D is the moulded depth (m);

I is the distance in metres between the hoisting point of the crane with arm raised at minimum range and the line of moulded depth of the facility; and

P is the empty weight of the facility (t);

and where said coefficient of relatoproductivity is higher than 100, and preferably higher than 125.

Description

The present invention relates to floating facility equipped with cranes and has been developed with particular attention paid to its possible application to the logistics of transportation of raw materials.
Amongst so-called "dry bulk" raw materials, coal and iron material represent the largest amount of freight transported by sea at a world level. Bauxite, iron ore and coal are raw materials of low intrinsic value. The sources of these materials and the consuming countries are frequently located in different continents, as is evidenced, for instance, by the intense traffic of iron material existing between Brazil and Japan, or by the traffic of coal between Australia and Europe.
The ever increasing international competition in terms of cost of the finished product (for instance, steel and electric power) has influenced transportation by sea of these raw materials, as well as the corresponding logistics.
In order to reduce the costs of procurement and, consequently, the cost of the finished product, in the last few decades there has been the tendency to build ships of ever greater carrying capacity, increasing the average amount of each shipment and reducing, as a result, the costs of transportation.
For the transportation of the aforesaid raw materials, prevalently ships known as bulk carriers, of the Panamax and Cape types, are used. In the last twenty years, the average capacity of these units has progressively increased in vessels of the Panamax type from a deadweight tonnage of 50-60 000 dwt to 70-75 000 dwt, and in vessels of the Cape type from 100-130 000 dwt to 150-170 000 dwt.
Of course, not all ports are able to receive such large ships.
In addition to the solution of necessarily resorting to smaller ships for ports with flats, in ports that lack adequate harbour facilities and infrastructures, such as in India, Indonesia, and China, crane ships or ships provided with booms, both of the self-loading type and of the unloading type, are widely used.
The above traditional solutions, which are based upon the criterion of adapting the facility of transport to the physical restrictions and to the lack of port infrastructures and facilities, lead to a considerable increase in transportation costs and hence in the costs for procurement of raw materials.
In the last few years, new logistic concepts and systems have been developed, amongst which the one examined here for solving the above-mentioned logistic requirements, enabling the use of ships that will guarantee optimization of freight.
The said alternative concepts prove to be more economically advantageous and flexible than the construction of specific port infrastructures or the dredging of ports.
The above alternative solutions emerge as true floating terminals that are able to guarantee the same function as a port terminal, but with lower costs in terms of investment and management, and with lower times involved for their construction, as well as a smaller environmental impact as compared to the provision and construction of traditional port infrastructures.
The simplest embodiment of such a floating facility equipped with cranes is the one generally referred to as "floating crane". This system, which basically amounts to the solution of mounting a crane on a pontoon was developed after the Second World War prevalently to enable operation in the framework of a port, and hence in sheltered waters.
At the moment, approximately 50 units are in operation, which are prevalently concentrated in the ports of Northern Europe, for example Rotterdam and Amsterdam, and in certain river terminals in the United States (e.g., on the Mississippi).
The above facilities are used for transferring the commodity from ocean-going vessels onto lighters or barges (in the operation of unloading the ship), or from the lighters or barges onto the ocean-going vessels (in the operation of loading the ship).
The aforesaid facilities are characterized by considerable flexibility, are able to handle various types of materials, both bulk materials, using grabs, and materials organized in packages and containers, using specially designed tools for picking them up.
The intrinsic limit to the above solutions lies in the sea worthiness and in the fact that usually there is not available on board the facility a structure that is able to function as a depot or storage area, where the materials can be temporarily stowed, both during the operation of loading and during the operation of unloading of the ship.
An excellent sea worthiness and the availability of a stowage area are basic requirements for enabling a degree of efficiency and operativeness that is altogether satisfactory, in particular as regards the possibility of ensuring, at least virtually, a round-the-clock functionality throughout the year.
Some twenty years ago, the present applicant developed transportable transporter cranes that can be mounted on ships of the bulk-carrier type, thus turning them into self-unloading ships. In this way, the operation of unloading of the ship may be carried out in open sea, hence making it possible to send Cape ships of large size even into areas without adequate draught. By way of reference, if four travelling cranes are used, it is possible to achieve an unloading rate in the region of 20 thousand tonnes a day of dry bulk material.
Another solution is represented by the ship Capo Noli, developed by the present applicant for coastal transportation of dry bulk materials, such as coal and salt. The ship in reference is equipped with four cranes, belts and hoppers and is able to unload directly into shore receiving facility by means of a jib measuring 35 metres in length, at a rate of 1200 tonnes per hour.
Yet another solution of a floating terminal developed by the applicant is the Bulktrieste floating terminal, at the moment moored head-on at the quay VII of the port of Trieste. This is a system enabling operations of unloading and loading of coal from ocean-going vessels onto lighters or barges dedicated chiefly to the logistics of ENEL (Italian National Electricity Board) electric power stations in the upper Adriatic.
The system envisages the use of four travelling cranes mounted on board the ocean-going vessel moored alongside the Bulktrieste terminal. In this way, it is possible to unload the coal onto barges or onto ships of small size. A mobile crane, installed on the floating terminal enables the positioning of the four travelling "cavalletto" cranes on board the ocean-going vessel. In the event of any lack of availability of lighters or barges, the coal can be unloaded directly onto the floating terminal, which is therefore usable as storage. The coal can subsequently be loaded onto lighters using the same four travelling "cavalletto" cranes installed directly on the Bulktrieste terminal.
Any contamination of the cargo is prevented by using different holds according to the type of coal.
The Bulktrieste floating terminal can unload coal ships at a rate higher than 20 thousand tonnes per day. The terminal is able to operate also as a covered storage for a total of 120 thousand tonnes, thus minimizing the risk of pollution from dust.
Proceeding in the present review of previous solutions developed by the applicant, we cite the Bulkgulf ship, which is currently operating off the wharf of the Gulf Industrial Investment Co. (GIIC) steelworks in Bahrain. This vessel tranships part of the load from large ocean-going vessels of the Cape type into its own holds, thus carrying out a typical intervention of lightening, i.e., lessening the load of the ocean-going vessel and overcoming the problems of draught of the port of the GIIC steelworks. After transhipping approximately 70 thousand tonnes from the ocean-going vessels, the ship Bulkgulf can moor at the wharf and carry out self-unloading onto shore, whilst the ocean-going vessels are unloaded by shore means. The experiments so far conducted in this regard demonstrate that the solution in reference is able to achieve a volume of importation higher than 5 million tonnes of iron ore per year.
In 1998, the present applicant studied and developed the floating storage transfer station called Bulkwayuù, which is currently moored by facility of piles and cables in the Lake of Maracaibo, in Venezuela. The Bulkwayuù loads coal coming from the barges of the Carbones del Guasare mine, which is the biggest producer of coal in Venezuela, onto ships of the Panamax type with the maximum amount of coal allowed by the draught of the lake, i.e. approximately 60 thousand tonnes.
In the case where there are no ships alongside the Bulkwayuù, the coal coming by the barges is unloaded into the holds of the floating storage to be subsequently used for loading on board ocean-going vessels even in the absence of barges.
The system is able to load ships at a rate of 30 thousand tonnes per day, with the possibility of exceeding 38 thousand tonnes per day. In 2001, the Bulkwayuù loaded 145 ships with a total of 6.7 million tonnes at an average rate, over 365 days, of 18, 405 tonnes per day.
Finally, the 15-thousand-ton deadweight floating facility called Bulk Kremi I, installed in the port of Bourgas in Bulgaria, provides a service of lightening of ocean-going vessels of the Panamax type of approximately 70 thousand tonnes in order to enable the vessels to meet the port requirement of a draught of 11 metres. In the port itself, both the ocean-going vessel and the floating facility Bulk Kremi I are unloaded by shore means. The service, offered to Kremikovtzi Steelworks (KWS), one of the most important steelworks in Bulgaria, chiefly regards the loading/unloading of iron ore or coal.
The experiments carried out by the present applicant and by other operators of the sector show that, in the implementation of floating-crane facilities of the type described, there emerge requirements that are altogether in contrast with one another.
For instance, as regards the loading/unloading capacity there exists the evident interest in increasing both the number of cranes and the maximum hoisting power of the individual cranes.
The increase in the maximum hoisting power of a crane usually determines a corresponding increase in the moment of inertia of the load corresponding to the hoisting capacity of the individual crane with respect to the side of the facility.
The need to install a larger number of cranes and/or to use bigger cranes of greater capacity, however, inevitably results in the need to provide a bigger floating facility, namely one having a greater length on the waterline, a greater breadth at maximum draught, a greater maximum draught, and a greater moulded depth.
The increase in the dimensions of the facility enables an improved stability and sea worthiness to be bestowed on the facility.
It follows, therefore, that the solutions according to the known art, however functional they may be, inevitably end up by privileging one requirement at the expense of another.
The purpose of the present invention is to provide a solution capable of overcoming the intrinsic limits of the solutions of the prior art described previously, with an optimal investment and management cost, i.e., cost/benefit ratio, and with a greater annual operativeness.
According to the present invention, the aforesaid purpose is achieved thanks to a floating facility presenting the characteristics recalled specifically in the ensuing claims. The invention also relates to the use of said floating facility.
Basically, the applicant has had the opportunity to verify that, for floating facility of the type described, the main characteristic parameters, such as the number of cranes, the maximum hoisting power of a crane, the moment of inertia of the load corresponding to the capacity of the individual crane with respect to the side of the facility, the block coefficient of the facility in reference at maximum draught, the length on the waterline of the facility, the breadth of the facility at maximum draught, the maximum draught, the moulded depth, the distance between the hoisting point of the crane with jib raised at minimum range, the line of moulded depth of the facility, and the empty weight of the facility in question, may be linked together, thus generating the so-called "coefficient of relatoproductivity ".
The present applicant has had the opportunity to verify that a floating facility of the type described, in which the aforesaid coefficient is generally higher than 100, and preferably higher than 125, presents characteristics of sea worthiness and efficiency in terms of capacity for loading/unloading material, and hence of operativeness, that are unexpectedly better than those of previously known solutions, it having been possible to verify that, for said previously known solutions, the above-mentioned relatoproductivity coefficient (defined as will be better illustrated in what follows) is found to be markedly lower than 100.
Albeit without wishing to be tied down to any specific theory in this regard, the applicant has been able to verify that the coefficient in question in effect brings mapping of an optimization function in a multidimensional space down to a one-dimensional criterion of discrimination based upon a single threshold value (chosen precisely at the value of 100 defined previously).
It should moreover be pointed out that in the above coefficient there are recalled parameters that are fundamental for the purposes of operativeness.
In this regard it is to be noted, for example, the length of the cables of the grabs, a factor of determining importance for the purposes of the oscillatory/hunting movement of the grabs, which must evidently be evaluated in such a way as not to involve phenomena of resonance due to elements causing excitation. These aspects have been examined in depth by facility of appropriate studies and experimental tests of sea worthiness of pontoons and through the technico-experimental study of the response operators of the cables-grab system of the cranes used for unloading.
The studies and, above all, the results of the tests carried out using models of pontoons in a tank and with models of grabs suspended from oscillating systems have enabled identification of the incidence that the various dimensional parameters (dimensions of the pontoon, dimensions of the crane, length of the hoisting cables of the grabs, etc.) and certain other constructional details (geometries of the intersections of the cables of the grabs, dimensions of anti-roll fins, distribution of the weights on board the pontoon, etc.) present, for different sea conditions, in regard to the motions and accelerations of the pontoon and of the grabs, and hence, in other words, have enabled identification of what are the effects of the variations of said parameters on the operativeness of the facility for different sea conditions.
In this way, if the percentages of incidence throughout the year of the different states of the sea for the area of sea in which it is intended to examine the feasibility of operating are known, it is possible to establish the different parameters in the most appropriate way for operativeness, productivity, reliability, and hence profitableness of operation.
The present invention will now be described, purely by way of non-limiting example, with reference to the attached drawings, in which:

Figure 1 is a general perspective view of a floating facility provided with cranes, which can be built according to the invention;
Figure 2 is a general perspective view of another floating facility, which can be built according to the invention; and
Figure 3 identifies in greater detail the quantities taken into consideration in the context of the present description.

In the figures of the attached drawings, the reference number 1 designates, as a whole, a floating facility equipped with cranes, which can be used for carrying out loading and unloading operations according to the criteria generically illustrated in the introductory part of the present description.
For example, in the view of Figure 3, which is designed to be used for bringing out the most significant parameters of the floating facility 1, the facility 1 is seen located in an intermediate position between a ship N of large dimensions (it may, for example, be a bulk carrier of the Panamax or Cape types) and a lighter or barge C. During the loading operation of the ship N, the facility 1 is designed to take from the lighter C bulk material W for being loaded onto the ship N. As the operation of unloading is being carried out, the facility 1 performs, instead, a complementary function, i.e., that of taking the material W from the ship N and then unloading it onto the lighter C.
It will be appreciated (for further details, useful reference may be made to the introductory part of the present description) that the facility 1 is provided with a capacity of stowage of the material W which enables it to perform a function of storage area or temporary depot, both during the operation of loading and during the operation of unloading.
This means that, at least in certain conditions of operation, the facility 1 is even able to operate in the absence of the lighter or barge C. Furthermore, at least in certain applications, the presence of the lighter C can prove in effect superfluous, given that the facility 1 can be configured in such a way as to operate (either moving or maintaining its mooring position) with respect to a fixed wharf or a floating facility (ocean-going vessel).
What has been said above corresponds, of course, to operating principles which are in themselves known and which, consequently, do not need to be illustrated in detail herein, also because they are of themselves not important for the purposes of understanding or implementing the present invention.
The above also basically applies as regards the possible structure of the facility 1, which is to be deemed in itself known and is essentially based on providing a hull S, generally having an approximately rectangular structure (hence, as a whole, a tank-like structure), possibly equipped with motor elements (note the propellers 20 visible only in Figure 3). On the hull S, there is provided a set of elements of equipment for carrying out the operations of loading and unloading described previously.
The said elements of equipment typically comprise at least one crane 12 (and typically a plurality thereof). Associated to the crane or the cranes 12 are auxiliary elements, such as hoppers 14 for unloading the material picked up in the main-deck area of the hull S, the said area being designed to function as storage area, and conveyor belts 16, as well as one or more loader belts or arms 18. All the elements in question are configured so as to be able to perform the operations of transfer of material from and onto the ship N, from and onto the lighter or barge C, and from and into the space for storing the material, designated by the letter M, provided on the facility 1.
The structure of the facility 1, which is represented in Figures 1 and 2, corresponds in itself to solutions of floating transfer stations (FTSs), which the applicant has already proposed for operations such as lightening and delivery on land, transhipment from ships to lighters or barges, as well as transhipment from lighters or barges to ships, in conditions of absence or lack of port infrastructures, limited depth of the sea, etc., the aim being to enable unloading/loading of large amounts of goods, such as dry bulk materials, like coal, iron ore, bauxite, middlings, etc., but also semifinished or finished products.
What has been said above also regards the possibility of configuring the facility 1 as a self-propelled floating transfer station (see the propellers 20 of Figure 3), which is capable of lightening, outside the port, ships, for example, of the Panamax or Cape bulk-carrier type, at full load, bringing them down to the draught allowed by the wharf available. Added to this is the possibility, for the facility 1, of transporting the material unloaded during lightening and to unload directly onto a wharf belt (configurable as belt for the final user, such as, for example, a steelworks), thus accelerating the overall discharging operation.
The specific choices of implementation adopted for elements such as the cranes 12, the conveyor belts 16, etc. are not in general critical for the purposes of implementation of the invention, provided that direct reference is, instead, made to the parameters that will be specified more clearly in what follows. Of course, the plants are designed and built according to the standards and experience of the applicant, with a view to heavy and continuous service in open sea.
Essentially, the solution according to the invention is based upon the recognition of the incidence which various overall dimensional parameters (dimensions of the facility, its displacement and corresponding draught, dimensions of hoisting of the grabs, etc.) present, for different sea conditions, with regard to the motions and the accelerations of the facility and of the grabs, it being thus possible to determine the effects that the variations of the said parameters have on the operativeness of the facility for different sea conditions.
In the above, due account is taken of the fact that facility such as the facility 1 illustrated in Figure 2 must be in conditions of guaranteeing continuous operation in open sea even in not altogether optimal conditions, such as conditions characterized by considerably high waves, namely, ones higher than 1.5-2 metres.
It has been found that the behaviour of facility such as the facility designated by number 1 in Figures 1 and 2 can, in effect, be reduced to quite a restricted set of essential factors. These are:

the number n of cranes 12 installed on the facility;
the maximum hoisting capacity Q_i of said cranes (i = 1, ..., n), expressed in tonnes;
the moment of inertia J_pi (expressed in t·m²) of a load equal to the hoisting capacity of the individual crane (i = 1, ..., n) with respect to the side, i.e., J_pi = Q_i·O_i ², where Q_i and O_i represent respectively, with reference to the i-th crane, the capacity in tonnes and the so-called outreach (expressed in metres), i.e., the horizontal projection of the maximum distance between the grab and the side of the facility (see also Figure 3);
the length L on the waterline of the facility 1, expressed in metres;
the breadth B of the facility 1 at maximum draught, also this expressed in metres;
the maximum draught T of the facility 1, again expressed in metres;
the block coefficient C_B of the facility 1 at maximum draught, defined as Δ/LBTγ, where Δ is the displacement of the facility in tonnes; γ = 1.025 t/m³ is the density of sea water; and L, B and T are the parameters of length, breadth and maximum draught respectively, defined above;
the moulded depth D, again expressed in metres;
the distance I in metres between the hoisting point of the crane with jib raised (minimum range) and the line of moulded depth of the facility in reference; and
the empty weight P in tonnes of the facility 1 (weight of pontoon and corresponding equipment, unloaded and dry, i.e., Light Ship Weight or LSW).

The meaning of the quantities which appear amongst the ones cited above and which refer to the geometry of the facility 1 is clarified in the view of Figure 3.
The parameters considered above can be combined together to give rise to a coefficient, called coefficient of relatoproductivity CR1ter, defined as follows: - CR1ter = (1/3) [ΣiQi·ΣiJpi·P(CB·B4L2/6T2 - D/T)/I3]0.2 with the index of summation i ranging from 1 to n, where n is the number of cranes.
In the case where all the cranes are identical to one another, hence each with a hoisting power equal to Q and a corresponding moment of inertia equal to J_p, the above formula simplifies as follows: - CR1ter = (1/3) [nQ·nJp·P(CB·B4L2/6T2 - D/T)/I3]0.2
The experiments carried out by the applicant prove that a value of the coefficient defined above equal to 100 constitutes an unexpectedly marked and clear line of discrimination between solutions that are altogether satisfactory from a functional standpoint and solutions that do not satisfy said characteristic.
A relatoproductivity coefficient CR1ter higher than 125 has been found to correspond to a particularly preferred choice.
It is, however, evident that, in the formula given above, various numerical factors (i.e., 1/3, the exponent 0.2, etc.) are mere normalization factors, which make it possible to bring the discrimination threshold value down to the reference value of 100.
The aforesaid advantages in terms of operativeness of the solution according to the invention are further accentuated, during the phase of unloading of the material W onto the facility 1, by the use of the hoppers 14. Given the same operation, in fact, the grab cycle (crane 12) is reduced by approximately 50% since the grab feeds the hopper, and the remaining operating path of the material towards the receiving point (hold or storage area) is provided by facility of conveyor belts 16 and the loading arms 18.
The fact of having a shorter grab cycle enables an increase in daily productivity, hence an increase in the annual handling capacity, with advantages both in terms of reduction in unit costs and in terms of the possibility of making available more free time for carrying out maintenance operations. A further factor of cost reduction derives from the containment of the risk of spilling of the material.
The fact of reducing the grab cycle moreover presents the further advantage of reducing the oscillations of the facility 1 due to load displacements.
The choice of adopting a number of cranes n equal to two, preferably in combination with conveyor belts and hoppers, has proved particularly advantageous both in terms of flexibility of operation at the unloading point and as regards the containment of down time required for setting the facility 1 in position. The above advantage results, of course, in a general increase in productivity.
In a particularly preferred way, for the parameter B (breadth of the facility 1) a choice of values of not lower than 30 metres has proven particularly advantageous.
The above choice, which is such as to give rise to facility having dimensions about five times larger than those of a traditional floating crane is particularly advantageous, in so far as it enables a reduction in oscillations, this both at the level of transverse/longitudinal static oscillations and at the level of transverse/longitudinal/subsultory dynamic oscillations, with considerable advantages in terms of control and stability of the grabs of the cranes. This choice thus proves advantageous for improving the characteristics of operativeness in non-optimal meteorological conditions, likewise reducing the loadings exerted on, and consequent stresses induced in, the mechanical facility and the mooring systems.
Experiments conducted by the applicant show that the solution according to the invention is able to ensure continuous operation with reference to the meteorological characteristics of direction and force of the wind, significant relative height of the waves, source and period of the (primary and secondary) waves, currents and tidal current. As regards the evaluation of the capacity of floating terminals for carrying out, in conditions of safety, operations of transhipment in the open sea or in non-protected open anchorage near ports, it has been deemed reasonable to assume reference parameters, beyond which the transhipment operations may entail risks of damage and breakage and hence jeopardize safety of the operations.
The limit values of the aforesaid parameters are:

maximum heeling due to static load Θ = 1.5°;
maximum significant amplitude of pitching Π_1/3 = 1.5°;
maximum amplitude of rolling Ω_1/3 = 1.5°;
maximum amplitude of subsultory movement H_1/3 = 2.0 m; and
maximum significant amplitude of hunting of the grab positioned at hatch level X_1/3 = 2.5 m.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated, without thereby departing from the scope of the present invention. This applies, in particular, to the coefficient values indicated in the claims, equal to 100 and 125: it is evident that, in identifying said values on a floating facility, due account must be taken of the quantitative tolerances inherent in the determination of the parameters.

Claims

A floating facility (1), equipped with systems for loading/unloading and transfer of materials (12, 16, 18) from floating facility onto quays or wharves or barges or other ocean going vessel and/or vice versa, and equipped with systems of on-board storage (M), the floating facility (1) being provided with a given number (n) of cranes (12), which can have a hoisting capacity with respect to the side of the facility and have a given maximum hoisting capacity (Q_i), with a corresponding moment of inertia (J_pi) with respect to the side of the facility (1), with a block coefficient (C_B) of the facility (1) at maximum draught, a length on the waterline (L), a breadth (B) of the facility at maximum draught, as well as a maximum draught (T), a moulded depth (D), a distance (I) between the hoisting point of said cranes (12) with jib raised, and the line of moulded depth of the facility, as well as a given empty weight (P), said floating facility (1) having a coefficient of relatoproductivity CR1ter defined as:

CR1ter = (1/3) [Σ_iQ_i·Σ_iJ_pi·P(C_B·B⁴L²/6T² - D/T)/I³]^0.2

where the index of summation i ranges from 1 to n, where n is the number of cranes, and where
Q_i is the maximum hoisting power of the i-th crane, expressed in tonnes;
J_pi is the moment of inertia of a load equal to the hoisting capacity of the i-th crane with respect to the side of the facility, i.e., J_pi = Q_i·O_i ², where O_i is the outreach expressed in metres, i.e., the horizontal projection of the maximum distance between the grab of the i-th crane and the side of the facility;
L is the length on the waterline of the facility in metres;
B is the breadth of the facility at maximum draught in metres;
T is the maximum draught in metres;
C_B is the block coefficient of the facility at maximum draught, defined as Δ/LBTγ, where Δ is the displacement of the facility (in tonnes), γ is the sea water density in tonnes per cubic metre; and L, B and T are the parameters of length, breath and maximum draught respectively, defined above;
D is the moulded depth in metres;
I is the distance in metres between the hoisting point of the crane with jib raised at minimum range and the line of moulded depth of the facility; and
P is the empty weight (lightship) of the facility in tonnes;
and where said coefficient of relatoproductivity is higher than 100, and preferably higher than 125.
The facility according to Claim 1, characterized in that said cranes (12) are all the same and each has a maximum hoisting power Q and a moment of inertia of a load equal to the maximum hoisting power with respect to the side of the facility J_p, so that said coefficient of relatoproductivity is defined as: - CR1ter = (1/3) [nQ·nJp·P(CB·B4L2/6T2 - D/T)/I3]0.2
The facility according to Claim 1 or Claim 2, characterized in that associated to said at least one crane (12) is at least one hopper (14) for unloading the material onto the facility (1), there being associated to said at least one hopper (14) at least one conveyor belt (16) for conveying the material towards the receiving point of the material on the facility.
The facility according to any one of Claims 1 to 3, characterized in that it is equipped with a number (n) of cranes (12) equal to two.
The facility according to any one of the preceding claims, characterized in that it has a minimum breadth of not less than 30 metres.
The facility according to any one of the preceding claims, characterized in that it is equipped with motor-drive facility (20) which render it self-propelled.
The use of a floating facility according to any one of Claims 1 to 6 for unloading and/or loading freight-carrying vessels, in particular bulk carriers.