EP1375336A1

EP1375336A1 - Hull particularly for water buses for inland and lagoon waters

Info

Publication number: EP1375336A1
Application number: EP03013410A
Authority: EP
Inventors: Claudio Pensa; Giovanni Stefanini; Gino Bertolo
Original assignee: ACTV SpA; Universita Degli Studi di Napoli di Federico II; Intermarine SpA
Current assignee: ACTV SpA; Universita Degli Studi di Napoli di Federico II; Intermarine SpA
Priority date: 2002-06-25
Filing date: 2003-06-20
Publication date: 2004-01-02
Also published as: ITTV20020071A1

Abstract

A hull, particularly usable for water buses for inland waters and lagoon waters, in which the centroid CB of the immersed volume is spaced from the centroid CF of the cross-section of the hull taken along the plane of the calm surface of the water, the centroid CB being further located forward of the center of the waterplane, the hull having maximum immersions at the bow and maximum beam on waterline in the stern. <IMAGE>

Description

The present invention relates to a hull particularly usable for water buses for inland and lagoon waters.

Currently, the problem of using ferries for urban transport that take into consideration as much as possible the protection of the inland waters of the lagoon, with particular regard for waves, is strongly felt, especially in lagoon cities such as Venice.

It has in fact been noted that there are considerable environmental impact problems, which substantially consist in the formation of a wide backwash of the propulsion system and therefore of a strong water current generated by the propeller while it accelerates backward, in the presence of high values of emissions at the exhaust, and finally in the generation of waves.

In relation to the listed problems, it is noted that a boat traveling in particular in shallow water (shallow in relation to the size and speed of the boat) undergoes an increase in drag that is linked to, among other factors, an increase in the energy expended to deform the sea (therefore greater wave generation occurs).

This rather complex phenomenon in any case entails an increase in drag and often a variation in longitudinal trim, which in turn causes a further deterioration of the performance of the hull.

Moreover, the most common breakdown of the drag of a hull, considered as a sum of wave generation, viscous pressure and friction, has a percentagewise weight that is highly variable according to the speed of travel; if it is necessary to also take into account the speed of the water bus, optimizing hull shapes entails assessing the proportions in which the various components involved have an effect, and on the basis of their weight minimizing the causes of drag, especially in the drag system that has the greatest influence (the wave drag, viscous pressure or friction system).

Considering here only the hydrodynamic aspect (the aspect specific to the architectural design of hulls), it is noted, moreover, that the formation of a wide backwash of the propulsion system and the presence of high values of emissions at the exhaust are tightly linked problems, since they are both dealt with by reducing total drag (which in fact reduces the thrust required and therefore the backwash of the propeller and the power to be delivered and accordingly the exhaust fumes).

The waves generated by the motion of the hull, however, are tightly linked to the so-called "wave component of drag".

This is one of the components of total drag, and therefore an attempt to reduce this component is in tune with the solution sought for the above-mentioned problems.

The distinction that has been made, however, has a reason for its existence: the quest to achieve minimum wave drag without severe compromises can in fact have negative repercussions on other components of total drag and therefore fail to solve the described problems.

The aim of the present invention is to solve the above-mentioned problems, eliminating the drawbacks noted above, by providing a hull, particularly usable for water buses for inland and lagoon waters, that allows to minimize the backwash of the propulsion system, to obtain low exhaust emission values, and to achieve maximum containment of wave generation.

Within this aim, an object of the present invention is to provide a hull that allows to achieve these characteristics together with an optimization of performance for at least two different operating speeds of the water bus, one of which is preferably 40% greater than the other.

Another object is to provide a hull that allows to minimize the negative effects of the shallow waters in which the water bus moves.

Another object is to provide a hull that allows to achieve high safety, understood most of all as transverse stability, good maneuverability, linked to operation, and optimum ease of steering.

Another object is to provide a hull that has low manufacturing and operating costs.

This aim and these and other objects that will become better apparent hereinafter are achieved by a hull, particularly for water buses for inland waters, characterized in that the centroid C_B of the immersed volume is spaced from the centroid C_F of the cross-section of the hull taken along the plane of the calm surface of the water, the centroid C_B being located forward of the center of the waterplane, the hull having maximum immersions at the bow and maximum beam on waterline in the stern.

Advantageously, the hull has longitudinal lines, which substantially represent the flow lines of the water, that are highly smooth and therefore nearly straight.

Further characteristics and advantages of the invention will become better apparent from the following detailed description of a particular but not exclusive embodiment thereof, illustrated by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a view of the cross-sections of the hull at the longitudinal plane of the bow;

Figure 2 is a view of the cross-sections of the hull at the longitudinal plane of the stern;

Figure 3 is a view of the waterlines of the hull at the horizontal plane of the bow;

Figure 4 is a view of the waterlines of the hull at the horizontal plane of the stern;

Figure 5 is a view of the body plan in the transverse cross-sections of the hull at the stern and bow;

Figure 6 is a table that represents the body plan of the hull related to the longitudinal vertical cross-sections;

Figure 7 is a chart that plots the data of Figure 6;

Figure 8 is a table that represents the body plan of the hull related to the half-breadths of the frames;

Figure 9 is a chart that plots the data of Figure 8.

With reference to the figures, a hull is considered which is used in particular in boats such as water buses for inland and lagoon waters.

The solution shown has been referred preferably but non-limitatively to the following dimensions, speeds and transport capacities:

L_OA (length overall) ≤ 25.000 m
B_MAX (maximum beam) ≤ 5.00 m

A speed of interest was also considered:

V₁ = 5.94 kn (11 km/h) speed in canal
V₂ = 10 kn (18.5 km/h) maximum full-load speed
V₃ = 10.8 kn (20 km/h) maximum half-load speed

V₃ was considered by assuming that it is reached with a margin of 5% of maximum available power

250 passengers ± 5
installable P_MAX = 147 kW

On the basis of the above, the present solution was orientated to provide a hull that has the highest L_WL/B_WL ratio (L_WL = length at waterline; B_WL beam at waterline) in order to make the hull as elongated as possible and therefore allow it to provide low values of R_W (wave component of total drag).

Again with the aim of "elongating" the hull as much as possible, the choice was also made to minimize bow rake and stem rake; to summarize, the ratio L_WL/L_OA was provided as high as possible, since L_OA is the maximum allowable longitudinal dimension of the craft.

Since it is not possible to optimize hull shapes only for the maximum speed, minimization of the consequent negative effects during travel at 10.8 kn was sought; the main one of these effects is the tendency to vary the longitudinal trim due to the considerable growth of the bow wave system; in practice, the stern tends to sink excessively, radically altering the immersed shape of the hull.

In order to avoid or at least contain this effect, the center of buoyancy C_B and the waterplane center C_F were spaced as much as possible.

It is noted that C_B is the centroid of the immersed volume and that C_F is the centroid of the cross-section of the hull taken along the plane of the sea surface, obviously when calm.

The fact of mutually spacing the two centers, particularly C_B toward the bow and C_F toward the stern, tends to shape the hull so as to increase considerably, with the mentioned forced sinking of the stern, the immersed volume of the hull at the stern and thereby the bow-down reaction required to minimize squatting.

To facilitate the visualization of the above, consider a hull that is very wide at the stern and immerses a large volume per immersion unit (of the stern).

At the same time, in order to prevent the immersed part of the hull from being too bulky at the stern with respect to the bow, the vertical dimension of the hull is reduced at the stern and increased at the bow.

This produces the shape according to the present invention, in which the point of maximum immersion is greatly shifted forward and the point of maximum breadth is shifted greatly toward the stern.

Again with the goal of obtaining hull shapes that are suitable for relatively high speeds, without however compromising performance at the lower speed, the shallowest inclination of the longitudinal cross-sections is provided in the stern region.

Substantially, the choice has been made to make the water astern of the hull return to its "rest" condition with a motion that is characterized by a strong upper component (to visualize: by contrast, the water can be relocated astern in the rest condition that occurs with a path that has no vertical components but has convergences - on the various horizontal planes - of the right and left fluid streams).

To obtain the intended effects, adjustments were made not only to the value of the inclination of the longitudinal lines but also to the constancy of said value, in view of the fact that minimizing shape variations entails - assuming the shape as a whole is correct - a reduction of the work applied to the fluid and therefore of drag.

Another aspect that might be considered as an additional element of the characteristic that can be ascribed to the particular hull that can be produced arises from observing the midship cross-section of any hull (i.e., the transverse cross-section that has the greatest area), which is substantially U-shaped.

If instead one observes the provided solution in an extreme bow cross-section, it appears to be V-shaped, with lateral segments that are often even convex (where the U has concave sides).

The conversion of the frames (transverse cross-sections) from the U-shape to the V-shape is one of the critical aspects of the shape of the bow.

Often, once the required quantity of immersed volume has been determined, the shape variation is provided by forming a so-called "shoulder", i.e., an unwanted shape discontinuity.

However, since it is believed that it is essential to avoid this circumstance, the immersed volume has been considered as a non-independent variable and an attempt has been made to render the waterlines (horizontal cross-sections) "substantially straight" in the bow region.

To summarize: by avoiding substantial convexities of the waterlines, the moment of inertia of the bow part of the waterplane has been minimized.

A prismatic coefficient CP that is a compromise among those deemed ideal at the lowest and highest speeds was chosen.

This value was determined experimentally, taking also into account the value of the ratio between the prismatic coefficients of the bow CP_F and of the stern CP_A.

In particular, in view of a stern shape that is more conditioned (in view of the issues described above), it was preferred to set the stern coefficient to a value that is still deemed good, and various bows with different CP_F values were tested.

The prismatic coefficient is one of the fineness coefficients of the hull.

These coefficients define the level of "fullness" of the ends of the hull in relation to its central part.

Clearly, CP_F and CP_A are understood as the levels of fullness of the bow alone and of the stern alone with respect to the central part of the hull.

In very approximate terms, one could say that by proceeding in this manner a stern is provided that is slightly unbalanced for the higher required speeds, whereas by testing various bows characterized by different CP_F values and evaluating the overall result (in terms of measured performance), the bow half capable of giving the boat as a whole an excellent behavior at the lower speed was chosen.

Having chosen, for the cited reasons, the maximum allowable length, it was deemed indispensable to compensate for the difficulties due to the great dimensions by characterizing the hull with great maneuverability.

Such maneuverability would have been assuredly provided to the hull in any case by the type of propulsion system chosen (for example an azimuthal propulsion system capable of virtually ensuring thrust in every direction), but in order to maximize this characteristic the moment of inertia of the diametrical plane (or centerboard plan) was minimized compatibly with all the other restrictions and conditions.

Substantially, the "amount" of centerboard at the bow and at the stern was reduced and was concentrated in the central region.

Two consequences were obtained in this manner:

a reduction in the yaw resisting moment (the rotation of the boat about a vertical axis) and therefore a faster course variation;
a placement of the center of rotation very close to the craft center, in order to minimize the body of water affected by the maneuver.

Two conditions for the possible placement of the centroid C_F of the cross-section of said hull taken along the plane of the calm surface of the water (also known as waterplane center or centroid of the center of flotation) and of the centroid C_B (center of buoyancy) arranged forward of the center of flotation are indicated in the particular embodiment; therefore, C_B1 designates the center of buoyancy and C_F1 designates the centroid of the waterplane when the craft is not loaded and dry (immersion 1.150 m and displacement 37.566 T).

The reference sign C_B2 instead designates the center of buoyancy and the reference sign C_F2 designates the centroid of the center of flotation when the vessel is fully laden (immersion 1.397 m and displacement 54.820 T).

In the first case, the centroid of the cross-section of said hull taken along the plane of the calm surface of the water (also known as center of the waterplane) C_F1 is set by the frame 20 at 11.882 m, and said centroid (center of buoyancy) C_B1 is set by the frame 20 to 12.832 m and by the base line LC to 0.77 m.

In the second case, the center of buoyancy C_B2 is placed by the frame 20 at 12.398 m and by the base line LC at 0.927 m, and said centroid of the center of flotation C_F2 is placed by the frame 20 at 10.972 m.

It has thus been found that the invention has achieved the intended aim and objects, a hull having been provided which is particularly usable for water buses for inland and lagoon waters and allows simultaneously to minimize the backwash of the propulsion system, to obtain low values of exhaust emissions and to achieve maximum containment of wave generation; further, the hull thus formed allows to achieve these characteristics together with the optimization of performance for at least two different operating speeds of the water bus, one of which is preferably 40% greater than the other.

The described hull also allows to minimize the negative effects of the shallow waters in which the water bus moves and to achieve high safety, understood most of all as transverse stability, good maneuverability, tied to operation, optimum ease of steering, and low manufacturing and operating costs.

The invention is of course susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

The materials and the dimensions that constitute the individual components of the invention may of course be the most pertinent according to specific requirements. Likewise, the placement of the centroid C_F of the section of said hull taken along the plane of the calm surface of the water (also known as center of the waterplane) and of the centroid C_B(center of buoyancy) varies according to the chosen dimensions, speeds and transport potentials of the hull.

The various means for performing certain different functions need not certainly coexist only in the illustrated embodiment but can be present per se in many embodiments, including ones that are not illustrated.

The disclosures in Italian Patent Application No. TV2002A000071 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A hull, particularly for water buses for inland waters, characterized in that the centroid C_B of the immersed volume (or center of buoyancy) is spaced from the centroid C_F of the cross-section of said hull taken along the plane of the calm surface of the water (or center of the waterplane), said centroid C_B being located forward of the center of the waterplane, said hull having maximum immersions at the bow and maximum beam on waterline in the stem.
The hull according to claim 1, characterized in that the longitudinal lines, which substantially represent the water flow lines, are very smooth and are therefore nearly straight in order to minimize the direction changes of the lines of current and therefore minimize shape drag.
The hull according to claim 1, characterized in that the moment of inertia of the diametrical plane (or centerboard plan) has been minimized.
The hull according to claim 1, characterized in that in an extreme bow cross-section, said hull has a substantially V-like shape with some convex lateral segments in order to make the waterlines (i.e., the horizontal cross-sections) in the bow region "substantially rectilinear", so as to avoid substantial convexities of the waterlines, minimizing the moment of inertia of the bow part of the waterplane.
The hull according to claim 1, characterized in that the "quantity" of centerboard at the bow and stem has been reduced and has been concentrated in the central region in order to obtain a reduction in the yaw resisting moment and therefore obtain a quicker course change as well as a placement of the center of rotation very close to the center of the boat, minimizing the body of water affected by the maneuver.
The hull according to claim 1, characterized in that in the condition in which the boat is not loaded and is dry, said centroid of the cross-section of said hull taken along the plane of the calm water surface (also known as center of the waterplane), indicated as C_F1, is arranged by the frame 20 at 11.882 m, and said centroid (center of buoyancy), designated as C_B1, is arranged by the frame 20 at 12.832 m and by the base line LC at 0.77 m.
The hull according to claim 1, characterized in that in the condition in which the boat is fully loaded (immersion 1.397 m, displacement 37.566 T), said center of buoyancy, designated as C_B2, is arranged by the frame 20 at 12.398 m and by the base line LC to 0.927 m, and said centroid of the waterplane C_F2 is arranged by the frame 20 at 10.972 m.