Patent Application
20230150610
The present invention relates to the design of seagoing vessels and can be applied to a majority of hull types, from slow-moving ships, rigs and barges to high-speed ships and boats that are operated to over planing speed, including sailing boats and multi hull vessels.
In particular, the invention relates to the configuration of a vessel where the vessel's aft part comprises a device that reduces the wave and turbulence resistance of the vessel.
When a vessel moves at the surface of a water mass, a number of different resistance factors act against the vessel's motion. The total resistance Rt in Newton [N] for a displacement vessel and a planing hull are illustrated in
As shown in
For this reason, the speed corresponding to FN of 0.4 is often referred to as the maximum hull speed for a displacement hull. Also planing hulls, optimized and designed to be operated at a speed above the maximum hull speed for displacement hulls, experience significant residual resistance Rr before it reaches planing speed.
The difference between Rt and Rf at a given speed represent the residual resistance, Rr, which mainly consist of wave resistance Rw.
R
t
−R
f
=R
r, and for practical use:Rr≈Rw.
In the speed range from around FN=0.30 and up to around FN=1.0, the resistance caused by wave making from the hull, Rw, usually is the most dominant resistance factor for most hull types. As shown in
For this reason, the transition speed range from FN=0.4 to 0.8 has previously been very challenging in view of achieving cost efficient operation. To overcome some of the considerable rise in wave resistance, and thereby to achieve reasonable god fuel economy (resistance/speed), designers have had to design a more slender hull. For a planing hull that needs to be ‘lifted’ out of the water to obtain less resistance, the key objective has been to keep the weight down. This effectively limits the field of application for a planing hull. Consequently, planing hulls are primarily used for smaller and lighter vessels.
A typical prior art displacement hull optimized for speed range below FN=0.4 has a streamlined aft hull section with reduced cross sections towards the stern of the vessel, as shown in
A typical prior art planing hull optimised for higher speed has a rectilinear hull shape from center towards the stern, ending in a flat transom underneath the water surface when floating motionless in a mass of water, as shown in
The waves generated by the hull, together with turbulence at the stern, represent lost energy. Depending on vessel type and speed, the residual resistance typical contributes to 30-80% of the total resistance to forward motion, as shown in
It is therefore crucial to minimize the wave resistance and turbulence resistance caused by the aft hull section of the vessel to reduce the total resistance to forward motion.
Lifting Foil
To reduce total resistance, some high-speed vessels are equipped with lifting foils. The purpose of lifting foils is to reduce the draft of the hull during high speed forward motion of the vessel, and often to lift the entire hull out of the water, thereby reducing the wave resistance for the hull and the wetted area that contributes to frictional resistance.
Trim Flaps
Trim flaps are widely used to limit a stern down trim for semi displacement and planing hulls. These flaps are usually hinged to the transom flush with the hulls underside. By adjusting the back of these flaps down at operational speed, and thereby forcing a water flow passing under the transom further down, a lift force is applied to the aft part of the hull.
Forward Propulsion from Aft Foil
Patent publications U.S. Pat. No. 7,617,793 B2 and WO 2016/010423 A1 both describe an aft foil mounted under the water surface at the stern of a displacement vessel, wherein the aft foil develops a continuous forwardly directed propulsion force exerted onto the vessel during forward motion of the vessel and thereby reducing the total resistance of the vessel.
To achieve said continuous forwardly directed propulsion force, the aft foil must be located in an upwardly directed water flow. Furthermore, the chord line of the aft foil must be tilted sufficiently downward in respect to the horizontal.
Small Concave Aft Foil
Patent publication KR200440081 (Y1) describes a small concave foil having a negative chord angel located under the aft part of a vessel having a vertical transom. The transom is located under the water surface during forward motion of the vessel. The small aft foil is claimed to develop a forwardly directed propulsion force exerted onto the vessel and to reduce the turbulence and wave formation behind the wet transom, thereby reducing the propulsion resistance for the vessel.
Guiding Fins for Displacement Vessel
Patent publication DE 2814260 A1 describes a displacement vessel having fins located under the water surface at the bow and/or stern to suppress bow and/or stern waves.
Negative Lift from Foil
Patent publication U.S. Pat. No. 4,915,048 A describes a planing vessel. The vessel has a deep draft bow with a fine entrance to prevent dynamic lift from the bow. At the stern the vessel has a foil to generate a downward force to counteract the planing lift from the underside of the aft hull during forward motion of the vessel. The foil is designed to prevent the vessel from being lifted out of the water caused by the planning forces acting on the aft hull and to keep the trim angle for the vessel neutral.
Extended Description of Claims
The present invention is set forth and characterized in the independent claim, while the dependent claims describe other characteristics of the invention.
In one aspect, the invention concerns a vessel for floating in a body of water.
The vessel comprises a longitudinal hull having an aft hull section and an aft body arranged at a distance from the aft hull section, thereby forming a passage between the aft body and a separation line of the aft hull section.
The term ‘longitudinal hull’ is hereinafter defined as a hull having a length larger than the width. Further, the separation line is hereinafter defined as a line extending in a transverse direction of the hull at which a water flow originally flowing along the hull is separated from the aft hull section above a minimum forward propulsion of the vessel, for example at maximum forward propulsion of the vessel. The separation line may for example be a step in the aft hull section upstream/in front of the hull's termination point.
Note that the term ‘a line extending in a transverse direction’ shall be understood to include any line having endpoints separated in the transverse direction of the hull. Hence, the separation line may be of any form such as straight, curved, zigzagged, or a combination thereof. The two endpoints of the separation line may be at the same longitudinal position of the hull and/or may be at the same height relative to a common reference level such as the water surface when the vessel is floating in the body of water.
The separation line is further defined by the hull having an abrupt change of direction in a longitudinal vertical plane of the hull. In one embodiment, said abrupt change of direction constitute a sharp edge or almost sharp edge. In another embodiment, said abrupt change of direction has a small radius, for example a radius of 50 mm or smaller.
Said aft body is defined by a maximum width measured in a horizontal plane in the transverse direction of the hull, a leading edge, a trailing edge and a chord line.
The chord line is defined as a straight line extending from the leading edge to the trailing edge in a longitudinal vertical plane of the hull. The length of the chord line may further be defined as the arithmetic mean chord line length calculated along the entire width of the aft body. In case the transverse width of the aft body is centred relative to the transverse width of the vessel's hull, said longitudinal vertical plane will be at the transverse centre line of the aft body.
The vessel further comprises a leading edge area and a trailing edge area.
The leading edge area is defined by the smaller of:
The definition of the first area is valid in those cases where the separation line is arranged at or downstream/aft of the leading edge. Likewise, the definition of the second area is valid in those cases where the separation line is arranged upstream/in front of the leading edge.
Note that the term ‘longitudinal vertical plane’ refers to a plane oriented perpendicular to a water surface when the vessel is floating motionless in the body of water and parallel to a bow-to-aft longitudinal orientation of the hull.
Alternatively, the second area of the leading edge area may be achieved by
Of course, in practice, the integration over the maximum width of the leading edge is achieved based on an approximation in which a finite set of minimum distances along the leading edge is acquired, for example at least 3 minimum distances which include the two outermost points and the midpoint of the leading edge relative to the transverse direction.
The trailing edge area is defined by the area as seen from astern constrained by the trailing edge, a water surface when the vessel is floating motionless in the body of water at a predetermined load condition and two longitudinal vertical planes intersecting the two points on the surface of the aft body defining the maximum width. As an example, the trailing edge area may be measured when the vessel has no payload or more preferably also without ballast, for example without payload and ballast and with empty fuel tanks and lubricant tanks, i.e. at the lightweight waterline.
Note that the term ‘the area as seen from astern’ signifies a vertical cross-sectional ±area of the vessel at the trailing edge of the aft body.
Said aft body and said aft hull section is preferably mutually configured so that the leading edge area is at least 0.8 times the trailing edge area, more preferably at least 0.9 times, even more preferably at least 0.95 times, even more preferably at least 1.0 times, for example 1.1 times the trailing edge area. If average values of the leading edge area and the trailing edge area Ate across the maximum widths of the aft body are considered, the leading edge area Ale corresponds to a leading edge distance H1, and the trailing edge area Ate corresponds to a trailing edge distance H2.
In this particular case, H1 is preferably at least 0.8 times H2, even more preferably at least 0.9 times H2, even more preferably at least 0.95 times H2, even more preferably at least 1.0 times H2, for example 1.1 times H2.
With the above ratio criteria between the leading edge area and the trailing edge area, a sufficient water flow is allowed to flow above the aft body's top surface to avoid, or at least significantly reduce, deviations from equilibrium in the water masses downstream the aft body during forward propulsion of the vessel. Deviation from equilibrium in the water masses immediately downstream the aft body will cause the formation of a stern wave, and thereby increase the vessel's total resistance during operation due to wave making. An insufficient amount of water over the aft body will form a depression of the water surface downstream the vessel compared to the level of the surrounding water surface. Any depression will be balanced by the surrounding water consequently contributing to the formation of the stern wave.
Another preferred criterion for reducing the vessel's total resistance is to designing the aft hull section with a double curvature in a longitudinal vertical plane of the vessel and/or such that the angel between tangent lines of the aft hull section immediately upstream/in front of the separation line in the longitudinal direction of the vessel and the water surface is kept small, preferably less than 20 degrees, more preferably less than 15 degrees, even more preferably less than 10 degrees, even more preferably less than 5 degrees, for example 0 degrees (i.e. parallel with the water surface). Such an aft hull section will ensure a minimum upward direction for a water flow in front of the aft body.
Please note that the expression “ . . . the separation line is located at or above the water surface” should be interpreted from the point of view of a person skilled in the art, taking into account the measurable technical effect of such a location. Hence the expression “at the water surface” should not be interpreted in a strict mathematical way.
Alternatively, or in addition, at least a part of the underside of the aft body, for example the entire underside, may be arranged below the water surface at or below a depth corresponding to 60% of the draft of the hull, for example 80%, when the vessel is floating motionless in the mass of water. As an example, the draft of the hull may be measured when the vessel has no payload or more preferably also without ballast, for example without payload and ballast and with empty fuel tanks and lubricant tanks.
The aft body and the aft hull section is preferably configured such that, during forward propulsion of the vessel, the net force component exerted onto the vessel from the aft body in the direction of travel of the vessel is zero or negative in at least a part of the speed range the vessel is operating in, for example in more than 10% of the vessels speed range or more preferably in more than 30% of the vessels speed range, or even more preferably more than 50% of the vessels speed range, or even more preferably more than 70% of the vessels speed range, for example in the full speed range the vessel is operated in. By “the vessels speed range” is meant from 0 knots and up to the vessels maximum speed at full power. The particular design fulfilling such criteria may for example be achieved by performing model tests or full-scale tests while measuring the forces acting on the supports for the aft body to the hull. Such tests can be performed with payload or more preferably without payload.
Note that a negative net force component in the direction of travel exerted onto the vessel from the aft body as described herein means that the aft body is adding drag force to the vessel through its supports.
Examples of relevant parameters that may be adjusted to achieve a zero or negative net horizontal force component in the longitudinal direction of the vessel are:
In yet another advantageous configuration, the aft body is designed to give a positive lifting force during forward propulsion of the vessel. Again, the particular design ensuring such an upward direction of the lifting force may be achieved by model tests or full-scale tests of a vessel in accordance with the invention described above.
In another advantageous configuration, the design and orientation of the aft body may be chosen such that, during forward propulsion of the vessel, the arithmetic mean direction of a resulting water flow immediately downstream of the trailing edge is orientated in the horizontal plane, i.e. parallel to the water surface, or substantially in the horizontal plane. The resulting water flow is set up by superposing a water flow passing the top surface of the aft body and a water flow passing the underside of the aft body. By such minimization of the upward or downward directed component of the resulting water flow downstream the aft body, said deviation from water flow equilibrium behind the vessel may be further reduced, which again causes a further reduction in the formation of stern waves. A horizontal water flow may be accomplished by for example orienting the chord line parallel or near parallel with said water surface when the vessel is floating motionless in a mass of water.
In an alternative configuration, the aft body may also be oriented with a chord line having a positive angle of attack relative to the water surface during forward propulsion of the vessel, for example an angle between 0° and 5° relative to the water surface, more preferable between 0° and 3°, even more preferable between 0° and 2°, for example between 0° and 1,5°.
In another alternative configuration, the chord line angle may even be slightly negative, for example −2° or −1°, as long as the result of the configuration yields a net force component exerted onto the aft body in the direction of travel of the vessel that is zero or negative as described above.
In yet another advantageous configuration, the chord line is orientated parallel with the water surface when the vessel is floating motionless in a body of water at the lightweight waterline. The term ‘parallel’ shall not be interpreted in its strict mathematical sense. Depending on various parameters such as the vessel's load conditions, the term ‘parallel’ can be interpreted as an orientation within a range ±2° relative to the water surface, or even within ±1° if the vessel conditions so allows. For example, if the different load conditions of the vessel results in an unchanged trim or near unchanged trim, the term ‘parallel’ may be interpreted narrower, even within ±0.5°.
Note that a positive angle is herein defined as an angle pointing upward in the direction of travel relative to the water surface.
In yet another advantageous configuration, the leading edge of the aft body is situated less than 20% of the length of the chord line aft of the separation line. This particular embodiment may contribute to reduce turbulence at low speed of the vessel. More favourably the leading edge is situated less than 15% of the length of the chord line aft of the separation or even more favourably less than 10%, even more favourably less the 5%, for example at or upstream the separation line.
In yet another advantageous configuration, at least a part of the trailing edge, for example the entire trailing edge, is located deeper than 35% of the maximum draft of the hull without ballast and payload when the vessel is floating motionless in a mass of water, more preferably deeper than 50% of the maximum draft, even more preferably deeper than 60% of the maximum draft, for example 80% of the maximum draft.
In yet another advantageous configuration, the length of the chord line is at least equal to the draft of the hull without ballast and payload when the vessel is floating motionless in a mass of water. The cord line length is more preferably 1.2 times the draft, even more preferably 1.5 times the draft, for example 2 times the draft. By exceeding a minimum length of the chord line, turbulence on the top surface and downstream the aft body is prevented or at least significantly reduced.
In yet another advantageous configuration, at least a part of the aft body, for example the entire aft body, is located upstream/in front of the vertical projection of a rearmost point of the hull.
In yet another advantageous configuration, the leading edge, for example the entire leading edge, is situated half the length of the chord line or more upstream/in front of the separation line, more preferably 60% of the length of the chord line or more, or even more preferably 70% of the length of the chord line or more, for example 80% of the length of the chord line or more, upstream/in front of the separation line. Further, the top surface and position may alternatively, or in addition, be designed such that a minimum distance in a longitudinal vertical plane of the hull between said top surface and the aft hull section upstream/in front of the separation line remains constant or near constant.
In yet another advantageous configuration, the aft body constitutes an integrated part of the vessel.
In yet another advantageous configuration, at least part of the leading edge, for example the entire leading edge, is located a horizontal length of ½ chord line or less downstream/aft of the separation line, more preferably less than ⅓ chord line, even more preferably less than ¼ chord line, even more preferably less than ⅕ chord line, for example at, or immediately downstream, the separation line.
In yet another advantageous configuration at least a part of the aft hull section located downstream/aft of the separation line is situated over said water surface when the vessel is laying still and floating in a mass of water. For example, the transom of the longitudinal hull may be located at or above the water surface.
In yet another advantageous configuration, the aft body and the aft hull section is configured so that the aft body during forward propulsion will not contribute to a significant change in draft of the aft hull section. This is in clear contrast to a typical lifting foil having a shape optimized for creating such a lift and contribute to a significant decrease in draft of the hull.
In yet another advantageous configuration, the aft body is designed such that a part of a water flow flowing over the top surface of the aft body is lifted above the water surface during forward propulsion of the vessel.
In yet another advantageous configuration, the separation line is located at or above the water surface, when the vessel is laying still and floating in a mass of water in a particular load condition such as without ballast and without payload. Another possible load condition may be with maximum ballast or with maximum payload.
In yet another advantageous configuration, the vessel further comprises a bow body located at or upstream/in front of a bow area. The bow body is configured to lead the water mass passing the upper surface of the bow body away from the bow area, or essentially parallel to the bow area, or a combination thereof. The design of the bow body and the bow area may be identical or similar to the bow body described in patent publication EP3247620B1, the contents of which are incorporated herein by reference. Particular reference is made to FIGS. 10-12 in EP3247620B1 and its related text. The proprietor of EP3247620B1 is the applicant in this application.
In yet another advantageous configuration, the aft body and the aft hull section is configured so that the draft of the hull during forward propulsion of the vessel will be at least 60% of the draft of the hull when the vessel is floating motionless in the body of water, or more preferably at least 70%, or more preferably at least 80%, or more preferably at least 90%, for example 100%.
In yet another advantageous configuration the maximum width of the aft body measured in a horizontal plane in the transverse direction of the hull is at least 60% of the maximum width of the hull measured at the water surface in the transverse direction of the hull when the vessel is floating motionless in the body of water, or more preferably at least 70%, or even more preferably at least 80%, or even more preferably at least 90%, for example at least 100%.
In yet another advantageous configuration, the longitudinal hull is a displacement hull or a planing hull.
In yet another advantageous configuration, the aft body is located between the water surface and 100% of the draft of the hull when the vessel is floating motionless in a mass of water.
In yet another advantageous configuration, the length of the chord line of the aft body is at least 5% of the length between perpendiculars of the vessel (L.P.P), more preferably at least 7%, or even more preferably at least 8%, or even more preferably at least 9%, for example at least 10% of the length between perpendiculars of the vessel.
The Invention—General Mode of Operation
During forward travel of the vessel, the upward tapered aft hull section upstream the aft body will give a water flow upstream the aft body a partly upward direction. The underside of the aft body will deflect a partly upwardly directed water flow in front of the aft body, causing a water flow under the aft body to flow in a primarily horizontal direction. The top surface of the aft body has a shape that redirects a water flow passing the top surface of the aft body from a partly upward to a horizontal or slightly downward directed water flow. The combined direction of the water flow downstream the trailing edge of the aft body, i.e. from the water flow passing over and under the aft body, then obtain an essentially horizontal direction. Hence, creation of stern wave due to the upwardly directed water flow at the aft hull section continuing in an upward direction behind the vessel is counteracted.
Further, as can be seen in
The aft body for a vessel according to the invention will also generate a lifting force that will prevent a stern down trim of the vessel during forward motion. The aft body of such an inventive vessel will however not provide a continuous forwardly directed propulsion force.
The aforementioned objects are thus achieved, namely to reduce the vessel resistance to forward motion over a wide speed range due to:
The inventive vessel can be adopted to different hull types and speed ranges; from typical rounded displacement hulls operated at speeds up to around FN=0.4 as shown in
The working principal of the inventive vessel is in general the same regardless of speed range and type of vessel. However, the type of vessel and operational cruising speed should be taken into consideration when designing and optimising the geometry of the inventive vessel to a specific hull and to a specific speed range as described later.
When applied to a traditional prior art displacement hull, the inventive vessel counteracts the upward directed water flow and the generation of a stern wave downstream the hull and to reduce turbulence under and behind the aft hull section, as shown in
When applied to a vessel with wetted transom below the water surface, like a semi displacement or a planing hull, the invention prevents turbulent flow behind the transom at low speed. At higher speed, when the water starts to separate from the hull behind the flat transom, the inventive vessel will effectively prevent the rise of water behind the hull and thereby counteract creation of stern wave, as shown in
For a typical prior art displacement hull with a streamlined aft hull section, the inventive vessel will usually contribute to reduced propulsion resistance from a speed corresponding to approximately FN=0.17-0.20 and up. For a typical prior art semi displacement or a planing hull, the inventive vessel will usually contribute to reduced propulsion resistance from stand still and all the way up to a speed exceeding FN=1.0.
Differences from Prior Art
With reference to the description above, the inventive vessel differs from the above described prior art vessels in the following ways:
Lifting Foil:
Prior art vessels with lifting foils reduce the propulsion resistance at high speed by lifting the prior art vessel partly or fully out of the water during operation. A prior art vessel will typical have two lifting foils, one at the front of the vessel and one towards the stern. Both foils will be located deep under the baseline of the hull to avoid that the low pressure on the top side of the foil has a negative impact on the hull (i.e. “sucking” the hull down). Furthermore, the lifting foils must stay submerged when the prior art vessel is lifted out of the water. If the lifting foils during high speed operation is located close to the water surface they will generate waves and also generate less lift. At low speed the lifting foils will increase the propulsion resistance of the prior art vessel considerably.
In contrast, the inventive vessel is designed to maintain the same draft whether it is laying still and floating in a body of water or traveling at operational speed. The inventive vessel lowers the resistance over a broad speed range, starting from low speed. Furthermore, the inventive vessel will have the aft body located between the base line of the hull and the water surface.
Trim Flaps:
The use of trim flaps is common in prior art vessels to limit the change in trim of semi-displacement and planing hulls due to forward motion of the vessel. By orienting the aft part of these flaps downward at speed, and forcing a water flow passing under the transom further down, a lift force is applied to the aft hull section. The downward directed trim flap effectively lowers the water flow surface level downstream the trim flaps, thereby increasing the distance to equilibrium between a water flow downstream the trim flap and the surrounding water surface. The trim flaps hence contribute to increased stern wave behind the prior art vessel, resulting in increased wave resistance.
The inventive vessel also has the ability to counteract an aft down trim of the vessel, but the wave formation is considerably less compared to prior art vessel with trim flaps. A trim flap does not have a water flow over the top side of the trim flaps during forward motion of the vessel, nor a leading edge, a passage or a leading edge area Ale as defined herein.
Forward Propulsion from Aft Foil
Both patent publication U.S. Pat. No. 7,617,793 B2 and patent publication WO 2016/010423 A1 discloses a displacement hull having an aft foil fixed to the aft part of the prior art vessel which is configured to generate a continuous forwardly directed propulsion force actin on the vessel during forward motion of the vessel.
To achieve said propulsion force, the aft foil has to be mounted in a sufficiently upwardly directed water flow during forward motion of the prior art vessel (as documented by model tests later in this document). An upwardly directed water flow can be achieved:
In addition, the chord line of the aft foil must be tilted sufficiently downward in the upwardly directed water flow for the aft foil to be able to generate a continuous forward propulsion force.
The inventive vessel is not designed with an aft body being configured to generate a continuously forwardly directed propulsion force. (Also this is documented by model tests later in this document.)
Prior art vessels disclosed in both patent publication U.S. Pat. No. 7,617,793 B2 and patent publication WO2016/010423 A1 are not designed to lead a sufficient amount of water over the aft foil during forward motion of the vessel. I.e., the leading edge area Ale (as herein defined) of the prior art vessel is smaller than 0.8 times the trailing edge area Ate (as herein defined). Accordingly, a water flow passing over the trailing edge of the aft foil is too small to achieve equilibrium in the water mass downstream the aft foil. In fact, it is an objective when designing the prior art vessels to locate the separation line below the water surface when the vessel is lying motionless in a mass of water to achieve the upwardly directed water flow downstream the separation line during forward motion of the vessel. Accordingly, it is an objective when designing the prior art vessels to keep the Ale divided by Ate ratio small. This is in clear contrast to the inventive vessel where the objective is to have the Ale divided by Ate ratio close to 1 to achieve equilibrium in the water mass downstream the aft body.
Aft hull sections of the prior art vessels according to U.S. Pat. No. 7,617,793 B2 are designed with a large angel β, being the angel between the tangent line of the aft hull section immediately upstream/in front of the separation line in the longitudinal direction of the vessel and the water surface, to achieve a sufficiently upwardly directed water flow upstream the aft foil. This is in clear contrast to the inventive vessel where the objective is to direct a water flow horizontally downstream the aft body.
Aft foils of the prior art vessels disclosed in both patent publication U.S. Pat. No. 7,617,793 A1 and patent publication WO 2016/010423 A1 are configured with a downward pointing chord line angle in relation to the water surface to generate a continuously forwardly directed propulsion force. The downward pointing chord line contributes to give the water flow passing the aft body's underside and top surface an upward direction. This is in clear contrast to the inventive vessel, which has an aft body with a chord line essentially parallel to the water surface to counteract such an upward directed water flow, thereby counteracting the formation of a stern wave.
The prior art vessels for some of the embodiments in patent publication U.S. Pat. No. 7,617,793 A1 are designed such that the minimum distance, in the longitudinal vertical plane of the vessel, between the top surface of the aft foil and the aft hull section upstream/in front of the separation line is changing (i.e. not constant). This results in a retardation of a water flow from the leading edge of the aft foil over a part of the top surface of the aft foil during forward motion of the prior art vessel. This reduction in the velocity of the water flow passing over a part of the aft foil is adding drag to the vessel. In contrast, an embodiment of the inventive vessel has a geometry of the aft hull section and the aft body's top surface that is designed to prevent such a retardation of the water flow by having a constant minimum distance (in the longitudinal vertical plane of the vessel, between the top surface of the aft foil and the aft hull section upstream/in front of the separation line).
The vessels disclosed in both patent publication U.S. Pat. No. 7,617,793 A1 and patent publication WO2016/010423 A1 are adapted only to displacement hulls, while the inventive vessel is adapted to both displacement hulls and planing hulls.
Small Concave Foil
Patent publication KR200440081 (Y1) describes a small concave foil located under the aft hull section of a vessel, where a vertical transom extent under the water surface during forward travel of the vessel. The objective of this solution is to reduce the wave formation and the turbulence behind a wet transom and to generate a forward thrust force acting on the small aft concave foil during forward motion of the vessel. Furthermore, the small concave foil is claimed to increase the pressure at the periphery of the leading edge of the small concave foil, thereby reducing stern down trim of the vessel.
In contrast to the inventive vessel, this prior art vessel does not achieve equilibrium for the water mass downstream the small concave foil during forward motion of the vessel. The leading edge area Ale of the small concave foil is shown to be about 0.5 times the trailing edge area Ate of the small concave foil.
The prior art vessel is designed such that the minimum distance, in the longitudinal vertical plane of the vessel, between the top surface of the small concave foil and the aft hull section upstream/in front of the separation line (i.e. the transom) is changing (i.e. it is not constant), in contrast to the inventive vessel.
The inventive vessel does not include a wetted transom where the aft foil's trailing edge is situated underneath the transom in contrast to the prior art vessel as shown in KR200440081 (Y1).
The inventive vessel is not designed to increase the pressure at the periphery of the leading edge of the aft concave foil, thereby reducing the resistance on the vessel, in contrast to the prior art vessel having a small concave foil.
The prior art vessel according to KR200440081 (Y1) is designed to generate a forward component Lx of the lift forces L, generating a horizontal forwardly directed thrust force acting on the small concave foil. The inventive vessel is not designed to generate a forwardly directed thrust force acting on the aft body.
The maximum width of the small concave foil measured in a horizontal plane in the transverse direction of the hull is only about 15% of the maximum width of the hull, in contrast to the width of the aft body which in one embodiment is at least 50%, preferably close to 100%, of the width of the hull.
Guiding Fins for Displacement Vessel
Patent publication DE 2814260 A1 describes a displacement vessel having fins located under the water surface at the bow and/or of the vessel stern to suppress bow and/or stern waves, thereby reducing the wave resistance.
As can be seen from the figures in DE 2814260 A1, the prior art vessel does not have a separation line as defined herein. I.e. that the separation line has an abrupt change of direction in a longitudinal vertical plane of the hull. Nor does the description of DE 2814260 A1 mention anything about a separation line.
In contrary, the inventive vessel includes a defined separation line, which is of vital importance to control a water flow behind the hull at different speeds for the vessel, and to avoid that a water flow will try to follow the shape of the hull giving the water flow an upward direction (i.e. the Coanda effect).
Furthermore, the inventive vessel has a superior speed range and is designed to minimize vortexes and turbulence created by the aft foil in the water flow.
Negative Lift from Foil
Patent publication U.S. Pat. No. 4,915,048 A describes a planing vessel. The vessel has a deep draft bow with a fine entrance. At the stern the vessel has a foil to generate a downwardly directed force to counteract the planing lift from the underside of the hull during forward motion of the vessel. In contrary, the inventive vessel includes an aft body where the force from the aft body acts in the opposite direction to the publication U.S. Pat. No. 4,915,048 A. The aft body of the inventive vessel imposes a lifting force to the aft hull section that counteracts a stern down trim of the vessel as speed increases.
(The support to fix the aft body to the hull, incl. the ball bearing, load cell, propeller and rudder is the same as in
In the following, embodiments of the invention will be described in more detail with reference to the drawings and definitions. However, it is specifically intended that the invention is not limited to the embodiments and illustrations contained herein but includes modified forms of the embodiments including portions of the embodiments and combinations of elements from different embodiments as come within the scope of the claims.
Throughout this application, the following definitions, numerals and letters in drawings, shall apply:
The hull sides of the vessel 1. I.e. not including the bow area 21 and the transom 7.
Displacement speed:
Transition speed:
Planing speed:
Operational speed:
General Design Criteria
The working principle and the main objective for the invention is the same for both slow or fast vessels 1. However, certain design issues should be taken in consideration when optimizing the inventive vessel 1.
Leading Edge Area/Trailing Edge Area
The common principle for all embodiments of the invention is to allow a sufficient water flow 51 to flow over the top surface 45 of the aft body 4 through the passage 50 during forward propulsion of the vessel 1. The cross sectional area of a water flow 51 passing the leading edge 41 of the aft body 4 should be equal to, or almost equal to, the area from the trailing edge 42 of the aft body 4 and up to the water surface 5 in order to achieve equilibrium in the water mass downstream the vessel 1 and thereby prevent the formation of a stern wave 9 when the vessel 1 is in forward motion. By equilibrium is meant that the water flow surface level 53 above the trailing edge 42 is at the same level as the (surrounding) water surface 5 during forward motion of the vessel 1, for example at operational speed. In
In general, the width of the aft body 4 in the transverse direction of the vessel 1 will be equal to, or almost equal to, the width of the transom 7 of the vessel 1.
Adaption to Different Speed Ranges
Advantageous embodiment for adapting the vessel for different speed ranges are shown and explained by aid of
When operating a vessel 1 according to the invention having a displacement hull at a low speed (FN<0.3), the aft body 4 may be positioned closer to the water surface 5. When the aft body 4 is placed closer to the water surface 5, the length of the chord line 43 can be reduced compared to a deeper positioning of the aft body 4. When operating the vessel at higher speed (FN≥0.3), there might be advantageous to position the aft body 4 deeper and to increase the length of the chord line 43.
As the speed increases, the upward momentum in a water flow 51 passing under the aft hull section 3 upstream the aft body 4 increases. The impact from the aft body 4 onto a water flow 51 should then be enhanced. This is achieved by increasing the length of the chord line 43 and to locate the aft body 4 closer to the base line 58, as the top surface 45 of the aft body 4 will redirect the water flow 51 more effectively then the underside 46 of the aft body 4. The increased cord line 43 and deeper located aft body 4 will then effectively counteract the increasing upward momentum of the water flow 51, thereby achieving an essential horizontal direction of a water flow 51 downstream the aft body 4.
As a rule of thumb, the cord line 43 should be greater than the draft of the aft body 4, typical by a factor of around 2.0 or greater.
At low speed an aft body 4 with a long chord line 43, and placed relatively deep, only contributes to a minor increase in resistance compared to a smaller and higher placed aft body 4. If the vessel 1 is supposed to be operated over a wide speed range, it might be advantageous to choose an aft body 4 with long chord line 43 placed at a greater depth optimized for the highest operational speed of the vessel 1.
The optimal depth and optimal length of the chord line 43 for minimizing the total resistance Rt for the vessel 1 may for example be determined by model tests and/or computational fluid dynamics (CFD) analyses.
Location of the Separation Line
The invention includes a separation line 6 at the aft hull section 3 controlling the separation of a water flow 51 from the aft hull section 3 at a defined line in the transverse direction (w) of the vessel 1 during forward motion of the vessel 1. The separation line 6 is preferably located close to the water surface 5 when the vessel 1 without payload is laying still and floating in a mass of water.
The separation line 6 can either be placed upstream/in front of, vertically above, or downstream/aft of the leading edge 41 as shown in
Turbulence—Design of the Aft Body and its Supports
When designing the aft body 4, including the supports 8 to fix the aft body 4 to the hull 2, it is advantageous to avoid creation of turbulence and vortexes.
If the outer ends of the aft body 4 in the transverse direction of the vessel 1 extends freely in the water during operation, it might be advantageous to reduce the thickness of the aft body 4 in a vertical plane towards the outer ends and/or to make the aft body 4 elliptical when seen from below (as shown in
Also winglets, as used in aviation, can be used to reduce the tip vortexes. It would then be natural to also make use of the winglets as supports 8 for the aft body 4.
The aft body 4 should preferably also be shaped according to shape of the aft hull section 3 upstream/in front of the separation line 6 and the resulting angle of attack of the water flow 51 (i.e. the angel between the water flow 51 upstream leading edge 41 and the chord line 43). Higher angel of attack requires increased length of the chord line 43. Furthermore, in order to obtain laminar water flow 51 without turbulence, and to prevent cavitation on the top surface 45, especially at higher velocity of the water flow 51, a thicker aft body 4 profile and/or more curved top surface 45, especially toward the leading edge 41, would be beneficiary. Alternatively, a high angle of attack for the front part of the aft body 4 can be avoided by keeping the angle γ of the tangent line TH low.
When attaching the aft body 4 to the hull 2 some care should be taken when designing the support 8. Besides ensuring sufficient structural integrity, the support 8 should preferably be made with a streamlined design. In addition, the support 8 should be oriented according to the direction of a water flow 51 where the supports 8 are located to avoid unnecessary propulsion resistance. It should be noted that under the aft hull section 3 of a displacement hull 2, a water flow 51 can become partly inwardly directed towards the longitudinal center line of the vessel 1.
If the aft body 4 is placed between the hull sides 2′,2″, as shown in
Alternatively, the aft body 4 may be fixed to the transom 7 of the hull 2. In
In order to prevent a rise of the water flow surface level 53 at the outer side of the hull sides 2′,2″ at the aft hull section 3 that might accrue during forward motion, and further to prevent this rise of the water flow surface level 53 to be deflected outward as stern wave 9 from the hull sides 2′,2″, it might be advantageous to taper the hull sides 2′,2″ of the aft hull section 3 inward towards the longitudinal center line of the vessel 1. An example of such a tapering of the hull sides 2′, 2″ is shown in
Adaption to Variation in Draft
Some vessels 1 experience a significant variation in draft DV when being operated due to different load conditions. To optimise the vessel 1 for such draft variations it would be advantageous to be able to adjust the amount of water passing over the aft body 4 (i.e. altering H1) according to the vessel's 1 draft DV, as well as the height H2 from the trailing edge 42 of the aft body 4 to the water surface 5.
By making the aft body 4 adjustable in a horizontal longitudinal direction of the vessel 1, an optimal water flow 51 can be led over the aft body 4 at different drafts DV of the hull 2. At shallow draft DV of the hull 2, the leading edge 41 can be arranged close to the hull 2, for example vertically below the separation line 6. As the vessel 1 is operated at a deeper draft DV of the hull 2, the leading edge area Ale can be increased by moving the aft body 4 horizontally further downstream the separation line 6.
Alternatively, or in addition, the front part of the aft body 4, or the entire aft body 4, can be made tiltable with a rotational axis parallel to the transverse direction of the vessel 1 and parallel to the water surface 5. When the leading edge 41 is tilted down, a larger water flow 51 is allowed to pass over the top surface 45. If the entire aft body 4 is tilted around said rotational axis close to aft body's 4 centre line, the trailing edge 42 will approach the water surface 5 while the leading edge 41 will become deeper as the chord line 43 of the aft body 4 is tilted downward (i.e. a smaller or more negative chord angel γ). This will contribute to a larger leading edge area Ale and a reduced trailing edge area Ate. However, to tilt the aft body 4 downward has the disadvantage of creating a non-desired upward direction of a water flow 51 downstream the trailing edge 42.
If the aft body 4 is fixed and the hull 2 is to be operated at different drafts DV, a compromise has to be found. An advantageous compromise could be to adapt the leading edge area Ale in view of the trailing edge area Ate for a draft DV corresponding to the deepest draft DV of the hull 2, or at least deeper than minimum operational draft DV of the hull 2.
Although the aft body 4 counteracts a stern down trim, the vessel 1 might experience some increased stern down trim as the speed rises, thereby increasing the distance from the trailing edge 42 to the water surface 5 at high speed. With this in mind, it might be advantageous to allow the leading edge area Ale to be greater than the trailing edge area Ate when the vessel 1 is floating motionless in a body of water. Alternatively, the leading edge area Ale can be increased as mentioned above as the speed of the vessel 1 increases. Also the geometry of the aft hull section 3 can be made with a flap or similar to make the leading edge area Ale adjustable.
Location of Propeller
The vessel's 1 propeller 12 can be located upstream/in front of the aft body 4 as shown in one embodiment in
Initial testing performed indicates that a location of the propeller 12 under the aft body 4 can be advantageous as the same thrust force [N] is generated from the propeller with a smaller power consumption [W] from the propulsion engine.
A Vessel Having Both an Aft Body and a Bow Body
The arrangement of an aft body 4 according to the invention as described will reduce the total resistance Rt for a vessel 1 above a certain speed of the vessel 1. Further, the inventive vessel 1 will counteract a stern down trim of the vessel 1 if the vessel 1 is being operated at higher speeds, for example above FN=0.3. As a negative consequence, the inventive vessel 1 can experience a larger bow down trim than a prior art vessel 1 not fitted with an aft body 4. Even if the total resistance Rt of the inventive vessel 1 is lower, the bow down trim of the inventive vessel 1 will result in an increased bow wave 22 and thereby an increased wave resistance Rw from the bow area 21.
The invention disclosed in patent publication EP3247620B1 concerns a bow design with a bow body 10 that counteracts creation of a bow wave 22, thereby reducing the wave resistance Rw from the bow area 21 and the total resistance Rt for the vessel 1. However, this particular bow design suffers the disadvantage that such a vessel 1 can experiences an increased stern down trim during forward propulsion, thereby creating greater wave resistance Rw from the stern. In other words, by reducing the formation of waves at one end of the vessel 1, the formation of waves at the other end of the vessel 1 is often increased.
By combining these two inventions (i.e. an aft body 4 and a bow body 10) on the same vessel 1 as shown in
Numerous model tests measuring the total resistance Rt has been performed and an overview picture of these tests are shown in
A prior art planing hull 2, as shown in
Also for planning vessels 1 numerous model tests has been performed.
As best shown in
As best shown in
As best shown in
In a third embodiment, the inventive vessel 1 comprises both an aft body 4 as described herein and a bow body 10 as described in patent publication EP3247620B1, the contents of which are incorporated herein by reference, in particular the
As a specific example of the third embodiment, reference is made to
Model Tests—Total Resistance of Model Vessels
To document the mode of operation of the inventive vessel 1 and to verify a reduction in total resistance Rt, the inventor has carried out model tests on the model vessels shown in
To be able to monitor thrust from a propeller 12, all model vessels 1 (except for the planning model vessels 1 shown in
During operation, the motor housing 15 applies pressure onto the load cell 17 and all thrust from the propeller 12 is transferred to the load cell 17. Consequently, the propeller thrust in Newton [N] is monitored and logged during operation of the model vessel 1. When the model vessels 1 is operated at constant speed the propeller thrust is equal to the total resistance Rt for the model vessel 1.
The speed of all model vessels 1 is measured with high accuracy Doppler GPS. The speed in meters per second [m/s] is converted to Froude number (FN) for each model vessel 1.
The measured results of the total resistance Rt for the model vessels 1 shown in
In
For the planing model vessels 1 shown in
All model vessels 1 are radio-controlled.
Model Test 1—Double Propelled Slender Displacement Hull
The length, width and draft DV of both model hulls 2 are 270 cm, 42 cm and 11 cm, respectively. The full-scale vessel 1 of this model vessel 1 has the separation line 6 located at the water line 5 and so has the model vessel 1. Consequently, in order to apply an aft body 4 as described above, there is no need to do any cut-out of the aft hull section 3 in order to make Ale equal to Ate.
With reference to the Model 16B, the length of the chord line 43 of the aft body 4 is 10 cm. The aft body 4 is attached to the aft hull section 3 such that the leading edge 41 is located 1 cm upstream/in front of the separation line 6. Further, the maximum (W) of the aft body 4 in the transvers direction (w) of the hull 2 is 42 cm, which is equal to the width of the model vessel 1. The underside 43 of the aft body 4 is placed 2.7 cm below the water surface 5 and the cord angel γ is orientated parallel to the water surface 5 when the model vessel 1 is floating motionless in a mass of water. The maximum vertical thickness of the aft body 4 is 1.0 cm. The aft hull section 3 has a double curvature in the longitudinal vertical plane of the model vessel 1 and the angel β between the tangent line TH and the water surface 5 is 0 degrees (i.e. parallel with the water surface 5).
During test runs of the prior art Model 16A maintained close to neutral trim throughout the entire speed range of the test. However, the model vessel 1 experiences some degree of increasing draft DV as speed increased.
Model 16B according to the invention obtained some bow down trim and increased draft for the bow area 21 as speed increased, leading to an increased bow wave 22 compared to the prior art model vessel 1 at comparable speeds.
As clearly seen from the pictures in
Model Test 2—Single Propelled Displacement Hull
The bow body 10 on Model 20B is in accordance with the patent publication EP3247620B1. Further, the configuration of the bow body 10 and bow area 21 is similar to the bow configuration shown in
Model 20C has the same bow body 10 and bow area 21 as Model 20B, but with an aft hull section 3 similar to the aft hull section 3 shown in
All three model vessels 1 have a hull length of 184 cm. The width for Model 20A is 36 cm and 34 cm for both Model 20B and Model 20C. Further, all three model vessels 1 have the same weight and thereby the same displacement volume, resulting in a draft DV of 14 cm for Model 20A, 15 cm for Model 20B and 15.2 cm for Model 20C.
The separation line 6 for Model 20A and Model 20B is located respectively 2.0 cm and 1.5 cm under the water surface 5 and for Model 20C at the water surface 5 when the model vessels 1 are floating motionless in a body of water.
Moreover, the length of the chord line 43 of the aft body 4 of Model 20C is 11 cm, and the maximum width (W) of the aft body 4 in the transvers direction (w) of the hull 2 is 33 cm. The chord angel γ is oriented parallel to the water surface 5 and the underside 46 of the aft body 4 is located 7 cm under the water surface 5 when the model vessel 1 is floating motionless in a body of water. The separation line 6 is located 5 cm upstream/in front of the transom 7 and the leading edge 41 of the aft body 4 is located vertically below the separation line 6. The maximum vertical thickness of the aft body 4 is 1.1 cm. The angel β between the tangent line TH and the water surface 5 is 8.5 degrees.
During model tests, all three model vessels 1 have a neutral trim when floating motionless in a body of water.
In order to compare the inventive Model 20C having an aft body 4 with a prior art Model 20B (without an aft body 4), and to exclude the tendency of the inventive Model 20C to generate a bow down trim of the vessel 1 due to the aft body 4, thereby preventing a stern down trim, the angel of attach of the bow body 10 for Model 20B and Model 20C are adjusted separately to obtain close to neutral trim and unchanged draft for their bow area 21 when they are in motion throughout the testing speed range. The wave making from the bow area 21 is then similar for the Model 20B and Model 20C. The bow body 10 contributes to a great reduction of wave resistance Rw from the bow area 21. The main differences in total resistance Rt between the Model 20B and the inventive Model 20C is thus isolated to be the difference between an aft hull section 3 without and with an aft body 4.
Model Test 3—Planing Hull
Both model vessels 1 have a length of 120 cm and a width of 40 cm. Further, the weight, and accordingly the displacement volume, is the same for the two model vessels 1, giving a corresponding draft DV of 5.5 cm for Model 22A and 6 cm for Model 22B when the model vessels 1 are floating motionless in a body of water.
The separation line 6 of Model 22A is located 5.5 cm under the water surface 5 and for Model 22B the separation line 6 is located at the water surface 5 when the model vessels 1 are floating motionless in a body of water.
The angel β between the tangent line TH and the water surface 5 is 20 degrees for Model 22B. The aft hull section 3 of Model 22B has a similar layout as shown in
During testing, both prior art Model 22A and inventive Model 22B are trimmed to neutral when floating motionless in a body of water.
Model Tests—Horizontal Forces Provided by an Aft Body
To document how the configuration of an aft hull section 3 and an aft body 4 effects the horizontal forces provided by an aft body 4 in a longitudinal direction of a model vessel 1, a series of model tests have been conducted. The model tests are performed on a model vessel 1 with configurations according to the invention and configuration according to prior art, where the aft body 4 is providing a continuous propulsion force on the model vessel 1 (i.e. a continuous forwardly directed horizontal forces in the longitudinal direction of the model vessel 1).
Model Vessel—Testing Set Up
Dimensions of the model vessel 1:
Maximum vertical thickness of all aft bodies 4: 1.1 cm, except for aft body 4 marked (B) in
The model vessel 1 shown in
During all model tests the leading edge 41 of the aft body 4 was located 10 mm downstream/aft of the separation line 6, the chord angel γ is 0 degree unless otherwise stated and the trim angel of the model vessel 1 was kept neutral when floating motionless in a body of water.
Results from Model Tests
The geometry of the inventive model vessel 1 (A) is configured to minimize the wave resistance Rw from the aft hull section 3. Hence, the inventive model vessel 1 (A) has a draft DV(A) of 80 mm, which entails Ale=1.0*Ate, an angle β(A) for the tangent line TH of 4.5 degrees and a chord angel γ(A) of 0 degree.
In order to obtain a continuous forward propulsion from the aft body 4 the configuration of the prior art model vessel 1 (B) is based upon a combination of the configurations found through the model testing to contribute to a forward propulsion. The prior art model vessel 1 (B) hence has a draft DV(B) of 100 mm, which entails Ale=0.71*Ate, an angle β(B) for the tangent line TH of 11.0 degrees and a chord angel γ(B) of −2 degrees.
From
Conclusion from Model Testing
When measuring the horizontal forces from the aft body 4 of a model vessel 1 according to the invention, it was revealed that the aft body 4 itself applied a backwardly directed force (i.e. resistance) on the model vessel 1. When the configuration of the aft body 4 and the geometry of the aft hull section 3 was altered, creating a vessel 1 beyond the scope of the invention, a forwardly directed force (i.e. propulsion) from the aft body 4 occurred under certain conditions.
A low Ale/Ate ratio, a high angel β of the tangent line TH and a downward tilted chord angel γ are important parameters to achieve a propulsion force from the aft body 4. Furthermore, a reduction of the chord length of the aft body 4 and an arrangement of the aft body 4 closer to the water surface 5 will also contribute to possibly achieve forward propulsion from the aft body 4.
The model tests demonstrate that a configuration seeking to achieve forward propulsion from the aft body 4 are contrary to a configuration seeking to achieve a reduction of the stern wave 9.
Hence a prior art vessel 1 will benefit from a low Ale/Ate ratio to achieve forward propulsion from the aft body 4. This is in clear contrast to the inventive vessel 1 which will benefit of a ratio of Ale/Ate≈1.0 to achieve equilibrium in the water mass downstream the aft body 4.
A prior art vessel 1 will benefit from a larger angel β of the tangent line TH to achieve forward propulsion from the aft body 4. This is also in clear contrast to the inventive vessel 1 which will benefit of small angel β of the tangent line TH to achieve a horizontal direction of a water flow 51 downstream the aft body 4.
A prior art vessel 1 will benefit from a negative chord angel γ to achieve forward propulsion from the aft body 4. Again, this is in clear contrast to the inventive vessel 1 which will benefit of horizontal, or near horizontal, chord angel γ to achieve a horizontal direction of a water flow 51 downstream the aft body 4.
A prior art vessel 1 having a larger angel β of the tangent line TH would also benefit from an even more negative chord angel γ. However, both a higher angel β of the tangent line TH and an increased negative chord angel γ will contribute to an increasing stern wave 9.
A prior art vessel 1 will benefit from a shorter chord length of the aft body 4 as a shorter chord length results in larger forward propulsion. In contrast, an inventive vessel 1 would need a longer chord length of the aft body 4 to be able redirect the upwardly directed water flow 51 upstream/in front of the aft body 4 to a horizontal water flow 51 downstream the aft body 4 without causing turbulence.
A visual comparison of models tested of the inventive vessel 1 described above and the prior art vessels 1 providing forward propulsion from an aft body 4 shows that the inventive vessel 1 generates a smaller stern wave 9 and has less sinkage at the stern relative to the prior art vessel 1. It is further observed through model tests, not included in this paper, that an inventive vessel 1 seeking to obtain a reduced stern wave 9 contributes to a larger reduction in total resistance Rt for the vessel 1 than a design according to the prior art seeking to obtain forward propulsion from the aft body 4.
In the preceding description, various aspects of the vessel 1 according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the vessel 1 and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiments, as well as other embodiments of the vessel 1, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20165953.9 | Mar 2020 | WO | international |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/057828 | 3/25/2021 | WO |
