FI127629B - Steerable contra-rotating propulsion system - Google Patents

Abstract

Various aspects provide for a ship (200, 600) having a main propeller (110) and a steerable contra-rotating propeller (steerable CRP) (120, 220, 620). The steerable CRP (120, 220, 620) may comprise a contra-rotating propeller (122, 222) and a transmission (130) coupling the contra-rotating propeller (122, 222) to the ship (200, 600). The transmission (130) may drive (e.g., spin) the contra-rotating propeller (122, 222) to generate thrust. The transmission (130) may direct the thrust of the CRP (122, 222) independent of the thrust direction of the main propeller (110), such that the steerable CRP (120, 220, 620) may be used to impart (e.g.) a lateral thrust while the main propeller (110) is imparting longitudinal thrust. The CRP may be directed to impart a longitudinal thrust, in parallel with the main propeller.

Description

STEERABLE CONTRA-ROTATING PROPULSION SYSTEM HAVING A SHROUD AXIALLY ENCOMPASSING BOTH MAIN AND CONTRA-ROTATING PROPELLERS BACKGROUND 1. Technical Field The present invention relates generally to marine propulsion, and more particularly to contra-rotating propeller systems. 2. Description of Related Art Historically, Improvements in efficiency, emissions, and the like often add to the cost of production and can reduce the reliability of a product. In some marine applications, propulsion efficiency may be increased with the use of a contra-rotating propeller located immediately behind, and rotating opposite, a lead propeller.

[0002] In typical contra-rotating propellers, two propellers are mounted on concentric driveshafts. The first (e.g., outer) driveshaft rotates the first propeller, and the second (e.g., inner) driveshaft rotates the second propeller in the opposite direction. Such systems are typically complex, and coupling of driveshafts is often often affected by mechanical efficiency. Such systems do not inherently provide navigation, and implementation of a rudder may be more difficult with a typical contra-rotating propeller system.

A ship may have a large propeller, for example as disclosed in PCT patent application publication no. WO 2009/126090, which is incorporated by reference herein. A large propeller may rotate more slowly than a smaller propeller (at equal thrust), which may improve efficiency. However, the added complexity and hardware may make implementation of a large propeller difficult. Managing a large flow field proximate to a vessel having a large area propeller may be challenging, and some implementations may be impacted by safety requirements.

A ship may have an azimuth thruster which provides directional control and forward thrust. Some azimuth thrusters incorporate a contra-rotating propeller. FR2927605 (Al) Relates to a thruster having at least two water propulsion rotors. DE20315579 (Ul) describes a ship propulsion system that comprises two propellers rotating at different speeds mounted on a concentric drive shaft arrangement inside a tube with open ends. WO8601483 (Al) describes a propeller drive with contra rotating propellers, wherein the shafts of the outer propellers are supported by bearings inside the Hollow shafts of the inner propellers. US5795200 (WO96 / 09954) describes a marine propulsion unit that has two contrarotating propellers driven by a single shaft through gearing which includes a set of static planetary gears, an external gear, and an internal gear. US2011033296 describes a contrarotating propeller marine propulsion device. US5441388 describes a ship drive with two counterturning propellers. JP2004168222 (A) describes a contra-rotating propeller device. WO9749604 (Al) describes a differential drive for a ship having two ship screws.

SUMMARY OF THE INVENTION

[0005] A first propeller may drive a ship. The navigation drive may comprise a second (e.g., contra-rotating) propeller, a propulsion system to rotate the second propeller, and a transmission to controllably change the second propeller's thrust direction with respect to that of the main propeller. The second propeller may be directed by the transmission to impart a lateral thrust to the ship to navigate the ship. The second propeller may impart a forward or reverse thrust to the ship (e.g., instead of, or in addition to, the first propeller). The second propeller may be coaxial with the first propeller at a first position (e.g., in an aligned position), and not coaxial at other positions (e.g., that impart lateral thrust).

[0006] A ship may comprise a main propeller coupled to the ship and configured to impart a longitudinal thrust to the ship (e.g., to propel the ship forward or backward). A steerable contra-rotating propeller (steerable CRP) may comprise a CRP disposed longitudinally with respect to the main propeller (e.g., disposed immediately ahead of or aft of the main propeller). CRP may be disposed to such that the flow fields of the propellers interact (e.g., substantially overlap) during Steaming. A CRP may be disposed to a Harvest rotational momentum imparted by a main propeller to the water.

A transmission may couple the CRP to the ship, and may drive the CRP (to provide thrust). The transmission may be configured to direct the thrust of the CRP over a range of angles (e.g., lateral angles from port to starboard). The transmission may align the CRP with the main propeller, such that they are coaxial and their thrust directions are parallel. The transmission may direct the thrust of the CRP independent of the main propeller by changing the thrust direction of the CRP (making it non-coaxial with that of the main propeller).

The main propeller and the steerable CRP indude a shroud which axially encompasses both the CRP and the main propeller. The shroud and CRP may be directed as a single unit by the transmission. A shroud may encompass only one propeller. In an out, shroud encompasses a CRP but not the main propeller. In an out, the shroud encompasses the main propeller but not the CRP. A first shroud may encompass a first (e.g., main) propeller and a second shroud may encompass a second (e.g., CRP) propeller.

A ship may have a large diameter propeller (inducting one or both of the main propeller and the CRP) having a diameter that is greater than 50% of the draft, inducting greater than 80% of the draft. The ship may have a Hull consisting of a Hull concavity. The Hull concavity may have a radius of curvature that is larger (eg, 5%, 10%, 50%, or even 100% larger) than the radius of the outer tip of the largest propeller (and / or a shroud around the propeller) , if induded). The radius of the Hull concavity (e.g., in a plane orthogonal to the propeller axis) may be at least twice as large as the radius of the propeller and / or shroud. An exemplary Hull may have a Hull concavity with a radius between 2 and 90 meters, induding between 4 and 70 meters, induding between 6 and 50 meters. A Hull concavity can have a radius that is, with respect to the propeller radius, between 0.5 x and 40 x (the radius of the propeller), induding between lx and 20x, induding between 1.5x and lOx. A Hull concavity can have a radius that, with respect to the propeller radius, is between 0.5x and 100x (the radius of the propeller), induding between lx and 70x, induding between 1.5x and 50x, induding between 2x and 20x.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates a side view of a ship having a propulsion system according to some embodiments.

FIGS. 2A and 2B illustrate side elevations of a steerable CRP comprising a shroud, according to some embodiments.

[0012] FIG. 3 illustrates a view of the Stern of a ship, according to some embodiments.

[0013] FIG. 4 is a perspective illustration of an aft portion of a ship, according to some embodiments.

[0014] FIGS. 5A - C illustrate different steering configurations, according to some embodiments.

[0015] FIGS. 6A and 6B illustrate an exemplary embodiment.

DETAILED DESCRIPTION

A single propeller may impart a non-thrusting moment (e.g., rotational and / or tangential momentum) to the water it passes through, resulting in reduced efficiency. A second, contra-rotating propeller disposed behind the first propeller may "Harvest" at least a portion of this otherwise Wasted momentum, Converting it to a forward thrust. A main propeller and a contra-rotating propeller may be sized (eg, with feedback from 3D CFD models and / or physical models of their flow fields at cruising speeds) such that a large portion of the nonthrust (eg, rotational / tangential) momentum of the first propeller is wholly harvested by the contra-rotating propeller. Preferably, the flow field of the fluid exiting the contra-rotating propeller has a minimum, or even no, rotational / tangential component. In such a design, efficiency may be increased (e.g., by at least 5%, including at least 10%, or even at least 15%, up to about 25%). The contra-rotating propeller may spread the thrust loading over a larger propeller area (e.g., over a larger number of blades), reducing the loading on each blade. Such a configuration may reduce wear (e.g., of bearings) and / or reduce fatigue.

Various aspects provide for a propulsion system (e.g., for propelling a marine vessel). The propulsion system may combine a main propeller (e.g., a fixed direction propeller providing only forward / reverse thrust) with a contra-rotating propeller whose thrust direction may be controlled independently of that main propeller (hence: steerable CRP). The steerable CRP may be located immediately ahead of or behind the main propeller (such that the centerline of the steerable CRP and the main propeller may be aligned coaxially on a "virtual" axis of rotation). This alignment may increase the hydrodynamic efficiency of the system. A transmission may direct the thrust in the direction of the CRP, independent of the main propeller in order to impart a thrust in a direction different than the thrust in the direction of the main propeller.

The propulsion system may comprise a main propeller and a steerable CRP having a contra-rotating propeller and a transmission coupling the contra-rotating propeller to the ship. The transmission may be configured to drive the CRP (i.e., "spin" or rotate the propeller blades per se). The transmission may include a central motor to spin the propeller blades through the center of the propeller. The transmission may include a rim-drive to spin the propeller blades through the outer portion of the propeller blades. CRP and main propeller may rotate at substantially the same RPM (Revolutions per minute). A CRP may rotate at a different RPM than that of the main propeller.

The transmission may be configured to direct the thrust of the CRP (e.g., change the centerline of the CRP about a steering axis). The thrust of the steerable CRP may be changed with respect to that of the main propeller, such that the axis of rotation of the steerable CRP's blades is not aligned with that of the main propeller. The ship may be steered by controlling the thrust direction of the steerable CRP (e.g., to impart a lateral thrust to the port or starboard). The transmission may comprise one or more hydraulic cylinders, electric actuators, geared (e.g., worm gear) actuators, and the like.

[0020] The centerlines of the propellers may be a baked coplanar. In some embodiments, the steerable CRP is configured such that the transmission directs at least a portion of the thrust of the CRP in a vertical direction with respect to the main propeller. In some cases, the steerable CRP may be configured to impart a combination of vertical and horizontal thrust, such that the centerlines of the CRP and main propeller are not coplanar. At least one, including both, of the main propeller and CRP may include a shroud or nozzle. In some cases, neither propeller has a shroud or nozzle.

[0021] FIG. 1 illustrates a side view of a ship having a propulsion system according to some embodiments. In exemplary FIG. 1, a ship 100 has a Hull 101 having a draft 102. Various embodiments may be implemented with a large ship having a draft greater than 2 meters, including at least 10 meters, including greater than 15 meters. An exemplary ship may have a draft between 4 and 25 meters, including between 6 and 18 meters.

A main propeller 110 may be coupled to an engine 103 (e.g., an LNG engine, a diesel engine, a turbine), and configured to impart a longitudinal thrust to the ship. In some ships, the main propeller may be a fixed propeller (e.g., coupled to the engine 103 via a rigid driveshaft) and only provide forward or reverse thrust. The main propeller may provide for lateral thrust in some embodiments (e.g., as part of a pod or azimuth thruster).

The main propeller may have a large diameter relative to the size of the ship (e.g., the ratio of the propeller diameter to draft). A large diameter propeller can provide increased propulsion efficiency as compared to a smaller propeller (that rotates at a higher speed to provide the same thrust). In some cases, the diameter 112 of the main propeller is greater than 50% of, greater than 75% of, greater than 85% of, greater than 90% of, or even greater than draft 102. An exemplary propeller may have a diameter that is at least 1.5 meters, including at least 2 meters. The propeller may have a diameter between 2 and 22 meters, including between 3 and 18 meters in diameter, including between 5 and 15 meters in diameter. Various embodiments may be implemented with smaller propellers (e.g., between 0.2 and 3 meters, including between 0.5 and 2 meters).

The propulsion system may comprise a steerable contra-rotating propeller (steerable CRP) 120, which may be powered by engine 103 and / or another power plant. The steerable CRP includes a contra-rotating propeller (CRP) 122 configured to rotate in the opposite direction of rotation of the main propeller. The CRP may have a diameter greater than 50%, greater than 75%, greater than 85%, greater than 90%, or even greater than draft 102. Typically, an CRT may have a diameter slightly smaller than that of the main propeller . CRP disposed ahead of the main propeller may have slightly larger diameter. An exemplary (e.g., aftward) CRP may have a diameter between 40% and 90% of that of the main propeller, including between 45% and 80%, including between 50% and 70%, such as 55% -65%. The CRP may include a hub-driven propeller (as shown in FIG. 1), a rim-driven propeller (including an electromagnetically rim-driven propeller), and other types of driven propeller.

[0025] The CRP may be powered by a transmission 130 that couples the CRP to the ship and drives the CRP (to provide thrust). Transmission 130 is typically configured to be controllable (e.g., via a navigation console) to direct thrust of the CRP over a range of direction independent thrust of the main propeller. In an embodiment, a ship consists of a fixed-axle main propeller (that does not provide lateral thrust), and the steerable CRP may be directed to impart a range of lateral thrust that can be used to steer the ship from port to starboard. In a straight ahead alignment (of the CRP centerline with respect to that of the main propeller), the steerable CRP may propel the ship longitudinally (e.g., forward or backward).

CRP 122 may be aligned longitudinally with respect to the main propeller, such that their centerlines are coaxial and their flow fields substantially overlap. In some embodiments, the flow field of one propeller (e.g., the front propeller) substantially completely encapsulates the flow field of the other (e.g., following) propeller. In some cases, the CRP is a disposed aft of the main propeller; in some cases (not shown) it is disposed ahead of the main propeller.

The rotational axis of the steerable CRP may be directed independently of the rotational axis of the main propeller providing a controllable lateral thrust of the steerable CRP with respect to the thrust direction of the main propeller (regardless of the thrust direction of the main propeller). An azimuth thruster may combine a rim-driven propeller (e.g., a main propeller) and a center-driven propeller (e.g., a steerable CRP). In some embodiments, an azimuth thruster combines a main propeller (that itself can impart lateral thrust) and a steerable CRP (e.g., whose lateral thrust may be directed independently of that main propeller).

Various embodiments may comprise a Lifeboat ramp configured to Stow and deploy a Lifeboat. The Lifeboat ramp may be mounted along the centerline of the ship (e.g., aft of the transom and / or integrated with the Stern). In FIG. 1, a Lifeboat ramp 140 is configured to Stow and deploy a Lifeboat 150. A Lifeboat ramp may extend from the Hull (e.g., aft of the transom or fore of the prow). The Lifeboat ramp may be integrated with the Hull. The Lifeboat ramp and transmission 130 may be integrated.

[0029] FIGS. 2A and 2B illustrate side elevations of a steerable CRP comprising a shroud, according to some embodiments. FIG. 2A illustrates a view of the starboard side; FIG 2B illustrates this view with a steerable CRP in section.

[0030] FIGS. 2A and 2B illustrate a ship 200 having a steerable CRP 220. In this example, a steerable CRP 220 consists of a rim-driven (eg, electromagnetically rim-driven) contra-rotating propeller 222. In this example, the steerable CRP comprises a shroud 221. .A shroud (or nozzle) that axially "surrounds" a propeller may increase power and / or efficiency. A shroud and a rim drive may be integrated. A shroud may axially surround the main propeller (not shown), the CRP (e.g., FIG. 6A / B), and / or both the main propeller and the CRP (as in FIGS. 2A / B). The shroud may have a diameter slightly larger than that of the largest propeller it surrounds. The shroud may be substantially frustoconical (e.g., with a larger diameter at the front end and a smaller diameter at the rear end). When integrated with a CPR, a shroud may also be steered by transmission 130, such that the CRP and shroud are directed as an integrated unit.

[0031] FIG. 2B illustrates a section of steerable CRP 220, and shows a contra-rotating propeller 222 disposed aft of a main propeller 110. In this example, CRP 222 has a diameter that is slightly smaller than (eg, 85-95% of) that of main propeller 110. A steering axis 230 may be located above (eg, directly above) a point directly aft (or even aligned with) the main propeller aft Terminus.

Transmission 130 may rotate CRP 222 (to provide thrust) and direct thrust of CRP 222 (in this example, laterally). In this example, transmission 130 directs CRP 222 and shroud 221 about steering axis 230 (see FIG. 5).

[0033] FIG. 3 illustrates a view of the Stern of a ship, according to some embodiments. In this example, the steerable CRP 220 is illustrated in an "aligned" configuration, in which the centerlines of the CRP and the main propeller are coaxial. FIG. 3 illustrates an exemplary outer radius 320 of a shroud 221 encompassing the main propeller and the CRP.

[0034] The centerline of the main propeller may be a vertical distance 330 from a baseline 106 of the ship. The centerline of the CRP may be a vertical distance 330 'from the baseline. In some embodiments, the distances 330 and 330 are substantially the same (e.g., within a manufacturing tolerance or a tolerance within which hydrodynamic effects are negligible). The larger of the distances 330 and 330 'may be slightly larger than the radius of the larger propeller (or the outside of the shroud if included) such that no portion of the steerable CRP extends below the baseline of the ship. In FIG. 3, both distances 330 and 330 'are slightly larger than outer radius 320 of shroud 221. Vertical distances 330 and 330' may be within 10% of each other, including between 1% of each other. In some embodiments, distances 330 and 330 'are different.

[0035] The propulsion system may be centered with respect to port 104 and starboard 105 sides of the ship. In an aligned configuration, the centerline of the main propeller may be a horizontal distance 340 from the starboard side, the centerline of the steerable CRP may be a horizontal distance 340 'from the starboard side, and these horizontal distances may be within 10% of each other, including within 1% of each other, including substantially the same. The centerlines may be substantially equidistant from the port and starboard sides, such that the horizontal distance 340 equals the horizontal distance 342 (centerline to the port side) and the horizontal distance 340 'equals the horizontal distance 342' (centerline to port side).

The ship may have a plurality of steerable CRP systems (e.g., with two or three main propellers). In an implement, a ship has a port and starboard main propellers, and each main propeller has a steerable CRP. A ship may have a center propeller and one or more propellers to each of the port and starboard sides. In some cases, all propellers include a steerable CRP. In some cases, not all of the propellers include a steerable CRP.

The Hull 101 (FIG. 1) of a ship may have a Hull concavity 300. The Hull concavity 300 may improve hydrodynamic flow properties of a ship having a large diameter propeller. Hull concavity 300 may have a radius (e.g., orthogonal to the centerline of the main and / or contra-rotating propellers) that is larger than the largest propeller radius (and shroud radius, if a shroud is included). The Hull concavity may be finite (i.e., not have an infinite radius). In an embodiment, the propeller has a diameter that is greater than 50% of the draft of the ship (including above 75%, including above 90%, or even above 100%). The Hull may comprise a Hull cavity 300 having a radius of curvature 310 that is larger than the outer radius of the propeller, particularly at least 40% larger, including at least twice as large, including at least four times as large. The Hull concavity 300 may have a radius of curvature 310 that is larger than the draft of the ship, including 2x, larger, 3x larger, 5x larger, 10x larger, or even 20x larger. Hull concavity typically has a finite curvature (i.e., is not completely flat).

In some cases, radius 310 is large enough that a portion (e.g., the center top portion) of the Hull concavity 300 extends above the waterline of the ship (when the ship is stationary). Such a concavity may fill with water when the ship is moving. In some embodiments, the shroud 221 axially encompasses the main and steerable propellers (of which at least the main propeller is a large diameter propeller). The shroud may have an outer radius 320 (FIG. 3), and the hull may have a Hull concavity 300 with a radius of curvature 310 that is greater than, including at least twice, or even five at most. times as large, including lOx as large as outer radius 320 of the shroud. Typically, radius 310 of the Hull concavity will not be so high that efficiency is reduced (e.g., as determined in a computer simulation of Steaming conditions). Radius 310 may be smaller than 50x, including smaller than 20x, including smaller than lOx, the largest radii of main propeller, CRP, and (if included) shroud. In an implementation, the radius 310 may be greater than 3 meters, including greater than 8 meters, such as above 15 meters, and may be less than 80 meters, including less than 30 meters.

[0039] FIG. 4 is a perspective illustration of an aft portion of a ship, according to some embodiments. A steerable CRP may be implemented at the aft portion of a ship, as shown. A steerable CRP may be implemented at the bow of the ship (not shown). Hull concavity 300 can improve flow of water past steerable CRP, improving efficiency.

FIGS. 5A - C illustrate different steering configurations, according to some embodiments. An angle of 500 between the thrust directions of the main propeller and the steerable CRP may be varied over a range of angles sufficient to provide navigation (e.g., up to +/- 35 degrees, such as for a SOLAS compliant vessel). The range of Angles may vary from at least 1 degree, including at least 5 degrees, including at least 20 degrees. In some cases, angle 500 is less than 85 degrees, including less than 75 degrees, including up to 55 degrees. A typical apparatus may be steered over a range of Angles up to +/- 50 degrees, including up to +/- 40 degrees.

The Angle 500 may be increased to increase the non-aligned component of the thrust (e.g., to make the ship "turn more tightly"). Angle 500 may generally be limited by requirement that steerable CRP not significantly degrade performance of main propeller and / or interact with Hull. Angle 500 may be limited by mechanical interaction between propellers and / or a shroud. In some cases, at least a portion of the interior face of the shroud is concave (e.g., substantially spherical) such that the shroud can move around the main propeller without contacting it.

[0042] FIG. 5A illustrates an "aligned" configuration, in which the schematic thrust directions of the main propeller and steerable CRP 220 are the same (in this case, thrusting aftward to move the ship ahead). FIG. 5B illustrates a configuration in which steerable CRP 220 is directing its thrust partially to the starboard. FIG. 5C illustrates a configuration in which steerable CRP 220 is directing its thrust partially to port.

A Hull may comprise one or more pockets 510 which may be shaped to receive a shroud and / or propeller (e.g., as it moves over Angles 500). A pocket or "divot" may comprise a Hull shape (e.g., a concavity) that "receives" or fits around the propeller or shroud (e.g., as it is redirected / revolved among various positions). The pocket may allow a propeller or shroud to move freely, even though it is located close to the Hull (e.g., with a propeller tip to Hull distance below 25% of the propeller diameter and / or shroud diameter). In exemplary FIGS. 5A-C, two pockets 510 are disposed on either side of the centerline, and are shaped to allow movement of CRP 220. In an embodiment, a Hull concavity and at least one, including at least two, pockets . Hull may comprise a Hull concavity without pockets; a Hull may comprise a pocket without a Hull concavity.

[0044] FIGS. 6A and 6B illustrate an exemplary embodiment. A ship 600 may comprise a CRP 620 having a shroud 621 associated with the CRP but not the main propeller. FIG. 6A illustrates a side elevation of a ship 600. FIG. 6B illustrates the shroud in section. In this example, transmission 130 directs shroud 621 and CRP 222 to direct at least a portion of the thrust of CRP 222 laterally. In some cases, a shroud encompasses the main propeller but not the CRP.

Various features described herein may be implemented independently and / or in combination with each other. An explicit combination of features in an embodiment does not preclude the omission of any of these features from other embodiments. The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this Disclosure. The scope of the invention should, therefore, be determined with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims (14)

REQUIREMENT A ship (200, 600) comprising: a main propeller (110) coupled to the vessel and designed to provide longitudinal pressure to the vessel in a first direction; and A controllable MRP (120, 220, 620) comprising: a counter-rotating propeller (122, 222) arranged longitudinally with respect to the main propeller, a housing (221); and a transmission (130) which couples the MRP to the vessel and is configured to rotate the casing and counter-rotating propeller about a steering shaft (230) to direct pressure from the MRP over a range of lateral directions regardless of the longitudinal pressure. from the main propeller; characterized by: The housing (221) axially surrounds the main propeller (110) and the counter-rotating propeller (122, 222). The vessel of claim 1, wherein the MRP unit comprises a rim-driven propeller. 20 The vessel of claim 2, wherein the rim-driven propeller comprises an electromagnetically driven rim-driven propeller. Vessel according to any of claims 1-3, wherein the guide shaft (230) is located above a point which is directly aft of the rear end of the main propeller. Vessel according to any of claims 1-4, wherein the main propeller has a diameter greater than 50% of a draft (102) of the vessel. 20165227 prh 29 -05- 2018 A party according to any of claims 1-5, wherein: the counter-rotating propeller (122, 222) comprises a rim-driven propeller disposed behind the main propeller (110); and the steering shaft (230) is located at the front end of the counter-rotating propeller (122, 5 222). Vessel according to any one of claims 1-6, wherein the guide shaft (230) is located above a point aligned with a rear end of the main propeller. 10 Vessel according to any of claims 1-7, further comprising a hull cavity (300) in a ship's hull (101), which has a radius of curvature (310) greater than an outer radius (320) of the casing (221). Vessel according to any of claims 1-8, wherein: The main propeller (110) has a diameter greater than 75% of a draft (102) of the vessel; and a ship's hull (101) comprises a hull cavity (300) having a radius of curvature (310) at least twice the outer radius of the main propeller. 20 Vessel according to claim 9, wherein the casing (221) has an outer radius (320), and the radius of curvature (310) of the hull cavity (300) is at least 2x larger than the outer radius (320). A vessel according to any of claims 9 and 10, wherein the radius of curvature of the hull cavity 25 is greater than 8 meters. Vessel according to any of claims 9-11, wherein the radius of curvature of the hull cavity in relation to the radius of curvature of the propeller is between 0.5x and 100x (radius of the propeller). A party according to any one of claims 1-12, wherein the main propeller (110) has a diameter greater than 50% of a draft (102) of the vessel, and a hull (102) of the vessel having at least one pocket (510). closest to the main propeller and disposed on either side of a center line of the vessel, the pockets being designed to prevent contact between the housing and hull as the propeller rotates over a range of angles (500). Vessel according to claims 1-13, wherein the casing is mainly in the shape of a truncated cone and has a larger diameter at a front end than at a rear end.