EP4660072A1

EP4660072A1 - Marine drive transmission with contra-rotating propellers marine drive transmission with contra-rotating propellers

Info

Publication number: EP4660072A1
Application number: EP25180062.9A
Authority: EP
Inventors: Andrea Pellegrinetti; Adone Bertolo; Keith Stanley; Drew ORVIETO; Alessandro Zocca; Cristian Pozzati
Original assignee: ZF Friedrichshafen AG; ZF Padova SRL; Zf Marine Propulsion Systems Miramar LLC
Current assignee: ZF Friedrichshafen AG; ZF Padova SRL; Zf Marine Propulsion Systems Miramar LLC
Priority date: 2024-06-04
Filing date: 2025-06-02
Publication date: 2025-12-10
Also published as: US20260028104A1

Abstract

A marine drive assembly has a housing extending along a central axis and defining a gearbox section and a driveshaft section. A bevel gear assembly is housed in the gearbox section and has a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear. A mounting flange is connected to and extends around at least part of the gearbox section. An inner shaft extends along the central axis and is operably connected to the first bevel gear for rotation in a first rotational direction about the central axis. An outer shaft is coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.

Description

TECHNICAL FIELD

The present disclosure relates generally to transmissions for marine applications, and more particularly to a marine drive transmission with contra-rotating propellers.

BACKGROUND

Contra rotating propellers are highly desirable for a number of marine applications and provide an increased blade area and high thrust in the water. Contra-rotating propellers have been utilized for stern drive and outboard motors. A drive system having two counter-rotating propellers provides improved thrust efficiency and better performance when operating in reverse or in tight quarters. In addition, the dual propellers remove a paddle wheel effect of a single propeller that typically forces the stern of the vessel in the direction of rotation, also known as side thrust.
Known contra-rotation propeller systems are described in U.S. Patent No. 5,083,989 , which discloses a drive transmission having contra-rotating propeller shafts which transmit contra-rotating drives to the shaft via respective planet carriers. Particular advantages are the equal divisions of torque between the shafts and the ability to place the thrust bearings in easy-to-access locations.
U.S. Patent No. 5,366,398 discloses a dual propeller marine drive assembly with counter-rotating propellers for a stern drive mounting arrangement. A vertical drive shaft extends through a vertical bore through the housing. Inner and outer concentric counter-rotating propeller shafts are supported by a spool in a lower horizontal bore. Passages are provided in the housing for communicating lubrication and/or exhaust with the horizontal bore.
U.S. Patent No. 5,601,464 discloses a transmission system for a counter-rotational propulsion device in an outboard motor arrangement. The transmission system converts the outboard drive from a single propeller drive to a counter-rotational dual propeller system. The transmission system involves a first transmission which selectively couples an inner propeller shaft with an existing driveshaft of the outboard drive. A second transmission of the transmission system is provided between the inner propeller shaft and an outer propeller shaft. The second transmission reverses the rotational drive direction input by the inner propeller shaft so as to drive the outer propeller shaft in an opposite rotational direction.
U.S. Patent No. 5,230,644 discloses a marine drive with two counter-rotating surface operating propellers, such as for a transom-mounted motor. The housing has a vertical driveshaft of reduced vertical size to enable raising the torpedo without raising the transom mounting location of the drive. An upper adapter spool has a lower threaded outer portion that mates with a threaded portion of the vertical bore of the drive housing. The lower threaded outer portion supports the upper gear for rotation about the driveshaft and supports the driveshaft for rotation within the adapter spool. A vertical bore structure enables assembly from above the majority of the vertical train components into a one-piece, unitary, integrally cast housing. The vertical distance between the adapter spool and the lower bearings supporting the vertical driveshaft is approximately equal to the propeller radius.
U.S. Patent No. 4,963,108 discloses a counter-rotating marine propeller drive system. The system comprises a large gear driven by an engine, and a plurality of small gears disposed so as to respectively mesh with the large gear at a plurality of fixed positions along the circumference of the large gear. Planet gears are respectively mounted to the gear shafts of the small gears. A sun gear and an inner tooth gear are respectively meshed with the planet gears. A rear propeller is mounted to an inner shaft serving as a gear shaft of the sun gear. A front propeller is mounted to a tubular outer shaft serving as a gear shaft of the inner tooth gear.
U.S. Patent No. 5,249,995 discloses a marine drive having two counter-rotating surfacing propellers. The housing defines a vertical bore for a vertical driveshaft. Inner and outer concentric counter-rotating propeller shafts are supported in the torpedo in the lower drive housing by a spool assembly locked and retained against rotation and against axial movement in the lower horizontal bore in the torpedo of the drive housing by axially spaced left-hand and right-hand threads. A thrust bearing assembly transfers thrust from the outer propeller shaft to the inner propeller shaft during rotation of the propeller shafts in an opposite direction and is located between the fore and aft driven gears.

SUMMARY

The present disclosure is directed to an inboard marine drive system with contra-rotating propellers. In some embodiments, the drive system exhibits improved thrust, particularly in the lower and midrange engine speeds. In accordance with one embodiment, the marine drive system is configured as a straight-shaft inboard drive system with contra-rotating propellers. Similarly, the drive system can be used to convert a traditional straight-shaft drive system with one propeller to a drive assembly having contra-rotating propellers. Compared to existing drive arrangements, the drive arrangement of the present disclosure has a bevel gear set that is located at or above the mounting flange. This arrangement reduces drag by providing a slender driveshaft portion of the housing that protrudes into the water beneath the hull. In accordance with one embodiment, a marine transmission of the present disclosure enables transforming the classic straight-line shaft with a single propeller into a transmission with two coaxial contra-rotating propellers. A bevel gear set allows rotation of an inner shaft and an outer hollow shaft in opposite directions, where the drive shaft is coaxially arranged with inner and outer output shafts. A marine drive system as disclosed herein is useful in high-power boats, such as those designed for water skiing and wakeboarding.
In some embodiments, the hydrodynamic shape of the in-water unit allows reduced drag force during boat cruising. For example, in some embodiments, a majority portion of the gearbox is contained within the boat's hull or within the hull's bottom recess. Stated differently, a majority portion of the gear box is positioned above the mounting flange (also known as an interface flange) which mounts to the bottom of the boat hull. In cases where the hull defines a recess for the drive system, the hull covers the hull recess and can be sealed to the bottom of the hull in its installed configuration. In some such embodiments, the hull mounting flange is sufficiently large and thick to enable transferring the thrust load to the hull frame. Such a flange can also provide a more even distribution of that load. In some such embodiments, the mounting flange can accommodate flush-mounted sacrificial anodes of large surface area that are used to prevent corrosion in critical areas of the transmission and drive assembly.
In some embodiments, the transmission strut can be omitted since it is not necessary to transfer propeller thrust loads from the drive line to the hull. By omitting the strut, water can flow in a less obstructed manner to the front propeller disc area. In some embodiments, the skeg can alternately or additionally be omitted to further reduce drag compared to traditional shaft line assemblies, while at the same time retaining the advantages of high-efficiency contra-rotating propellers. In some embodiments, the skeg is removable, enabling substitution of one type or shape of skeg for another skeg as may be desired to create enhanced wake shapes for water sports.
In accordance with some embodiments, transferring the thrust of contra-rotating props directly to the hull body enables the use of softer rubber mounts on the engine/gearbox, which improves noise, vibration, and harshness (NVH). In some embodiments, the drive is decoupled from the gearbox output shaft by moving the interface inside the hull. This allows for a sealing system that is indifferent to misalignments between the input shaft and the bevel gear. In some such embodiments, the gearbox employs crown splines to compensate for misalignments.
In some embodiments, propeller thrust is completely absorbed from the hull, rather than from thrust bearings as is the case in a traditional shaft line assembly.
A marine drive assembly in accordance with some embodiments of the present disclosure have a lubrication circuit with different sizes of radial openings in the hollow shaft to exploit centrifugal force while running. This converges lubrication oil to the rear end adjacent the propellers where the needle bearing cage and sealing are located. In some embodiments, no vent is necessary because the oil temperature during operation remains stable at a temperature below 40° C due to the cooling effect of water flowing around the drive assembly.
Embodiments of the present disclosure provide an increase in global efficiency of the transmission compared to the classic shaft line, in addition to retaining the many advantages of contra-rotating propellers. Advantageously, the arrangement of the transmission enables the use of contra-rotating propellers in a straight-shaft inboard drive.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been selected principally for readability and instructional purposes and not to limit the scope of the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of a drive assembly with contra-rotating propellers, a strut, and a skeg, in accordance with an embodiment of the present disclosure.
FIG. 2 is a cross-sectional view of the drive assembly of FIG. 1.
FIG. 3 is a side view of an inboard drive assembly having contra-rotating propellers and lacking a strut, in accordance with an embodiment of the present disclosure.
FIG. 4 is a cross-sectional view showing the drive assembly of FIG. 3.
FIG. 5 illustrates a side view of an inboard drive assembly with contra-rotating propellers lacking a strut and skeg, in accordance with an embodiment of the present disclosure.
FIG. 6 is a cross-sectional view showing the drive assembly of FIG. 5.
FIG. 7 is a top view of the drive assembly of FIG. 1.
FIG. 8 is a top view of the inboard drive assembly of FIG. 3.
FIG. 9 is a cross-sectional view showing details of a bevel gear assembly, in accordance with an embodiment of the present disclosure.
FIG. 10 illustrates a top view of a bevel gear assembly, in accordance with an embodiment of the present disclosure.

The figures depict various embodiments of the present disclosure for purposes of illustration only. Numerous variations, configurations, and other embodiments will be apparent from the following detailed discussion.

DETAILED DESCRIPTION

Disclosed is a marine propulsion system. In one example, the propulsion system has a drive assembly configured to attach to a straight drive shaft of an inboard motor such that the drive shaft is coaxial with inner and outer shafts of the drive assembly. The drive assembly has a housing extending along a central axis and defining a gearbox section and a driveshaft section. A bevel gear assembly is housed in the gearbox section and has a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear. A mounting flange is connected to and extends around at least part of the gearbox section. In such way, a majority portion of the bevel gear assembly is above the flange. An inner shaft extends along the central axis and is operably connected to the first bevel gear for rotation in a first rotational direction about the central axis. An outer shaft is coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis. In use, the inner and outer shafts drive contra-rotating propellers driven by the inner and outer shafts of the drive assembly.

OVERVIEW

Despite advancements of existing marine drive systems having contra-rotating propellers, additional challenges remain. For example, existing drive systems may utilize planetary gear sets, which tend to be more complicated and noisier than a bevel gear transmission. In addition, existing drive transmissions require a strut for mounting the transmission to the boat hull. Further, some arrangements require the gearbox to be located outside of (i.e., below) the boat hull. Therefore, a need exists for an improved marine drive assembly with contra-rotating propellers.
The present disclosure addresses this need and others by providing a marine drive assembly having a majority portion of the bevel gear assembly located above the mounting flange. In such arrangement, the gearbox or a majority portion thereof is located within the hull of the boat. The bevel gear assembly drives inner and outer shafts that rotate in opposite directions to drive contra-rotating propellers. When used with an inboard drive shaft, for example, the drive shaft can be coupled to the drive gear of the bevel gear assembly so as to be collinear with the central axis of the drive assembly. Then drive shaft then drives the inner shaft while the contra-rotating bevel gear drives the outer shaft. Numerous advantages and embodiments will be apparent in light of the present disclosure.

EXAMPLE EMBODIMENTS

FIG. 1 illustrates a side view of an inboard drive assembly 100 with contra-rotating propellers 110a, 110b, in accordance with an embodiment of the present disclosure. The drive assembly includes a housing 102 that extends along a central axis 101 from a first end 102a to a second end 102b. The housing 102 includes a gearbox section 104 that encases a bevel gear assembly 150 (not visible in FIG. 1). The housing 102 has a driveshaft section 106 that houses propeller drive shafts 160, 162 (not visible in FIG. 1) that extend from the bevel gear assembly 150 to drive contra-rotating propellers 110. Propeller drive shafts 160, 162 are sealingly attached and extend through the second end 102b of the housing 102 to engage front and rear propellers 110a, 110b. An input shaft 140 is sealingly attached to and extends through the first end 102a of the housing 102 to engage the bevel gear assembly 150 at its first end 140a. The input shaft 140 is configured and arranged to couple at its second end 140b to a motor or engine, such as an internal combustion engine.
An interface flange or mounting flange 120 is attached to the housing 104 and has a planar shape configured for mounting to a boat hull. The flange 120 extends around at least part of the housing 104. For example, the flange 120 extends around the lower and aft portions of the housing 120 such that the housing 104 passes through the flange 120. The flange 120 is sized and configured to be secured to a bottom of a boat hull, such as by use of bolts or other fasteners 122. As shown in FIG. 1, a majority portion of the gearbox section 104 is above the mounting flange 120 and an entirety of the input shaft 140 is above the mounting flange 120. As also seen in FIG. 1, a geometric center C of the gearbox section 104 is above the flange 120. All or a majority of the driveshaft portion 106 is below the flange 120. In this example, all of the first end 102a of the housing, where connections are made to the input shaft 140, is above the flange 120. In one example, the flange 120 can be secured to the hull using 6-12 bolts, such as 10 bolts arranged around a perimeter of the flange 120. The flange 120 can be sealed to the hull using commercially available sealing compounds.
The drive assembly 100 of FIG. 1 includes an optional strut 180 connected to the driveshaft portion 106 and configured to be secured to the bottom of a boat hull, such as by using bolts, adhesive, or combination of these. The strut 180 can provide additional stability to the drive assembly, but the strut 180 is not required in all embodiments owing to the majority of the gearbox section 104 being above the flange 120. The drive assembly 100 of FIG. 1 also includes an optional skeg 190 attached along a bottom of the driveshaft section 106. The skeg 190 can provide additional stability to the boat and assist with preventing drift. On the other hand, omitting the strut 180 and/or the skeg 190 advantageously results in a less-obstructed flow path for water to the front of the propellers 110.
FIG. 2 is a cross-sectional view of the inboard drive assembly 100 of FIG. 1. The bevel gear assembly 150 is housed within the gearbox section 104 of the housing 102. The bevel gear assembly 150 includes a first bevel gear 152 arranged to rotate about the central axis 101 and is positioned in in the forward portion of the gearbox section 104 of the housing 102. A second bevel gear is arranged to rotate about the central axis 101 and is positioned in the rearward or aft portion of the gearbox section 104 of the housing 102. A third bevel gear 156 is arranged to rotate about an axis that is perpendicular to the central axis 101. The third bevel gear 156 is arranged to engage both the first and second bevel gears 152, 154. The first end 140a of the input shaft 140 engages the first bevel gear 152 via a spline connection to drive an inner shaft 160, which is operatively connected to and rotates the rear propeller 110a. Due to engagement with the third bevel gear 156, the second bevel gear 154 rotates in an opposite direction compared to the first bevel gear 152. The second bevel gear 154 drives an outer shaft 162 that is arranged coaxially with the inner shaft 160, where the outer shaft 162 rotates in an opposite direction compared to the inner shaft 160.
As shown in FIG. 1, the flange 120 extends forward and downward at an angle α1 from -2 to -5°, or about -3.5° relative to the horizontal. The input shaft 140 and central axis 101 extend upward at an angle α2 from 15 to 20°, or about 17.5°. Thus, the input shaft 140 is oriented at an angle α3 to the flange 120 from 15 to 25°, or about 20°, in some embodiments. In this example, the central axis 101 defines an angle α3 of about 20° with respect to a plane of the flange 120.
As can be seen in FIG. 2, the input shaft 140 is arranged along the central axis 101 and is coaxial with the inner shaft 160 and outer shaft 162. In contrast to traditional outboard motors in which the drive gear is the pinion gear (third bevel gear 156 as identified here), the first bevel gear 152 is the drive gear in the drive assembly 100. A needle bearing 166, such as a needle bearing cage, is located between the aft portion of the inner shaft 160 and the driveshaft section 106 of the housing 102. In this example, the needle bearing 166 is arranged within the cylindrical body 111 of the forward propeller 110b. Adjacent the needle bearing 166 is a lubrication opening 170 that communicates with the hollow inside of the inner shaft 160. Centrifugal force of the rotating shafts moves lubricating oil along the inside of the inner shaft 160 and to the bevel gear assembly 150 via a second lubrication opening 172 positioned opposite of the second bevel gear 154. In some embodiments, the inner shaft 160 defines a helical groove 161 that transfers lubricating oil uphill from the aft portion of the housing 102 to the gearbox section 104. A second needle bearing 168, such as a needle bearing cage, is between the outer shaft 162 and the driveshaft section 106 of the housing 102.
Note that all of the first bevel gear is above 152 the bottom of the flange 120; a majority of the second bevel gear 154 is above the flange, and an entirety of the third bevel gear 156 is above the flange 120.
FIG. 3 is a side view of an inboard drive assembly 100 that lacks a strut, in accordance with an embodiment of the present disclosure. FIG. 4 is a cross-sectional view showing the drive assembly 100 of FIG. 3. Owing to the location of the bevel drive assembly 150 at or above the mounting flange 120, the mounting flange 120 efficiently transfers propeller thrust loads to the hull without the need for a strut. The propeller thrust can be transferred directly to the hull body using rubber mounts on the gearbox. This design provides reduced drag and enhanced propulsion efficiency. Other features of the embodiments shown in FIGS. 3-4 are discussed above.
FIG. 5 is a side view of an inboard drive assembly 100 lacking both a strut 180 and a skeg 190, in accordance with an embodiment of the present disclosure. FIG. 6 is a cross-sectional view showing the drive assembly 100 of FIG. 5. Other features of the embodiments shown in FIGS. 5-6 are discussed above. A dashed line represents a hull 200 of a boat having an inboard motor 210 configured to drive the input shaft 140. In this example, the hull 200 defines a hull recess 202 configured to accommodate connection between the drive assembly 100 and the input shaft 140. In other embodiments, the drive assembly 100 can be mounted and sealed to the hull 200 after cutting an appropriate opening to enable access to the drive shaft 140. Note that when the drive assembly 100 is mounted to the hull 200, the flange 120 covers the hull recess 202 or opening. The propellers 110 have a clearance height H to the bottom of the hull 200. In one embodiment, the clearance gap H of at least 0.75 inch (about 2 mm) based on a 16-inch (about 40.5 mm) maximum diameter front propeller 110b. The angle α3 of the drive assembly 100 can be adjusted to accommodate a larger propeller, as deemed necessary.
In this example, a skeg 190 (shown in FIG. 2) can be removably attached to the driveshaft section 106 of the housing 102. As shown in FIG. 6, for example, the skeg 190 can be attached using a sliding or socket-type fitting 192, where corresponding features on the skeg 190 can be inserted into the fitting 192 and then the skeg 190 translated axially along the central axis 101 towards the propellers to fix the skeg 190 in place. Alternately or additionally, fasteners can be used as needed to secure the skeg 190, as will be appreciated.
FIG. 7 illustrates a top view of an inboard drive assembly 100 with contra-rotating propellers 110 and strut 180, in accordance with an embodiment of the present disclosure. FIG. 8 is a top view of an inboard drive assembly 100 without the strut 180, in accordance with another embodiment. The bevel gear assembly 150, or at least a majority portion of it, is above the flange 120 and encircled by the flange 150. In one embodiment, the flange 120 has length L of about 450-500 mm, or about 485 mm, and a width W of 225-300 mm, or about 250 mm. In some embodiments, the driveshaft section 106 of the housing 102 has an outer diameter D1 of less than 100 mm, or about 90 mm. In some embodiments, the gearbox section 104 has an outer diameter D2 of less than 150 mm, or about 135 mm (shown in FIG. 9).
FIG. 9 illustrates a cross-sectional view and FIG. 10 illustrates a top view showing details of the bevel gear assembly 150, in accordance with some embodiments. The gearbox section 104 of the housing 102 and flange 120 are shown. A flange axis 120a extends along a top surface of the flange 120, where the top surface of the flange 120 is the surface that would interface with the hull 200 of a boat (shown in FIG. 5) when the drive assembly 100 is installed for use. As seen here, a vast majority of the first bevel gear 152 is above the flange axis 120a, the entirety of the third bevel gear 156 is above the flange axis 120a, and a majority portion of the second bevel gear 154 is above the flange axis 120a. When considered as a whole, a majority portion of the bevel gear assembly 150 is above the flange axis 120a. In some embodiments, 60%, 70%, 75%, 80% or more of the bevel gear assembly is above the flange axis 120a.
An input shaft 140 is operatively connected through the first end 102a of the housing 102 to the first bevel gear 152. In some embodiments, the first bevel gear 152 and/or the input shaft 140 has crown splines to reduce or minimize any misalignment that may be present between the input shaft 140 and the inner shaft 160. When the input shaft 140 rotates, the first bevel gear 152 rotates about the central axis 101 and engages the third bevel gear 156, which rotates about a radial axis 156a. Rotation of the third bevel gear 156 causes the second bevel gear 154 to rotate in an opposite direction compared to the first bevel gear 152. In this way, the bevel gear assembly 150 is configured to drive the inner shaft 160 in a first rotational direction about the central axis 101 and the outer shaft 162 in an opposite second rotational direction about the central axis 101. In FIG. 9, the lubrication opening 170 can be seen, which allows transfer of lubricant oil between the inner shaft 160 and the oil reservoir 172 in the housing 102.
In use, a drive assembly 100 of the present disclosure can be used to convert a traditional inboard drive assembly with straight drive shaft and a single propeller to a drive assembly 100 with two contra-rotating propellers 110. Owing to the location of the gearbox section 104 of the housing 102 being located at the flange 120, where a majority portion of the bevel gear assembly 150 is above the flange 120, the drive assembly 100 does not require a strut 180 (shown in FIG. 1), which is typically required in existing drive assemblies to transmit thrust forces to the hull. Since propeller thrust acts directly on the hull body, softer rubber mounts can be used to provide reduced noise, vibration, and harshness. Also, in some embodiments the skeg 190 (shown in FIG. 1) can be omitted or can be removably attached to the housing 102. In the case of a removable skeg 190, the skeg 190 can be replaced with a skeg of a different shape as desired for wake effects desired in water sports. When the strut 180 and/or skeg 190 are omitted, the drive assembly 100 has reduced drag in the water and provides a less obstructed water flow path to the propellers 110.

FURTHER EXAMPLE EMBODIMENTS

The following examples pertain to further embodiments, from which numerous permutations and configurations will be apparent.
Example 1 is a marine drive assembly, comprising a housing extending along a central axis and defining a gearbox section and a driveshaft section. A bevel gear assembly is housed in the gearbox section and has a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear. A mounting flange is connected to and extends around at least part of the gearbox section. An inner shaft extends along the central axis and is operably connected to the first bevel gear for rotation in a first rotational direction about the central axis. An outer shaft is coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.
Example 2 includes the marine drive of Example 1, where a majority portion of the bevel gear assembly is above the mounting flange. In some embodiments, 60%, 70%, 75%, or 80% or more of the bevel gear assembly is above the mounting flange.
Example 3 includes the marine drive of Example 1 or 2 and further comprises a first propeller attached to the inner shaft and a second propeller attached to the outer shaft. During use the first propeller rotates in a first rotational direction and the second propeller rotates in an opposite second rotational direction about the central axis.
Example 4 includes the marine drive of any of the foregoing Examples, where the central axis defines an angle from 15-25° with a top surface of the flange, preferably about 20°.
Example 5 includes the marine drive of any of the foregoing Examples and further comprises a skeg attached to the driveshaft section of the housing.
Example 6 includes the marine drive of Example 5, where the skeg is removably attached to the driveshaft section.
Example 7 includes the marine drive of any of the foregoing Examples, where the housing lacks a strut.
Example 8 includes the marine drive of any of the foregoing Examples, where the inner shaft defines a helical groove.
Example 9 includes the marine drive of any of the foregoing Examples, where the first bevel gear is a drive gear.
Example 10 includes the marine drive of any of the foregoing Examples, where the mounting flange extends around a lower and aft portion of the gearbox section.
Example 11 includes the marine drive of any of the foregoing Examples, where the mounting flange has a width of less than 300 mm and a length of less than 500 mm.
Example 12 includes the marine drive of any of the foregoing Examples, where the driveshaft section has an outer diameter of less than 100 mm, preferably about 90 mm.
Example 13 includes the marine drive of any of the foregoing Examples, where the gearbox section has an outer diameter of less than 150 mm, preferably about 135 mm.
Example 14 is a boat having a hull, the boat including the marine drive of any of the foregoing Examples, an inboard motor in the hull, and a drive shaft operably coupled to the inboard motor extending rearward from the inboard motor to the marine drive.
Example 15 includes the boat of Example 14, where the hull defines a bottom recess and the wherein mounting flange extends around an outside of the bottom recess.
The foregoing description of example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto. Future-filed applications claiming priority to this application may claim the disclosed subject matter in a different manner and generally may include any set of one or more limitations as variously disclosed or otherwise demonstrated herein.

Claims

A marine drive assembly, comprising:
a housing extending along a central axis and defining a gearbox section and a driveshaft section;

a bevel gear assembly housed in the gearbox section and having a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear;

a mounting flange connected to and extending around at least part of the gearbox section;

an inner shaft extending along the central axis and operably connected to the first bevel gear for rotation in a first rotational direction about the central axis; and

an outer shaft coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.
The marine drive of claim 1, wherein a majority portion of the bevel gear assembly is above the mounting flange.
The marine drive of claim 1, further comprising a first propeller attached to the inner shaft and a second propeller attached to the outer shaft, wherein during use the first propeller rotates in a first rotational direction and the second propeller rotates in an opposite second rotational direction about the central axis.
The marine drive of claim 1, wherein the central axis defines an angle from 15-25° with a top surface of the flange.
The marine drive of claim 1, further comprising a skeg attached to the driveshaft section of the housing.
The marine drive of claim 5, wherein the skeg is removably attached to the driveshaft section.
The marine drive of claim 1, wherein the housing lacks a strut.
The marine drive of claim 1, wherein the inner shaft defines a helical groove.
The marine drive of claim 1, wherein the first bevel gear is a drive gear.
The marine drive of claim 1, wherein the mounting flange extends around a lower and aft portion of the gearbox section.
The marine drive of claim 10, wherein the mounting flange has a width less than 300 mm and a length less than 500 mm.
The marine drive of claim 1, wherein the driveshaft section has an outer diameter of less than 100 mm.
The marine drive of claim 12, wherein the gearbox section has an outer diameter of less than 150 mm.
A boat having a hull and comprising:
the marine drive of claim 1;

an inboard motor in the hull;

a drive shaft operably coupled to the inboard motor extending rearward from the inboard motor to the marine drive.
The boat of claim 14, wherein the hull defines a bottom recess and the wherein mounting flange extends around an outside of the bottom recess.