Patent Application
20160090164
This disclosure relates to marine drives. Particularly, this disclosure relates to tractor-type drives, those having forward facing propellers configured to pull a boat through the water.
Marine drives may be generally classified as inboard, outboard, or inboard/outboard. In an inboard drive, the engine and transmission (or drive) are mounted in the hull and a propeller shaft extends through the bottom of the hull. In an outboard drive, the propeller drive and engine are generally configured as a unit attached to and located outside the hull. Inboard/outboard drives, also referred to as stern drives, have an engine mounted in the hull connected to a drive unit mounted outside of the hull, typically on the stern.
Marine drive units can be further classified as pushing-type and tractor-type. Pushing-type drives generally rely upon propellers facing rearward relative to the boat and generating propulsive force that pushes the boat through the water. Tractor-type drives generally rely upon one or more forward, bow-facing propellers that produce propulsive force to pull the boat through the water. Tractor-type drives may also be referred to as pulling-type drives.
A similar tractor-type drive is described in U.S. Pat. No. 7,226,327, assigned to AB Volvo Penta.
An embodiment of this disclosure includes a steerable tractor-type drive for a boat. The drive includes a [Fm1]drive support mountable to a stern of the boat and a gear case (or drive housing) pivotally attached to the drive support about a steering axis. At least one pulling-type propeller is mounted on a propeller shaft extending from a front end of the gear case, the propeller shaft to be rotated by a vertical drive shaft perpendicular to a propeller shaft axis. The steering axis is offset forward of the vertical drive shaft.
Another embodiment of this disclosure includes a drive for a boat. The drive has a gear case with at least one front-facing propeller for pulling the boat through the water. The drive also has a drive support for mounting the gear case to the boat. The gear case pivots relative to drive support about a steering axis to steer the boat. The gear case and the drive support are configured such that the at least one propeller is located forward of the steering axis and a center of pressure generated by water rushing past the gear case during a turn is located rearward of the steering axis.
Another embodiment of this disclosure includes a boat. The boat has a hull, thereby having a bow and a stern. The boat includes at least one pulling-type propeller forwardly mounted to a gear case. A drive support steerably mounts the gear case to the stern of the boat. The gear case rotates about a steering axis positioned such that a center of pressure generated by water rushing past the gear case during a turn is located rearward of the steering axis.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiments, when considered in conjunction with the drawings. It should be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.
The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicated similar elements and in which:
Exemplary embodiments of this disclosure are described below and illustrated in the accompanying figures, in which like numerals refer to like parts throughout the several views. The embodiments described provide examples and should not be interpreted as limiting the scope of the invention. Other embodiments, and modifications and improvements of the described embodiments, will occur to those skilled in the art and all such other embodiments, modifications and improvements are within the scope of the present invention. Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective features of method aspects or embodiments may be applied to apparatus, product or component aspects or embodiments and vice versa.
As used herein, the terms “front” and “forward” are defined based on the drives as mounted to the boat with respect to a bow to stern direction of the boat. Likewise, the terms “back”, “rear”, “rearward”, and “aft” are also defined based on the drive as mounted to the boat with respect to a bow-stern direction of the boat.
Applicants have determined that in some situations, significant steering loads can be caused by the high transverse loading from forward facing propellers. These steering loads can be felt by the operator through the steering wheel and may present a challenge to some operators. Such steering loads may be more pronounced during steering maneuvers, particularly at high speeds. The propeller forces from forward facing propellers cause a torque about the steering axis during steering. The steering forces may be caused by the increased lift of the propeller blades that rotate into the water flow, combined with the decreased lift of the propeller blades that move with the water flow. These steering forces can occur in either direction as the gear case is pivoted. The resulting torque biases the propellers and the gear case to attempt to continue to rotate in the direction of steering.
The drive 100 is configured to have improved steering by reducing the net torque around its steering axis. The drive 100 is configured to be mounted to the stern 210 of the boat 200, and to pull the boat 200 through the water. In order to pull the boat 200 through the water, the drive 100 can include a dual propeller arrangement, including a forward propeller 104 and a rearward propeller 108, each of which is considered front-facing, i.e. mounting to a front end of a drive housing 120. The forward and rearward propellers 104, 108 can be driven by a pair of propeller shafts 112 that are coaxial and counter-rotating. The propeller shafts 112 are housed within and extend from the front end of the gear case 120. The propeller shafts 112 coincide with a propeller shaft axis P shown in
Similar to the prior art shown in
The drive 100 further includes a drive support 140 for mounting the drive housing 120 to the stern 210 of the boat 200, particularly the boat's transom 220. The drive support 140 allows the drive housing 120 to pivot relative to the boat 200 about a substantially vertical steering axis S and about a substantially horizontal tilt/trim axis T. The drive support 140 may include a transom shield 142 fixed to the transom 220 and a gimbal ring 144 pivotally mounted to the transom shield. In the embodiment shown, the gimbal ring 144 pivots relative to the transom shield on the steering axis S and the drive housing 120 pivots relative to the gimbal ring on the tilt/trim axis T, although other arrangements are possible. The universal joint 119 is positioned at the intersection of the steering axis S and the tilt/trim axis T. By pivoting the drive housing 120 on the steering axis S, the drive 100 is able to direct the propulsive force of the propellers to steer the boat 200. An underwater portion 124 of the gear case 120 acts as a rudder to deflect water flowing past the underwater portion 124.
The connection between the drive support 140 and the drive housing 120 defines a steering axis S about which the drive housing 120 pivots. The drive housing 120 may be selectively pivoted about the steering axis S in response to operator input by mechanical, hydraulic, pneumatic or other actuation means known in the art. Unlike prior steerable tractor-type drives, the drive 100 of this disclosure has its steering axis S offset from the vertical drive shaft axis D. Therefore, the steering axis S and the drive shaft axis D are not coaxial. In the illustrated embodiment, the steering axis S is moved forward, or ahead of the drive shaft axis D. Both the steering axis S and the drive shaft axis D may be generally considered as lying in a plane (see X-X in
More specifically, displacing the steering axis S in a forward direction relative to the drive shaft axis D provides a dual set of advantages resulting in steering force reduction. First, moving the steering axis S forward, closer to the planes of rotation of the forward and rearward propellers 104, 108 reduces the steering torque about the steering axis S by decreasing the moment arm of each propeller force FP (see
The underwater portion 124 has a leading edge 125 and a trailing edge 126, as seen in the side view of
Mitigation of net steering torque can be better understood, with reference to the force diagram of
On the other hand, the underwater portion 124 of the drive housing 120 is rotated into the flow of water rushing past the drive 100 during the turn. The water provides a force FW upon the underwater portion 124 acting at a pressure center located behind the steering axis S and in a direction substantially opposite to the initial direction VI. The water force FW results in a housing force FH located rearward of the steering axis S that provides a torque that opposes the torque of propeller forces FP around steering axis S. Therefore, the net steering forces on the drive 100 as felt by the operator are reduced as compared to other drives of the steerable tractor-type.
The housing force FH can be optimized by adjusting the projected surface area of the side profile of the underwater portion 124 of the gear case 120, thereby adjusting the surface area rearward of the steering axis S upon which oncoming water impinges to increase or decrease the magnitude of FH.
Although the above disclosure has been presented in the context of exemplary embodiments, it is to be understood that modifications and variations may be utilized without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents. Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective features of method aspects or embodiments may be applied to apparatus, product or component aspects or embodiments and vice versa.
