1. Field of the Invention
The invention disclosed herein relates to a propulsion system for controlling the direction of passage of a vessel underway at relatively low speeds without utilizing the power of the vessel's main engine(s). The invention particularly relates to combinations of water thrusters installed in the bow and stern of vessels, especially power and sail pleasure boats, that can selectively propel the craft forward or backward or laterally. The system's design allows the thruster apparatus to operate for long periods without overheating.
2. Description of the Related Art
The use of thrusters as a means of enhancing the turning capability of a boat or ship is well known in the marine arts. When maneuvering to enter or exit a dock or marina, small single engine boats of at least thirty plus feet in length and ships of any length are in tight quarters and are at the mercy of the prevailing current, wind direction and the tendency for a single engine prop to turn the boat's stern. A miscalculation in where the boat's engine, just turning above stalling RPM, and the boat's corresponding momentum will take the craft can result in an ever so seemingly light contact with a bulkhead or another boat in its slip. Yet, that light contact damage will cost thousands of dollars to remedy. But the experienced boater knows the risk can be remedied by installing bow thrusters. They can turn the bow quicker in short distances than a rudder and engine combination that gives the Captain more control.
A pair of thrusters can also be installed in the stern of the boat, preferably connected to the transom. These provide a capability to turn the stern laterally and, in consort with the bow thrusters, rotate the boat on its axis. They also are a great assist to single engine boats when they are backing into a slip. Depending on which way the engine shaft rotates, the boat's prop in reverse gear turns the stern of the boat to port or starboard but with stern thrusters installed and operating to port or starboard this tendency can be balanced to allow the boat to back straight into the slip.
Another advantage of bow and stern thrusters is their capability to move the boat forward or backward at extremely slow speed when operated in tandem. When entering a crowded fairway of a marina, the flow of the thrusters can be directed to the stern of the boat and thereby provide a small forward motion to the vessel with an instant capability to turn the vessel if so necessary.
One problem that compromises the scope of use of bow or stern thrusters in the current art is the use of air-cooled electric motors to power the thrusters. Under air-cooling, the electric motors heat up and must be shut down before they are damaged. Therefore, they cannot be used continuously during a cruise so some of their advantages are not always available to the Captain. Nor can they be used for trolling in open waters. However, the instant invention overcomes that problem.
U.S. Pat. No. 3,675,611 to Glass describes a boat having a plurality of water jet nozzles at the bow and stern to assist in steering the boat. The water-jet nozzles also provide auxiliary drive to propel the boat. As described, the water-jets of the patent are restricted to maneuvering in an about the marina and are not capable of extended, continuous operation. The patent does not overcome the problems resolved by the instant invention.
U.S. Pat. No. 3,911,851 to Canazzi describes bow thrusters and stern thrusters for maneuvering a boat in confined places. The four thrusters receive their stream of water from a single point source which distributes the water to the thrusters from four circumferentially spaced outlet ports at ninety degree interval. Precise lateral movement of the boat under this feed configuration is questionable as is the net forward thrust provide to the boat when all four thrusters are in play.
Thus, a boat control system solving the aforementioned problems is desired.