The present invention relates to an improved boat construction, and more particularly, to a power boat with an inboard propulsion and boat handling system providing improved boat speed and controlled boat performance.
Power boats have either outboard or inboard propulsions systems. Outboard propulsions systems include a combined outboard motor and propeller, pivotally mounted to the stern of a boat, in which the propeller pushes the water backward from behind the boat so as to thrust the boat forward. Steering of the boat is accomplished by turning the combined outboard motor and propeller on its pivotal mount in a particular direction to direct the bow of the boat in that same direction. Inboard propulsion systems include one or more powered inboard mounted propellers or impellers which drive a boat, as well as a separate or interconnected steering device or rudder which is mounted outboard of the boat to control the direction of the boat, as desired.
The efficiency of propulsion, that is, the proportion of the motor power output that is utilized for propelling the ship through the water, is determined by the difference between the approaching velocity of the water ahead of the propeller, which velocity is equal to the speed of the boat, and the velocity of the water displaced astern of the propeller at each revolution. When a boat starts up its motor and begins to move, small quantities of water are given a large sternward acceleration by the propeller; when the boat is underway, large quantities of water are given a relatively small acceleration.
If a boat could operate in a solid unyielding medium, each revolution of the propeller would cause the boat to travel a distance equal to the pitch of the propeller. In actuality, water is a yielding substance which gives way under the pressure or impact of the propeller. As a result, the actual forward motion achieved at each revolution is only about 60%-70% of the pitch. This difference, in relation to 100%, is known as the slip of the propeller. On the rear or suction side of the propeller, a negative pressure is produced, which is greater as the angle of incidence of the propeller blades is larger and their speed of rotation is higher. If the negative pressure is too great, the flow of water around the propeller blades is disrupted and bubbles filled with water vapor are formed. This phenomenon is known as cavitation. For this reason, high-speed propellers have very wide flat blades with low angles of incidence, to minimize losses in propulsion efficiency.
Another factor which inhibits or retards boat speed is the drag created by externally mounted rudders for steering or guiding the boat. As can be appreciated, externally mounted rudders provide a large surface which is pulled through the water and act to reduce the efficiency of propulsion by the rudder operating as an outside intervening force.
Other aspects of boat operation, all of which are related, at least in part to boat propulsion and drag, are also important. These other aspects include steering and handling of the boat in deep and shallow water, operation of the boat when the trim or longitudinal position of a boat is changed relative to the waterline, and control of the boat during banking movements.
As will be disclosed in the detailed description that follows, the present invention relates to an inboard propulsion and handling system in which the efficiency of the propulsion system is not only increased, but the overall performance and control of a boat containing the inboard propulsion system is enhanced. This includes better operation of the boat in shallow water, as well as greater overall control during trim and bank movements.