Patent Application
20060275131
Not Applicable
Not Applicable
The present invention relates to a propeller of a boat.
Every boat based on its design and intended use will require a different type of propulsion system. One of the most common types of propulsion system is the propeller propulsion system which is essentially a propeller submerged under water and attached to the boat such that rotation of the propeller in the water thrusts the boat forward. An inboard or outboard motor rotates the propeller which displaces water in an astern direction. In particular, the displaced water develops a reactionary force which thrusts the boat forward.
The amount of thrust created by the blades of the propeller is dependent upon many factors. For example, one factor that determines the amount of thrust created by the propeller is the angle of attack of its blades. Generally, the greater the angle of attack of the blades; the greater the amount of thrust created by the propeller. Other factors external to the blade design also affect the amount of thrust created by the propeller. For example, seaweed and kelp may get tangled within the blades of the propeller themselves when the boat travels in waters (e.g., seas, rivers, and lakes). The tangled seaweed and kelp add weight to the propeller such that the motor must exert more energy to maintain the propeller's rotational speed compared to the amount of power required to rotate the propeller if the propeller had not been entangled with seaweed and kelp. Also, the tangled seaweed and/or kelp may be so entangled with the propeller that the propeller stops rotating. The problems discussed above with seaweed and kelp being entangled with the propeller is further accentuated if the propeller rotates at a low speed (i.e., boats traveling less than about seven miles per hour) because the propeller is not able to break free from the entangled seaweed and kelp.
Accordingly, there is a need in the art for an improved propeller to address deficiencies in the prior art discussed above.
A propeller is provided which has a unique design such that it is capable of shedding and cutting seaweed and kelp as the boat travels through water having seaweed and kelp. The unique design of the propeller's blades also allow the propeller to shed and cut seaweed and kelp at low speeds (i.e., low revolutions per minute or boats traveling at less than about 7 miles per hour). Further, the propeller may be fabricated from a urethane material such that the blades of the propeller break/snap off when the blades hit an object thereby preventing stress on the shaft and electronics. Additionally, the boats are quieter and run smoother when the propellers of the present invention are used to propel the boats.
The propeller of the present invention may have at least two blades, and more preferably, five blades. Each of the propeller's blades may have a leading edge and a trailing edge. The leading edge may have a logarithmic spiral configuration. More particularly, the leading edge may define a leading edge angle which is defined by a tangent line to the leading edge and a line defined by the center of the propeller and the contact point of such tangent line to the leading edge. The leading edge angle may increase at approximately a logarithmic rate along the leading edge starting from the blade base at about at least 27 degrees to the blade tip at about 90 degrees. This logarithmic spiral shaped leading edge cuts and/or sheds seaweed and kelp off of the leading edge such that such seaweed and kelp does not affect the blades propulsion characteristics. Moreover, the logarithmic spiral shaped leading edge provides skew to the planform for blade stability and noise reduction.
The radial cross sections of each blade may also have the same general shape. For example, the thickness ratio of the cross sections of each blade may be about 12%. Additionally, the camber percentage of the cross sections of each blade may be about 3%.
For low speed boats, the propeller is preferably fabricated from urethane plastic such that the blades break/snap off when the blades hit an object to prevent stress on the propeller shaft and electronics. A propeller having blades with the above configuration fabricated from urethane provides sufficient stiffness for performance yet allows the blades to break/snap off when the blades hit an object.
These as well as other features of the present invention will become more apparent upon reference to the drawings wherein:
The drawings referred to herein are for the purposes of illustrating the various aspects of the present invention and not for the purpose of limiting the same. Referring now to
A front face of the propeller 12 is shown in
The propeller 12 may be mounted onto an output shaft 24 of the interface 22. More particular, the hub 18 of the propeller 12 may have a through-hole 26 formed therethrough. The through-hole 26 may be sized and configured to receive the output shaft 24. For example, the through-hole 26 which has a round configuration may match the output shaft 24 which may be a round bar. The output shaft 24 is inserted through the through-hole 26 of the hub 18 to mount the propeller 12 onto the output shaft 24. Additionally, the through-hole 26 is also formed with an internal groove 28 (see
The propeller 12 is locked onto the output shaft 24 through two nuts 32a, b that thread onto a threaded portion 34 of the output shaft 24. Once the output shaft 24 is inserted through the hub through-hole 26, the threaded portion 34 of the output shaft 24 is exposed. A first nut 32a is threaded onto the threaded portion 34 to tighten the propeller 12 onto the output shaft 24. A second nut 32b is then threaded onto the shaft's threaded portion 34 to lock the first nut 32a on the shaft's threaded portion 34. Accordingly, during operation of the propeller 12, the propeller 12 is locked onto the output shaft 24.
Referring now to
The spiral shape of each leading edge 36 may approximate a logarithmic spiral. In particular, as shown in
At the tip 48 of the blade 14, the leading edge angle 40 may equal 90 degrees and at the base 46 of the blade, the leading edge angle 40 may be at least about 27 degrees. As such, as the leading edge angles 40 are calculated along the leading edge 36 beginning from the base 46 to the tip 48 of the blade 14, the leading edge angle 40 increases at a faster rate along the length of the leading edge 36. The rate of increase in the leading edge angle 40 along the leading edge 36 may approximate a logarithmic function. This logarithmic spiral helps the blades 14a-e, as the propeller 12 rotates, to cut and shed seaweed and kelp off of the propeller 12. Moreover, the logarithmic spiral shaped blades 14a-e may cut and shed seaweed and kelp off of the propeller 12 at low speeds. Accordingly, a propeller 12 having the above characteristics may be employed in slow speed boats designed to traverse waters containing seaweed and kelp. The logarithmic spiral shaped blades 14a-e also provide skew to the planform for blade stability and noise reduction.
Each of the propeller blades 14a-e may have a straight trailing edge 52a-e, as shown in
Referring now to
Each cross section of the blade 14 has substantially the same general shape. For example, each cross section of each blade 14 may have a curved leading edge 36a, 36, as shown in
Additionally, the cross sections of each blade 14 may have an ideal thickness ratio of about twelve percent to about fifteen percent, and preferably, each cross section of each blade 14 may have an ideal thickness ratio of about twelve percent. Referring now to
Moreover, the cross sections of each blade 14 may have a camber percentage in relation to a mean camber line 66 and a mean chord line 68 less than three percent to prevent cavitation. The camber percentage is a ratio of the largest distance 70 between the mean camber line 66 and a mean chord line 68, and the chord length 64. The mean chord line 68 extends in a straight line from the leading edge 36 of the blade cross section and terminates at the trailing edge 52. More particularly, the mean chord line 68 terminates at the mid point of a rear flat surface 72. The mean chamber line 68 is a line formed by tracing the midpoint between the front face surface 58 and the back face surface 60 of each cross section. As shown in
The propeller 12 discussed herein may be fabricated from a metal, plastic, or other material dependent upon the intended use and purpose of the boat 10. For low speed boats 10, preferably, the propeller 12 is fabricated from urethane plastic. Fabricating the propeller 12 from urethane plastic allows the blades 14 to break off when the blades 14 hit an object such that the motor and electronics are not stressed. Accordingly, a propeller 12 incorporating the various aspects discussed herein fabricated from urethane plastic provides a propeller 12 that has sufficient stiffness for the propelling a boat yet the blades are able to snap/break off when the blades 14 hit an object.
The above various aspects of the present invention were discussed in relation to a blade 14 having a cross sectional shape of an airfoil. However, it is also contemplated within the scope of the present invention that the various aspects of the present invention discussed herein may be employed with other blade types such as hybrid, NASA, Troost, and Ogival depending on the desired speed of the boat, propeller revolutions per minute, available horsepower and boat weight.
The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.
