Disclosed herein is an inventive dual propeller assembly that can be manually or automatively assembled and includes a leading propeller, a torsion bushing, a thrust washer, a drive sleeve, and a trailing propeller. The propellers were coupled with an alignment system that did not require welding of the two propellers. The leading propeller includes a cylindrical hub and a plurality of blades that extend from an outer surface of the cylindrical hub. The trailing propeller includes a first cylindrical hub having a plurality of grooves, a second cylindrical hub having a cylindrical mount ring, and a conical profile formed between the first cylindrical hub and the second cylindrical hub. The outer surface of the first cylindrical hub is designed to mate with the inner surface of the cylindrical hub of the leading propeller. The trailing propeller is secured and aligned coaxially with the leading propeller. The trailing propeller can be effectively and consistently used with existing propellers.

A propeller includes a propeller shaft, a plurality of first blades, and a plurality of second blades. The first blades are connected to the outer peripheral surface of the propeller shaft so as to be rotated synchronously with the propeller shaft. The second blades are connected to the outer peripheral surface of the propeller shaft, so that they are rotated in the same direction as the first blades. The second blades are located in front of the first blades and correspond to the first blades in a one-to-one manner. The size of the second blades is smaller than the size of the first blades, and the rotation direction of the second blades is the same as the rotation direction of the first blades. Thereby, the propeller of the present invention can improve the operation efficiency of the boat at high speed without increasing the size of the first blades.

A drive system is provided for propelling a ship through water. The drive system has two propellers. The propellers are coaxial so that one propeller engages the incoming water first, and the other propeller engages the water after it passes through the first propeller. The drive system has a stator that causes a first rotor to rotate. The first rotor is connected to, the first propeller to cause the first propeller to rotate. The first rotor also causes a second rotor to rotate. The second rotor is connected to the second propeller to cause the second propeller to rotate.

A drive system is provided for propelling a ship through water. The drive system has two propellers. The propellers are coaxial so that one propeller engages the incoming water first, and the other propeller engages the water after it passes through the first propeller. The drive system has a stator that causes a first rotor to rotate. The first rotor is connected to, the first propeller to cause the first propeller to rotate. The first rotor also causes a second rotor to rotate. The second rotor is connected to the second propeller to cause the second propeller to rotate.

A marine propulsion system, supported by a strut, comprising an inner propeller shaft supporting a first propeller adjacent a trailing end thereof, and the inner propeller shaft is connected to the drive shaft for receiving and supplying a first portion of torque to the first propeller as well as transfer thrust, generated by the first propeller, along the inner propeller shaft back to the drive shaft. An outer propeller shaft supports a second propeller adjacent a trailing and thereof, and the outer propeller shaft surrounds the inner propeller shaft. A differential gear set receives a second portion of the torque and supplies the second portion to the outer propeller shaft so that the second propeller rotates in an opposite rotational direction to the first propeller. The thrust, generated by the first and the second propellers, is conveyed along either the inner or the outer propeller shafts, to the drive shaft.

A marine propulsion system, supported by a strut, comprising an inner propeller shaft supporting a first propeller adjacent a trailing end thereof, and the inner propeller shaft is connected to the drive shaft for receiving and supplying a first portion of torque to the first propeller as well as transfer thrust, generated by the first propeller, along the inner propeller shaft back to the drive shaft. An outer propeller shaft supports a second propeller adjacent a trailing and thereof, and the outer propeller shaft surrounds the inner propeller shaft. A differential gear set receives a second portion of the torque and supplies the second portion to the outer propeller shaft so that the second propeller rotates in an opposite rotational direction to the first propeller. The thrust, generated by the first and the second propellers, is conveyed along either the inner or the outer propeller shafts, to the drive shaft.

Disclosed is a propeller having at least first and second blade assemblies located one above the other. Each of the blade assemblies has a plurality of blades that extend radially outward from a shaft. The shaft can be coupled to a suitable land, sea or air vehicle (e.g., a ship). The blades of the first blade assembly lie above and alternate out of phase with the blades of the second blade assembly. Each of the blades of the first and second blade assemblies slopes downwardly relative to the shaft such that the leading sides thereof are located lower along the shaft than the opposite trailing sides. The blades of the first blade assembly are aligned with respective ones of the blades of the second blade assembly to establish substantially continuous and long downwardly sloping surface areas capable of maximizing the propulsion force generated by the propeller.

Disclosed herein is an inventive dual propeller assembly that can be manually or automatively assembled and includes a leading propeller, and a trailing propeller which are coaxially aligned and secured with a propeller shaft and a locking nut. Various embodiments are disclosed with and without interior grooves for alignment. In all embodiments, the two propellers are secured and aligned with a propeller shaft and locking nut assembly.

Disclosed herein is an inventive dual propeller assembly that can be manually or automatively assembled and includes a leading propeller, and a trailing propeller which are coaxially aligned and secured with a propeller shaft and a locking nut. Various embodiments are disclosed with and without interior grooves for alignment. In all embodiments, the two propellers are secured and aligned with a propeller shaft and locking nut assembly.

A propulsion device for a ship is introduced. The propulsion device for the ship comprises a duct having a nose corresponding to the front vertex of a hydrofoil cross-section and a tail corresponding to the rear vertex of the hydrofoil cross-section, wherein the shape of the duct cross-section comprises: an outer surface formed upward in a convex shape at the front end of the duct and formed downward in a concave shape at the rear end of the duct; an inner front part of the duct formed downward in a convex shape at the front end of the duct; an inner rear part of the duct formed downward in a convex shape at the rear end of the duct; and a parallel part for connecting the inner forward part and the inner backward part in parallel to each other.