ship propeller types, Lecture notes of Marine Engineering

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Types of propeller

Propulsion system produce thrust force to propel the ship forward.

Propulsion system gets energy from main engine to produce this force.

Types of propulsion devices

• Waterjet propulsion.
• Vertical axis propulsion( voith Schneider and cycloidal).
• Oscillating foil propulsion.
• Paddle wheel and vane wheel.
• Screw propulsion i. Contra rotating and tandem. ii. Twin screw. iii. Controllable and fixed pitch. iv. Ducted propeller. v. Podded propeller. vi. Azimuthing propeller. vii. Overlapping propeller viii. Surface piercing propeller ix. Supercavitating propellers.

Jet Propulsion

Vertical-Axis Propellers

Paddle and vane wheel

Paddle Wheels Propulsion (Midship)

Screw propellers.

Propeller (5-blade) & Rudder

Controllable pitch

• In a controllable pitch propeller, the blades can be made to turn about their individual axes through a mechanism inside the boss, thereby changing the pitch of the propeller blades. A stepless change in the pitch of the blades from full ahead to full astern can be made without changing the speed or direction of revolution of the propeller. Controllable pitch propellers have several advantages over conventional fixed pitch propellers, including the ability to utilize the full power of the machinery in all conditions of operation. High initial and maintenance costs are disadvantages. Controllable pitch propellers are also slightly less efficient than fixed pitch propellers.
• Controllable pitch propellers are used only in ships which require full power operation at widely different speeds or which are fitted with non- reversing propulsion machinery, e.g tugs, trawlers and small warships with gas turbine engines.

Contra rotating propeller

• A contra-rotating propeller (set) consists of two propellers rotating in opposite

directions on coaxial shafts, one propeller being placed close behind the other.

The aim is to reduce the rotational energy losses in the slipstream. The required

thrust load is distributed between two propellers so that the efficiency is higher

than with an equivalent single propeller. Contra-rotating propellers have the

disadvantages of greater weight and the complexity of the gearing and coaxial

shafts. The sealing of the shafting against the ingress of water from outside is also

a major problem. The aft propeller has a slightly smaller diameter than the

forward propeller. The pitch of the two propellers is selected so that the available

delivered power is absorbed and the slipstream rotation caused by the two

propellers cancel each other. Apart from their long-standing use in torpedoes,

contra-rotating propellers have been tried out in a submarine, and more recently

in a Japanese bulk carrier and a car carrier with improvements in efficiency up to

15 per cent. The mechanical complications of fitting contra-rotating propellers

have inhibited their use