Ship’s Rudder – Effects of Defects and Design Features

(a) Why a Breached Hollow Rudder Can Add to Fuel Costs

• A hollow rudder is designed to provide buoyancy at the stern of the ship.
• When the rudder is breached, sea water enters the hollow space, resulting in loss of buoyancy.
• The loss of buoyancy causes the stern to sit deeper in the water, increasing the aft draught.
• Increased aft draught leads to the propeller operating deeper, which increases hydrodynamic resistance.
• Water ingress into the rudder creates turbulence and disturbed water flow around the rudder and propeller.
• To maintain the same ship speed, higher engine power is required, resulting in increased fuel consumption.

(b) Why Excessive Pintle Clearance Should Not Be Tolerated

• Pintles support the rudder and fit into gudgeons with very small designed clearances.
• Excessive clearance permits sideways and vertical movement of the rudder.
• Such movement imposes additional bending stresses on the rudder stock.
• In heavy seas, shock and impact loads increase wear and may cause misalignment.
• This can lead to vibration, poor steering response, accelerated wear, and in extreme cases, structural failure of the rudder assembly.

(c) Why Fitted Bolts Are Used in Connecting Upper and Lower Rudder Stocks

• The upper and lower rudder stocks are required to transmit high steering torque.
• Fitted bolts provide a close, interference fit with no clearance in the bolt holes.
• They ensure accurate alignment of the two stock sections.
• Steering loads are transmitted in shear through the bolt shanks, rather than relying on friction alone.
• This prevents relative movement, reduces stress concentration, and minimizes the risk of fatigue failure.