Panting

Panting refers to the in-and-out flexing or pulsation of the shell plating at the ends of a ship, mainly caused by variations in sea pressure during pitching motions in rough weather.

When a ship moves through heavy seas, especially while pitching, the water pressure acting on the bow and stern changes continuously. These fluctuating pressures cause the side shell plating to vibrate and flex. The effect is known as panting.

The forward end of the ship is affected more severely than the aft end because:

• The bow directly encounters incoming waves while the ship is making headway.
• Water pressure at the fore end changes rapidly as the bow rises and falls in the sea.

The affected areas are mainly:

• Forward shell plating near the bow
• Side shell plating at the fore peak region
• To a lesser extent, the aft end of the ship

Effects of Panting

Panting can lead to:

• Repeated flexing and vibration of shell plating
• Fatigue stresses in plating and framing
• Loosening of rivets or welded joints
• Cracking or deformation of structural members
• Reduction in structural strength if not properly reinforced

Therefore, special strengthening arrangements are provided at the forward and aft ends of the vessel to resist panting stresses.

Pounding

Pounding refers to the heavy impact experienced at the bottom forward part of the ship when the bow emerges from the water during pitching and then slams violently back onto the sea surface.

This condition usually occurs when:

• The ship is pitching heavily in rough seas,
• The fore part lifts clear of the water due to heaving and pitching motions,
• The bow then falls heavily onto the wave surface.

The effect is most severe when the vessel is in the light ship condition, because the bow rises more easily out of the water.

The main area affected by pounding is:

• The bottom shell plating in the forward region of the ship,
• Especially near the forefoot and forward bottom structure.

The stern may also experience similar impacts from following seas, but usually to a lesser extent.

Effects of Pounding

Pounding produces:

• Severe impact stresses on bottom plating
• Buckling or deformation of bottom structure
• Cracks in shell plating or framing
• Structural fatigue and weakening
• Damage to internal supporting members

To withstand these heavy impact loads, the forward bottom structure is specially strengthened.

Special structural arrangements are incorporated in ship construction to resist the stresses caused by panting and pounding.

Structural Arrangements to Resist Panting

The following strengthening arrangements are provided mainly at the bow and stern regions:

1. Panting Beams

Panting beams are horizontal beams fitted across the ship near the bow and stern.

Their purpose is to:

• Support the side shell plating,
• Reduce excessive flexing,
• Increase structural rigidity against panting stresses.

2. Panting Stringers

Panting stringers are horizontal girders fitted along the ship side in the panting region.

They:

• Connect frames together,
• Provide additional stiffness to the shell plating,
• Help distribute fluctuating sea pressure loads.

3. Close-Spaced Framing

Frames in the panting region are spaced closer together than in other parts of the ship.

This:

• Provides better support to shell plating,
• Reduces plate vibration and deformation.

Structural Arrangements to Resist Pounding

To resist pounding stresses at the forward bottom region, additional strengthening is provided.

1. Increased Bottom Plating Thickness

The shell plating near the keel and forward bottom region is made thicker.

Usually:

• The first few strakes of bottom plating on either side of the keel are increased in thickness.

This enables the structure to withstand repeated impact loads.

2. Plate Floors

Solid plate floors are fitted at closer spacing in the forward bottom region.

These:

• Strengthen the bottom structure,
• Distribute pounding stresses more effectively,
• Prevent deformation of bottom plating.

3. Additional Internal Reinforcement

Extra brackets, girders, and stiffeners may also be provided in the fore peak and bottom structure to improve strength and rigidity.