Hatch covers: weathertightness, seals and what drives cargo claims

Wetted cargo is one of the most common and most expensive claims in bulk shipping, and it almost always comes in through the hatch cover - not a cracked hull but a perished seal, a blocked drainage channel and worn cleats. Those happen to be the parts you keep cheaply aboard. Here is what leaks and what to watch.

Seals: not age but permanent set

The rubber cover packings work on compression: the compression bar presses them to a set depth, forming a tight line. They wear out less from age than from permanent set - rubber, once crushed, stops springing back and no longer makes contact. The signs are a flattened compression print, cracks, missing pieces and hardening. The seal is renewed in lengths or all round, matching the profile and hardness to the cover system; a random profile will not give the right compression.

Compression is measured, not judged by eye

Correct compression is checked by the print method (compression tape) or a gap gauge between the bar and the channel - too little leaks, too much destroys the rubber. A bent or corroded compression bar and worn cleats throw that geometry off. A new set of seals on a bent bar will not give tightness - it is a system, not a single part.

Drainage and non-return valves

• Drainage channels along the coaming carry away water that gets past the first line - blocked, they spill it straight into the hold.
• Non-return valves at the channel ends are meant to keep deck water out; seized or lost, they are a quiet cause of wetting.
• They are the cheapest parts in the whole arrangement, and the most often left out of the spares.

The mechanics: cleats, wheels, drive

Wedges, eccentric cleats and side cleats hold the compression at sea - worn or slack, they let the cover lift as the hull works in a seaway. Wheels, rollers, chains and hydraulic cylinders handle opening; their wear is not a tightness issue, but a seized cover can hold up discharge. A tightness test - hose or ultrasonic - after any major renewal confirms the arrangement holds again.

How this works with us

Give us the cover maker and type, or the seal dimensions and profile, and we match the rubbers, drainage non-return valves, cleats, wheels and cleating parts to the system, with certificates. Seals and small drainage parts are worth keeping aboard - we will suggest a set for the hatch perimeters. All from the deck equipment catalogue.