PCC vs PCTC: How Detection Differs

Pure car carriers and pure car and truck carriers are often discussed as one ship type, but their decks are built differently, and that changes what detection has to do. A PCC is built around fixed decks with about 1.7 metres of clearance, stacked close together for cars. A PCTC adds liftable decks and strengthened lanes so that some decks can open up to around 6.7 metres for trucks, machinery and other high-and-heavy cargo. The same fire behaves differently in each.

How do PCC and PCTC decks differ?

In height, strength and flexibility. On a typical PCC, every loading bay has roughly 1.7 metres of vertical clearance, which maximises the number of cars a hull can carry. A PCTC keeps car-height decks for most of its capacity but fits hoistable deck panels that can be raised to increase clearance, on some ships from 1.7 to 6.7 metres, and strengthens certain decks and ramps for axle loads far above a car's. A 6,500-unit ship can carry cargo units of up to about 136 tonnes on its reinforced decks. Raising a deck for high-and-heavy cargo reduces the total number of cars the ship can take.

Why does deck height matter for detection?

Because it sets the distance between the fire and a deckhead detector. On a 1.7-metre deck the smoke and heat from an overheating car reach the deckhead quickly, but there is little room for them to spread before they are diluted by the forced ventilation that SOLAS requires in closed vehicle spaces. On a raised PCTC deck the detector may be five or six metres above the source, and the hot gases have to rise, collect and survive the airflow before they register. The 2026 SOLAS amendments set detector spacing by deck height for this reason.

Why does the cargo mix matter?

Because high-and-heavy cargo changes what can be seen and reached. Trucks, buses, construction and agricultural machinery are tall enough to block the lines of sight that cameras and flame detectors rely on, and they carry their own fire loads: large fuel tanks, hydraulic oil and, increasingly, large traction batteries on electric trucks and buses. A PCTC deck can hold a mix of these and cars on the same voyage, with raised and lowered panels changing the space from one loading to the next.

What does this mean when specifying detection?

That the design has to be checked against each deck configuration the ship actually uses, not the general arrangement drawing. For a PCC the questions are mainly about ventilation and the density of cars. For a PCTC they include what happens to coverage when decks are raised, whether tall cargo blocks the view, and whether detection still reaches a source five metres below the deckhead.

• Confirm coverage and response time for each deck height the ship uses, including decks raised for high-and-heavy cargo.
• Check lines of sight against tall cargo, not an empty deck.
• Include the cargo mix in the fire plan: fuel, hydraulic oil and traction batteries on trucks and machinery.
• Test under normal ventilation, as SOLAS requires for the installed system.

Sources

• 1. MacGregor (TTS) — 'Car decks and ramps' product sheet: hoistable car decks and ramp systems for PCTC and ro-ro ships.
• 2. Industry descriptions of PCC and PCTC design — typical PCC loading-bay clearance ~1.7 m; liftable panels raising clearance to ~6.7 m on some decks of a 6,500-unit PCTC; decks for units up to ~150 short tons (~136 t).
• 3. SOLAS II-2/20 as amended by MSC.550(108) — ventilation of closed vehicle spaces and detector requirements, with spacing by deck height under the FSS Code amendments in MSC.555(108). As analysed in 'SOLAS II-2/20 Explained'.
• 4. Companion analyses — 'Why Fire Detection Is Difficult on Ro-Ro Vehicle Decks' and 'Does Deck Ventilation Delay Fire Detection?'.