Compare high-pressure and low-pressure marine boilers in terms of typical applications and characteristics.

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The main idea is that the steam pressure a boiler delivers largely determines its size, complexity, and typical use on a ship. High‑pressure boilers are designed to produce steam at significantly higher pressures, which makes them ideal for driving propulsion turbines and large power-generating equipment. Because the energy per unit mass of steam is greater, the system can be more compact and lighter for the same propulsion or electrical output. These boilers typically employ robust water‑tube designs, require careful water treatment and control, and use stronger materials to handle the higher temperatures and pressures. The payoff is higher cycle efficiency and a smaller footprint for the prime mover and associated equipment, but at the cost of greater complexity and capital cost.

Low‑pressure boilers, by contrast, deliver steam at lower pressures and are generally simpler and larger. They’re well suited for ship services that don’t need high-energy steam—things like heating, accommodation steam for laundry and galley, humidification, and other auxiliaries. Their simpler construction and lower operating demands make them cheaper to build and easier to maintain, though the trade‑off is a larger physical size and a lower potential efficiency gain in the power cycle.

So, high‑pressure boilers are chosen for propulsion and main power applications where compact, efficient steam supply is crucial, while low‑pressure boilers are chosen for auxiliary services where simplicity, cost, and larger steam capacity at lower pressure are more important.