They use diesel engines.
Actually, M/S stands for "motor ship", M/V stands for "motor vessel" and S/S means "steam ship". The Latter response is correct RMS on British ships refers to Royal Mail Ship. MS = Motor ship. SS = Steam Ship. In naval (military) usage USS is "United States Ship"; HMS is "Her (His) Majesty's Ship" etc.
Leisure cruise ships originated from the Peninsular & Oriental Steam Navigation Company in 1822.
The term "S.S." in the name of a ship stands for "Steam Ship", if it is a surface vessel - in the Navy, "SS" stands for Submersible Ship, or submarine. All vessels have some type of prefix designator to denote the type of ship it is. For example, M/V or MV stands for Motor Vessel, SV stands for Sailing Vessel, etc.
SS as in SS Rotterdam means Steam Ship. Ships with this prefix are almost gone now for very few steam driven merchant ships are left on the seven seas. Most merchant ships today have the initial "MV" meaning Motor Vessel. Also seen are "MS" meaning motor ships. These vessels are propelled by very large diesel engines. Royal Clipper Cruise ships use the prefix "SV", for these are very large sailing vessels. "USS" is reserved for the United States Navy and HMS for Her Majesty's Navy (Britain) The Queen Mary 2 is "RMS" which is "Royal Mail Ship" and she is probably the last of that designation to sail upon blue water.
SS is short for Steam Ship and used on civilian ships. NS would be Nuclear Ship and there was at least one civilian nuclear powered vessel. USS is a prefix designation for a military ships that stand for "United States Ship". HMS is a prefix designation for a British ships that stand for "His(Her) Majesty's Ship". Other ship designations you may see are 'MS' which stands for 'Motor Ship' and 'M/V' which stands for 'Motor Vessel'.
A steam engine on a ship meant that the vessel could sail against the wind. Nor would lack of a wind mean the vessel would risk becoming becalmed - a problem often faced by sailing ships.
First were sailing ships, THEN steam ships.
When dry steam enters a wet steam filled vessel, it can cause the wet steam to condense as the dry steam releases its latent heat energy to the surrounding wet steam. This condensation increases the moisture content in the vessel and may lead to water accumulation.
Motor Ship (nautical vessel designation; also see SS for steam ship)
Steam clippers were sailing ships that had a steam engine amidships to be used in the absence of wind. They were also able to maneuver around a harbor easier than a sailing vessel. There were several steam clippers of note. A link is posted to one of the more famous ones, a vessel that went down with a huge treasure aboard.
SS = Steam Ship, HMS = His Majesties Ship, RMS = Royal Mail Ship, MV = Motor Vessel, RV = Research Vessel, NS = Nuclear Ship
An "ironclad" was a naval vessel constructed during the early Age of Steam. Armored with steel or iron plating, these ships were largely invulnerable to the naval artillery and musketry of the day.