▁An ▁ocean ▁l iner ▁is ▁a ▁passenger ▁ship ▁primarily ▁used ▁as ▁a ▁form ▁of ▁transport ation ▁across ▁se as ▁or ▁o ce ans . ▁Lin ers ▁may ▁also ▁carry ▁cargo ▁or ▁mail , ▁and ▁may ▁sometimes ▁be ▁used ▁for ▁other ▁purposes ▁( such ▁as ▁for ▁pleasure ▁cru ises ▁or ▁as ▁hospital ▁ships ). ▁ ▁C argo ▁vessels ▁running ▁to ▁a ▁schedule ▁are ▁sometimes ▁called ▁lin ers . ▁The ▁category ▁does ▁not ▁include ▁fer ries ▁or ▁other ▁vessels ▁engaged ▁in ▁short - se a ▁trad ing , ▁nor ▁dedicated ▁cru ise ▁ships ▁where ▁the ▁voyage ▁itself , ▁and ▁not ▁transport ation , ▁is ▁the ▁prime ▁purpose ▁of ▁the ▁trip . ▁Nor ▁does ▁it ▁include ▁tr amp ▁steam ers , ▁even ▁those ▁equ ipped ▁to ▁handle ▁limited ▁numbers ▁of ▁passengers . ▁Some ▁sh ipping ▁companies ▁refer ▁to ▁themselves ▁as ▁" lines " ▁and ▁their ▁container ▁ships , ▁which ▁often ▁operate ▁over ▁set ▁routes ▁according ▁to ▁established ▁sched ules , ▁as ▁" lin ers ". ▁ ▁Ocean ▁lin ers ▁are ▁usually ▁strongly ▁built ▁with ▁a ▁high ▁fre eb o ard ▁to ▁with stand ▁rough ▁se as ▁and ▁ad verse ▁conditions ▁encountered ▁in ▁the ▁open ▁ocean . ▁Additionally , ▁they ▁are ▁often ▁designed ▁with ▁th icker ▁h ull ▁pl ating ▁than ▁is ▁found ▁on ▁cru ise ▁ships , ▁and ▁have ▁large ▁capac ities ▁for ▁fuel , ▁food ▁and ▁other ▁consum ables ▁on ▁long ▁voy ages . ▁ ▁The ▁first ▁ocean ▁lin ers ▁were ▁built ▁in ▁the ▁mid - 1 9 th ▁century . ▁Techn ological ▁innov ations