Probably from Middle Chinese compound 入船 (nyip zywen, literally “entering ship”).

• (Tokyo) にゅうせん [nyùúséń] (Heiban – [0])^[1]
• IPA^(key): [ɲ̟ɨːsẽ̞ɴ]

入(にゅう)船(せん) • (nyūsen) 

1. the arrival in port or harbor of a boat or ship
2. a boat or ship that is coming into port or harbor

• 出船(しゅっせん) (shussen): the departure from port or harbor of a boat or ship; a boat or ship departing port or harbor

入(にゅう)船(せん)する • (nyūsen suru) suru (stem 入(にゅう)船(せん)し (nyūsen shi), past 入(にゅう)船(せん)した (nyūsen shita))

1. (said of a boat or ship) to arrive at a port or harbor

• 出船(しゅっせん) (shussen): (said of a boat or ship) to leave a port or harbor

Compound of 入り (iri, “entry, entering”, the 連用形 (ren'yōkei, “continuative or stem form”) of verb 入る hairu “to enter”) +‎ 船 (fune, “boat or ship”).^[2]

• (Tokyo) いりふね [ìrífúné] (Heiban – [0])^[1]
• IPA^(key): [iɾʲiɸɯ̟ne̞]

入(いり)船(ふね) • (irifune) 

1. the arrival in port or harbor of a boat or ship
2. a boat or ship that is coming into port or harbor
3. (slang, archaic) the act of going to have fun in a red-light district

• 出船(でふね) (defune): the departure boat or ship; a boat or ship departing port or harbor

入(いり)船(ふね) • (Irifune) 

1. a surname

入(いり)船(ふね)する • (irifune suru) suru (stem 入(いり)船(ふね)し (irifune shi), past 入(いり)船(ふね)した (irifune shita))

1. (said of a boat or ship) to arrive at a port or harbor
2. (slang, archaic) to go to have fun in a red-light district

• 出船(でふね) (defune): (said of a boat or ship) to leave a port or harbor