expression, godan verb (-ru)
feel secure; rest easy; be in safe hands
Idiomatic expression meaning to be in a very safe, reliable situation, as if on a large, stable ship. Often used in the form 大船に乗った気持ち (feeling as if on a large ship). The literal meaning 'to board a large ship' is rarely used independently.
彼に任せておけば大船に乗った気持ちだ。
With him in charge, I feel completely at ease.
この計画なら大船に乗ったつもりでいられる。
With this plan, I can rest easy.