IPA: //ʌnˈsiːˌwɜːrði//
KK: /ʌnˈsiːˌwɜːrði/
Not suitable or safe for traveling on the sea.
The old boat was declared unseaworthy and could not be used for fishing trips.
Unseaworthy → It is formed from "un-" (meaning not) and "seaworthy" (from Old English "sǣweorþig", meaning fit for the sea). The word "unseaworthy" means not fit for the sea or unsuitable for sailing.
Think of 'not' ('un-') being added to 'fit for the sea' ('seaworthy') — that's why unseaworthy means something that isn't suitable for sailing.