Is one who is unable to pray in the mosque in congregation or attend Friday prayer due to travel and work on board a ship sinful, given that he can pray individually and determine the Qibla?

There is no harm in praying aboard a ship, and no sin in not praying in the mosque if it is not nearby. If you are traveling (i.e., you have exceeded the distance at which prayers are shortened), the Friday prayer is waived for you, and it is permissible to shorten the four-rak'ah prayer unless you intend to stay for four days or more. However, if you are not traveling, you must strive to attend the Friday prayer if there is no excuse. The Friday prayer is only performed in congregation and is not performed on a ship. Whoever misses the Friday prayer, whether due to an excuse or not, must pray it as Dhuhr. There is no sin in not attending Friday prayers and congregational prayers due to an excuse, and it is hoped that the reward of congregational prayer will be attained through sincere intention.