You should not need a repellent on the ship as mosquitoes do not like air conditioning or salt water and I have never had a problem on any ship anywhere. Mosquitoes will bite during the day but attack mainly at and after dusk so as the others say it might be good to take some for those times when you might be at risk as when you are in damp uncultivated surroundings or staying ashore overnight. Ida

Certaily if you go inland in Malaysia , Vietnam and China

I would.