Yes, it's an honour system. If you really need a shower, for example if you get covered in grease, then you can take one. The rule is there to prevent everyone

Yes, it's an honour system. If you really need a shower, for example if you get covered in grease, then you can take one. The rule is there to prevent everyone on station taking long daily showers. Some jobs are unofficially allowed to shower on more days e.g. kitchen/galley, vehicle maintenance, stewards. Medical probably, too, though there isn't usually much work.