The alcohol limit for a seafarer on duty differs between UK and international waters, so you’ll need to be aware of where you’re sailing. 

Within the UK, according to the Railway and Transport Safety Act (2003), the limits are [4]:

  • Blood alcohol: 50 milligrams in 100 millilitres
  • Breath: 25 micrograms in 100 millilitres
  • Urine: 67 milligrams in 100 millilitres

Internationally, according to TCW Regulation VIII/1, the limits are [4]:

  • Blood alcohol: 0.05%
  • Breath: 0.25 milligrams per litre
  • Urine: N/A