sea mile 
noun
A unit of distance equal to a minute of arc of a great circle and varying (because the earth is not a perfect sphere) between approximately 2,014 yards (1,842 metres) at the equator and 2,035 yards (1,861 metres) at the pole. Compare with nautical mile.It's ironic really that Omeath is closer to Warrenpoint than any other town, only one sea mile, but if you asked anybody if they knew anybody in Omeath and vice versa, the answer is usually few....
- Rescuers said that the ship was hit by a strong storm some seven sea miles off the Daqin Island near Longkou, which might have caused the gas explosion.
- He said all boats were fishing on the borderline and were allowed to travel through the reserve which extends out three sea miles from the shore.