In our eleven year circumnavigation
, we have had to change course many times offshore
to avoid ships.
When we started out, we checked around the horizon every fifteen minutes, and we quickly learned that was not frequent enough.
When we checked the horizon every ten minutes, disturbing encounters with ships no longer happened.
The closest and scariest encounters occurred when we were sailing on reciprocal courses with a ship ---both vessels heading directly at each other, bow to bow. In those instances, a gaze around the horizon every ten minutes was just enough to keep us out of trouble.
Even out in the "Big Empty" - 3000 miles - from Galapagos
to French Polynesia
, we saw 5 to 6 ships, and one of our friend's yachts was even run down by a ship in the same area.
For us, the ten minute check works extremely well. If a person is sailing in a fast multihull
, then checking the horizon every ten minutes would probably not be adequate to assure safety
. We average sailing 150 miles a day - 6.25 knots - around the clock, and the ten minute horizon check works at that average speed.