Originally Posted by deblen
A ship cruising at 20kts covers 5nm in 15 minutes. Keeping your radar
on 12nm range in shipping
lanes helps to prevent them from sneaking up on you.
Don't nap more than 15 min.(Joking)
And here's the details if you oversleep and wake up 14 minutes too late.
At 20 kts that's roughly 33'/second. A sailboat at 5 Kts will be a hair over 9'/second.
Beam of a large ship might be 150'. More for the largest container ships. Then allow about 40' from bow to stern of the sailboat. So to start from one side of a ship and cross in front of it and clear the other side you would have to cover a minimum of 200' which would take 22-25 seconds.
In that time a ship at 20 kts would cover about 800'.
So if you woke up to see a ship heading straight for your boat you would have time to cross completely across the bow if the ship was more than 800' away.
Again this is a worst case scenario, crossing all the way across the bow of a large ship. Other angles and situations would give you more time to react.
However naval vessels can move a lot faster than 20 kts so in case of an encounter with them all bets are off. On the other hand, they do generally keep a better watch and are almost certainly aware of your position, course and speed.
I am in no way advocating this action. The calculations are there just to illustrate how close you could get to a big ship and still avoid a collision