1:1 ON YOUR DATE
Rules of Thumb for Sailing
Your height of eye in a yacht's cockpit is probably 2-3 metres, in which case the horizon is 3-4 miles off. Add that to the visible range (NOT the luminous range) of a light at night and you know your distance off when it dips (you can if you wish correct for tide unless it's a lightship). This is quite accurate; if you do not correct for tide you are further off, except at high water.
If you can see the bow wave of a ship on the horizon, or the hull of another boat on the horizon, she is two and a half miles off.
In daylight, you can tell the colours on a large buoy at about a mile. You will see the buoy at a distance of about 2 miles.
You will see a light buoy at a distance of 2 to 3 miles at night. At about 200 metres the light will reflect from the surface of the sea.
You see a man walking as a tiny moving line at half a mile, the movement of people's arms and legs at about 400 yards and their faces at 250 metres.
A light coloured beach can be seen at about 4 miles. You're in to less than a mile when you can discern individual trees.
You can see individual windows in a house just inside two miles.
You will usually see a lighthouse at 7 to 8 miles off.
Note when a buoy or other landmark is 4 points (45º) on the bow (easy to judge) and read the log if you have one. If not, note the time and guess the speed. When the mark is abeam, the distance you have travelled is the distance you are from it. (allow for tide).
If closing a sandbank marked by buoys, or a coastline marked by lighthouses, do so at an acute angle to the line of buoys or lights and you are bound to see one.
To get a good bearing of a mark ahead, point the boat at it. And always take back bearings of whatever you pass.
If you are beating towards a destination keep dead downwind of it (so any shift will free you). Sail towards any forecast windshift.
Always lee bow the tide. (Keep the tide under the lee bow).
A transit is a free check on your compass deviation - never miss one. Your compass may be lying to you but at least it lies consistently.
If you get a single position line, which is clear of a danger, but you know there is a danger in the vicinity, alter course and sail down the position line until you can cross that line with another one.
Top Tips from Portishead Cruising Club
posted 5th April 2011