Container Ships and the Cruising Sailor - Part 2
by Nancy Knudsen on 26 Mar 2006
Will he see you? . .
It’s the worst conditions so far of our 12-month journey. We’re in the narrow Gulf of Suez, it’s dark, with about 30kts gusting 40 on the nose –the engine is helping us through the rocky waves. To starboard, there is a two way shipping lane crowded with monsters going both ways. Ahead and all round are oilrigs, grotesque silhouettes blaring white light into the night. To the left and ahead is the coast crowded with the lights of tanker wharves. Green water is coming over the dodger. We have to tack into and out of the shipping lane and between the oilrigs. The radar is on. Our radar reflector is pretty good. Would container ships see us? Never – there’ll be no sleep tonight for our crew of two …..
If there are dangers in daylight for the cruising sailor who doesn’t take full responsibility for the avoidance of collisions, is this better or worse at night? Intuitively, you would think that a light on an ocean would be clearer than a feather of a sail against white horses, glare and clouds. So let’s examine the real situation – first by looking at the rules regarding lights at sea.
The first premise of rules about lights on vessels is that they are applicable for the conditions of a dark night and clear sky.
And the rules are (see diagram assistance at the end of the article):
Power driven vessels over 50 metres – that’s your container ship – must carry mast head lights visible for 6 miles, green starboard, red port and white stern lights must be visible for three. Between 12 and 50 metres, the numbers reduce to 5 and 2 miles respectively. Under 12 metres, 2 and one mile – and that’s a fishing boat. Craft smaller than 7 metres only need carry a white all round light and side lights.
Sailing vessels less than 20 metres and more than 12 metres (that’s many cruising sailors) red and green side lights and a stern light visible for 2 miles, OR a tri-light arrangement at the top or near the top of the mast - red and green side lights combined with a stern light, making a 360 degrees total. If the vessel is less than 12 metres, then the lights need only be visible for one mile. If less than 7 metres, the same applies, with the additional provision that if the boat is not equipped with these, a light should be shown ‘in sufficient time to prevent a collision’.
However, you don’t have to be in bad conditions to be pretty sure that a container ship won’t see you at night. Why?
First, the focal plane of any normal yacht’s navigation lights is + or – 5 degrees, and the loss of effective light outside this arc is 50%. This is a staggeringly large loss of effectiveness.
Let’s take the case of a yacht less than 12 metres, showing the regulation lights visible at a one-mile range. (Remember this requirement is stipulated to be for a dark night, with no background lights, and clear air.) However, anywhere near land there are often lights around or the glow of cities to reduce visibility, and if there is moisture in the air, this will also reduce visibility again. There is also likely to be salt on the yacht’s lights, and, if she is sailing, then she is almost certainly heeling more than 5 degrees.
The original one-mile visibility is therefore reduced as follows:
Original light visibility distance: 1.00 nm = 1,852.0 metres
Salt on the lens reduce by say 10% 0.90 nm = 1,666.8 metres
Moisture in the air, reduce by say 10% 0.80.nm = 1,481.6 metres
Interference surrounding lights say 10% 0.70 nm = 1,296.4 metres
Reduction due to heeling, say 50% 0.35 nm = 648.2 metres
So the resultant actual light visibility distance is .35 nm, or 650metres, or less than half a nautical mile.
Neglecting the speed of the yacht and assume a ship’s speed of 15 knots (one mile every four minutes) and assuming the watch officer sees the light at this range and acts instantly (unlikely) then the ship has less than two minutes to act to avoid collision.
To put the rudder hard over takes about 15 seconds. For the ship to answer her helm and make any significant alteration of course takes at least another 40 seconds, so that, of the available time, 55 seconds may have now elapsed. Let’s assume the officer has acted immediately and put the wheel ‘hard a-starboard’, the troubles are not yet over if the ship is large and deep laden and especially if the depth of water is less than twice the ship’s draft.
Once the ship starts swinging, the bow may clear the yacht, but the speed of the swing will be increasing. To check this, once the bow is clear, he puts the rudder ‘hard a port’, but the swing will continue to starboard against the port rudder for about 40 degrees, depending on how fast the ship was turning when the rudder was changed, This is due to the tremendous inertial forces generated by the turn and the length of the ship.
This means that although the ship misses the yacht with its bow, it has an excellent chance of giving it a swipe with the stern as the radius of the stern’s swing is greater than that of the bow. This is because a ship pivots about one third length from the bow, so that the bow is inside the turning circle, but the stern is well outside it.
Even if it appeared that the stern might miss the yacht, the entrained water would probably do the trick and suck the yacht into the ship’s side and possibly the propeller. This was the case when Sir George, a Peterson 44 being sailed by the owner Rick Everest and one crew, was hit by an Indian Navy ship and dismasted off Cochin on India’s west coast (See Sail-World article )
One does not need to be a genius to see that a yacht in close proximity to a ship is in a very perilous situation. This is more so at night, and if it were not seen, then nobody would know anything about it. No noise of impact would be heard on the ship, and no shock felt, as that would be absorbed by many thousands of tonnes of ship and cargo. Probably the first anybody on the ship would know that she had utterly destroyed a yacht was when the ship arrived at her next port and found some odd bits of rigging clinging to her anchor, or some strange paint along the side of her hull. This is how some ships involved in a collision have been identified in their next port.
There is another factor in making yacht lights difficult to see from a ship’s bridge, and that is the difference in height.
If the lights on a yacht are carried on the bow or pulpit, they shine horizontally only a couple of metres above the water. The ship’s officer may be about 30-40 metres above the water so he cannot see the lights, as he is well above the focal plane of them.
Even if the lights are carried on a 15 metre mast in a combined lantern, he is still 25 metres above the focal place and they would be hard to see.
The sensible lights for a yacht, therefore, would be the Tri-lights the masthead which have a better chance of being seen, and they should be as bright as possible, because neither green nor red are colours that have good penetration in a murky atmosphere. By placing the lights at the masthead they are further away from the spray and thus have a better chance of showing more clearly than lights placed on the hull. However they will still suffer degradation of visibility because of salt and heeling effect and are harder to clean.
The conclusion is: He is not going to see you!
A yacht sailing at night, therefore, should never be left without a lookout on deck, and you should be armed with a VERY powerful torch to shine at a ship’s bridge as soon as he sees a ship approaching. If possible you should steer to pass port to port with all haste. However, dependent on the angle of approach, in choosing a direction to best avoid the ship, bear in mind that ships, whenever possible, alter course to starboard to avoid collision. Don’t forget that some vessels, particularly container vessels, are capable of speeds in excess of 30 knots.
In the conditions described at the beginning of this piece, with visibility hampered severely by bad weather, the lights of other ships, coastal lights, lights from the oil rigs, and the fact that our own lights were obstructed by water and salt, there would have been little or no chance of any of the container ships noticing that we were present. It was completely up to us to stay away from them.
In the next part I will discuss how radar can help the cruising sailor, closing speeds, some rules we as cruising sailors often forget and some on-board gear that may assist a boat to stay clear of danger.
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