Most of us sail in and out of our home port with little concern about the depth of water, more worried about avoiding commercial shipping and fishing boats. What happens when we go cruising along an unfamiliar coastline, where the entrance to our selected haven is protected by a bar?

1. Implement safety procedures for crew and boat

All crew must be on deck, wearing life jackets, with the boat locked up. For a sailing vessel == always have the jib up, even if it is not drawing, in case the motor fails.  

2. Understand what scend means

Scend is the distance from sea level to the bottom of the trough of a wave. The trough can be taken as being equal to the height of the wave above sea level, or more simply as half the height of the wave. This means that with a 3m sea running over a bar the depth available to you may be 1.5m less than you would have in a flat sea.  

3. Calculate the state of the tide

The safest way to enter a river which is protected by a sandbank of any kind is to go over the bar on an incoming tide. The reason for this is thoroughly understood by ocean yachtsmen and coastal sailors and motor boaters who are experienced at crossing bars, but not by the less experienced. If you have wind and current opposing each other the waves will stand up high and be more likely to break. At the change of a current, in this case the tide, the seas will become longer and slope more and will break less.  

4. Tell someone on land

If after calculating the depth available you decide that it is worth trying to enter the harbour the next rule is to tell somebody on the land that this is your plan. These days there are excellent volunteer organisations, such as the Coastguard. Not all are manned 24 hours but I would assume that nobody would increase the danger of crossing a bar by doing it at night and therefore there would be somebody monitoring the radio.  

5. Seek advice and local knowledge

It is not only good practice to tell the people ashore what you are doing but very often they can give you the latest advice and local knowledge on conditions at the bar. If they do not tell you the harbour is closed or that the bar is dangerous, then you can go ahead.  

6. Observe the conditions before entering

Let us assume that the tide is coming in and there is a sea running which is lumpy but not curling and breaking. Stand off and have a good look at what is happening at the entrance. It is easy to see where the waves begin to feel the bottom and swell above the general level of the water. Stay back from there and to the side and just watch the waves for a while to see if there is any regular pattern to them, or whether there are random waves coming in from the side which could be dangerous if you did not expect them. This happens quite often.

Are they are running in threes or sevens? Is there a bigger one every now and then? While you're doing this, be careful that you aren't picked up by a wave and carried, before you are ready, into the entrance. It is quite common for a secondary bar to form further to sea from the main one. If you should get between the two without realising, a big wave could easily trip on the first bar and throw you into the second. That, if you were not ready for it, would be disastrous.  

7. Go for it

Sometimes you can be lucky and see a prolonged flat spot. If so, charge right for the entrance and get into the calm water just as quickly as you can. As you get more experienced you will realise that a prolonged flat spot is quite easy to pick as distinct from just a short gap in the waves.

It is more likely, though, that you will have to pick a particularly big wave so that you have plenty of water, and come in on the back of that. You will almost certainly be following lead lights or keeping between channel markers to keep you in the safest part of the entrance.  

8. Never get ahead of the wave you are on ...

unless there is substantial water in front of you. Not only might the wave behind break, but you might finish in too little water. Keep on the back of the wave as it collapses and breaks with the bow just behind the white water. If you get further forward there is the possibility of dropping into an air pocket and your bow dropping dangerously low. Sit in the patch of white water as the wave foams and collapses under you, keeping ahead of the breaking water from the wave behind. Once the wave has collapsed and the water smoothed out, the problem of scend disappears. When you're certain that you are through the bar you can go ahead, knowing you have performed one of the most dangerous manoeuvres in boating, apart from...  

9. Leaving again

Even more dangerous than entering a bar is going out over one, particularly if the tide is ebbing. As the waves try to cross the bar the outgoing tide stands them up and makes them shorter and steeper and makes them break. As you go towards the bar you're in calm water and you cannot see beyond the first line of breakers. Consequently you cannot get an idea of the pattern or sequence of the waves. I have been caught many a time, particularly where there have been breakwaters and the bar has been dredged, when it seemed likely that I could leave harbour. But when I've actually got to the point of leaving I have seen that it would be too dangerous. It is hard to imagine circumstances so pressing as to make one cross a bar on an ebbing tide.

Unless the local coastal patrol tells you it is safe to leave, my advice is that you go to a bar of the other kind and do some extensive research.