This article first appeared in The Glynns Volume 8 and is re-presented here with additional photographs and hyperlinks.


north channel

Any boat passage between Scotland and North East Ireland is influenced by the strong tidal streams which run through the narrows. The navigator may have to aim off right or left to allow for the side-ways effect, or ‘set’, of the current; or adjust his calcuation for speed of passage because of a fair or a foul tide. A contrary tide can hold a boat stationary for three or four hours whereas a fair one can more than double its speed towards its objective.

As one reads of raids, troop landings or calls for reinforcements in the wars between the two countries, it adds interest to have some understanding of the effect of the periodic movement of the waters on such operations. In general, given a knowledge of the subject and a chance to pick your time of departure, tides are a helpful factor.

The strength of the stream however causes considerable problems, for close to points of land or near underwater obstructions, occur areas of disturbed water variously known as races, rips or overfalls. A race is a good description since a tide which may run at 3 knots along the coast will speed up to 5 in the vicinity of a headland. The common Gaelic word was the vivid ‘coire’, meaning a cauldron. In these areas vertical faced waves with breaking crests and no pattern will be found, powerful enough to swamp an open boat in moderate weather, and put at risk even quite a substantial vessel in a gale.

“Were ye ever at the back of Sheep Islan’ on the first two hours of running’-aff tide?”


Sheep Island from Larrybane Bay


This was a question I overheard recently in a seaside pub from an old salt trying to impress a new boat owner. If you can answer yes to that question, there is no need to explain what a tide rip is like. Going through one can be an exhilarating experience in a well found boat of adequate size but more often a frightening one in an open boat, particularly when the stream is running against the wind. The waters really roar as they tumble round the boat’s gunwhale.

Tides 2 diagram 001

Figure 1 shows the situation, in simplified form, halfway through the flood tide with something like a billion tons of water on the move from the Atlantic to fill the north half of the Irish Sea. The figures beside the arrows indicate the rate in knots at spring tides.

Figure 2 shows the situation half way through the ebb when the tide is flowing at its strongest in the opposite direction.

Tides flow for approximately six hours twelve minutes, so that the first of flood occurs an average 50 minutes later each day, and at the same time roughly every fourteen days. Spring tides, when the streams are strongest, occur three days after each full and new moon, with neaps when streams are weakest at the first and last quarters. The jagged and broken coastline on the northwest side of the Channel means that there are many eddies and ‘counters’ which is the fisherman’s term for a stream, usually inshore, running back in the opposite direction to the main tide.

To understand this effect look at a fast flowing brook or small river and observe small chips of wood being carried up against the run of the water in the lee of rocks or along the bank, The effect in the sea is exactly the same but on a vast scale. However, unlike a river, the situation in the sea is changing every hour, as the strength and direction of the stream varies with the pull of the moon. An experienced boatman gets to know where the dangerous water will be at each stage of the tide, when he can go safely through, and when he can use a counter to make headway against a foul main tide.

Slough na More at slack water

Slough-na-more between Rathlin and Ballycastle Bay is dangerous, for example, from two to four hours after high water Belfast (which corresponds with start of ebb and acts as a reference point), but the area where it occurs is quite free from tidal disturbance at other parts of the cycle. The strongest stream of all, eight knots at springs, is over 30 miles from the narrows off the Rhinns of Islay, doubly frightening because there it meets the Atlantic swell with no shelter from the land. Rathlin and Sanda off Kintyre form jagged obstructions to the flow in waiter and inevitably cause complex eddies.

“Ye don’t take much account o’ tides once ye have an outboard,” a Carnlough fisherman remarked to me recently. This is only too true. With the almost universal use of engines, the knowledge of inshore eddies and the local names for them is rapidly being lost. Where, for instance, is St. Patrick’s Tower and at what state of the tide does it occur?

Fair Head

An old coasting skipper described it to me as a ‘wall of water’ raised off Fair Head but just when and where I have not been able to find out. I think I saw it once but unfortunately did not note any details.  The art of good pilotage lies not so much in knowing how to take your boat through one of these rips as knowing how to avoid getting into one at all. Tides could be helpful for a short operation.



Rathlin and Torr Head

                  Rathlin and Torr Head


A smuggler running a cargo on to Rathlin while the preventive boat lay south of Torr Headwould know for certain that he had 4 or 5 hours to work undisturbed during the flood when the gaugers could not come up on him against the stream.



A boat able to travel at 4 knots can make the 36 mile passage from Red Bay  to Gigha on one six hour ebb tide, provided she avoids the inshore eddies at the start of the trip. She will actually sail 24 miles (6 hours by 4 knots) through the water and be carried along a further 12 miles or so by the tide, which in this case is running in exactly the desired direction.

Red Bay ( photo aerialni)

Red Bay (photo:aerialni)

One or two actual events further illustrate the theme. Three one-man canoes in September last made the 13 mile passage from the east coast of Rathlin to the shore of Kintyre under the lighthouse in three hours by starting at the first of flood, with the tide on their quarter, aiming for a point about five miles north of their objective to allow for the stream pushing them sideways as they crossed. If they had started three hours later they would have had a fast passage across the open water but would have been arriving at Kintyre just as the ebb was starting when there is a particularly nasty rip in that area. Six hours later or earlier they would have been unable to make any progress at all.

Their speed through the water of about three knots is probably similar to that of the barlinns of ten oars in use in mediaeval times.

Birlinn ( West Highland Galley)

Birlinn (West Highland Galley)

In April 1568 Shane O’Neill succeeded in picking a favourable moment to attack the McDonnells when the clans were scattered sowing the crops. He first burnt McDonnell’s new house at Red Bay, then pursued the Scots, whom he outnumbered by two to one, towards Ballycastle, eventually cornering them in Glentaise.

The Scots were commanded by Sorley Boy.  James, Lord of the Isles, (Sorley’s elder brother), seeing from his castle on the north tip of Kintyre smoke signals for assistance from his castle on the south tip of Kintyre, took the first boat crew available and set off in his galley at the start of the ebb to come to Sorley’s assistance. Before leaving he told his brother Alexander to gather the main forces and follow as quickly as possible.

James succeeded in joining Sorley before Shane attacked next morning, but did not have enough men to influence the outcome. The accounts are too vague as to times for precise interpretation, but reading the battle from a tidal viewpoint, it seems that Alexander took a tide to get his boats south from the Clyde and the Isles, but fifteen hours later had nine galleys with a hundred men in each ready to leave. He could not usefully set out however until a suitable ebb, 24 hours behind James. By the time he arrived James was mortally wounded, Sorley a captive, and the battle was lost.

The world has changed but tides have not. Brecain, the trader, was drowned in 440 A.D. with all his fleet of 50 curraghs in the tide rips around Rathlin ; whether this was due to ignorance of the tides or bad luck we do not know. Men have changed too. St. Columba had several frights in the tide rips but survived because he possessed the advantage of being able to calm the waters with a prayer. Would that we of little faith could do the same today!