Notes on the tidal situation off the SE part of Ireland

I have said in previous notes that the north going stream in the Irish Sea starts flowing north at low water Liverpool/Dublin, there is however an anomaly in the above area, especially west of Carnsore point. I discovered this by accident many years ago, though the locals had always known about it, nobody had asked them! Having done the passage north with a compiler of the Irish Pilot guides this is now well known but needs a little more explanation.

The tide turns in the Kilmore Quay area about two to three hours before the main current in the Irish Sea, this is very useful for going north, however it becomes a great disadvantage going south. I will illustrate this with a few examples.

I will take the passage from Kilmore Quay to Pwllheli first as this was when I first discovered this anomaly returning from an early Cork week with my son, I had promised him a “fry up” going across Abersoch bay, we arrived far too early for this leading me to work out why, this was also when I discovered the advantages of talking to the locals.

This passage is over ninety miles and under normal circumstances would take me well over thirteen hours, however there have been times when I have completed the passage in under eleven! If you leave Kilmore about two and half hours before low water Liverpool you will have tide under you to Carnsore and then nearly eight hours of north going stream with you across the Irish sea. If you can do around seven knots a big hint here is to put about an extra ten degrees northing into your course, when the tide starts running south you will be north of Bardsey and will be able to “ferry glide” across the current and catch the south going stream through Bardsey sound and across Hell’s Mouth, though this looks long on the chart you will arrive at Pwllheli well before you expected.

I usually do this passage if I can leave Kilmore before eight in the morning, however if this is not possible I will still take advantage of the tidal situation and go to Arklow, or in fine weather anchor off Polduff, which avoids having to go north or south of the Arklow bank, with a shorter passage to Pwllheli the following day. It is fifty miles to Arklow which on a normal passage would mean fighting some tide at one end of the passage or another. However, again leaving Kilmore a couple of hours before low water Liverpool you will carry the current all the way, making for a very short passage. It is possible to carry the tide north of Wicklow Head, a major tidal gate on this coast, if you leave Kilmore early enough, this would put somewhere like Greystones within reach.

The other advantage of leaving Kilmore at this time means that there is no depth problem at the entrance, which has begun to silt.

Going south is a very different prospect, however I will try to illustrate the best way of avoiding the worst of the foul tide. If you plan to do the passage from Pwllheli to Kilmore you will have to factor in the early change of stream at Carnsore where the tide runs at its strongest, this means to enable you to have tide with you there you will have foul tide nearly all the way until about ten miles north of the point this is why I prefer to use Arklow as a stop on the way.

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Some observations around the tidal situations of Aberystwyth

Now that the marina at Aberystwyth has become usable again here are some notes on taking advantage of the tidal situations in Cardigan Bay in passages to and from Aberystwyth.

High water Aberystwyth is half an hour or so before Pwllheli, this period can be very useful in passage planning to allow entry to each port on one tide. However there is a much more significant factor to consider in this respect and that is tidal current.

As my notes on Bardsey sound (available at the marina office) say, tidal currents in the Irish Sea are controlled by high/low water at Liverpool and not, except very close to, the local harbour. Even though the current is less strong in Cardigan Bay it can still at times reach nearly a knot. This means that if you are planning to arrive at Aberystwyth a little after half flood you will have the tide with you most of the way. Lets look at this carefully, say high water Aberystwyth is 1600, and you plan on a six hour passage and wish to arrive a couple of hours before this, 1400. High water Liverpool is three and a half hours after Aberystwyth so the tidal currant in this case will not start running north until 1330 (low water Liverpool) so you will have the ebb tide from Liverpool with you until that time. So for most of your passage you will have half a knot or so with you giving about half an hour advantage, if you don’t factor in this arrival will be too early and you might have to wait outside (not pleasant in an onshore breeze).

Going the other way the same principle applies, if you leave Aberystwyth two hours before local high water you will have the Liverpool flood with you all the way so probably giving you a local half ebb entry to Pwllheli.

If anyone wishes to discuss this in more detail with reference to a specific case please contact me.

Richard Smith

Imladris Berth 2B2

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Last Updated: 14 February 2021

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Some notes on the tidal situation around Bardsey

The sound and shoals round Bardsey have over the years earned a fearsome reputation. In some conditions this reputation is well earned, however in most summer conditions with reasonable care the area is very straight forward.

There are two major points to understanding Bardsey which though well known are worth repeating. The first though obvious is sometimes misunderstood, is that slack water is not at the time of the local high and low water but is governed by high and low water Liverpool. In fact about three-quarter’s of an hour before. The second is that the current does not run in exactly opposite directions on the flood and ebb, east west on the flood and south east on the ebb.

For a full understanding we need to look at the full picture of the southern Irish Sea. If we imagine that at low water Liverpool there is a wave, the crest of which lies between Carnsore Point and South Wales. This is the local high water, during the flood at Liverpool this moves in a north easterly direction up the Irish Sea turning into an easterly direction north of Anglesey. As this crest moves north so to does the local high water until it eventually reaches Liverpool six hours later when it reverses its flow to become the ebb.

I will deal with the north going stream first which I will refer to as the flood. If you look at the chart the Irish Sea is fairly wide in the Cardigan Bay area narrowing down considerably when at Bardsey then widening again. All the water travelling north up Cardigan Bay is forced round Tremadoc Bay and out across Hell’s Mouth, this is happening throughout the period of the flood. Hence what seems to be the peculiar tidal currents in the Abersoch, Pwllheli area, relate to Liverpool and not the local tide times which will also make this area much easier to understand. It is all this water from Tremadoc Bay which shoots through Bardsey Sound and can accelerate it to up to eight knots. At the same time Bastram Shoal to the south of the island also directs the current in a westerly direction. This is why though the main direction of the flood is north east you can gain a great advantage to the west leaving at the best time. It is also when the area is at its most dangerous, not only do the different directions of the currents disturb the sea, but the numerous shoals confuse things even more. In fact it is sometimes more disturbed round the outside of Bardsey than through the sound itself. There is another element to bear in mind at this point, Carreg Du the large rock on the landward side stands where the current is at its strongest. This acts rather like a blunt bowed ship creating an enormous wash. If there is a strong west or north west wind this is when this area becomes very dangerous, in fact I have seen a twelve ton boat totally out of the water here!

The ebb or south going stream has very different properties in that the flow down the Irish Sea is in a south westerly direction. This means that it is only the water down the north side of the Llyn Peninsula that is trying to force its way through the sound, resulting in up to two knots less current than the flood, and a south easterly direction. This usually means that the area can sometimes be calmer than on the flood as the prevailing winds are not from this direction. Along the north side of the sound, and in fact all along the coast to Cilan, the water falls away in a southerly direction. This results in a narrow band close to the shore with very little current, making the area round Carreg Du not as treacherous. This is also where it is quite possible to make very good progress against the tide, keep well in from Cilan onwards, inside the Gull Islands and very close to the cliffs through the sound. Beware, there is a covered rock in the small bay west of St Mary’s Well. Unfortunately the same cannot be done on the flood.

Now comes the sixty four thousand dollar question, when to go through. This is very much guided by the weather, obviously if there is a strong wind and the likelihood of wind against tide then slack water is the only time when conditions should be reasonable, especially on the flood against a north westerly. However well you plan to be at the sound at slack water, in strong conditions the shoals round Bardsey will not be pleasant, the Tripods are particularly nasty and for a large area round them.

However in moderate conditions and with the wind with the tide it is very useful to makes use of the extra speed over the ground. When going in a westerly direction there is a young flood from Cilan which starts flowing about one and a half hours before slack water. To makes the best use of this arrive at Cilan at this time and keep well in. You will then be shot through the sound with the current helping you to the west for a considerable distance. Coming the other way it is important to reach Cilan before the westerly stream starts, as the ebb helps you across Hell’s Mouth, though not as much as on the flood. I usually try to aim for Bardsey at about half ebb, if you keep well north of the rumb line coming across this enables you to run down onto the sound from the north with the tide with you, then to carry it through the sound to Cilan.

Richard Smith

A printable copy of this note is available (without pictures).

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Last Updated: 25 June 2016

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