Tides and swimming in Myrtleville

Republishing this important article from 2014 on our local tides.  If you don’t have time to read it all, just skip to How might this impact my swim?  It’s important to know.

From Bernard Lynch & Ian Venner

This note is intended for those new and not so new to coastal swimming and simplifies some of the calculations and facts which you may well expect to see.  Much of it is specific to Myrtleville.

The tidal streams (coastal currents) are the most important part of the tides you need to understand as a swimmer.  Most OW swimmers average between 2-3km/hr.  Tidal streams near the shore in the harbour can run at between 0.5 to 1.0 km/hr – so they can make a very big difference to your swim.  The speed of the tidal stream varies during each High Water/ Low Water (HW/LW) tidal cycle, and also varies between spring (very high/very low) and neap (not very high/not very low) tides.  Spring tides occur a day after a full moon and recede over a period of one week to a neap.

The spring/neap maximum flow rate can vary from 0.5 to 1.5km/hr.  The flow rate within a 6 hour tide range will be three times as strong at its fastest (in the middle of the six hours) as in the first and last hour. This is explained by the Rule of Twelfths.

Rule of Twelfths

The level of water does not rise or fall at a constant rate throughout the 6 hour duration of a rising or falling tide.  The amount by which it will do so can be estimated mentally by means of the following rough guide:

  • 1st hour rise or fall = 1/12 of Range
  • 2nd hour rise or fall = 2/12 of Range
  • 3rd hour rise or fall = 3/12 of Range
  • 4th hour rise or fall = 3/12 of Range
  • 5th hour rise or fall = 2/12 of Range
  • 6th hour rise or fall = 1/12 of Range

This impacts tidal speed too – the fastest speed being in the middle of the period between HW and LW. In the table below, assuming a 12 foot rise and fall in the tidal height (typical for Cork Harbour) and a maximum tidal flow rate of 1.5km/hr, you can see the how fast the tide moves and rises/falls.

Time after HW Twelfths Change in Depth in that hour Avg tidal flowkm/h
+0.5hr 1/12 1’ 0.5
+1.5hrs 2/12 2’ 1
+2.5hrs 3/12 3’ 1.5
+3.5hrs 3/12 3’ 1.5
+4.5hrs 2/12 2’ 1
+5.5hrs 1/12 1’ 0.5

What else influences tides?

Other factors can influence tidal heights and flow rates. Low pressure will increase tidal height (think of it as less atmospheric pressure pushing down on the water).  Lots of recent rain will increase the strength of the ebb, especially out of Cork Harbour and Fountainstown too (it’s just more water trying to get out).

How might this impact my swim?

So what does all this mean for swimmers?  Be conscious of the time of HW – not because the beach might be more or less sandy, but because it should influence where/how you swim.  Swim against the prevailing tidal flow, so that if you get tired you will have the benefit of it on the way back.  For example, you might consider a swim from Myrtleville to Church Bay and back on the third hour of a falling tide (tide against you going to Church Bay and with you coming back).  You should not consider doing it on the third hour of a rising tide (tide with you going to Church Bay and against you coming back).

In reality, the tidal flows between Myrtleville Beach, the Dutchman and Bunny’s are fairly limited.  There is a little more effect to consider if going Myrtleville/Fountainstown and particularly at Bunny’s point where the push or pull can be significant on the 3rd and 4th hour. If needed, there are plenty of escape routes onto the rocks between Myrtleville and Fountainstown – weather dependent. Going to Church Bay, however, puts you into much stronger tidal flows and you really need to plan your timings. Generally you would not plan a swim past the Dutchman unless the tide was ebbing (going out) for the return leg. Equally, anything further afield needs careful planning with someone who knows the area and tides.

So what direction does the tide flow?

The diagram below broadly illustrates the direction of flow of the tides around the Myrtleville area.  Tides, especially close inshore, are subject to back-eddies and counter-currents, and there are a few of these to be found in the area shown.

To check tides, either purchase a tide table or click on this link.

You should always know the tide before you swim.  Swim Safe.

New Swimmers evening – June 11th: 19:30 – Help wanted

June 11th, 7.30pm: Eilis Burns will be bringing a group of new open water swimmers to Myrtleville on Tuesday, June 11th at 19:30.

Any of the regular Myrtleville swimmers who can be around that evening to give any help would be appreciated. We need swimmers used to the sea to join the group for the swim and watch out for anyone who needs some support.  Also, any kayakers or SUPs available would be very welcome.

Please come down if you can. Remember what your own first swim was like and help out:-)

Some of the new swimmers in 2014 with Eilis and Mike Harris.

Some of the new swimmers in 2014 with Eilis and Mike Harris.

14 February – Denis’s Day.

This 14th of February, let’s give due homage to the Valentinest Valentine of them all.

Denis.  One name – that’s all that’s needed.  Like Pele. Bono. Rasputin. Prince.  One name – a single word – and everyone knows who you mean.  His fame abounds.  That one name conjures up the images.  Female admirers flock to see him swim.  Meet him.  Be with him. Warm him, post-swim. 

Some use other single words to describe him.  Casanova. Charmer. Langer (they’re just jealous fellas, Denis – don’t mind them: it’s seeing the queue for a spin in the Yaris that drives the other men mad).Yes, of course, there are begrudgers.  No man with such a magnetic attraction for d’opposite sex could avoid the envy of other, less sensually successful men.  As his adoring mnás surround him each day, the other men wonder, “how does he do it”? 

How does he have them flock to him, while he loudly laments, “Ye’re all ancient. ‘Tis young wans we want down here, not a load of ould cougars.  Young wans, I’m tellin’ye. The rest of ye can bring de buns, though, then go down the slip out of sight of the newer models.  We need upgrades around here.”

How does he survive – and thrive?  “Treatin dem mean, to keep dem keen, like.” And yet – still they come to pay homage.  Feeding him.  Lauding him with buns. Amazing.  He must have phenomenal pheromones.

Let’s not wonder too much.  Let’s just learn from him, lads.  Acknowledge and admire him.  His is the way, the truth and the light.  Follow the path of Denis and the rich Bounties of life will be yours too (or if not Bounties, some nice buns at least).  Denis’s Day.  One to celebrate.  Get up, ya good thing.

Volunteers needed – always. Let’s work together.

It’s a great time of year for planning which swims to enter over the Summer.  Some are taking entries already and Carol Cashell is putting the Munster OWS Calendar together (thanks, Carol 🙂 ).  

While you’re making your plans, give some thought to helping out at one of the swims.  Most swims are very glad to get offers of help – registering, timekeeping, parking, kayaking, boat-support – the list of jobs goes on and as numbers of entrants rise, more volunteers are needed.  

Here’s a blast of Canned Heat to get you in the volunteering mood.

All pictures thanks to Siobhan Russell.

Seal attacks!!! Kindof. Sorta. Maybe, like.

Consternation in Myrtleville this morning!  Kerfuffle! Discombobulation! Mad stuff altogether.

I was plodding along out by the corner at Bunnyconnellan when I saw three swimmers approaching.  At speed.  I mean – speed.  It was the intrepid trio of Bernie, Jim and Trev.  I turned around to head back to the beach – with them about 200 metres behind me.  I was 500m out.  As you can see from the first picture below (that’s me there in the distance on the left) they passed me – at speed, like – and were a good 200m ahead of me hitting the beach. 

Now, I’m slow.  I know that.  I’m fine with it.  I’m not that slow, though.  They’re not more than twice as fast as me.  Not on a normal day.  This was NOT a normal day.  The trio – they shouted – had suffered repeated, vicious, co-ordinated and just generally feckin awful seal attacks by up to nine seals.  It started at two but they were definitely talking about nine by the end of it.  I didn’t see any myself.  Must have been going too slowly.

I think the second picture below is Trevor explaining how close they had come to near death at the hands of Sealus Attackus Beastus.  Either that or he’s saying how big the seal was – which would take a bit away from the drama of the attack, to be honest, if it was that size.  I say IT, but I mean THEM – THEM, dozens of THEM.  You can see Bernard staring out to sea anxiously in case THEY were coming on still.  Terrifying, like.  No way was it just a couple of ould seals out for a quiet swim.  No way.  Attack.  Definitely an attack.

Despite their horrific experience, the trio posed for a picture with a fan (sound, lads) and then made their way shakingly up the beach, discussing googling “Seal Attacks” and whether warning signs should be put up.  Mad stuff.  Mad.

BE CAREFUL OUT THERE! Watch out for dogfish too.  Now THEY are vicious, I can tell ya that.  Don’t start me about dogfish.