Tidal curves

[david_e]

Having learnt about tides on my YM course, I decided to get an almanac. So this week-end went for maiden sail and plotted return time in almanac, Milford Haven, to allow a little, plus a bit, so could get back to the club and watch Wales (ho, ho, ho) and England (yeah baby).

Anyway, as went through the harbour mouth in the ebbing tide, heaps of water no need to rush back at all. Have a closer look at local tide tables, check neaps against springs, and yes - it is on average just over 5 hours flooding and just under 71/2 ebb. Get home check Milford Haven, even spread, check Holyhead, even spread.

So, will there be a tidal curve for a secondary port published somewhere or will I have to make my own, and how is the best way to go about it?

I think that this is reasonably important because with the prevailing winds, Pwllheli is quite exposed, and would prefer not to get caught out in an unpleasant situation if it can be avoided.

 

[bigmart]

The easiest way I know to get secondary port Tidal curves is with Bellfields Tideplotter program. I just checked the curve for Pwllheli & it is quite useful. The program will run on a PC under Windows & also has a Pocket PC version for use if you have a PDA.

I don't have any connection with Bellfield but I feel this is an excellent program & very good value for money.

Martin

 

[Guest]

Just to show impartiality, you could also look at www.tideplotter.co.uk I use that and get the free version for my windows PDA. It covers all of the UK, Northern France and the Netherlands £9.95. Again I have no connection with this company.

<font color=red>"You only see what you recognise, and you only recognise what you know"<font color=red>

 

[david_e]

Ooh extra quick, many thanks, where do you get them and will it run on Palm?

 

[Guest]

Go to the web site I showed you, you can download it now if you want. Don't know about Palm, sorry.

<font color=red>"You only see what you recognise, and you only recognise what you know"<font color=red>

 

[bedouin]

Around the Solent they do publish tidal curves for secondary ports - but that is because they are somewhat unusual.

Otherwise you use the same curve for the secondary port as for the primary port. You apply the secondary port corrections to the primary port data, just as you were taught, then use those figures (times, range) on the tidal curve for the primary port.

 

[Guest]

I see Belfield and tideplotter are the same /forums/images/icons/laugh.gif Sorry my mistake.

<font color=red>"You only see what you recognise, and you only recognise what you know"<font color=red>

 

[bigmart]

If you try the website you may find the demo will give current curves.

Martin

 

[david_e]

That is what I would expect to be the case and is what they taught me on YM recently, but experience proved different, and from what Big Mart is saying it could be different in practice. I was expecting about 2.2m whereas I had 3.9 on the sounder which is about 4.0 in reality.

 

[bigmart]

Sorry but I think you'd better trade in your Palm for an Ipaq.

Martin

 

[david_e]

Thanks again, have just ordered it on CD for the free game!

 

[BrendanS]

Had a thread on this recently where I asked the same question. I've just renewed my subscription, and can confirm there is no Palm version.

If enough of us ask for it, maybe we'll get it, though I suspect not, as it's not as easy to port from Windows on a pc to Palm as it is to port to a Windows CE type operating system

 

[david_e]

ta

 

[vyv_cox]

I think you need to use a little interpretation sometimes, and this is one of them. Look at the tidal flow atlas for Milford Haven and you see it is quite complex, with the flow changing between up the Bristol Channel and northwards into Cardigan Bay. This has an influence on the curve, as you might expect. Holyhead has no such problem, flow is all one way into Liverpool Bay, then it changes and flows 180 degrees on the ebb. Result is that the ebb/flood curve is quite symmetrical.

Pwllheli is pretty straightforward, sea flows into Cardigan Bay from the south on the flood and to south on the ebb. Virtually no flow comes around Bardsey on the ebb, although if you anchor in Aberdaron Bay you will notice considerable movement there but this does not extend much further east. I would expect the tidal curve for Pwllheli to be pretty symmetrical. Not really much of a problem though - I have entered Pwllheli many times at LW springs drawing 5ft 6 ins and not been near touching.

 

[david_e]

Yup, the IPAQ is a better bet than my Handspring - other things to buy first though)

 

[david_e]

Thanks Vyv, it is all new, previous boat had a lift keel and drew 1.8m, I touched once at LWS, but just wound it up and took care after that. Current boat draws 1.9m so need 2.0m to be comfortable. The chart indicates a depth of 0.5m at LWS, plus the channel is 0.5m below chart datum, (so that = 1.0m, have I got this right?)so the idea is to work out as accurately as possible the tolerance. Will be interested to see the Belfield curve when the disc arrives - main point is, I do not want to touch at all!! Quite a few of the sports boats get stuck regularly, not sure what they draw though.

Haven't worked/plotted the diamonds out yet but as you say the streams look straightforward. The pilot book talks about an eddy from Porth Ceiriad area that flows around Bardsey, taking you close to the headland and back the other way, 2 hours before and after HW Dover (think from memory- book is on the boat).

 

[extravert]

The harbour entrance at Pwllheli has got considerably deeper recently. Before the winter of 2001/2002 the depth on the bar was the minimum I have known, but the dredging that winter made it considerably better.

Despite what vyv_cox reported, I found that before the 2001/2002 dredging I could not get in for about an hour either side of low water at MLWS, with a draft of 1.8m. I spent quite a few cold evenings bobbing around at anchor behind the training wall waiting for the tide, along with other similarly constrained boats.

In 2001 I needed 1.0m of tide height to get over the bar. The bar is not now the position of the limiting depth. Rather now it seems to be just off Partington's boatyard, and I need 0.7m of tide to get over that. This may have changed again though with recent dredging.

I don't know what your source of depth data is for Pwllheli harbour, but if it is a standard chart, I would suggest that it is out of date because of the continuous dredging at Pwllheli. This could be the cause of your differences with your calculated and actual depth. My experience of just touching with 0.7m of tide with a 1.8m draft suggests that the minimum charted depth should now be 1.1m.

The marina at Pwllheli put a tidal curve on their noticeboard daily. Why not get a copy of that one day and go out and do a bit of your own survey. As the harbour entrance is so small it won't take long, and you will then have data that you can trust (for a year anyway).

Adventures of the <A target="_blank" HREF=http://www.xrayted.fsnet.co.uk>Teddy Bear Boat</A>

 

[david_e]

Interesting, I have thought about dropping a line at he entrance from a dinghy one day - but when it gets warmer. What sort of time frame either side of LW were you allowing in your X-boat?

 

[graham]

You dont need to wait ,this months is available as a free demo on their website(Bellfields).

Ive had a look at it and it is excellent.

You have to also realise that tidal predictions are affected by barometric pressure and wind .A full meter more or less than prediction is not uncommon.

 

[extravert]

Not that simple :-(

At MLWN I have always been able to get in and out.

At MLWS I could not get in or out 1 hour either side of LW, prior to the winter 2001/2002 dredging. Lesser tides was a lesser wait.

Since then I have had little problem, even at springs. From memory MLWS at Pwllheli is about 0.7m so the tide height is not below 0.7m very often or for long. In 2002 I made at entrance at 0.7m of tide height, but only just.

Adventures of the <A target="_blank" HREF=http://www.xrayted.fsnet.co.uk>Teddy Bear Boat</A>