UK Tides Times

Take a look at your various apps and how well they agree with each other. Easytide web site from UKHO does 7 days ahead agrees with Reeds, as does Admiralty "Total tide" program (at, I think about £70 a year) which can see into the future properly. I don't claim to understand the detail, but I think that many apps, even if they correctly claim to use UKHO data, don't use enough of it (harmonic constants) to be in alignment with UKHO calculations. I have seen HW time differences of up to about 40 mins and heights differences of up to 20cm between apps. Now, it's all an inexact science, and I wouldn't cut things so close that I was into the 20 cm risk area. I use Navionics tides a lot, but they don't agree with the almanac. I now await correction from someone more knowledgeable than me.
 
Amulet said:
Take a look at your various apps and how well they agree with each other. Easytide web site from UKHO does 7 days ahead agrees with Reeds, as does Admiralty "Total tide" program (at, I think about £70 a year) which can see into the future properly. I don't claim to understand the detail, but I think that many apps, even if they correctly claim to use UKHO data, don't use enough of it (harmonic constants) to be in alignment with UKHO calculations. I have seen HW time differences of up to about 40 mins and heights differences of up to 20cm between apps. Now, it's all an inexact science, and I wouldn't cut things so close that I was into the 20 cm risk area. I use Navionics tides a lot, but they don't agree with the almanac. I now await correction from someone more knowledgeable than me.
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ATT are UKHO who are the standard, at least here (and for many others too) and as you rightly point out they also pop up in the guise of easytide.

Some apps use Reeds with varying degrees of success - I'm not sure if they manually input the data and then just apply the SP offests but in any event they are not always accurate (but neither is Reeds - there is usually a small difference between Reeds and UKHO)

Reeds and the apps that derive data from her can be upto 1m out on a secondary port on a big spring.

Tide7 appears to take all it's information from Easytide (probably why it is 7 days only) I have had tide7 for years and trust it..

..that is insofar as I trust any tidal predictions.
 
Amulet said:
Take a look at your various apps and how well they agree with each other. Easytide web site from UKHO does 7 days ahead agrees with Reeds, as does Admiralty "Total tide" program (at, I think about £70 a year) which can see into the future properly. I don't claim to understand the detail, but I think that many apps, even if they correctly claim to use UKHO data, don't use enough of it (harmonic constants) to be in alignment with UKHO calculations. I have seen HW time differences of up to about 40 mins and heights differences of up to 20cm between apps. Now, it's all an inexact science, and I wouldn't cut things so close that I was into the 20 cm risk area. I use Navionics tides a lot, but they don't agree with the almanac. I now await correction from someone more knowledgeable than me.
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For those who actually read our sponsors magazine, Yachting Monthly had an excellent article on tide apps, including comparison of tide predictions with the official UKHO ones. Worth a look.
Absolute Tides states that it uses UKHO data, and U.K. Tides app seems to align precisely. Navionics predictions differ.
 
On Tuesday 29th October I took Khamsin round to Ullapool for winter haul-out. It was a beautiful, totally windless day.

My tide app indicated low tide at Ullapool was 13:45. As I passed the final navigation buoy off the harbour at exactly 13:45 it was plainly obvious that the ebb tide was still running very quickly; which explained why my previous four miles had taken noticeably longer than I had calculated it would. :(

I would have accepted a few minutes discrepancy, but this was a big one.

An error of that magnitude would be very significant had I been navigating round Greenstone Point with a strong "wind against" :eek-new:
 
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Robert Wilson said:
On Tuesday 29th October I took Khamsin round to Ullapool for winter haul-out. It was a beautiful, totally windless day.

My tide app indicated low tide at Ullapool was 13:45. As I passed the final navigation buoy off the harbour at exactly 13:45 it was plainly obvious that the ebb tide was still running very quickly; which explained why my previous four miles had taken noticeably longer than I had calculated it would. :(

I would have accepted a few minutes discrepancy, but this was a big one.

An error of that magnitude would be very significant had I been navigating round Greenstone Point with a strong "wind against" :eek-new:
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It may not explain your error, but tidal height and tidal flow don't necessarily have a simple relationship. You cannot assume that looking at the time of high water will tell you when the tidal flow will change. The tidal wave coming down Loch Broom could still have been raising the level at Ullapool. Instances of this abound, even if this is not one of them.
 
Sandy said:
Do you mean the adjustment for atmospheric pressure or the amount of water running off the land into an estuary?
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Both really, but we just had a series of tides which were about 20cm higher than predicted by UKHO website due to the effects of a nearby storm. It was not especially rainy here at the time as I recall. (The photo show the weakness in my memory.)
2019-09-29 12.06.21.jpg

We had another close call yesterday too...
 
Amulet said:
It may not explain your error, but tidal height and tidal flow don't necessarily have a simple relationship. You cannot assume that looking at the time of high water will tell you when the tidal flow will change. The tidal wave coming down Loch Broom could still have been raising the level at Ullapool. Instances of this abound, even if this is not one of them.
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Thank you for that info. It's something that has always puzzled me about low/high water at pointA and the flood/ebb flow at Point B.
If the low water time at e.g. Ullapool was given at 13:45 surely water has stopped ebbing/flowing out from further up the loch and past the given location (Pier, buoy, headland or wherever)/

I appreciate it probably has something to do with flow dynamics, but in a confined estuary/sea loch? :confused:
 
Robert Wilson said:
I appreciate it probably has something to do with flow dynamics, but in a confined estuary/sea loch? :confused:
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That's just the sort of place where this can occur. As a more pronounced example, look at the Falls of Lora at the entrance to Loch Etive. The Falls is (are?) narrow and mostly quite shallow, leading into 20+ miles of Loch Etive, generally much deeper and wider than the Falls. The flow at the Falls changes direction about 2 hours later than local high/low water.
I'm not sure but I think the topology around Ullapool and Loch Broom is similar if on a smaller scale.
Because of the constriction of the flow at the Falls, as the level outside the loch moves up or down tidally, water tries to get in or out of the loch in sync but the rate is restricted so, as high tide is reached, the level in the loch is below the outside sea level so, even as the tide falls, the level outside is still higher than the loch level for some time so the flow continues in until the level in the loch matches the sea level outside.

I thought that would be a simple explanation but now I'm not sure. :ambivalence:

Derek
 
cpedw said:
That's just the sort of place where this can occur. As a more pronounced example, look at the Falls of Lora at the entrance to Loch Etive. The Falls is (are?) narrow and mostly quite shallow, leading into 20+ miles of Loch Etive, generally much deeper and wider than the Falls. The flow at the Falls changes direction about 2 hours later than local high/low water.
I'm not sure but I think the topology around Ullapool and Loch Broom is similar if on a smaller scale.
Because of the constriction of the flow at the Falls, as the level outside the loch moves up or down tidally, water tries to get in or out of the loch in sync but the rate is restricted so, as high tide is reached, the level in the loch is below the outside sea level so, even as the tide falls, the level outside is still higher than the loch level for some time so the flow continues in until the level in the loch matches the sea level outside.

I thought that would be a simple explanation but now I'm not sure. :ambivalence:

Derek
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A good example of "flow after high/low tide point", thank you.

I suppose that the huge difference between the flow I experienced past the Buckle Point buoy at the time of dead tide and the scary flow at the Falls of Lora is indeed due to the almost incomparable difference in topography.

Loch Broom inland of the buoy is about 5nm long with depths up to 50 metres and the "narrow" point at the buoy is about 0.6nm wide with c.20.5m depth.

Loch Etive is about 15nm long with depths up to 145m; the Falls are about 0.01nm wide with depths around +1.7m to -6m

Even my schoolboy maths explains that that would lead to a gigantic difference in performance !!
(all depths at low tide, taken from Navionics)

:encouragement:
 
Going back to the original premise: How to work out what the tides will be some weeks or months in advance, given that the free online sites usually only forecast 7 days ahead; can I offer what follows? If anyone thinks I’m miles off, then I’d welcome corrections:

Step 1. Look ahead to the period that you are interested in, call it ‘Date X’. Find the moon phase on Date X - online sites do provide that sort of information many moons (boom boom) in advance. If your chosen date doesn’t fall exactly on full, new, half waxing or half waning, then applicate a number of days before or after one of those obvious moon phases.

Step 2. Using the same moon phase site, look around your current date (minus 22.5 / plus 7 days) and find the date that has the same moon phase (or number of days before or after) as Date X; call this ‘Date Y’.

Step 3. Go to your free online tide site and look at Date Y (note that although most free online sites only look forward 7 days, they do seem to go back about a month or so, though I’ve not looked into this depth). The tide times on Date Y will be very close to the tidal times on Date X. The tidal heights might be off because of the periodic variations in earth-lunar distance and earth-sun distance, but if it was (say) 3 days after Springs on Date Y, it will also be 3 days after Springs on Date X.

Alternatively, go to your desired Date X in your diary and count backwards in 29.5 day chunks. When you get to a date that’s close to you (minus 22.5 / plus 7 days) note that as Date Y, click into your free online tide site on Date Y and you have the same result (and same caveats) as above. For obvious reasons this is much easier if you’re only forecasting a month or two in advance.

Sorry about the noddy step-by-step description, but I couldn't find an eloquent piece of prose to describe how I do it! Shout me down if you think I’m wrong, but it’s a system that works for me. I’ve never taken the time to cross check against an Almanac at the planning stage, but I’ve also never pitched up and found the tides doing anything horribly unexpected…
 
Steveberry said:
Going back to the original premise: How to work out what the tides will be some weeks or months in advance, given that the free online sites usually only forecast 7 days ahead; can I offer what follows? If anyone thinks I’m miles off, then I’d welcome corrections:

Step 1. Look ahead to the period that you are interested in, call it ‘Date X’. Find the moon phase on Date X - online sites do provide that sort of information many moons (boom boom) in advance. If your chosen date doesn’t fall exactly on full, new, half waxing or half waning, then applicate a number of days before or after one of those obvious moon phases.

Step 2. Using the same moon phase site, look around your current date (minus 22.5 / plus 7 days) and find the date that has the same moon phase (or number of days before or after) as Date X; call this ‘Date Y’.

Step 3. Go to your free online tide site and look at Date Y (note that although most free online sites only look forward 7 days, they do seem to go back about a month or so, though I’ve not looked into this depth). The tide times on Date Y will be very close to the tidal times on Date X. The tidal heights might be off because of the periodic variations in earth-lunar distance and earth-sun distance, but if it was (say) 3 days after Springs on Date Y, it will also be 3 days after Springs on Date X.

Alternatively, go to your desired Date X in your diary and count backwards in 29.5 day chunks. When you get to a date that’s close to you (minus 22.5 / plus 7 days) note that as Date Y, click into your free online tide site on Date Y and you have the same result (and same caveats) as above. For obvious reasons this is much easier if you’re only forecasting a month or two in advance.

Sorry about the noddy step-by-step description, but I couldn't find an eloquent piece of prose to describe how I do it! Shout me down if you think I’m wrong, but it’s a system that works for me. I’ve never taken the time to cross check against an Almanac at the planning stage, but I’ve also never pitched up and found the tides doing anything horribly unexpected…
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If you want to know 'near enough' for vague planning purposes, springs are 2 days after a full moon etc, and Springs are at noon and slinging-out time in Portsmouth, breakfast and tea time in Plymouth.
It's not hard to get the big picture.

If you need to publish a schedule of races, with local HW times for all of next year, it's harder to get good data that won't result in someone whingeing you've published HW Boghampton-on-Sea 12 minutes out.

Decide what you need, then if necessary, pay for it and be happy.
 
Drift:
Tides a mystery for one Greek chap. He is the goto fellow at Port Heli (daughter was babysitting Patna there this summer), as a much younger man he came to the UK and was in Plymouth, (at the Marine School I think). He told her he spent many days visiting the quay and taking measurements to try to get a handle on the tides....until someone introduced him to a tide table.
 
Steveberry said:
Going back to the original premise: How to work out what the tides will be some weeks or months in advance, given that the free online sites usually only forecast 7 days ahead; can I offer what follows? If anyone thinks I’m miles off, then I’d welcome corrections:

Step 1. Look ahead to the period that you are interested in, call it ‘Date X’. Find the moon phase on Date X - online sites do provide that sort of information many moons (boom boom) in advance. If your chosen date doesn’t fall exactly on full, new, half waxing or half waning, then applicate a number of days before or after one of those obvious moon phases.

Step 2. Using the same moon phase site, look around your current date (minus 22.5 / plus 7 days) and find the date that has the same moon phase (or number of days before or after) as Date X; call this ‘Date Y’.

Step 3. Go to your free online tide site and look at Date Y (note that although most free online sites only look forward 7 days, they do seem to go back about a month or so, though I’ve not looked into this depth). The tide times on Date Y will be very close to the tidal times on Date X. The tidal heights might be off because of the periodic variations in earth-lunar distance and earth-sun distance, but if it was (say) 3 days after Springs on Date Y, it will also be 3 days after Springs on Date X.

Alternatively, go to your desired Date X in your diary and count backwards in 29.5 day chunks. When you get to a date that’s close to you (minus 22.5 / plus 7 days) note that as Date Y, click into your free online tide site on Date Y and you have the same result (and same caveats) as above. For obvious reasons this is much easier if you’re only forecasting a month or two in advance.

Sorry about the noddy step-by-step description, but I couldn't find an eloquent piece of prose to describe how I do it! Shout me down if you think I’m wrong, but it’s a system that works for me. I’ve never taken the time to cross check against an Almanac at the planning stage, but I’ve also never pitched up and found the tides doing anything horribly unexpected…
Click to expand...

The older generation of Admiralty Charts used to give the time of "HW F&C" for major ports on each chart. That was the time of HW at the Full moon and New Moon, which is pretty constant. Moon phases can be predicted well into the future, and navigators would know. Reasonably accurate tide times can be estimated by interpolation.
 
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