UK Tides Times

[Amulet]

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.

[obmij]

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.

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.

[dunedin]

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.

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.

[LadyInBed]

I must be one of the few who still has a copy of the UKHO DOS programme Electronic Tidal Prediction System, it still works well in a DOS Box and a damn sight faster on todays PC's compared to the Amstrad I first ran it on

[Robert Wilson]

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"

[Amulet]

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"

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.

[SAPurdie]

Do you mean the adjustment for atmospheric pressure or the amount of water running off the land into an estuary?

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...

[Robert Wilson]

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.

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?

[cpedw]

I appreciate it probably has something to do with flow dynamics, but in a confined estuary/sea loch?

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.

Derek

[LadyInBed]

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

Derek

Agreed, not easy to explain.