Garmin Bluechart tide data problem

[greenalien]

Does the Garmin show double high water curves?

No - that's one of my complaints

Navionics on my phone certainly does, which makes me wonder about the validity of their claim. I used it (in conjucntion with an almanac/charts before I get flamed) taking my boat from Soton to Poole the other weekend, and the tidal stream info and tide height info all seemed pretty close to Reeds / Admiralty Tidal Atlas info.

So if they could get a license to use the data, why can't Garmin do likewise? I think it may be time to seek an answer from the Hydrographic office and am currently awaiting a response from them regarding licensing of accurate tidal data.

 

[Coronet32]

Tides on Garmin

I did notice a small error on my new Garmin 620 with Bluechart Tides but it says 17:45 0.1m today and UKHO is 17:58 0.3m.

Couldn't help finding this thread and saw early on that greenalien had his plotter set to WET [Western European Time] - I believe this is Western 'mainland' Europe which is GMT/BST +1? This might account for the larger inaccuracies experienced!?

Also, this is a new chart VEU456S and tide graphs show double high tide and young flood stand for Southampton!

 

[Amulet]

That would be nice! However, all I really want is the data on the electronic chart to be the same as in the paper almanacs. Is this really too much to ask?

Unfortunately, yes, it is too much to ask. If the UK Hydrographic office won't license the full harmonic constants no-one can do the same calculation as them and get the same answer. I assume that they are also not prepared to release annual tide tables which they calculate for brute force inclusion in software.

I do not know anything about the detail of their licensing schemes (but in keeping with forum tradition I'll spout off anyway). All of the nav packages I have seen either give tidal info very close to the alamanac for only a week ahead, or give good approximations (+- 15 mins or so, +- 0.1 metre or so) for the whole year. I suspect that this is controlled by the UKHO licensing.

I would have thought one might be able to reverse engineer the harmonic constants from the published tide tables, but someone wiser than me needs to advise on that. (Many license agreements do in any case forbid reverse engineering.)

 

[AntarcticPilot]

Unfortunately, yes, it is too much to ask. If the UK Hydrographic office won't license the full harmonic constants no-one can do the same calculation as them and get the same answer. I assume that they are also not prepared to release annual tide tables which they calculate for brute force inclusion in software.

All tide gauge data (from which tidal constants are calculated) is freely available from the British Oceanographic Data Centre. Deriving tidal constants from these is A-level maths (at least, it was 40 years ago; the curriculum may have changed!); it is simply Fourier analysis. Deriving tidal constants from the tide gauge data is a copyright activity; it passes the UK test of requiring significant effort to carry out (originality is not required in the UK). But there is nothing stopping people using the same measured values to derive their own constants.

However, constants derived by slightly different routes, or using slightly different time series will have slightly different results. I wouldn't expect all tidal predictions to get the same answer, and expecting tidal prediction to be accurate to minutes is not realistic. There are also confounding issues like the double high tide around the Solent, as well.

 

[fergie_mac66]

when you switch on the garmin do you read the notice that comes up same as all plotters it warn that info shouldn't be used for navigation also that there are errors! On top of that pressure systems vary both tide height and time. so guess you have to make allowance for errors and check and double check with the paper charts you should be running at the same time in case of failures

edit even the paper charts will show errors !

 

[sailaboutvic]

We’ll all I can say is they missed out a large Island on my charts and a reef , and only after 4 Email and loads of excuse from it a private Island to the chart is only for coastal navigation that decided I can have a new upgrade when the chart is up dated , (when??) maybe some time in 2012 I was told maybe in the mean time I should just go back to using paper charts or sail well away from land .

 

[greenalien]

Couldn't help finding this thread and saw early on that greenalien had his plotter set to WET [Western European Time]

Western European Time, also known as Greenwich Mean Time, the time zone used in the UK, Ireland, and Portugal, among other countries (from Wikipedia)

I assume that they are also not prepared to release annual tide tables which they calculate for brute force inclusion in software.

The Hydrographic office are entirely happy to supply tide table info - for a fee. However, Garmin don't appear to be interested.

this is a new chart VEU456S and tide graphs show double high tide and young flood stand for Southampton!

Now that is VERY interesting - if they can put the correct info onto new charts, how can they justify not providing the info on other ones? I'll have to ask them...

 

[Cass_IoW]

I have just had a protracted phonecall with Garmin UK with regard to this problem.
And they claim this is the first they've heard of it.
Luckily my experience of this problem did not involve a safety issue but just very annoying.
While racing in the solent I used the tide vector arrows to decide on a course to a mark way out in the main tide stream off of old Castle point. the Plotter shows a medium flood tide to the East however when we got out into the stream it was a strong Ebb to the west causing us to struggle to reach the mark and consequent loss of race position. Whilst I understand that plotters are only an aid the information they display should be accurate. especially almanac data which is readily available. a couple of years ago I changed from an old Lowrance plotter to the Garmin. The Lowrance never had this problem. Reading the posts here It seems Garmin are reluctant to sort the issue with their software people. and basically if the info is not accurate its not worth having at all in fact dangerous. The outcome of my discussions with them will decide where my next replacement comes from.

 

[richardbrennan]

The East Shambles Buoy off Weymouth has been in the wrong position for years. I have bought this to the attention of the staff on the Garmin stand at various Boat Shows, but certainly the last time I was in that part of the world, a couple of years ago, it had not been corrected.