28 February 2013

Tide watches - Are they reliable?

Well... yes... and no!
But before you move to another blog, allow me explain my (modest) opinion. Professionally speaking, the tide measurement standards worldwide are defined by and the responsibility of each coastal nation's hydrographic offices. In UK that's a responsibility of the United Kingdom Hydrographic Office, in the States that responsibility is shared between a civilian authority (the NOAA's Office of Coast Survey) and a naval one (the Naval Oceanographic Office) and in Portugal the competent authority on the matter is the Instituto Hidrográfico (IH), in Lisboa.
So... everywhere in the world (at least on the seaside world) the standards for tide prediction are defined by a government agency or institution. Meanwhile the UK's UKHO somehow assumed a hegemonic (no critic intended!) position in the world and has a protocol with most of the maritime nations to use their data and publish what is now considered worldwide as the most complete and extended collection of nautical publications. Their Admiralty charts and Admiralty publications (covering the entire planet) are a standard of excellence recognized by the industry and, therefore, considered equal to every nation's material.
Meaning that, if you want to navigate on the safe side and be legally protected on the eventuality of a grounding (knock on wood!) with your vessel or boat, you better stick to this tide tables and nautical charts while making your navigation calculations. Any deviation from that and you will face yourself alone in a maritime court, accepting the full liability for the damages.
But many years ago the electronic revolution took place and those winds of change also arrived to the navigation world.
The sextant was replaced by the GPS, the paper charts were replaced by the electronic plotters (ECDIS) and the computer based tide calculation programs started to appear. These were basically the current tide tables programmed in an informatics form. There is nothing against it. The only question here is the quality of the end product. It all depends of the programmer. If he has done a good job you'll have a reliable tool. On the other hand if he didn't know what he was doing or if he was using inadequate data for the programming (garbage in... garbage out!) you'll have an unpredictable tool. If your life depends on that (and at sea normally does!), it's better not to rely on it.
Having said that, where does this leaves our tide watches?
Well, to the best of my knowledge not a single one on the market today assumes that their calculation algorithms are based on the official data collected from the official institutions. Therefore not even one amongst them can be recognized as a certifiable nautical tool. If you search a little on the net, you'll see lots of posts regarding these equipments. Most of the times with people complaining about their inaccuracy, while the watchmakers sometimes claim that their programs are even more accurate than the official tide tables and that they totally rely on the competence of the hydrographic technicians that produced these informatics appliances.
So... where does this leaves us?
Well, if you want to be on the safe side, if you are navigating in unknown waters or if you have to plan a route that you know in advance that will be delicate in terms of tide prediction... stick with the paper tide tables. And use your head for the math.
This was my first tide watch, bought in Brasil about seven years ago: the Casio G-Shock G-Lide GL-150-2V, here showing its tide table window.
This is not really a true useful tide watch, since you cannot, at any moment, check the accurate height of tide and corresponding times of highs and lows. The only thing that you have is a curve showing the present (not so accurate) tendency of the tidal movement and even that is divided in two-hour intervals. It has, nevertheless, a precise calculator for sunset and sunrise time (accurate to a couple of minutes) which I use quite often in my professional life. The calculator for moonrise and moonset, together with the moon age, share the same precision. However, as a tide watch it's nearly useless.
Sadly all the tide watches from Casio (and they are a few) suffer from the same problem: an overly simplified tide function. Which is a shame. After all, in many aspects, these guys rock when we speak about digital watches.
But its design is gorgeous, isn't it?

Finally, needing a more accurate tool for my work, I ended up buying, last year, the Quiksilver Moondak. The main reason was that this watch had the port of Funchal on its data bank and, hence, the information was straight-up. Therefore, I'd be relieved of additional mental calculations from a close-by reference port. In my case it could easily be Lisboa, five hundred miles away. I think you can get the picture!.
I'd much prefer to have bought their Deep 300, a more quality piece of watchmaking. However I was not aware of their precision and wasn't prepared to spend 300 Euros in a product that could be deceptive.
On the other hand... 100 Euros for the Moondak... well... what a hell!
Conclusion? Actually, I'm quite happy with the equipment. It turned out to be much more accurate than my wildest dreams.
Want an example?

Tides for Funchal, 24, February, 2013:

From the IH website:                  Quiksilver Moondak:
00h 54m - 2.22mts (HW)          00h 51m - 2.31mts (HW)
07h 07m - 0.46mts (LW)          07h 03m - 0.51mts (LW)
13h 12m - 2.12mts (HW)          13h 10m - 2.23mts (HW)
19h 12m - 0.47mts (LW)          19h 10m - 0.51mts (LW)

 As you can see, there isn't a lot separating the official numbers from a wristwatch calculation. However, you even cannot rely on the differences and use them as standard corrections. I've found that a difference of two minutes and five centimeters today is not, necessarily, the same tomorrow. So, use the data prudently.
The Quiksilver Moondak, showing its main menu, with time, day of the week, moon phase, date and tide curve. The real gem, however, is its Tide Menu, where the most detailed tide calculations are made. A good example of what a tide watch is supposed to be. By a mere hundred bucks.