Tidal coefficient

[AntarcticPilot]

I have only used the coefficients as a quick indicator of how big/small a tide might be. In days long by, when I did my passage planning as per RYA, I think that I would have found the French approach easier.
I am a little amused by the talk about accuracy. Tidal calculations may be a little more accurate than wind prediction, but not much.

+1! The astronomical part is pretty well nailed down, but the meteorological aspects are not! And in regions with shifting shoals, the basin dynamics can change quite quickly. The prediction technique is much simpler than atmospheric modelling, but does not take atmospheric effects into account at all, and it assumes basin resonances remain constant. And as with the weather, larger scale features are modelled better than smaller scale ones.

Tidal predictions are really only accurate at places with tide gauges. Elsewhere, they are essentially linear interpolations and can affected by local geography and dynamics. It is turbulent flow in many areas, and that is notoriously intractable!

 

[RunAgroundHard]

The calculations are accurate, stuff that makes them not accurate, is also taught by the RYA.

Example. I have dried out along side Loch Aline pier, and the boat floated exactly when the arithmetic said it would. Tested by pushing against the wall.

I think the claims that they are only accurate at tidal gauges does. Not stand up to scrutiny. The Uk has been messing about with this stuff for centuries.

 

[AntarcticPilot]

The calculations are accurate, stuff that makes them not accurate, is also taught by the RYA.

Example. I have dried out along side Loch Aline pier, and the boat floated exactly when the arithmetic said it would. Tested by pushing against the wall.

I think the claims that they are only accurate at tidal gauges does. Not stand up to scrutiny. The Uk has been messing about with this stuff for centuries.

It is, however, true. The linear interpolations are good enough a lot of the time, but not invariably. I would never trust a tidal calculation to better than about half an hour or about 10% of the range.

 

[NormanS]

It's a well known fact that if you're aground and waiting on the tide coming in to float you off, it's always later than you hoped.

On another point, I always use Oban tide times for the West Coast. Most places are within half an hour, and the Tide Tables handily give a whole lot of "constants". Working with local tide times gives you a better feel for what's actually happening, than tide times from hundreds of miles away. A glance at the range of the tide gives me a pretty good understanding of what rates to expect at the places where it matters.

 

[Chiara’s slave]

We were treated today to the amusing spectacle of the RSYC race fleet, including the XOD class, overtaking us on the inside. We weren’t racing, just returning to the harbour, so kept downwind of the racers. In a southerly breeze that means further offshore. The tide turns inshore at Yarmouth about 90 mins before HW, so they had 2 knots of positive tide, we had 2 knots of negative. To any mk1 eyeball this is kind of obvious, but not on a chart. The timing is also different on springs, just to confuse.

 

[dunedin]

……….

On another point, I always use Oban tide times for the West Coast. Most places are within half an hour, and the Tide Tables handily give a whole lot of "constants". Working with local tide times gives you a better feel for what's actually happening, than tide times from hundreds of miles away. A glance at the range of the tide gives me a pretty good understanding of what rates to expect at the places where it matters.

Yes, the CCC Sailing Directions (at least the Outer Hebrides one) specifically recommends using the local standard port of Ullapool, not Dover - not just because it is more intuitive but also more accurate, as they say the difference between Dover and Ullapool can vary by up to 40 minutes.