Does this site mislead?

[vyv_cox]

Re: Tidal constants (+/- 20 minutes)

Well said. There is far too much emphasis on secondary port calculation in RYA syllabuses (or is it syllabi?) The reality is that everybody does the calculation in some way or another and then adds half a metre just in case. Those that don't can be seen stranded on rocks and sandbanks all around the coast. I've got a few photos of them myself. Anybody who thinks they can calculate even to 250 mm is deluding themselves.

 

[kimhollamby]

Proudman Labs

Having had a chance to read your post and the statement avoid (ybw) 'tidal info like the plague' I suggest you check out http://www.pol.ac.uk

Autotide and Easytide will always agree - they are based on the same data and calculations. Two rights doesn't make the Proudman data wrong.

In any event this is splitting hairs because I happen to agree with the post from NigeCh, namely that reliance on tide times to the nearest few minutes or inches will always lead to pain, sooner or later. That's no excuse for inaccuracy but then I don't believe we are publishing inaccurate data.

kim_hollamby@ipcmedia.com

 

[hlb]

Re: TIDES - IMPORTANT ANSWERS

It's the pop up page that displays the tide data for Plymouth. It's off the righthand side of the screen. I cant get at the Maximize or X butons or the scroll bar. But everything else works fine.
Thanks for the trouble.

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[incognito]

My last word (for now, anyway).

Interesting.

I checked the reference suggested.

They make a big issue of the accuracy of their predictions, which take into account up to 120 components (that is 120 harmonic components, of the form Asin(wt + a) where A is amplitude, a is phase angle).

What a farrago in order to provide tables and curves you and Mr C. dismiss so easily !

What a waste of taxpayers and academic salaries !

I am sorry, but my references suggest that tide tables ARE very accurate. The inaccuracies in the height of tide at any place and time are due to the combination of inaccuracy in chart datum and surge. Surge factors are not outside prediction, but CD shifts are more difficult.

That is why it is important to get the tidal prediction right - use them to the nearest 0.1m IMHO - so that you can then add on safety factors for the unusually dry summer, the reputed shifts in the shoals you have to pass thru. Thank goodness you CAN do this, 'cos - if we had to add on extra safety factors (VIV:you can do it to .25 if you like) for the possible inaccuracies of TTs - we could go nowhere safely except around high water.

When it comes to anchoring, the accuracy of TTs are a true Godsend, as the effects of surge and CD are taken out of the equation, and the scope can be confidently laid out after looking at your tide tables and NPxxx co-tidal charts.

 

[kimhollamby]

And to reassure you...

...I am not arguing against SH calcs. Far from it I was using such a system on an old Psion 3a to plan cruises in company years ago (it was the only way I could get info for the following year and it also helped a great deal when dealing with four or five secondary ports at once). We'd feature SH calcs here, I'm sure, was it not for the fact that we couldn't see UKHO trying to do anything other than make us pay a fortune for it, esp now they have Easytide. In fact, we got talking quite closely with one of the third party developers...until the whole copyright issue loomed large.

But the flip side is that I don't think our Proudman figures are worthy of being avoided "like a plague", especially as many of the local printed tide tablesare based upon them (which in turn must mean a lot of people use them).

All good debate and you've caused us to take a hard look at the way the info is presented, which is no bad thing at all.

kim_hollamby@ipcmedia.com