Converting old tidal stream chart to HW Dover?

[GTom]

Just bumped into a venerable tidal stream chart on Belfast lough, referenced to HW Belfast, each chartlet named "xy hour of ebb/flow":



Am I correct, that "first hour of ebb" = HW Belfast, practically = HW Dover (only 15min difference) and "first hour of flood" = HW Dover minus 6hours?

 

[Spirit (of Glenans)]

In simple terms that would be the case, but if you take a look at the Easytide for Belfast and Dover today you will see HW fairly close together but a considerable difference in the LWs.
It's better not to generalise in the way you propose, but to reference Dover on each occasion you use it.

 

[GTom]

Indeed, noticed the big difference in LW. More confusing then, because I got 6 chartlets named xx hour of ebb, another 6 named xy hour of flow. Doesn't add up, if the flow and ebb durations are not the same.

 

[VicS]

Indeed, noticed the big difference in LW. More confusing then, because I got 6 chartlets named xx hour of ebb, another 6 named xy hour of flow. Doesn't add up, if the flow and ebb durations are not the same.

Why not reference your tidal stream charts to the times of high and low water for Belfast. It is a standard port.

Looking at just today's tide times You can see the duration of the food and ebb at Dover are significantly different whereas they are almost the same at Belfast. HW Belfast may be only a few minutes different to HW Dover but LW tims are different by best part of 2 hours. Clearly the times for LW Dover will not be any good for using your tidal stream charts .

However you could take LW as being mid-way between the times of successive HW times, but there would be no point when you could simply use the tide times for Belfast



[table="width: 120, class: outer_border, align: center"]
[tr]
[td]Dover [/td]
[td]0609 (L) [/td]
[td]1106 (H) [/td]
[td]1829 (L) [/td]
[td]2320 (H) [/td]
[/tr]
[tr]
[td]Belfast [/td]
[td]0420 (L) [/td]
[td]1035 (H) [/td]
[td]1643 (L) [/td]
[td]2259 (H) [/td]
[/tr]
[/table]

 

[lw395]

Just bumped into a venerable tidal stream chart on Belfast lough, referenced to HW Belfast, each chartlet named "xy hour of ebb/flow":

View attachment 78168

Am I correct, that "first hour of ebb" = HW Belfast, practically = HW Dover (only 15min difference) and "first hour of flood" = HW Dover minus 6hours?

If you want more than a very vague 'big picture', I'd look for some better tide charts.
Also find Admiralty charts and look at the tidal diamonds.
Both rates and directions will vary between neaps and springs. Likewise the time differences for HW and LW between Belfast and Dover probably vary between neaps and springs.

The reality will also vary according to the weather.
Some things probably change over the years too.
There are several sets of tide data available for the Solent, trying to reconcile them all is a hobby in itself, then they go and move all the mud around in Portmouth and build a breakwater or two in Cowes...

I would think the 'first hour of ebb is roughly a snapshot at HW + 0030, intended to be valid as an approximate average for HW to HW +1hr.
But there are places where the ebb starts before or after HW...

 

[Spirit (of Glenans)]

Just bumped into a venerable tidal stream chart on Belfast lough, referenced to HW Belfast, each chartlet named "xy hour of ebb/flow":

View attachment 78168

Am I correct, that "first hour of ebb" = HW Belfast, practically = HW Dover (only 15min difference) and "first hour of flood" = HW Dover minus 6hours?

If the atlas is referenced to Belfast tides why bother with Dover's tides at all?
You have access to good info on the times of Belfast's tides and you can only use it there. It's a tidal chart of a very small area, whereas the ones published by UKHO sometimes encompass areas bigger than could be referenced to a single Standard Port hence the reference to Dover.