Some help with tide please!

Rivers & creeks

Rivers & creeks

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We're working our way back from the annual holiday cruise, we arrive Dover tomorrow (Friday 21st) and then we go in one hit from Dover to Harwich via Foulgers. In the past I've basically managed to do this with favourable tide all the way, mainly by not hurrying it. I'm studying the tidal atlas and I can't seem to make it work, I know that whatever I do I need favourable tide all the way from Dover to North Foreland, otherwise it gets silly. But then I seem to end up with adverse tides for about half the way.

Can anyone work out a departure time for me from Dover Saturday morning? Our speed through the water is best averaged at 4.5knots if I'm being a.honest and b.sailing rather than motoring. Thanks!
 
Spun it up in PC Plotter ...

Optimum passage evaluation gives ...

Dover > Harwich
Best Time Elapsed time Arrival time
**** 0:00 14 hours 09 mins 14:09 Saturday, August 22, 2015
1:00 14 hours 19 mins 15:19 Saturday, August 22, 2015
2:00 15 hours 07 mins 17:07 Saturday, August 22, 2015
3:00 15 hours 24 mins 18:24 Saturday, August 22, 2015
4:00 15 hours 30 mins 19:30 Saturday, August 22, 2015
5:00 14 hours 49 mins 19:49 Saturday, August 22, 2015
6:00 14 hours 59 mins 20:59 Saturday, August 22, 2015
7:00 14 hours 57 mins 21:57 Saturday, August 22, 2015
8:00 15 hours 10 mins 23:10 Saturday, August 22, 2015
9:00 14 hours 51 mins 23:51 Saturday, August 22, 2015
10:00 14 hours 38 mins 00:38 Sunday, August 23, 2015
11:00 14 hours 27 mins 01:27 Sunday, August 23, 2015
12:00 14 hours 18 mins 02:18 Sunday, August 23, 2015
13:00 14 hours 12 mins 03:12 Sunday, August 23, 2015
14:00 14 hours 50 mins 04:50 Sunday, August 23, 2015
15:00 15 hours 19 mins 06:19 Sunday, August 23, 2015
16:00 15 hours 20 mins 07:20 Sunday, August 23, 2015
17:00 15 hours 18 mins 08:18 Sunday, August 23, 2015
18:00 14 hours 58 mins 08:58 Sunday, August 23, 2015
19:00 14 hours 59 mins 09:59 Sunday, August 23, 2015
20:00 14 hours 59 mins 10:59 Sunday, August 23, 2015
21:00 14 hours 59 mins 11:59 Sunday, August 23, 2015
22:00 14 hours 41 mins 12:41 Sunday, August 23, 2015
23:00 14 hours 31 mins 13:31 Sunday, August 23, 2015


(All times UTC, +1h for BST)

which unfortunately suggests the best time to depart is either 01:00UTC or 13:00UTC!

(Note that the software, annoyingly, only calculates optimum times on whole numbers speed wise. 4.5kts becomes 4 knots. However experience suggests that the optimum time doesn't vary much and in the overall scheme of things the variance is not significant)

However, an 05:00UTC departure results in a passage time just 40mins longer than the optimum and that's what I'd go for ...

Dover > Harwich
Leg to WP Latitude Longitude Bearing Distance Fuel Leg time (no tides) Leg time (incl.tides) CTS ETA (incl. Tides)
Dover East 51° 07'.300N 001° 20'.700E Start 05:00 Saturday, August 22, 2015
1 St Margarets 51° 08'.600N 001° 24'.400E 60.8° 2.66 0.71 35 mins 24 mins 60° 05:24 Saturday, August 22, 2015
2 S Brake 51° 15'.800N 001° 26'.900E 12.3° 7.37 1.96 01 hours 38 mins 01 hours 18 mins 11° 06:43 Saturday, August 22, 2015
3 N Foreland 51° 22'.800N 001° 27'.800E 4.6° 7.02 1.87 01 hours 33 mins 01 hours 28 mins 1° 08:11 Saturday, August 22, 2015
4 Fisherman 1 51° 34'.600N 001° 23'.600E 347.5° 12.09 3.22 02 hours 41 mins 02 hours 58 mins 342° 11:10 Saturday, August 22, 2015
5 Black Deep 8 51° 36'.363N 001° 20'.583E 313.2° 2.57 0.69 34 mins 36 mins 320° 11:46 Saturday, August 22, 2015
6 Sunk Head Tower 51° 46'.664N 001° 30'.569E 31.0° 12.02 3.20 02 hours 40 mins 03 hours 37 mins 30° 15:24 Saturday, August 22, 2015
7 Cork Sand Beacon 51° 55'.284N 001° 25'.248E 339.1° 9.23 2.46 02 hours 03 mins 01 hours 59 mins 342° 17:23 Saturday, August 22, 2015
8 Landguard 51° 55'.374N 001° 18'.804E 271.3° 3.98 1.06 53 mins 01 hours 02 mins 269° 18:25 Saturday, August 22, 2015
9 Harwich Shelf 51° 56'.877N 001° 18'.213E 346.4° 1.55 0.41 20 mins 24 mins 341° 18:50 Saturday, August 22, 2015
______ ______ _____________ _____________
Totals 58.48 15.59 12 hours 59 mins 13 hours 50 mins
Nm Litres using 4.5 knots using 4.5 knots
(Plan speed) (Plan speed)


(Sorry about the formatting but the forum doesn't recognise tab characters)

So that's leave at six in the morning (local time) and get in to Harwich well before the bar shuts about eight in the evening (local time again)

HTH
 
Thanks Erbas, six o'clock it is. Did you have a computer programme to do all that? I'm interested in the average speed, although 4.5k through the water we'd get help from the mainly favourable tide. Does that radically alter things?
 
Colvic Watson said:
Thanks Erbas, six o'clock it is. Did you have a computer programme to do all that? I'm interested in the average speed, although 4.5k through the water we'd get help from the mainly favourable tide. Does that radically alter things?
Click to expand...

The software I use is called PC Plotter (chosen because it works with the same Navionics charts as our Raymarine chart plotter).

It works off your chosen average speed (but only in whole numbers for optimal passage plan calcs as earlier mentioned) and then extrapolates the tidal stream data from the same tidal stream points as you'll find on an Admiralty chart. It seems to work quite well!

The programme is a bit clunky in places, although much improved with the latest version upgrade

The lack of column spacing makes it a bit hard to read the passage plan properly but if you look carefully you'll see that the passage time per leg without tidal influences is stated first and then the time for the leg taking into account the tide. The ETA is calculated with the tidal influence

Or to put it another way, the radical alterations have already been done :)
 
I hesitate to comment and it is not in the spirit of this Forum to disagree with another Forumite who is helping a colleague (if Erbas will forgive me) - and you all know my ignorance of things comfuter - and I know that it is very silly to suggest that a table written on paper is more accurate than a computer programme but a 6am start is surely squandering the best tide from Dover to North Foreland on Saturday morning. It's ok but its not the best. I have to dive in the shower now preparatory to going out to a dinner party so I literally don't have the time to look through my tables but I would suggest that the journey should only take you 12 hrs at 4kts (that's from a very quick look and I might resile from that if I do a proper work up) and that there is a shorter route - Foulger's, cross the Sunk Sand, diagonal across the Swin to Goldmer Gat and straight into Harwich. This is all very hasty so I might need to apologise but I do think there is a better start time.
 
Disagree away! If there's a better plan I want to know about it :)

I have manually worked up the tides a dozen or more times and haven't beaten the software yet though

OK, I've plotted the suggested route. It is shorter. Less than 2 miles shorter but it's shorter :)

On Saturday morning the tide turns favourable off Dover at about 02:00UTC - an 02:00UTC departure gets you to Harwich Shelf at 14:29UTC with a passage time of 12:29

You get a fair tide all the way to Fishermans but a variable amount of foul tide from there to Landguard

Departing 3 hours later at 05:00UTC gets you to Harwich Shelf at 17:48UTC with a passage time of 12:48

You still carry a fair tide most of the way to Fishermans, it turns in the last hour or so and after that it doesn't make a drastic difference compared to the earlier departure

Plus, if you fall behind on the passage plan the tide turns in your favour on the run in the Harwich and stays that way for several hours

I did say that 05:00UTC wasn't the optimum time to depart but the price paid is less than half an hour for a considerably more civilised departure time

Pick it to pieces, please! Genuinely, I'm not claiming to be the worlds leading expert on nav and always willing to learn from others :)
 
sailorman said:
what happens if one goes outside the Kentish Knock & LSH, rather than fiddle about inside
Click to expand...

That's my preferred route, much easier than all that nasty swatchway stuff! I usually leave Dover 2 hrs before HW Dover, which is also convenient for getting out of Granville Dock.
 
OK, going outside the Kentish Knock is 2 miles further (and you could probably shave a bit as I've gone via Long Sand Head 'cos I like a mark to aim for)

Sticking to my 05:00UTC departure the ETA at Harwich Shelf is 18:44UTC with a passage time of 13:44

The optimum departure time remains the same at 02:00UTC with a passage time of 12:08

Interestingly, the tidal influence is much more noticeable going the outside route where you lose over an hour and a half if you leave later compared to losing less than half an hour if you dice with death through the gats
 
Ought to mention that without thinking about it I plotted the route via Fishermans not Foulgers - wild horses wouldn't drag me in amongst that lot! Don't think it'll make much difference to the original route and the Tiller Girl route uses the SW Sunk anyway (the Middle Sunk being, IIRC, a bit iffy at the mo)
 
Erbas said:
OK, going outside the Kentish Knock is 2 miles further (and you could probably shave a bit as I've gone via Long Sand Head 'cos I like a mark to aim for)

Sticking to my 05:00UTC departure the ETA at Harwich Shelf is 18:44UTC with a passage time of 13:44

The optimum departure time remains the same at 02:00UTC with a passage time of 12:08

Interestingly, the tidal influence is much more noticeable going the outside route where you lose over an hour and a half if you leave later compared to losing less than half an hour if you dice with death through the gats
Click to expand...
where did you go after LSH, Cork Bn or S Cork
 
Foulgers is more shortist plus reasons earlier. I'm dead grateful for the advice Erbas, looks like 5am it is. When TG has finished his shower - and put a towel on for heaven's sake this isn't the lounge - we'll get the pen and paper vs computer bake off. Frankly I was surprised I could leave it until 5am so we'll see...
 
Colvic Watson said:
Foulgers is more shortist plus reasons earlier. I'm dead grateful for the advice Erbas, looks like 5am it is. When TG has finished his shower - and put a towel on for heaven's sake this isn't the lounge - we'll get the pen and paper vs computer bake off. Frankly I was surprised I could leave it until 5am so we'll see...
Click to expand...

Okayyy, last one for an hour or so! ...

Via Foulgers and clearing to the South of S. Cork to save a bit of mileage (but watch your depth around S. Cork) ...

Dover > Harwich
Leg to WP Latitude Longitude Bearing Distance Fuel Leg time (no tides) Leg time (incl.tides) CTS ETA (incl. Tides)
Dover East 51° 07'.300N 001° 20'.700E Start 05:00 Saturday, August 22, 2015
1 St Margarets 51° 08'.600N 001° 24'.400E 60.8° 2.66 0.71 35 mins 24 mins 60° 05:24 Saturday, August 22, 2015
2 S Brake 51° 15'.800N 001° 26'.900E 12.3° 7.37 1.96 01 hours 38 mins 01 hours 18 mins 11° 06:43 Saturday, August 22, 2015
3 N Foreland 51° 22'.800N 001° 27'.800E 4.6° 7.02 1.87 01 hours 33 mins 01 hours 28 mins 1° 08:11 Saturday, August 22, 2015
4 Long Sand Outer 51° 34'.588N 001° 28'.362E 1.7° 11.79 3.14 02 hours 37 mins 02 hours 51 mins 355° 11:03 Saturday, August 22, 2015
5 Long Sand Middle 51° 35'.559N 001° 26'.343E 307.7° 1.59 0.42 21 mins 22 mins 322° 11:25 Saturday, August 22, 2015
6 Long Sand Inner 51° 38'.783N 001° 25'.337E 349.0° 3.28 0.88 43 mins 55 mins 350° 12:20 Saturday, August 22, 2015
7 Sunk Head Tower 51° 46'.355N 001° 30'.218E 21.8° 8.15 2.17 01 hours 48 mins 02 hours 41 mins 24° 15:01 Saturday, August 22, 2015
8 Clr S. Cork 51° 51'.289N 001° 23'.248E 318.9° 6.55 1.75 01 hours 27 mins 01 hours 21 mins 326° 16:23 Saturday, August 22, 2015
9 Landguard 51° 55'.374N 001° 18'.804E 326.1° 4.92 1.31 01 hours 05 mins 01 hours 02 mins 321° 17:25 Saturday, August 22, 2015
10 Harwich Shelf 51° 56'.877N 001° 18'.213E 346.4° 1.55 0.41 20 mins 23 mins 341° 17:49 Saturday, August 22, 2015
______ ______ _____________ _____________
Totals 54.89 14.64 12 hours 11 mins 12 hours 49 mins
Nm Litres using 4.5 knots using 4.5 knots
(Plan speed) (Plan speed)

Saves you an hour on the passage (somewhat to my surprise I will admit)

And if you leave at 02:00UTC it's 11:17 to Harwich which is a bigger difference (and that may be a realistic reflection of the tidal streams or an artefact of the software extrapolation - but then its only doing what we do by experience and guesswork)

You pays yer money :)
 
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