Crossing the Thames - some help with a new route please

[Otter]

I'm used to going from Harwich but now the boat's in Southwold I'm not nearly so sure. We leave on July 8th for Dover and HW (Dover) is 14.40 and it's just before springs. But I can't see how to avoid a lot of adverse tide, I'll need the tide from North Foreland to Dover to be favourable otherwise that part of the journey is grim. Through the water we passage plan at 5.5knots but if we need to crack on to reach a gate we can cruise in comfort at 6.5k through the water. Is there a way to do Southwold to Dover in one go without huge amounts of adverse tide?

 

[tillergirl]

I'll need the tide from North Foreland to Dover to be favourable otherwise that part of the journey is grim.

Quite! Spot on.

My instinct is it has to fight against 'some' adverse tide (but Javelin's thread a week or so back was interesting). My tables start from Deben (on the grounds that's the the northern extremity of the Estuary) but it is easy to think through the Southwold to 'Estuary' tides. I'll do some workings on the basis of 6kts but I am currently investigating a 'roof' leak following the violent rain yesterday. I'll have a think this evening.....

 

[PaulRainbow]

I cannot see how you can do Southwold to Dover in one leg without pushing some tide, shortest route i can see is about 80 nm. Looks like you'll have about 4hrs of foul tide however you do it.

On the 8th July the tide starts to turn foul at Dover at 1300 BST and again at about 0130 BST on the 9th. So if you need a favourable tide between North Foreland and Dover those are your latest times to arrive at Dover and you need to work backwards from there.

 

[Bru]

Spinning it up in PC Plotter with a route that goes via Long Sand Head, Kentish Knock and then inside the Goodwins (ware crossing the Sunk TSS system) ...

All times UTC, add 1 hr for BST

Optimum time for departure at a vessel average speed of 5.5kts is 07:00 UTC

You lose about 20 minutes to foul tide between Kentish Knock and South Brake, otherwise it's fair tide all the way with a passage time of 12:40 and an ETA off Dover of 19:40UTC

Leaving earlier you get clobbered by a longer foul tide (departing at 05:00UTC your ETA would be 18:38UTC, you lose an hour to foul tide all the way from Kentish Knock to St. Margaret's Head

A further fiddle suggests that you gain nothing by making a much earlier or later departure, taking the foul tide on the leg from Kentish Knock to South Brake is the best option for a daylight passage

Departing Southwold at 07:00UTC and upping the speed through the water to 6kts, whilst you pick up more foul tide (it's then foul from Kentish Knock to St. Margaret's) gets you into Dover an hour earlier at 18:42UTC

This is going by the "outside" route which is what I'd do.

The 6 knot table ...

Southwold > Dover
Leg to WP Latitude Longitude Bearing Distance Fuel Leg time (no tides) Leg time (incl.tides) CTS ETA (incl. Tides)
Southwold Ent 52° 18'.780N 001° 40'.540E Start 07:00 Friday, July 08, 2016
1 Southwold App 52° 18'.300N 001° 40'.900E 155.4° 0.53 0.26 05 mins 05 mins 156° 07:05 Friday, July 08, 2016
2 Long Sand Head 51° 47'.861N 001° 39'.305E 181.8° 30.45 15.23 05 hours 04 mins 04 hours 19 mins 176° 11:24 Friday, July 08, 2016
3 Kentish Knock 51° 38'.000N 001° 40'.100E 177.1° 9.87 4.94 01 hours 38 mins 01 hours 23 mins 169° 12:47 Friday, July 08, 2016
4 S Brake 51° 15'.800N 001° 26'.900E 200.3° 23.68 11.84 03 hours 56 mins 04 hours 07 mins 196° 16:55 Friday, July 08, 2016
5 St Margarets 51° 08'.600N 001° 24'.400E 192.3° 7.37 3.68 01 hours 13 mins 01 hours 22 mins 194° 18:17 Friday, July 08, 2016
6 Dover East 51° 07'.300N 001° 20'.700E 240.8° 2.66 1.33 26 mins 25 mins 247° 18:42 Friday, July 08, 2016
______ ______ _____________ _____________
Totals 74.56 37.28 12 hours 25 mins 11 hours 42 mins
Nm Litres using 6.0 knots using 6.0 knots
(Plan speed) (Plan speed)

(sorry about the formatting, the forum software isn't clever when it comes to tabular data)

Note that the departure is from the entrance to Southwold Harbour and the destination waypoint is off the East entrance to Dover

BIG NOTE! LW Southwold that morning is 06:40UTC 0.8m

Depending on draught and bravery, you may have to leave earlier or later due to depth constraints at Southwold

(If you let me know your preferred departure time, I'll spin that up and post the resulting passage table)

 

[PaulRainbow]

ETA off Dover of 19:40UTC

My ATT software gives 1940 UTC as a foul tidal stream. In fact, he'll have had the tide against him for several hours, all the way from North Forland.

 

[Bru]

My ATT software gives 1940 UTC as a foul tidal stream. In fact, he'll have had the tide against him for several hours, all the way from North Forland.

Yes, at 6kts that is correct. The tide turns foul between Kentish Knock and South Brake and doesn't turn fair again until you're knocking on the door of Dover

But the tidal stream on the outside route is not that strong and by the time you get inside the Goodwins you're on the declining side of the stream rate curve

Between Kentish Knock and South Brake you lose 11 minutes to foul tide, between South Brake and St. Margaret's you lose 9 minutes. Total loss to foul tide on the passage is just 20 minutes. On the other side of the coin, you gain everywhere else and over the whole passage you get in 43 minutes earlier than you would if there was no tidal stream at all

On that passage you've got to take a foul tide somewhere and that seems to be the best place to do it (even though I'd normally try for the foul tide early in the passage 'cos flogging a foul tide at the end of a long day is a chore)

 

[Bru]

Bit more info ...

Between South Brake and St. Margaret's on the day in question, the tide turns from foul to fair about 18:00UTC

Hence at 5.5kts rather than 6kts, by the time you get to South Brake the tide is on the turn and you gain about 3 minutes on the penultimate leg rather than losing time

The upside of that is that if you have a slower than planned passage, the tide will come to your assistance in the later stages

The kicker though is still getting out of Southwold that close to LW

 

[PaulRainbow]

All of my previous passage planning has been for motorboats, planned speed 15kts, so i'll be interested to see how my plan for this trip would compare to the seasoned sailers route. Basically, i'd leave Southwold and head straight for the Long Sand Head Two Way Route, i'm less than 20m so it's OK for me to go through there. I'd pass just east of the Drill Stone ECM and around the Goodwins to the East.

I would probably favour a midnight departure from Southwold. Plenty of water and my foul tide would be in the middle of the passage. I'd be concious that if a got delayed i'd get hit by some foul tide right at the end of the passage, but it wouldn't be too strong unless i ws very late.

How would a midnight departure look in your software Bru ?

 

[Bru]

All of my previous passage planning has been for motorboats, planned speed 15kts, so i'll be interested to see how my plan for this trip would compare to the seasoned sailers route. Basically, i'd leave Southwold and head straight for the Long Sand Head Two Way Route, i'm less than 20m so it's OK for me to go through there. I'd pass just east of the Drill Stone ECM and around the Goodwins to the East.

I would probably favour a midnight departure from Southwold. Plenty of water and my foul tide would be in the middle of the passage. I'd be concious that if a got delayed i'd get hit by some foul tide right at the end of the passage, but it wouldn't be too strong unless i ws very late.

How would a midnight departure look in your software Bru ?

Crap

Actually, it's not that much slower at 6kts - 13:08 passage time - but the tide is foul all the way from Southwold to Kentish Knock. Fair enough, you get a fair tide from then on but the only advantage is taking the foul at the start rather than towards the end of the passage and it's a slower passage, partly in the dark and with an anti-social departure time

(That's sticking with the route inside the Goodwins, I'll plot up an outside route in a minute when the kettle has boiled )

 

[PaulRainbow]

Leaving at midnight GMT, I should be getting almost 4 hours of fair tide from Southwold, starting at over 2kts and slowly decreasing.

 

[Bru]

Leaving at midnight GMT, I should be getting almost 4 hours of fair tide from Southwold, starting at over 2kts and slowly decreasing.

Off Southwold at midnight there's about 1.6kn of fair tide running parallel to the coast. By 02:00 the tide is on the turn. So you get a bit of a lift for the first couple of hours but then by 03:00 there's up to 2.0kts of foul tide and it doesn't turn fair again until you're past Long Sand Head. No way you get 4 hours of fair tide (double checked the software against the tidal stream atlas just to be on the safe side, it's not wrong!)

 

[PaulRainbow]

Off Southwold at midnight there's about 1.6kn of fair tide running parallel to the coast. By 02:00 the tide is on the turn. So you get a bit of a lift for the first couple of hours but then by 03:00 there's up to 2.0kts of foul tide and it doesn't turn fair again until you're past Long Sand Head. No way you get 4 hours of fair tide (double checked the software against the tidal stream atlas just to be on the safe side, it's not wrong!)

Don't forget i'm leaving at midnight GMT, not UT. But yes, not quiet 4 hours but you had said it would be foul all the way from Southwold

 

[Bru]

Don't forget i'm leaving at midnight GMT, not UT.

Cheat!

But yes, not quiet 4 hours but you had said it would be foul all the way from Southwold

Yes, I was less precise than I could have been. The leg from Southwold to Long Sand Head overall is negative tidal gain (what's gained in the first couple of hours is wiped out and then some by what's lost in the last three hours)

Leaving an hour earlier at 23:00UTC on the 7th improves matters by an hour making that first leg to Long Sand Head almost exactly tide neutral.

But either way the overall passage time is still longer leaving at night compared to leaving the next morning and taking the foul tide in the latter stages of the trip

 

[Otter]

Thanks all. The mention of midnight out of Southwold gave me the willies - SWMBO would veto that flat and I wouldn't be that keen myself. But not sure why, we left Gurnsey at 2am and running aground there is a bit more terminal.

Bru's 07.00 departure and 5.5knots looks good but it's a long day, we could loose a day at first to drop down to Harwich for a night, though by the time we've faffed about getting into Harwich and nicking a buoy outside Levington I wonder how much time we save? What would the departure be if we went Southwold to Ramsgate? Does it cut out the North Foreland gate?

 

[PaulRainbow]

Note my times are BST, not UT.

Going the outside route to Ramsgate is about 65nm, you can maybe shave 4 or 5 nm off of that if you go through Black Deep, but i wouldn't bother.

1330 BST is the very latest you'll want to be at Ramsgate, unless you want to push 2+ kts of tide. At 65 nm you have to allow 11 hours, minimum. I make that 0230 BST dep.

If you don't like the previous options, i'm betting you won't like a 0230 start

In which case, leave Southwold at 0900 BST, the tide will have just turned but not be moving very fast, you'll have a bit more depth to get out. You'll have a fair tide all the way to Harwich, arrival about 1500 BST. Can you not stop at Harwich for the night ? Shotley saves you half hour each way to SYH.

 

[Marmalade]

If you can drop down the evening before a stop at halfpenny pier saves the trip up the Orwell or the lock in at Shotley. Then it's c. 55m, from memory, to Dover - far more civilised.

 

[Bru]

If you can drop down the evening before a stop at halfpenny pier saves the trip up the Orwell or the lock in at Shotley. Then it's c. 55m, from memory, to Dover - far more civilised.

Ha'penny Pier is a wonderful stopover and I love it .... but only if I can get on the inside! I won't go on the outside having watched the antics of boats out there from the comfort of the inside

Whenever I plan to use the pier, I make allowance for going somewhere else if there's no space - usually Shotley in our case but having to lock in and and out may not suit when on a passage

 

[Bru]

Crunching the options for Ramsgit instead of Dover ...

Passage planning back on 5.5kts as originally specified (shorter passage should obviate the need to get the hammer down)

PCPlotter reckons the optimum departure from Southwold (harbour entrance) is 07:00UTC giving a passage time of 10:27 with the tide turning foul on the final leg down to the approach to Ramsgate.

 

[PaulRainbow]

Not wishing to appear critical or argumentative (just for a change)

It seems the main criteria with the PC Plotter suggested routes is to minimise the effects of tide on the journey time. But as the OP's said he must have fair tides from North Foreland onwards some user input would be needed because that passage leaves him with the best part of 4 hours foul tide at the end of the trip. The tide is turning at Kentish Knock.

I'm doing my planning a bit more manually by using ATT and planning backwards from the destination and the desire to arrive with a fair tide. That of course leaves the OP with departure times that he finds undesirable.

Can't please some people

 

[Bru]

To clarify, PCPlotter, if asked, will calculate the passage times at hourly departure intervals over 24 hours

It then lists the results and indicates which departure time gives the quickest passage overall

It's up to the user to decide whether to use the suggested departure time or not and if not the list gives a useful indication of how much difference it will make

Although the OP initially assumed he'd want a fair tide from North Foreland onwards (not unreasonably) when running the optimum departure time routine it becomes clear that is not the best option

If I may be so bold, starting from an assumption (in this case "we must have a fair tide from North Foreland to Dover") is not ideal, and could even be said to be poor practice, unless there is an absolute need to do so (a tidal harbour destination or a tide gate etc).

I'm on the mobile but if I remember later I'll post up the results table from the optimum departure time routine