Laying off for the tide - eg on a channel crossing

[smallplasticboat]

Does anyone ALREADY have a little Excel spreadsheet to take the grunt work (while feeling green) out of the mid-channel course adjustments enroute to France (or back)?

I normally assume when setting out (contingent of course on boat speed etc) that the cross tides will probably more or less "net out" and that I want to head a little uptide of my destination.

I have painstakingly created a little table of the hourly tidal streams (thank you Admiralty Tidal Stream Atlas - NP250 The English Channel) relevant to my upcoming crossing from the Solent to Cherbourg, and I wanted to wrap a little Excel thing around it, into which - before departure - I would key in a relevant Dover HW time (and height - so it could figure the rough tidal coefficient or springs/ neaps position).

And then in mid-trip - when I wanted to make a course correction - I could grab my phone, launch excel, tap in the current time, an estimate of the average upcoming SOG, and the distance and bearing to (eg) Cherbourg - with the idea that excel would then generate a course to steer (CTS) to compensate for the tides. Just like we do by hand, only less illness (and error) -prone.

I have been planning for a while to write such a sheet, but not quite reached the point at which I have found a compelling solution.

I ask with some hesitation both as I know I would enjoy doing it myself (if I had had enough time), and I am sure I will come in from some flak for such a heinous idea. By the way, I am aware that there are commercial solutions – but I’m a tight so-and-so!

Thanks for reading!

 

[Spirit (of Glenans)]

It would probably just be an awful lot easier to just work it out the traditional way. Less taxing on the grey matter.

 

[smallplasticboat]

Thanks for your insight, Spirit. Perhaps I should not have bothered to post the question then!

I feel that a little pre-trip investment can yield y helpful results by

Still ... if there's anyone with excel skills who (like me) thinks this is actually an easy matter but (unlike me) has/has had the time and interest to think about this ... I would love to hear from you.

 

[Daverw]

I would expect that many errors would creep in using excel, the tides are not exact and excel will expect them to be, normal navigation methods build this in easily which excel would not. I would just enjoy the sail , plan as normally using many of the guides and deal with what I was faced with on the other side

 

[Rhylsailer99]

there is an unusually high set of spring tides mid July to watch out for.

 

[stuartwineberg]

Well worth investing in Neptune passage planner. Have a look at Neptune-navigation.com. Been a user for years and wouldn’t be without it. No connection at all just a satisfied customer. All you do is point and click to set your route, tell it your travel date and it tells you optimal time to depart and course to steer for each leg. Also shows you your predicted actual water track.

 

[DipperToo]

Well worth investing in Neptune passage planner. Have a look at Neptune-navigation.com. Been a user for years and wouldn’t be without it. No connection at all just a satisfied customer. All you do is point and click to set your route, tell it your travel date and it tells you optimal time to depart and course to steer for each leg. Also shows you your predicted actual water track.

I also use Neptune Planner (for Android) - very useful tool indeed.

 

[Daydream believer]

Over the years, travelling from the Thames estuary to places like Camaret, Holland or even round Uk I have found that the number of actual cross tide trips are minimal.
Bradwell Idmuiden or Ostend. Dover Boulogne, IOW to Cherbourg. CIs( hardest area to predict) to Roscoff etc. Across the Irish Sea. All the rest are either with or against the tide, Typically along the French coast to so XTE is a bit academic. Once one has done them once the old logs will have the details if saved. The shorter ones are so simple that any calculations can be done in one's head. In most cases within sight of land.
It is easy to over think these things

 

[tillergirl]

All my tables are based on such an Excel table which is easy to create. But it works in the Thames Estsuary because the channels, sands and obstructions mean that you cannot use a single course for the whole passage. What you are missing is when using the multi-correction technique for an example of a cross Channel passage you will be slower, sailing more! Such a passage needs the single correction technique (aka known above as the Traditional method. Simpler, shorter, quicker. Get a copy of Reeve-Fowkes.

 

[[70521]]

Thanks for your insight, Spirit. Perhaps I should not have bothered to post the question then!

I understand that you are resistant to suggestions that doing it on a sheet of paper is abhorrent, but it really is easier.

I have written spreadsheets that you could run a small nation by and can honestly say the easiest way it to draw a line on the the tide atlas and collect the data then add it up in your head - you will need that for your spreadsheet.

Unless you are crossing a TSS then it really is a matter of pointing at a point 5 nm uptide at the ETA and setting off. I am the member of the school of approximated navigation on long passages. Head in that direction until you have drunk enough tea or have a landfall, politage is another matter.

 

[laika]

I understand that you are resistant to suggestions that doing it on a sheet of paper is abhorrent, but it really is easier.

I'll agree with that although I understand that folks are doing that thing where a poster says "I want to do X, has anyone done it before?" and everyone piles in with "don't do X do Y" (which the OP already knows how to do but is asking about X).

For this task you'd need at minimum the set of raw tidal data points which you'd need to interpolate between to get a drift for each 1/Nth of an hour estimating new position as you go with inputs of position, coefficient and estimated leeway. And then there's a lifetime of tweaking and optimising. Personally if I were to do it I wouldn't do it as a spereadsheet but that's simply because my excel-fu is not that strong. I would suggest that Sandy, Spirit (of Glenans) and others are right in saying that it's more work than doing it by hand for a couple of decades worth of cross-channel jaunts but hey, there are lunatics out there that spend hundreds of hours on open source software so no harm in asking if it's been done

.

 

[Mudisox]

Often going across the Channel further down, I find that the greatest problem is predicting speed and hence where you will be near the end of the crossing.
Especially Dartmouth/Salcombe to Lezardrieux/Paimpol. Yes,one can turn the key to maintain predicted progress, but 100 miles at 5 or 7 knots makes a wide difference.

 

[Chiara’s slave]

Often going across the Channel further down, I find that the greatest problem is predicting speed and hence where you will be near the end of the crossing.
Especially Dartmouth/Salcombe to Lezardrieux/Paimpol. Yes,one can turn the key to maintain predicted progress, but 100 miles at 5 or 7 knots makes a wide difference.

Ansolutely. Our speed differemtial in different conditions is much wider than most. Nav of this sort ends up being seat of the pants, the wind almost never does what the forecast when yoi’re planning says it will. I suppose a spreadsheet could constantly recalculate, and update our heading, but its going to need to be pretty smart to tell me when to gybe for a lee bow, and when to gybe back to arrive at the up tide destination. Besides, it’s all part of the fun.

 

[Tranona]

Over the years, travelling from the Thames estuary to places like Camaret, Holland or even round Uk I have found that the number of actual cross tide trips are minimal.
Bradwell Idmuiden or Ostend. Dover Boulogne, IOW to Cherbourg. CIs( hardest area to predict) to Roscoff etc. Across the Irish Sea. All the rest are either with or against the tide, Typically along the French coast to so XTE is a bit academic. Once one has done them once the old logs will have the details if saved. The shorter ones are so simple that any calculations can be done in one's head. In most cases within sight of land.
It is easy to over think these things

But if you are south coast based, particularly west of the Solent and your cruising grounds are France cross tide passages dominate your start and finish. Accuracy is important because of narrow window you are aiming for - Cherbourg, Alderney for example and the penalty for getting it wrong severe. The issue the OP raises is important - the re-assessment of CTS when you are roughly halfway across when you get into the stronger tidal streams is critical to ensure you are in good shape for an up tide landfall. In the past the key piece of information was knowing your position (remember the shaky RDF routines) rather than calculating the offsets. Now that accurate position is taken for granted a little bit of mental arithmetic is a good challenge.

 

[[70521]]

I'll agree with that although I understand that folks are doing that thing where a poster says "I want to do X, has anyone done it before?" and everyone piles in with "don't do X do Y" (which the OP already knows how to do but is asking about X).

True, but this is an Internet forum and as we all know a) the question asked is rarely answered and b) thread drift usually happens within 10 postings.

For this task you'd need at minimum the set of raw tidal data points which you'd need to interpolate between to get a drift for each 1/Nth of an hour estimating new position as you go with inputs of position, coefficient and estimated leeway. And then there's a lifetime of tweaking and optimising.

Ideal if you like the idea of sailing, but prefer to tweak data and applications or varnish for months.

I wonder if the spreadsheets account for air pressure and the amount of water moving in the tide?

Personally if I were to do it I wouldn't do it as a spereadsheet but that's simply because my excel-fu is not that strong. I would suggest that Sandy, Spirit (of Glenans) and others are right in saying that it's more work than doing it by hand for a couple of decades worth of cross-channel jaunts but hey, there are lunatics out there that spend hundreds of hours on open source software so no harm in asking if it's been done

I am often surprised at the amount of time and effort, I shall use a word I have used before even though many people did not like it, eNavigators take when working up a passage plan and then constantly look at their phone/tablet worrying where they are.

 

[LadyInBed]

Passage planning is great if the passage goes to plan!
I once did a trip from Paimpol to Gurnsey, the plan involved getting out of Paimpol when there was water in the approach channel and catching the north going current up the Little Russel, unfortunately, I picked up a rope on the prop and by the time that I had partly cleared it I had missed the window for the Little Russel. I couldn't use the engine to increase my speed and ended up tacking back and forth across the mouth of the channel. Luckily, a Royal Naval Reserve boat who had heard my VHF updates came out and towed me in. My kids were really excited, as they got taken aboard the RNR boat for a mug of hot chocolate.