Allowing for tides etc on medium length trips?

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kcrane

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As a newbie I've been reading navigation books so I am not completely at sea next season (pun). It may just be me, but are they all a strange mix between quite confusing (rhumb lines and great circles) and greatly simplified ("work out the course and then sail in that direction" - with me thinking, but what if the wind won't let you?).

Real question is, if you are sailing, say, to the Channel Islands from the Solent, how do you plan the journey in real life, taking into account the tides and leeway and wind direction?

Do you plan it on paper, work out the effect of tide on each leg and then come up with a single course? Or do you put a lot of closely sequenced waypoints into the plotter and let it minimise cross-track error between them, or what? Above all, what if after all of your careful planning, the wind turns out to blow from the direction of your intended course? /forums/images/graemlins/smirk.gif
 
Do you mean "how come that question if you have 38ft yacht?".

Have done plenty of sailing on bigger than that, including 50ft motorboats - but mostly warm water, small tides, 20 mile runs. I know enough to do it without too much concern, but not at all convinced I'll be doing it the best way - hence looking for practical advice, rather than theory <g>
 
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Real question is, if you are sailing, say, to the Channel Islands from the Solent, how do you plan the journey in real life, taking into account the tides and leeway and wind direction?:

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My planning would be a bit informal, but would consist at least of:

1. write down times of high tides at destination. Also write down the times that the direction of tidal flow will change in the channel.

2. Look at destination, and work out if there are any times that would be much better to arrive than others eg. if it's only accessible at high tide, or if there's a strong tidal current that you need to catch at the other end.

3. See which direction the wind is forecase from.

4. Work out what speed made good in the right direction I will average over the distance to target.

5. Work out what time I have to leave to arrive at target about 2/3 hours before the best arrival time.

6. Consider if this allows me to leave my departure point at a time that gives a favourable tidal flow out.

7. If not, then work out which in the circumstances is more important, arriving at the ideal time, or leaving at the ideal time, bearing in mind that I may not arrive at teh ideal time anyway (General Moltke: "No plan survives contact with the enemy").

8. I work out the estimated journey time. Let's say it's 14 hours. With a Channel tide at about 90% to my desired course, deduct 12 hours where the tide will cancel itself out, means the net drift will be 2 hours of tide either East or West as appropriate. Calculate course to steer as being enough to compensate for that net 2 hrs tidal drift, and so that I will arrive on the up-tide side of target.

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Do you plan it on paper, work out the effect of tide on each leg and then come up with a single course? Or do you put a lot of closely sequenced waypoints into the plotter and let it minimise cross-track error between them, or what? Above all, what if after all of your careful planning, the wind turns out to blow from the direction of your intended course? /forums/images/graemlins/smirk.gif

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I do it in my head, not on paper, apart from the times of tides etc. which I write down.

I would NOT do a series of waypoints, or even follow a direct line to the end waypoint, since that involves fighting the tide. Instead, just stick to the course to steer, and only use the final waypoint as I'm approaching the target.

If the wind is blowing direct from target, then learning the principle of lee-bowing saves hours of passage time!
 
Thanks that is the kind of info I meant. I've done courses and read books, no-one mentioned the obvious (at least when someone mentions it to you) fact that if you are out for 12hrs, on balance, tides will balance out ('ish).

Also the checklist of what to plan in what order (and what to do if it doesn't work out neatly) is useful stuff.
 
I don't think navigation has ever been an exact science. From the time you leave port your plans need to be monitored, and updated as needed
 
I'm a great believer in the well go out and try it school of learning but for this problem I really do recommend a bit of theory reading before you go.
Can I commend Reeds Skippers Hand Book pp12-27 at a cost of £7.95 it could save you hours of downtide and downwind angst.
The "well it all cancels out" school of thought does work most of the time but when it doesn't it's a right PITA.
 
Hi,
Simon and Colmce has given you great advice, would add the suggestion of doing another course with th RYA as a foundation to work from.
Good luck
 
There's a lot of folk who've been associated with boats for a number of years, and they are - to a man - convinced that 'expert skills' are acquired by some form of osmosis i.e. the longer you're around, the more you know. It's about the difference between 20 years' experience, repeated once - and 1 year's experience, repeated 20 times.....

You can learn some of the mechanics of calculating tidal streams and tidal heights quite quickly, but the seamanship of how, where and when to apply these 'tools' is not so quickly acquired. The 'newbie' navigation books and the yottie magazines are fond of illustrating the very simple Needles to Cherbourg example, suggesting that summing the incremental vectors relevant to 60 miles and about 12 hours ( 5 knots - 2 'rectilineal' tides ) leaves very little residual tidal displacement to bother about.

Sometimes, on that specific trip, that works. But it certainly does NOT work on the majority of trips that are not 60nm/5kts/2tides; that are along or diagonally across rectilinear tides; where sizeable course changes and/or changes in tide-stream direction are encountered..... And your 'BroadBlue' will normally do considerably more than 5 knots!

The 'summing' idea mentioned can often be positively dangerous, for it does not show you how far from your direct course the tide is pushing you towards unexpected hazards - and in the example of Solent to Guernsey, can easily put you on the wrong side of the Casquets, Ortac and Burhou, in the dark. Reading the appropriate 'Passage Information' sections in Macmillan's - with a highlighter pen and chart - is instructive.

The 'Yachtmaster Standards Panel' places considerable emphasis on learning to work the tides, and their collective expertise is vast. By all means 'go out and try it', but do be prudent and anticipate some unexpected outcomes while your experience builds. Then reflect on all that, ask questions of those who really know, and build your own judgement and nav skills on a combination of the two.

Not everyone can become a Master Mariner just by following a 'Haynes Workshop Manual'.....
 
Please dont think I'm being high handed, but you really should get some training
before setting off for the Channel Islands.
Some of the UK's most treacherous coastline with lots of offlying rocks and really really fast tides and races..Swinge..Alderney race..etc all combine to conspire against the unprepared.
The very fact that you had to ask this question shows that you are not ready for this.
The Yachtmaster Shorebased course teaches Tides/Currents/Passage Planning in some detail, enough to answer the question you have posed.
I'm all for flying by the seat of your pants..but CI is not the place to experiment.
There are some on-line YM course providers..or some fast track ones too.
The normal college 23 week courses will already have started now.

Steve.
 
It's not quite like bilbobaggins says.

First off, I would say look at the tide tables: if springs then you can't ignore the tide, if neaps then you can almost do it in your head.

For springs, do the academic plot in the tidal atlas. That will give a good indication of whether your course will take you within shouting distance of the rocks.

Then go modern, select waypoints, not of the kind you aim for, but of the kind you keep to one side of. Then if you tack or otherwise stray from the straight and narrow, you know when to change course or, in the extreme, when to start the engine.

In the end, bilbobaggins is right: safety first.
 
My passage planning process goes something like this:

Invariably, a passage has one or more absolutely critical points with respect to tide. Points where you simply must have the tide with you, or have the tide slack. Then think about tide to 'get out' and 'get in'.

Think about these first. Then sketch out a plan to acommodate them. Then think about optimising the tidal flow in the less critical parts and refine your plan. Bear in mind that you may be better to wait-out a tide when it just won't work. Then think about access to your ports of refuge and the hazards associated with them. Then think about hazards on the way that you need to watch for.

Only then actually look at your expected track over the ground and your optimal course to steer. Think through worse case scenarios eg your speed drops below 4kn and the tide is carrying you cross track onto a hazard. Then sum the tides based on a best guess and steer in that direction.

Then tear-up the plan because you are actually going faster or slower or in a different direction to the one you assumed. You almost never end-up saiing the plan unless you are prepared to use a lot of engine, but you now know (and have written down) the critical issues and have logical starting point.

All IMHO and accepting that TMTOWTDI.
 
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Then tear-up the plan because you are actually going faster or slower or in a different direction to the one you assumed. You almost never end-up saiing the plan unless you are prepared to use a lot of engine, but you now know (and have written down) the critical issues and have logical starting point.

All IMHO and accepting that TMTOWTDI.

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"Planning is everything; the plan is nothing" (General Eisenhower)

The process of planning is what counts. It makes sure you are thoroughly familiar with the features of the passage, the hazards along the way and fixed points (like tidal windows - essential around the CIs) you must take into account. It also gives you a benchmark for re-planning as things develop.

Planning is not a one-off. Its a continual process of thinking ahead.
 
Also, a good idea when planning to sketch out some pilotage notes for far end with basics like key buoys, any transits, clearance bearings, marina/harbour master/port control VHF channels etc etc... and then do one or two for alternative 'refuge' destinations..... I keep a spiral bound note book on board for just that purpose... lots easier than trying to read an almanac or chart in bad weather... and doesn't matter if it gets wet....
 
One other thing..... don't forget to consider what time you will encounter other navigational hazards on a passage... a good example is the channel TSS's.... if possible, these are best crossed during daylight, and also, think about the state of the tide when you cross them... ie if its just turned west, when you enter the west bound lane, then you'll likely encounter more traffic as the ships start looking to gain maximum benefit from the tide.... but if its just turned east, the traffic may well be lighter... a real benefit at night....
 
You can sieve through the advice you have already got, but I will suggest a couple of other pointers.

Firstly, you do need to try and estimate the tidal effect over the duration of your passage. Do the best you can - I know your actual passage will not go exactly to plan, but we will deal with that in a moment. Try to estimate what the tide will be doing over the 10/12 (whatever) hours you will be on passage. Arrive at a 'course to steer and assuming you have already started by taking account of other constraints like headlands to get round, tidal races to negotiate etc, you can set off on your passage.

Secondly don't worry about your actual course not being in a straight line. Your track over the ground will be a large curve, or an 'S' shape etc depending on the tide. If you have done the calculations half decently, it all comes out in the wash as you get across.

Finally, a good rule of thumb is to have a bit of a reality check every time you halve the distance to your destination. In other words, at half way, check whether you are where you expect to be. Are you going faster/slower? Has the tide set you more/less? GPS lets us know exactly what is going on - don't ignore the data. If you need at adjust the course a little at half way to make sure you end up uptide and upwind of where you want to be - it’s easier to do it then, than when you are being swept down the Alderney Race, when you had been aiming for Braye Harbour.

Hope that helps...
 
I'd discount the ineviable relies along the lines of 'if you have to ask this question you shouldn't be going / don't leave harbour until you have YM and n years experience'.

Theory courses are good at teaching you CTS, EP, fixes etc but tend not to put it together. If you've made it throught the course and understood it, you have the necessary skills. Now is the time to (a) put it into practice and (b) learn how to apply the lessons in the real world, to realistic degrees of accuracy.

There are various ways of tackling the channel crossing problem but they all have one thing in common: you must be sure of being the right side of your destination when you reach the other side, i.e. don't be caught down-tide.

Work out your crossing time. For your boat I'd start with a 6 knot average. Work out which direction the tide will be running when you are say 5 miles N of Alderney, then set a waypoint a couple of miles up-tide. You may need to modify this later if you're going a lot faster or slower than expected.

Now a few methods.

1. Put in your waypoint then, once clear of the Solent, hit 'goto' and let the gps guide you. It may be a little less efficient than working the tide as you go and it will horrify the purists but it's safe and it works!

2. The CTS method
Work out how long you expect the tide to run in each direction; that's your tidal set in the CTS calculation.
When you know the wind direction, estimate leeway. With your shallow keels I'd start with run/broad reach: nil, Beam reach: 5°, close reach: 10°, beating 15°.
Plot your CTS and go for it. Once or twice during the passage, check that things are going as expected and alter course if you're not where you expect to be.

3. Plot it out hour by hour. Too much like hard work for my money but some prefer it that way.

The trip you are planning may be complicated by the Casquets TSS so you'll probably have to put in a waypoint to route you around the ends of the scheme. Best not to cross it if it can be avoided.

The other things you need to consider are ports of refuge and alternate destinations in the event of problems with boat or weather. Quite a few ports in that area are open only a few hours around HW and some are too small for multihulls (e.g. Perros Guirec). Doing your first trip around neaps would be sensible.
 
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