Son of What Now Skip - September

[timbartlett]

Another wide-ranging and loosely-defined scenario for this month's "son of what now skip"

You are planning a passage across a wide channel — fifty or sixty miles wide — through which the tidal steam runs at up to four knots, and which has a busy and enthusiastically-policed traffic separation scheme running along the middle. The TSS consists of two traffic lanes, both about seven miles wide, separated by a separation zone that is five miles wide and with two-mile separation zones on each side.

The direct route to your destination involves crossing the separation scheme at an angle of about forty five degrees — but this, of course, is forbidden.

How do you plan the crossing?

As "last month" (well, two weeks ago, actually), it's an open-ended question and there are no right or wrong answers -- but let's not get bogged down in yet another colregs thread or the merits or otherwise of AIS. Let's just assume that our hero regards the colregs as holy writ, and remember that rule 10c says:

A vessel shall so far as practicable avoid crossing traffic lanes, but if obliged to do so shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow

You can pick any boat you like, so long as it is less than 20m long, but I would suggest that the most interesting answers are likely to be those that relate to slower boats -- those cruising at 15-20kts, say, rather than those who "cruise" at 40+.

I'll pick the most interesting answers and publish them in MBY, attributed to your Forum username, but edited if necessary for length, spelling, etc.

Enjoy.
Best regards
Tim

 

[benjenbav]

Tim

Your confuser has edited 10(c) a bit: you missed out the bit about right angles:

A vessel shall so far as practicable avoid crossing traffic lanes, but if obliged to do so shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow

 

[PaulGooch]

Think i'd just travel along the coast until directly "opposite" point B, then run straight across. Minimises the crossing time/distance, complies fully with the TSS rules and would only add about two miles to the crossing.

 

[hlb]

With my legendary passage planning skills. I'd set off about 45 deg, then 90 deg across the first TSS, then 45 deg across the middle bit. Then 90 deg across the second one.

The trusty plotter would work out the tides and keep us on course, then take us to our final destination all on their own. Take only a few seconds t plot, job done.

Police about.......Make smoke.

 

[timbartlett]

Tim

Your confuser has edited 10(c) a bit: you missed out the bit about right angles:

Thank you.

I've edited the original, for the sake of those who follow.

 

[jfm]

I'm a bit confused about this son of WNS. What is there to say? You'd run along the coast (well away from the TSS) then cross at right angles and land at B, or you'd cross at right angles immediately then run along the coast to B, or some halfway house. The choice about where to cross depends on wind/weather/lee shores/fetch, and which coast is nicer in terms of scenery, safe havens, pubs, fuel, whatever

When crossing, remember not to impede safe passage of ships who are using the lane (cue debate on the poor drafting of COLRegs, and what does "impede" mean, as opposed to the "keep out of the way of" requirement elsewhere in the regs)

Another alternative is to join the appropriate lane of the TSS (at an acute angle, as prescribed in rule 10) and run along it, but in a pleasure boat that would normally be less scenic than running along the coast. It would however iirc nicely give you basically right of way over any crossing raggies, which is a nice change and would please iangrant no end

 

[benjenbav]

Rightio. First a couple of assumptions:

1 I'm going from A to B.

2 The orientation of the chartlet is north-up

3 There are no nightmarish hazards off either coast

4 There are two high tides per day in this area

The diagonal is approximately 75/80 miles. In my 15/20 knot plugger, I will need more than one tide assuming that I will end up doing say 110 miles. I'm going to allow 8 hours.

Plan #1 is to leave an hour or maybe even two before slack water ahead of the east-bound flow and then set off in a generally easterly direction, keeping well south of the scheme (but also north of the shore!) until I am about fifteen nautical miles to the west of point B. I will then turn north and head across the lanes and separation scheme on a heading at right angles to them. By the time I'm clear of the lanes and the separation scheme I will have been taken, say, seven NM further east (assuming a maximum flow of 4 knots and 2 hours to get across the scheme) and will then turn east again and head for port with a few miles of eastering to make and making landfall round about slack water.

If the wind was above F4 from the east and with any north in it then I would switch to plan #2: still leaving at the same state of the tide but crossing early and then taking advantage of the shelter offered by the coast on the north and heading downtide east towards point B.

 

[timbartlett]

What is there to say?

Well, you've said quite a lot! Thank you

As I said, I'm quite keen to avoid yet another colregs/AIS thread: I was hoping that this one would be more about passage planning -- witness the contrast between hlb and paul gooch's answers.

FWIW, my sketch (below) shows half a dozen legitimate options, all of which have some merit, but which are dramatically different. Even without allowing for tide, Route 5 is over twenty miles longer than route 4, for instance.

Rightio. First a couple of assumptions:
1 I'm going from A to B.
2 The orientation of the chartlet is north-up

(1) Yes
(2) Not necessarily, but it makes it much easier to describe directions if we take it to be north up.
(Other points) Yes

 

[jfm]

Well, you've said quite a lot! Thank you

Ah yes, fair cop

Route 5 is over twenty miles longer than route 4, for instance.

Yup, but boating isn't about getting there in the shortest DTW. Route 5 might have a nice restaurant stop, or some nice cheap fuel, or be good in a strong southerly wind sheltering behind huge cliffs, or just be more scenic. There's no info in the Q but in real life a skipper would take the whole "scenery" aspect into account

 

[benjenbav]

Tim, I'm sure it is against the rules of s-o-wns but I'd be very interested in your view about the merits of taking your route #3 in, say, a 40 knot planing boat; particularly changing course to a diagonal across the separations outside the lanes where (if Pythagoras is to be believed) the distance saved would be only just over a mile and anyone monitoring you on radar would see a fast thing darting about madly.

 

[PaulGooch]

Ah yes, fair cop



Yup, but boating isn't about getting there in the shortest DTW. Route 5 might have a nice restaurant stop, or some nice cheap fuel, or be good in a strong southerly wind sheltering behind huge cliffs, or just be more scenic. There's no info in the Q but in real life a skipper would take the whole "scenery" aspect into account

I knew about the restaurant and the cliffs, that's why i went that way

 

[jfm]

I knew about the restaurant and the cliffs, that's why i went that way

I like your approach to navigation. I bet you, like me, might just abandon the whole second leg of the passage and order some more wine

 

[PaulGooch]

I like your approach to navigation. I bet you, like me, might just abandon the whole second leg of the passage and order some more wine

It would seem silly to leave the shelter of those cliffs

 

[timbartlett]

Tim, I'm sure it is against the rules of s-o-wns but I'd be very interested in your view about the merits of taking your route #3 in, say, a 40 knot planing boat; particularly changing course to a diagonal across the separations outside the lanes where (if Pythagoras is to be believed) the distance saved would be only just over a mile and anyone monitoring you on radar would see a fast thing darting about madly.

It's not exactly "against the rules", because I'm not quite sure what the "rules" are: they are probably only just starting to evolve! But I am quite keen to avoid stifling discussion by favouring one route over any other: As I said at the outset there are no "right" or "wrong" answers: the whole point is a discussion about how and why people reach the conclusions they do. It's certainly not about how closely anyone else's answer matches mine!

But I will let you into a secret.... (PM on its way!)

 

[PaulGooch]

There was a real life discussion of a trip almost identical to this a short while ago, http://www.ybw.com/forums/showthread.php?t=238297

I question Tim's assertion the route 5 is 20 miles longer than route 4. Using Bluechart, i make it about 47 miles from Eastbourne to Boulogne. It's only 51 miles running up the coast to Dungeness before crossing. Not identical to Tim's "map", but pretty close.

 

[timbartlett]

There was a real life discussion of a trip almost identical to this a short while ago, http://www.ybw.com/forums/showthread.php?t=238297

I question Tim's assertion the route 5 is 20 miles longer than route 4. Using Bluechart, i make it about 47 miles from Eastbourne to Boulogne. It's only 51 miles running up the coast to Dungeness before crossing. Not identical to Tim's "map", but pretty close.

I see where you're coming from. Here's how I arrived at my numbers:-
If the channel width is 60 miles, then if you start at A and go sixty miles East then sixty miles North, you arrive at B having covered 120miles.

If you ignore the TSS and go straight from A to B, it's 84 miles. (Good old Pythagoras and the sons of the squaws on the other two hides)

If you follow route 4, I make it 92 miles (Pythagoras again)

But a slight change in the geography could make a radical difference to the numbers, so please believe me when I say that I regard the detailed maths of this hypothetical situation as pretty irrelevant: the point is that there are good reasons for choosing to go a longer route, just as there are good reasons for going a shorter one.

Here's a supplementary question if anyone is interested in picking it up:
1. Do you make any plans to allow for the tide?
2. If you use an autopilot, do you use "steer to waypoint" or "steer to compass" or a bit of each? And if you use waypoints, how do you decide where to put them?

 

[PaulGooch]

I see where you're coming from. Here's how I arrived at my numbers:-
If the channel width is 60 miles, then if you start at A and go sixty miles East then sixty miles North, you arrive at B having covered 120miles.

If you ignore the TSS and go straight from A to B, it's 84 miles. (Good old Pythagoras and the sons of the squaws on the other two hides)

If you follow route 4, I make it 92 miles (Pythagoras again)

But a slight change in the geography could make a radical difference to the numbers, so please believe me when I say that I regard the detailed maths of this hypothetical situation as pretty irrelevant: the point is that there are good reasons for choosing to go a longer route, just as there are good reasons for going a shorter one.

Here's a supplementary question if anyone is interested in picking it up:
1. Do you make any plans to allow for the tide?
2. If you use an autopilot, do you use "steer to waypoint" or "steer to compass" or a bit of each? And if you use waypoints, how do you decide where to put them?

I think i was off on the day we were supposed to do Pythagoras

Answers to supplementary questions :

1. Yes, if at all possible. 2 knots of tide have the potential to make up to 4 knots difference to my speed and cause an increase in fuel. I'd plan the passage to make the most effective use of the tides, without making the journey at silly-o-clock. As it's 60 miles across and 60 miles along, i'd split the trip into two legs. My boat has a cruise speed of 16-18 knots, i use 15 for passage planning, so each leg would be around 4 hours.

I'd find it a more leisurely trip to use route 2 or 5. Do half one day and overnight, then do the other half the next day. I'd have a whole day to do the leg along the coast, so would then pick a time to leave that made best use of the tides.

2. No autopilot, but i generally plot a course on the chart plotter. Routes 2 and 5 would have a waypoint at the start, any point along the coast that requires a course change and one at the end. 3 and 4 would have waypoints at the start, each point across the TSS where a course change is needed and one at the end. I personally see no need for 1 and 6.

All IMO

 

[hlb]

As many times stated. Our getting up time is around ten. Setting off time is there for around 11 AM. There can be about an hours variation on this, dependant on the night before.

Question
1/. See above.

2/ Can you steer to compass?? Never knew that. (why bother)

3/ The way points go in very roughly, less it's important at all. Like dont hit anything.

Dont mostly bother about overfalls. MF is quite capable of most, plus it's alot of faf going round. So mostly just plough on. WE can always aim out of them if we have to.

As with JFM. The plan, depends on loads of decisions, mainly around when the chip shop closes, coupled with the aforsaid, getting up time. Sleepy time is around 4PM, so we need to be there before then.

So there you have it, we plan around what we want to do. Not what the tide is doing or anything else. There could be exceptions of course. Mostly we seem to get round most of England or France and Scillies, mostly Wales and Ireland now. With no prob's.

It's mainly about what time they will let us out of the lock, if to soon, go tomorrow.!!

 

[MapisM]

Let's just assume that our hero regards the colregs as holy writ

Non sequitur.
Any real world wns hero would fix B on the plotter, set the a/p to waypoint, and hammer the throttles.
Job done, in less than a couple of hours.

 

[timbartlett]

Non sequitur.
Any real world wns hero would fix B on the plotter, set the a/p to waypoint, and hammer the throttles.
Job done, in less than a couple of hours.

OK, a year on and £20k lighter (having paid the fine imposed by Kolfestone magistrates ) what would he do?

Or what would you do?