Crossing a Traffic Separation Scheme

[Joe from ny]

What is a traffic separation scheme?


Edit: Never mind, I left the app to go to google.

[Dockhead]

Originally Posted by carstenb

I believe we have beaten this animal to death in the CTS thread. Seaworthy Lass won that round by developing anew method to cross currents effectively.

So we actually do have a mathematical answer to this.

Actually this is much simpler than calculating a CTS across a changing current. If we assume that the current is constant, then this is just a simple vector calculation. So we've always had a simple mathematical answer to this, not taking anything away, of course, from SWL's brilliant work last year on the CTS thread, which concerned a much more complex question.

[Tellus]

Originally Posted by Dockhead

I would be interested to see how you calculate that. Never heard of such a technique.

In german it´s called "Hundekurve", in flight operations called "homing"
It´s the way a plane do fly by strong sidewind. The pilot got the home signal, a fix point.
Google-Ergebnis für http://upload.wikimedia.org/wikipedia/commons/thumb/2/22/NDB_Homing.svg/220px-NDB_Homing.svg.png

[Dockhead]

Originally Posted by Tellus

In german it´s called "Hundekurve", in flight operations called "homing"
It´s the way a plane do fly by strong sidewind. The pilot got the home signal, a fix point.
Google-Ergebnis für http://upload.wikimedia.org/wikipedia/commons/thumb/2/22/NDB_Homing.svg/220px-NDB_Homing.svg.png

Interesting - that's a constant bearing route, not constant heading nor rhumb line route. That would be just about the slowest way across; not compliant with the rules, and in general, not recommended for a boat. If current speed = boat speed, you would literally never arrive.

I imagine its main use is for flying before GPS and nothing but a radio beacon for navigation. A dead simple way of finding the airfield, and in a plane with high speed relative to the wind, you wouldn't care too much about the extra distance flown through air. On a boat - very different situation.

[Dockhead]

Originally Posted by Dockhead

Interesting - that's a constant bearing route, not constant heading nor rhumb line route. That would be just about the slowest way across; not compliant with the rules, and in general, not recommended for a boat. If current speed = boat speed, you would literally never arrive.

I imagine its main use is for flying before GPS and nothing but a radio beacon for navigation. A dead simple way of finding the airfield, and in a plane with high speed relative to the wind, you wouldn't care too much about the extra distance flown through air. On a boat - very different situation.

And even pilots recognize this disadvantage:


"

Bei Seitenwind wird das Flugzeug im Verlauf des Fluges von der ursprünglichen Anfluggrundlinie zur Seite versetzt. Es müssen fortlaufend Kursänderungen vorgenommen werden. Somit wird das NDB nicht auf direktem (kürzestem) Weg, sondern auf einer gekrümmten Bahn angeflogen. Das Zielflugverfahren lässt sich nur für den Anflug auf ein NDB verwenden, nicht aber für den Abflug.
Für die VFR-Navigation haben die genannten Nachteile keine große Bedeutung. Daher ist Homing hier das gängige Verfahren, um ein NDB anzufliegen. Anders verhält es sich mit der IFR-Navigation. Hier ist ein exakter Anflugkurs vorgegeben. Daher kann dort dieses Verfahren nicht angewendet werden.
Dank satellitengestützter Navigation ist es heute relativ einfach, den Weg über Grund, die Zielpeilung und daraus den Vorhaltewinkel (WCA) für den Direktanflug zu bestimmen."

www.de.wikipedia.org/wiki/Homing_(Luftfahrt)

"Homing[edit]
The ADF may be used to home in on a station. Homing is flying the aircraft on the heading required to keep the needle pointing directly to the 0° (straight ahead) position. To home into a station, tune the station, identify the Morse code signal, then turn the aircraft to bring the ADF azimuth needle to the 0° position. Turn to keep the ADF heading indicator pointing directly ahead. Homing is regarded as poor piloting technique because the aircraft may be blown significantly or dangerously off-course by a cross-wind, and will have to fly further and for longer than the direct track."

http://www.eng.wikipedia.org/wiki/Ra...rection_finder

[conachair]

Where do these explanations come from?
I can just see rule 10 c -
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.

No mention of why, is there more somewhere in the irpcs?


Edit:Mr Google to the rescue.. Both right.

"Rule 10 states that ships crossing traffic lanes are required to do so "as nearly as practicable at right angles to the general direction of traffic flow." This reduces confusion to other ships as to the crossing vessel's intentions and course and at the same time enables that vessel to cross the lane as quickly as possible."


http://www.imo.org/OurWork/Safety/Na...ollisions.aspx

[hoppy]

Originally Posted by conachair

Where do these explanations come from?
I can just see rule 10 c -
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.

No mention of why, is there more somewhere in the irpcs?

Ummm because it is the fastest way to cross and therefore the least time is spent in the TSS. That seems to be the a pretty good reason.

[conachair]

Originally Posted by hoppy

Ummm because it is the fastest way to cross and therefore the least time is spent in the TSS. That seems to be the a pretty good reason.

See edit above, not only that.

[George64]

It is not the RYA stating this, it are the Colregs

[jeremiason]

"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".

This happened to me regularly in San Francisco Bay going north or south across the entrance to the Bay. There were regular 4-5 knot maximum currents at the bridge (6 knots in January) and slightly less within several miles of the Golden Gate Bridge.

The Traffic Separation Scheme extends from Sea, under the GG Bridge and east into the Bay, effectively cutting it in half and requiring anyone wanting to go north or south to cross the channels.

These currents made it NOT PRACTICLE to cross at a right angle and instead I used the the current to speed my crossing of the channel.

Of course I would always use maximum separation when crossing in front of other vessels or wait for them to pass before crossing the traffic separation scheme.

[goboatingnow]

Originally Posted by hoppy

Ummm because it is the fastest way to cross and therefore the least time is spent in the TSS. That seems to be the a pretty good reason.

It may not be the fastest way to cross , there is no requirement to cross the TSS in any given time , the primary reason is to present the correct crossing aspect to the vessels in the lane

Dave

[roetter]

Originally Posted by simonpickard

Hello all, Quick question, and I'm sure I'm missing something silly here but in the RYA training guides it says to cross a TSS at a right angle heading, even if the course over ground, due to say tide, means you're "sliding" through the water thereby taking longer. Why wouldn't you adjust for any current, tide, etc, so your course over ground is as close to a right angle to the TSS as possible? Regards, Simon

Most times the current in a TSS will be in direction of the traffic flow. If that is the case then a 90 degree heading to the TSS will get you across fastest independent of the strength of any current. Angling into the current, will take longer to cross. The distance travelled will be less, but it will take you longer. Assume travelling at 5 knots in 4 knots of current., you would have to angle into the current so much that hardly any of your speed is used to cross.

[chiangkent]

It is totally correct to cross a TSS at a right angle heading, even if the course over ground.

Reason is for avoiding collision, because you shall show the right aspects to other ships by navigation lights or ship's shape in case that other ships cannot find your course and speed make good so as to determine what actions shall be taken. If you correct the drift, the light aspects will be changed and mislead the act to avoid collision.

[TxCoastSailor]

Originally Posted by roetter

Most times the current in a TSS will be in direction of the traffic flow. If that is the case then a 90 degree heading to the TSS will get you across fastest independent of the strength of any current. Angling into the current, will take longer to cross. The distance travelled will be less, but it will take you longer. Assume travelling at 5 knots in 4 knots of current., you would have to angle into the current so much that hardly any of your speed is used to cross.

Exactly.

If the current gets to 5 knots and you try to compensate you go nowhere and you never get across the TSC.

On the other hand if you ignore the current and head straight across a TSC with a width of 2.5 nm you will cross in one half hour whatever the current.