Tides, daft question but....

[Kev1n]

No, in most cases you are unlikely to end up back where you started. The tides rotate around certain points and any land in the way will affect the uniformity of their flow. Further out to sea you have a better chance of getting back to where you started. Sailors crossing the English Channel often aim to completed a full tide cycle so for the first six hours of the crossing the tide flowing across their route takes them in one direction and for the second six, the tide compensates by moving them back in the right direction.

Stores, you could also start them on a few exercises like the ones the RYA Yachtmaster use. These require a student to combine the hour-by hour tide direction with a bearing that the boat is steering on. E.g. the boat is on a bearing of 090degrees and at speed six knots, the tide set is 000 degrees with set of 2 knots, how far from its original position will it travel? Ave speed? Etc. Also you can add in lee-way and calculations for compass variation and deviation if you want to provide a further challenge. Finally, ask them to calculate the heading (i.e. the direction the boat needs to face) for it to arrive at a certain point. Done on paper by drawing angle or use trigonometry to calculate. Then tell them to look up amphidromic points for more info on the tides.

[phill_itofish]

No, in most cases you are unlikely to end up back where you started. The tides rotate around certain points and any land in the way will affect the uniformity of their flow. Further out to sea you have a better chance of getting back to where you started. .

Ah if only id read this before i plotted it out lol.

Anyway here's what i came up with, based on the first lot of data on the table. (obvioulsy from what kevs saying, in reality this would all be wrong because once you drift for an hour the data will not be the same for that location)



Each Circle Represents an hour

Total Distance Travelled 6.944Km
Average Speed .0405 Knots

[Tadpoleman]

north tide going out = Nowt
South tide comming in = Sin
Thats how i remember.................

[Stores]

Interesting thread and interesting results from my group this morning.

Before we start, thanks Kev1n for your extension activities........but imagine the Bash Street Kids..........................

Anyway we reckon....

- none of the data gets you back to where you start, based solely on tidal movement:

- the first set of data would have an end result between 0.23 knots and 0.4 knots north of the start point, veering slightly to the west.

- the second set of data has the end result between 0.25 knots and 0.45 knots from the start, just fractionally west of north.

-the final piece of data has a result between 0.25 knots and 0.5 knots and it ends NW of the start.

Strangely the first and last tracks form a deflated Christmas balloon while the middle set of data is almost twice as long (north to south) but never gets wider than 0.15 knots.

As each set of results show an end result nearer the shore than the start I asked the students what they made of that...........nothing. I then prompted that anything lost at sea should end up where?....nothing. I then said the logical conclusion was that any body, cargo, whatever should end up on the shore somewhere (OK they say) - but it doesn't says I, reinforced with the fact that in 50 years of fishing I've only come across one washed up body and very little jetsam or flotsam - why?....nothing - something to take into consideration in the future when teenagers get into trouble on piers or inflatables or when swimming - kids from Cannock have no concept of the sea, how it works, what it's powers are or the consequences of getting things wrong.

At that point the Head arrived, cutting through my room. Happy New Years were exchanged and, as the kids were commenting on one anothers flow graphs he took an interest and I commented that he would know the answer. I explained the lesson, presented him with the problem and his first comment was "if this is the North Sea then the prevailing westerly wind will be more powerful than the tidal effect". The kids sat agog, the Head enhanced his reputation and I said... "not bad for an RE teacher"

Have passed the data onto the head of Maths and it's in the "Interesting Lessons" file