Tides - I really dont understand them....

[drowningbitbybit]

Okay, tides....
They're caused by the moon's gravitational pull, as the earth rotates. And they alter by a touch less than an hour a day due to the moon orbiting the earth

Im okay so far.... so the way we're taught to look at tides is to think of two big 'waves' rolling around the world 12 hours or so apart.

But...
With an hour to kill at work, Ive been looking at tide times.
So, tide times today (GMT)

London Bridge 11.54
Kew Bridge 12.46
Richmond 12.53

...So thats an hour difference in less than 15 miles.... That makes the earth circumference about 360 miles (seems unlikely...)

Richmond 12.53
Witterings 09.45

...So thats three hours difference, despite the fact they're on almost exactly the same line of longitude. So this 'wave' isnt in a straight line...

Newquay 15:35
Croyde 16:24

...But croyde is east of newquay!
Oh, right, the world goes backwards when it gets to devon

I dont understand tides....

[Phil]

its becuse of the land mass mate in this case

Richmond 12.53
Witterings 09.45

the english chanle acts as a bottle neck restricting the movment of water so it slows down

as for newquay and croyde the moons gravitional pull has has to get water from the sea as croyde is set in like a cove between ireland, newquey gets the high tide first becuse the only thing east of royde is the bristol chanel so its not gonna be able to pull water from there see what i mean

[drowningbitbybit]

Um, yeah, I get what you're saying and had kind of figures the 'bottleneck' thing...

(Maybe using the thames as an example was a bad idea, but its next to my house and I like seeing the tourists getting their feet wet)

But...

Things like Bognor and Start point, both on the south coast and less than 200 miles apart (yeah, I know start point faces the atlantic much more than Bognor but bear with me!) and they're seven hours different!

Surely that means they should be a quarter of a planet away!

By the time start point is at high tide, bognor is already past low tide - I dont need to surf, I could sea-ski to bognor!

Maybe I should've been an oceanographer, then they'd pay me to do this at work on a friday afternoon instead of me avoiding work by doing this on a friday afternoon


It's all 'cos I keep looking at the charts... is the wind going to drop enough to make it worth the drive to the south coast tomorrow..?

[sinistapenguin]

In most of the places I surf if the tide is low you have to walk for miles, if the tide is high you don't

That's about as much as I know about tides!!

[tomcat360]

this kinda makes me think about this place ive seen pics of in canada- some bay up there has something like a 30 foot change in tide. i saw it in one of my old textbooks, theyve got boat racks below all the old deadrises to hold them off the rocks when the tide falls. absolutely insane

[Broosta]

Tides are a very complex idea to get your head round - my advice is just obey the tide charts, don't try to understand the whys and wherefors, just be there at the correct state of tide and thats all you need to know .

I had a bit of a read of 'Surf Science' by Tony Butt and Paul Russell - I can only take v small doses at at a time cos its well tech ! It says tides are affected by things like 'the Coriolis force' and 'Amphidromes' .
The Coriolis force is responsible for everything in the northern hemisphere to turn right and everything in the southern hemisphere to turn left... apparently, and Amphidromes are imaginary centres of rotation which tides swirl around .

Coriolis force - http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

Amphidromes - http://www.madsci.org/posts/archives/may97/861368730.Es.r.html

[drowningbitbybit]

Tides are a very complex idea .... don't try to understand the whys and wherefors...
'the Coriolis force'...'Amphidromes' ... in the northern hemisphere to turn right and everything in the southern hemisphere to turn left... apparently, and Amphidromes are imaginary centres of rotation which tides swirl around

Oh good, thats all clear then

All I know is I got it hideously wrong today. Long trip to the beach to find a blown out wave, so another hour to a different spot to find potentially perfect conditions but the tide making it unsurfable (knew it would, but I thought I'd check...) and not having the time to wait for it to drop

Oh well, you seek, you find, you b*gger it up sometimes....

[meister]

this kinda makes me think about this place ive seen pics of in canada- some bay up there has something like a 30 foot change in tide. i saw it in one of my old textbooks, theyve got boat racks below all the old deadrises to hold them off the rocks when the tide falls. absolutely insane

far thats crazy

[calisurfer]

this kinda makes me think about this place ive seen pics of in canada- some bay up there has something like a 30 foot change in tide. i saw it in one of my old textbooks, theyve got boat racks below all the old deadrises to hold them off the rocks when the tide falls. absolutely insane

I went to victoria in canada this summer on a sailing trip and their harbor has a 16 foot change and it was crazy