HI ALL
I HOPE THIS IS AS POPULAR AS THE POLISHING BOARD THREAD :-)

I WAS AT THE AIRPOT YESTERDAY AND ARRIVED AT HIGH TIDE WIND WAS GOOD WATER WAS FLAT WITH A LITLE ROLLING CHOP .
BY THE AFTERNOON LATE EVENING THE WIND HAD INCREASED THE TIDE HAD DROPPED AND WAS MUCH CHOPPIER

MY QUESTION, IS IT FLATTER AT HIGH TIDE DUE TO LESS TURBULENCE FROM THE WIND BEING CLOSER TO THE HIGHT OF THE RUNWAY ?

THERE WAS A 2.5M DIFFERENCE ON THE HIGH TIDE MARK

CHEERS LEO

The water could have been choppier later in the day because it was windier later in the day.

So do I. You might have ventured into "wind against tide" territory. I've searched the internet, cannot find an explanation. I suspect a bottom effect.

A related topic. Why did they build the runway so high in the first place?

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Ian K said...

So do I. You might have ventured into "wind against tide" territory. I've searched the internet, cannot find an explanation. I suspect a bottom effect.

A related topic. Why did they build the runway so high in the first place?

Ian, I suspect that they wanted it level with the rest of the airport

There also happens to be a road running under it, so they had to clear that, but I don't know which one came first.

thanks moby for stating the obvious love the level too

what i want to know is how wind acts over the runway with more or less of a drop ?
if the wind was the same speed. I believe its going to better to sail it at high tide just wanted to know why if my presumption are correct. and if so bring on global warming !!
cheers

Haha,

I guess looking at it we are considering wind shadows? So if the water was level with the runway there would not be a wind shadow. If the water is one meter below then perhaps there is a wind shadow of x meters. But how does the wind work? It varies all the time.

You see on TV those wind tunnel tests of various shapes with smoke flowing through. Even quite streamlined shapes create a fair bit of disturbance. Just rambling here now. Perhaps a phyisist or fluid mechanic can explain.

more were i'm going

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Mobydisc said...

Haha,

I guess looking at it we are considering wind shadows? So if the water was level with the runway there would not be a wind shadow. If the water is one meter below then perhaps there is a wind shadow of x meters. But how does the wind work? It varies all the time.

You see on TV those wind tunnel tests of various shapes with smoke flowing through. Even quite streamlined shapes create a fair bit of disturbance. Just rambling here now. Perhaps a phyisist or fluid mechanic can explain.

also need to take into account the airport is on a river - the tidal flow in that section is a lot faster than the area to the south . on top of that weve had a lot of rain so the river it self is also flowing more than usual.

it was noticabley flatter in the area south of the river mouth on wed.

If waves generated on the non-tidal parts of Botany Bay move into the outrushing tide of the Cooks river they'd have to get bunched up closer together. The opposite effect of those airport moving footpaths which spread the pedestrians out as they step on.

Not quite there because the waves generated by a noreaster would be going with the tide. But waves do diffract. Could they bend around the end of the runway and double back, or reflect off something else, with still enough energy to be noticeable? Maybe the tide was coming in?

Quite often the nor-easters later in the day shift further to the north and if the wind is building you'll still be running the same lines down the runway as you were before due to the extra pressure. When this happens bigger, older, nastier chop will be getting in closer to the runway than if the wind was more offshore.

If you don't break all your gear it can be fast.

Sam.

sam the wind was a bit more north in the arvo for sure .. it did make a difference to the approach and bare off ... so that might be more a factor than the hight of airport to the water . but the angle "from gps tracks" didn't change that much and the chop wasn't rolling it was more like turbulence on the water. this is why i was asking the question to hight of tide .
In regards to tide i got caught in the mouth of the river a few weeks back on my speed board and I was quite surprised at the the speed and ferocity of the tide running out, but in saying this im not sure how this would effect the ride close to runway.
i'm sure there are lots of variables that can effect ride / water quality I'm just keen to know peoples views - experiences for my quest for the big 40

Sam's probably closest to the money.