Tides are not really something that is subject to a great deal of "accuracy".

Tide times are governed primarily by the cycle of the moon and your particular position of longitude.

Example:- Where I live, peak spring tides (ie the nights of full and new moon) occur at 9 pm (give or take 20 minutes). Consult your local tide tables and look at the times of those tides and you will find they are pretty much the same time of day or night every time.

Remember the tide tables are predictions only. The tide is two waves of water that constantly travel around the world.

Tide heights are subject to local and prevailing conditions, eg land masses, river flows, wind surge and rainfall.

When you say "tide watch", I assume you are referring to a wrist watch or other device that has a tide program in it. For it to work you would no doubt have to calibrate it by inputting your longitudinal location.

If you are using it to determine the best time to go surfing etc, I think one could say that they are "accurate" enough.

If you are using it to determine when you are able to cross a bar with a keel yacht, I suggest use of tide tables is a far better option. Cheers

I have a had a "Rip Curl" Tide Watch for about 8 years now. It's on it's 3rd band, and 2nd battery.

It is NOT digital. The watch (clock) is the one with hands, with separate hands for the tide height, and tide range, and a moon phase dial.

The tides are based around a 12hr and 25 minute cycle, instead of a 12/24hr cycle. This style of watch needs to be set by yourself, for your current location.

I think I paid about $350 in 2002, and I've probably paid about $90 in total, to get new bands and battery.

I live in Torquay, and repairs are done here. But when I lived in Sydney, I would just mail it down to Torquay, and and they would have the watch mailed back in about 1 week. Same with wetsuit repairs. Turn around within the week.

They are accurate. It is purely and simply a 12hr and 25 minute cycle (approx).

However, on any given day you have 2 high tides, and 2 low tides (excluding about 1 day a month, do the maths). But, one high tide is (almost) always higher than the other, and vice versa, one low will be lower than the other. On some cycles, on some days, at some locations, there may not be too much difference in height between High & Low within 1 cycle....

For example, at some locations it might go from a 0.7m Low, to a 1.2m High, but on a different day (same location) it might go from a 0.1m Low, to a 2.1m High. It is these fluctuations that may give you the impression that the watch is wrong.... Take a tide chart along, and check it with your watch, and read the fine print about adjusting for your locations.....

There is nothing wrong with the watches. But some of the watches don't have the detail that the Tide Charts have, but some of the digital Tide Watches do have that detail....

Wineman said...

Simondo said...

They are accurate. It is purely and simply a 12hr and 25 minute cycle (approx).

...except in WA or precisely Fremantle.

Go to graphs above & check the tides for WA - They are approx 24hr cycle

Anyone know why Sydney & Perff which have almost same latitude have TOTALLY different tide cycles?????

My basic (mis)understanding of tides is they are basically gigantic swell or upwelling of water that move around the oceans and seas of the world following the moon. So I guess when the moon is over Sydney its not over Perth. I think tide height does not correspond with latitude but with longitude.

So the tides in Sydney are going to be reasonably similar to those in Townsville as they are on similar longitudes but quite different to Perth as the longitudes are quite different.

cisco said...

Wineman said...
Anyone know why Sydney & Perff which have almost same latitude have TOTALLY different tide cycles?????

Yep. Because there is a thumping great island in between them.

Thanks Capt'n Obvious.

Wineman said...

cisco said...

Wineman said...
Anyone know why Sydney & Perff which have almost same latitude have TOTALLY different tide cycles?????

Yep. Because there is a thumping great island in between them.

Thanks Capt'n Obvious.

Haha, you did ask lol

spot quizz - if the moon controls the tides, why are there two high tides a day

i have a freestyle watch with very accurate tide times all programmed in for different locations around the world. but in australia it's only good for perth gold coast and sydney.

i still like my watch and it's good enough for an indication of tide times in (for example) darwin if you know how to set it. it's waterproof to 100m and never missed a beat.

The moon pulls the water on the earth and on the earth as well. In fact, our planet doesn't spin around it's centre, it spins around the center of mass of the earth and moon combined. It just so happens that that centre point is a spot within the earth but not at the centre of the earth. So the planet wobbles around that spot as it spins. That sets up the two waves.

Or you can think of it like this - when the moon is directly overhead, it's pulling the earth and all the water. The water can move more quickly so you get a high tide when the moon is overhead. On the other hand, when the moon is directly underfoot (the opposite side of the planet), the whole planet is moving away from the water surface so you get another high tide. And the low tides are caused by the water being drawn towards the high tide points.

cisco said...

colinwill78 said...

spot quizz - if the moon controls the tides, why are there two high tides a day

It is actually caused by the gravitational pull of both the moon and the sun but the moon being closer exerts a greater influence. (I think that is correct.)

I would have to refer to a text book for a deeper explanation.

i think there's a bit of truth in that too

Far be it from me to pull any members, cisco, whether single or collective!

The effect I'm talking about is known as "nutation" as has been well understood for a long time - eg en.wikipedia.org/wiki/Nutation

There are also a couple of other wobbles in the rotation of the earth (eg precession) but they're of much longer period and so less noticeable.

cisco said...

If the Earth has nutation as you describe and an extra gravitational influence was introduced, such as a close encounter with a large comet, it is imagineable that it might cause a 180 degree flip of the Earth's rotational axis. Yes??

No. It is imaginable that a close encounter with a comet the size of Venus would pull the Earth (and Moon - it's a binary system) out of its orbital path around the Sun. Then we'd either freeze or fry depending on whether we ended up closer to or further from the Sun. The Sun and Moon would no longer be the same apparent size and solar eclipses would be a thing of the past. Did any of that happen in Moses time? I think not. It'd also be pretty blinkin' hard to miss something the size of Venus there close by in the sky. Tiny comets can fill half the sky and are clearly visible so imagine how big something the size of Venus would be... so why no mention of it in Egyptian writings? They were pretty keen on that stuff.

With Earth's orbit disrupted, it's also pretty unlikely we'd finish up in the same orbital plane as the rest of the planets as we are. If Venus was a captured comet then it's also also pretty unlikely that it'd end up in the same orbital plane as the rest of the planets, going around the Sun in the same direction as the other planets and even spinning on its axis in the same direction as all the other planets (comets have random axial spin).

And why would a comet Venus even be captured? Much tinier comets come in from the Oort cloud, get much closer to the Sun than Venus and then whizz back out to the Oort cloud all the time. Halley's comet does it on a regular basis.

There ya go... 5 minutes critical thinking shows why Velikovsky was wrong. You can stop wasting your time with that stuff now.

Darwin's theory is the accepted theory because it's the best available to explain the observed facts, pure and simple. If something better came along, it'd be ditched in no time flat. That's how science works.