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Old 11-08-2019, 16:40   #31
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Re: Questions on neap and spring tides. Is anyone able to help?

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Oh my, so these calculations can be fairly vague and inaccurate anyway? Feels like yo can never know enough
No, tide predictions are really very accurate, until abnormal weather events make them less so.....
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Old 11-08-2019, 16:55   #32
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Re: Questions on neap and spring tides. Is anyone able to help?

Where I am we have "mixed" tides (go back to post #4 and review what they are). We have a tidal range of about 15 feet on the "springs" and a coupla feet or so on the "neaps", That is not important while you are on passage, but it is when you anchor out.

In your area the tide range may not be important but in my area or more accurately, in certain areas in my area, it can be really important.

Take Vancouver, BC for example, under the second Narrows Bridge (Iron Workers Memorial Bridge), the current is much more dramatic in a wide range of tide, highest high to lowest low, than in Neap periods where the current isn't so bad. Best not to go under the bridge in a Spring tide in full run.

Now I"m going to lie and say our tides are every 6 hours when in reality they are something like every 6 hours and 19 minutes (too lazy to look up). But this simple method is easy to learn, remember and use.

In the first hour of a 6 hour tide, 1/12 of the total flood (or ebb) comes in, second hour 2/12ths of the flood (or ebb) comes in, third hour 3/12ths of the flood comes in, fourth hour 3/12ths of the flood comes in, fifth hour 2/12ths of the flood comes in, and sixth hour 1/12th of the flood comes in.

So you can see in the first and sixth hour, you will have the least tidal current (which is actually a misnomer) to deal with, whereas in the third and fourth hour you will have a heavier current to handle.

And to put the fear of God into you, a video of Skookumchuck in British Columbia, and yes boaters do go through this area at slack (about a ten minute window, boats wait not to far away in a staging area). At slack the water is flat:



You can appreciate the current in Skookumchuck will vary with the neap and spring tides and where in the above formula of 1/12ths it is. If the tide is ending its 6th hour, the current won't be that dramatic, but in a Spring tide in the 3rd and 4th hour, quite dramatic.
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Old 11-08-2019, 17:28   #33
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Re: Questions on neap and spring tides. Is anyone able to help?

fif.ed:

Quote: "Feels like yo can never know enough "

Well yes, but the reality is that you needn't know much :-)! Your garden variety yottie just needs to know enuff so's he won't run aground. So s'posing your boat has a draft of five feet. And s'posing you promise yourself never to go "inside" (to landward) of the TEN foot contour on the chart of your locality. Would you run aground? Of course not! You'd have about five feet of water under you keel at MLT (Mean Low Tide). What more do you need to know?

So you gotta tie together and use in unison what you learn from your Tide and Current Tables and your chart. Use electronics all you like, but NEVER rely on them only. Apply human intelligence to what they tell you!

In our waters pinnacles and "half tide rocks" abound. They are marked on your chart - for the most part :-) But sometimes they are not. It's a big coast! So NEVER rely on electronic gizmos alone. Learn to "read the water".

We have many, many places where 20 feet from shore you have 300 feet of water at MLT. We have places where a mile from shore there is a nasty little pinnacle, maybe 50 feet square at the top, that is covered with 2 feet of water at MLT. On stormy days you see it, on calm days you don't. So learn to "read the water", and don't get hung up on the science of all.

The science is just for passing exams. To stay afloat, you don't need to know much at all. But you do need to be able to "read the water" :-)


For amusement, go here:


All the best

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Old 11-08-2019, 18:02   #34
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Re: Questions on neap and spring tides. Is anyone able to help?

rsn48

Having sailed in the Salish Sea and Burrard Inlet for some 60 years, I'm really quite keenly aware that all you say is correct.

But our new friend, fif.ed, wants to know what he needs to know to pass his exam, and he has said that he is soon departing on a cruise. He has NOT said where he is located, so what we have to say needs to be fairly general. Let us not scare the pants of 'im with all the science. That simply isn't good teaching technique :-)!

You might like to know that on that lovely summer's day in '58, I'd just gone down to the old Pier "C" at the foot of Burrard Street. The bridge under construction was clearly visible from the old "ramp", as we called it, connecting Burrard Street to Howe Street. You entered Pier "C" from the ramp. I had walked the length of the freight shed while checking on some inbound freight, and gone out onto the north end of the pier. In that interval, the Second Narrows Bridge had come down. A friend of mine, a welder working for Allied Shipbuilders next door to the bridge, was among the first responders into the wreckage. Nasty business!

You may also like to know that the only time I've made a thorough fool of myself in Burrard Inlet was in a King's Cruiser towing a brace of three Enterprise dinghies down from Belcarra to Burrard Civic marina on a falling tide. I blew for the rail bridge to open, but it didn't. In the ensuing kafuffle I managed to get a painter around my shaft, but managed to get within reach of Hooker Chemicals wharf on the last of the dying RPM, so in the end there was no harm done. Except for scaring myself silly wandering through that caustic soda/ chlorine plant after dark :-)! .

So let's do our new friend a favour and help him gently on his way :-)!

TP
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Old 11-08-2019, 19:20   #35
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Re: Questions on neap and spring tides. Is anyone able to help?

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If you look at the link below you'll see that in the PNW we have two tide sets a day, one greater than the other. Scroll down to the 9 day image it says "next spring tide Aug 14th, 11.4 feet." at the top of the image. You can see that there are two sets of unequal tides that day, only one of which is the spring tide.

https://www.tide-forecast.com/locati...n/tides/latest

Also look at the second link I posted in #4 about the 4 different types of tides.
I don't know if I'm reading this right but I think I've seen the same on several posts. My understanding is that Spring Tides do not occur every month but only when the moon, sun and earth align to form greater forces of gravity. Very different. Then the high tides are higher. Who knows. Terminology can differ. Has nothing to do with Spring although Spring Tides may occur in the Spring.
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Old 11-08-2019, 19:38   #36
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Re: Questions on neap and spring tides. Is anyone able to help?

Yes, Mithril, you have it right. The word "spring" in "spring tides" have nothing to do with the season of spring. The term is simply the term for the highest tide(s) that occur in a "moon's time". It happens that in my native language, Danish, the phrase for what we so prosaically call "a month" translates quite literally as "a moon's time".

However, for various historical reasons, mainly to do with religion and the papal bureaucracy, the space of time we call a "month" today, is not really determined by the celestial travels of the moon. We could do a bunch of geometry if you like, but it's probably enuff to know that a "synodic month", the time that elapses between each time the sun and the moon "meet", i.e "are in synod" or perfectly aligned, is 29.53 days. That is why any given State of Tide, such as LW occurs at a different time each day of a CALENDAR month which is a construct of man.

The synodic month is a phenomenon of nature, and, try as they might, neither the papal bureaucracy nor the French Academy can do anything about that :-)!


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Old 11-08-2019, 19:48   #37
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Re: Questions on neap and spring tides. Is anyone able to help?

[QUOTE=TrentePieds;2951827]Yes, Mithril, you have it right. The word "spring" in "spring tides" have nothing to do with the season of spring. The term is simply the term for the highest tide(s) that occur in a "moon's time". It happens that in my native language, Danish, the phrase for what we so prosaically call "a month" translates quite literally as "a moon's time".

However, for various historical reasons, mainly to do with religion and the papal bureaucracy, the space of time we call a "month" today, is not really determined by the celestial travels of the moon. We could do a bunch of geometry if you like, but it's probably enuff to know that a "synodic month", the time that elapses between each time the sun and the moon "meet", i.e "are in synod" or perfectly aligned, is 29.53 days. That is why any given State of Tide, such as MLW occurs at a different time each day of a CALENDAR month which is a construct of man.

The synodic month is a phenomenon of nature, and, try as they might, neither the papal bureaucracy nor the French Academy can do anything about that :-)!


Lived in Kobenhavn. Good memories. Still not quite my understanding but when moon, sun and earth all line up increasing gravity. Doesn't happen every lunar month but only at certain times. I will research in more detail.
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Old 11-08-2019, 20:35   #38
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by Mithril Bham View Post
...... Still not quite my understanding but when moon, sun and earth all line up increasing gravity. Doesn't happen every lunar month but only at certain times. I will research in more detail.
Might I suggest you have a quick look at the first link in post#2 and if you want more detail, try the second link.
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Old 11-08-2019, 20:40   #39
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by Mithril Bham View Post
I don't know if I'm reading this right but I think I've seen the same on several posts. My understanding is that Spring Tides do not occur every month but only when the moon, sun and earth align to form greater forces of gravity. Very different. Then the high tides are higher. Who knows. Terminology can differ. Has nothing to do with Spring although Spring Tides may occur in the Spring.
The very first link in this thread has a definition and description by NOAA.

If you look at their graphic you can see that when the moon is new, between the earth and the sun, and when the moon is full, on the side of the earth away from the sun, there are spring tides, twice a lunar month.

https://oceanservice.noaa.gov/facts/springtide.html

Perhaps you're concerned with the tilt of the moon's orbit which puts it above and below the perfect alignment? When there is a full moon and it is not above or below the ecliptic is there a lunar eclipse.
This has nothing to do with the regular definition of spring tides.
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Old 11-08-2019, 20:48   #40
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Re: Questions on neap and spring tides. Is anyone able to help?

Mithril.

Yes, a spring tide ONLY happens once in a synodic month, specifically when the sun and the moon are lined up on the SAME side of the earth. Due to the "wobble" of their relative orbits sun, moon and earth are rarely perfectly in line. On the odd occasion when they are, we get the "super spring tides" that in this part of the world we call "king tides". They are the very highest of spring tides. When the alignment isn't perfect, we just have your garden variety spring tides. This is because the gravity of the sun is augented by the gravity of the moon so the "bulge" of water that these combined gravitational attractions draw up, and which circles the earth, is the highest it ever is.

When sun and moon are in alignment on opposite sides of the earth, we have two "bulges" of water going around the earth, but each one of lesser height that the "combined" one in the first example. So we have high tides alright, but not spring tides.

When the moon "quarters" the sun, i.e. when there is NO alignment on a straight line, the gravitational pull of the moon raises a bulge that is a quarter way around the earth from the one raised by the sun. Again we have high and low tides, but the highs are lower than they were in the previous two examples.

Low water is simply the "hollow" between the bulges and are the RESULT of the high waters.

But as you can now see, the complex celestial geometry generated by the interaction of the earth's rotation about the sun and the moon's rotation about the earth in combination with the wobble of the orbits makes prediction of tides a very, very complicated business. Add to those difficulties the ones that are introduced by the geology of the earth that obviously influences the flow of water around the globe. If you get your jollies from math, then by all means pursue the study. If you'd rather go sailing, then there is no need to. Just review what I said in previous posts.

Since you were in Copenhagen, you might like to know that a chap name of Thyco Brahe had an observatory on a little island called Hven not far from Copenhagen in the Sound twixt Denmark and Sweden. This was back in the late 16th Century. A lady by the name of Dava Sobel wrote a book about John Harrison who invented the marine chronometer, and in it she referred to old Tycho. I was able to help her with a detail in the book that wasn't quite correct in the first edition, and she sent me a copy of the book IN DANISH. MySaintedFather was enormously pleased when I gave it to him for his birthday :-)

You might like to google Dava and get one or two of her books. But for the work of Thyco Brahe and John Harrison, there could have been no chartplotters today :-)!

TP
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Old 11-08-2019, 20:53   #41
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Re: Questions on neap and spring tides. Is anyone able to help?

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Mithril.

Yes, a spring tide ONLY happens once in a synodic month, specifically when the sun and the moon are lined up on the SAME side of the earth. Due to the "wobble" of their relative orbits sun, moon and earth are rarely perfectly in line. On the odd occasion when they are, we get the "super spring tides" that in this part of the world we call "king tides". They are the very highest of spring tides. When the alignment isn't perfect, we just have your garden variety spring tides. This is because the gravity of the sun is augented by the gravity of the moon so the "bulge" of water that these combined gravitational attractions draw up, and which circles the earth, is the highest it ever is.

When sun and moon are in alignment on opposite sides of the earth, we have two "bulges" of water going around the earth, but each one of lesser height that the "combined" one in the first example. So we have high tides alright, but not spring tides.

When the moon "quarters" the sun, i.e. when there is NO alignment on a straight line, the gravitational pull of the moon raises a bulge that is a quarter way around the earth from the one raised by the sun. Again we have high and low tides, but the highs are lower than they were in the previous two examples.

Low water is simply the "hollow" between the bulges and are the RESULT of the high waters.

But as you can now see, the complex celestial geometry generated by the interaction of the earth's rotation about the sun and the moon's rotation about the earth in combination with the wobble of the orbits makes prediction of tides a very, very complicated business. Add to those difficulties the ones that are introduced by the geology of the earth that obviously influences the flow of water around the globe. If you get your jollies from math, then by all means pursue the study. If you'd rather go sailing, then there is no need to. Just review what I said in previous posts.

Since you were in Copenhagen, you might like to know that a chap name of Thyco Brahe had an observatory on a little island called Hven not far from Copenhagen in the Sound twixt Denmark and Sweden. This was back in the late 16th Century. A lady by the name of Dava Sobel wrote a book about John Harrison who invented the marine chronometer, and in it she referred to old Tycho. I was able to help her with a detail in the book that wasn't quite correct in the first edition, and she sent me a copy of the book IN DANISH. MySaintedFather was enormously pleased when I gave it to him for his birthday :-)

You might like to google Dava and get one or two of her books. But for the work of Thyco Brahe and John Harrison, there could have been no chartplotters today :-)!

TP
NOAA and the dictionary disagree with you. Spring tides occur both on new and full moons.
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Old 11-08-2019, 23:38   #42
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Re: Questions on neap and spring tides. Is anyone able to help?

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NOAA and the dictionary disagree with you. Spring tides occur both on new and full moons.
Right.

For that matter, TP cannot spell Brahe's calling name(s). He had the choice between Tyco and Tyge Ottesen and failed.
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Old 12-08-2019, 00:51   #43
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Re: Questions on neap and spring tides. Is anyone able to help?

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Thanks. Does everyone experience neap and spring tides at the same time all over the earth?

Or it varies what day, by different location?

In South Australia, we experience "Dodge" tides. That is where there is little or no difference between high and low tides, thus, no water movement.
It's a bugger for fishing.
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Old 12-08-2019, 04:54   #44
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Re: Questions on neap and spring tides. Is anyone able to help?

Understanding and using tides (you can’t fight them) is one of the most satisfying things about cruising.

The max spring tide normaly occurs about two days after a new or full moon. The heights of HW and lows ofLW will gradually decrease and increase accordingly. Put more simply the RANGE ( HW minus LW) will decrease down to neaps, and then start to increase.

I assume you are UK based. If so learn to use tidal flow diagrams, normaly based on HW Dover, remembering that all times are in GMT or UT as it is now called.

A fascinating subject that many Day Skippers initially struggle with but well worth mastering.
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Old 12-08-2019, 10:01   #45
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Re: Questions on neap and spring tides. Is anyone able to help?

First, even though the OP may be a newbie and student and who knows where he/she lives, others are reading this thread as they try improve their knowledge of tides. So lets juicy it up and throw in a "King" tide.

A King tide is a Spring tide on steroids and I just grabbed a definition from the net:

"When the sun and moon are in alignment – as is the case with a new or full moon – their combined gravitational pull results in exceptionally high tides, known as Spring Tides. These Spring Tides become King Tides when the moon is in its perigee due to the stronger gravitational force of the moon on the earth's oceans."

And perigee is (from the net) - "Apogee and perigee refer to the distance from the Earth to the moon. Apogee is the farthest point from the earth. Perigee is the closest point to the earth and it is in this stage that the moon appears larger."

And I will reveal my most profoundly stupid thing I did on a boat. So I'm sailing my 24 foot C&C sailboat out of Mosquito Creek in North Vancouver. When I went out I checked the fuel in the external tank and it was more than enough for a sail and a return trip. But when we motored under the Lions Gate Bridge heading out for our evening sail, the wind had done its summer trick of totally disappearing. Now for some reason that will remain a mystery to me, most pleasure sail craft never carried VHF radios. None of my boat owning buddies ever had a radio on board back in the mid 70's to early 80's.

So we motored everywhere and returned again heading under the Lion's Gate Bridge at approximately 11:00 PM, so nice and dark and in those days very isolated - no boats - except large merchant ships entering the port area there. And right under the bridge at the narrowest point, I ran out of gas. So me and my buddy are floating around and I am profoundly aware that a ship may soon be running me over as I'm almost right in the middle of the transit lane.

After a brief moment of panic, I decided to pump the bulb hoping there was some small amount of gas at the bottom of the tank and in the long connecting hose. And there was! I'd pump several times and the motor would work for about two minutes then quit again. I ultimately, repeating this process, got the boat to break water dock, but not into her slip. I tied up at the break water and returned the next day with fuel for the trip to the slip.

I went out and bought a VHF radio and was the first among friends to have one."

PS: I've posted the Ripple Rock explosion several times on Facebook and forums, never gets old.
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