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Old 11-08-2019, 09:25   #16
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Re: Questions on neap and spring tides. Is anyone able to help?

Some tide & current tech info from Canada
Phenomena - Tides, Currents, and Water Levels


Some things I've learned over a lifetime of watching:

Locally (Gulf of Maine/Bay of Fundy)
Local fishermen call Spring & Neap Tides Full and Dead Tides.
"Full" tides have the greatest spread between Hi & Lo (a higher Hi tide & a lower Lo tide)with consequently larger Tidal Currents. This happens every other week year round.
"Dead" Tides" occur the weeks preceeding & following a week of Full Tides year round with consequent lower Hi Tides & higher Lo Tides and smaller Tidal Current.
If you look at the tidal prediction graphs over a period of several "months/moons" & compare to the local moon cycle times,you can see the direct relationship of this 29.5 day cycle. Ignore the calendar month & watch the (approx) 7 day periods.
Yes-there are a couple of times per year (spring & fall" that so-called "super or king" tides occur,with slightly higher & lower levels.But these are still in the normal 29.5 day cycle & are of no special consequence to most navigation.
Locally,the Fullest (Spring) Hi tides for a 7 day period will occur at or near noon & midnight with the Lo at 6:00AM & 6:PM EST.

Consequently,the 3 days leading up to & the 3 days after the Fullest(noon/midnight) Hi are locally said to be "springing" & "dropping".


Local tides swings (Neap week to Spring week)can vary from approx 23ft to 28 ft with consequent change in tidal current velocity.



Hope this helps. / Len
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Old 11-08-2019, 09:46   #17
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Re: Questions on neap and spring tides. Is anyone able to help?

Sounds like you have TWO tasks in hand: 1) passing your exam and 2) using your newly acquired knowledge while at sea.

For 1) all that has been said above is what you require to give the "right" answers to pass your exam.

For what you need for 2) let me elaborate a little: You haven't said where your are, so we can't know which of the 3 KINDS of tide you have where you are. But you can tell us.

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. My rule is that I want 5 feet of water under my keel at the lowest tide that will occur while I'm in the anchorage. Because we have mixed tides, that would normally be at the "low, low" water. I use the TIDE tables in conjunction with the contours on the chart to determine where I can put the hook.

What is much more significant while you are on passage is what the CURRENT is doing. The CURRENT TABLES (which are different from the tide tables, but generally contained in the same booklet or on the same web site) will tell you that. Because of our rather large RANGE we have commensurately FAST CURRENTS which in some passes will run 6 knots. It's obviously futile to go against a 6 knot current in a 5 knot boat :-).

The time when the current is predicted to turn is in the tables. The time when the current turns direction is called "slack water", and knowing when that occurs is much more important than knowing the height of the tide when you are on passage when you are in waters with a great tidal range.

Consider what a 2 knot current on your beam will require in terms of allowing for it in your course to steer: For every 5 miles you move forward you will move 2 miles sideways. Just draw on paper a little rectangle 5 inches long and 2 inches wide. Draw a diagonal in it. That diagonal will form an angle of 20ļ with the long side of the rectangle, and that is the steering correction you need to apply to track on the rhumb line.

All that just to tell you that what you need to answer on an exam and how you need to think about when at sea are two different things :-)

Anyway, focus on passing your exam. With that behind you, you can always come back here with questions about the practical stuff.

All the best

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Old 11-08-2019, 10:00   #18
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Re: Questions on neap and spring tides. Is anyone able to help?

AJ:

"Tidal datum" (the "benchmark") is fixed during a certain period (20 to 25 years), and then revised. The new Benchmark, the "Tidal Datum" is then published in Notices to Mariners. It is your job as navigator to annotate your charts as necessary. The tide tables published annually are based on the then current TD.

For a yachtsman to pay very much attention to this stuff will just blind himself with science :-) I the daily navigational work of a yachtsman there is really no need to consider the TD.

The weather effects you speak of, "storm surges" are capricious and cannot be accommodated in predictive tables. I would think that on the coast of NC you'd be much more weather conscious than we hare here in the Salish Sea.


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Old 11-08-2019, 10:32   #19
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Re: Questions on neap and spring tides. Is anyone able to help?

Trente,

The increased tides and sea level are more of an issue for fixed docks, but I've noticed the (favorable) impact on areas that were previously very skinny water. And in the Bahamas, crossing into Little Harbor, Abaco for me with a 5.5 foot draft is much easier now than charts would indicate. A fixed dock near me in NC built in 2004 lifted off the pilings in the last king tide - that never would have happened in 2004.

As for updating paper charts from NTM's I gave that up about three years ago. Don't have the time, data in US waters from electronic charts is excellent, and I'm using electronic charts almost exclusively anyway. Hence the question, and from your answer it seems possible that I'm seeing tide data that's 20 years old, unless NTM's are being updated in the electronic charts.

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Old 11-08-2019, 11:16   #20
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by AJ_n_Audrey View Post
Related question: I live in the Wilmington, NC area where sea level rise has had an outsize effect. We have seen more than six inches of sea level rise in the last 15 years, as much as eight, depending on how you measure, and we get three times as many yearly flooding events as before 2000.

So, the question is, do tide tables reflect the new normal? Are they updated every so many years to take into account the real high tide levels?
I'm fairly certain that increased general water level has no impact on the tide schedule. That said, since tide levels along a coast are primarily a function of geography (ie Bay of Fundy), if there is more water to run in and run out, it may, in some instances, change the schedule and current incrementally. While I doubt this is the case I really don't know.
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Old 11-08-2019, 11:36   #21
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by AJ_n_Audrey View Post
Related question: I live in the Wilmington, NC area where sea level rise has had an outsize effect. We have seen more than six inches of sea level rise in the last 15 years, as much as eight, depending on how you measure, and we get three times as many yearly flooding events as before 2000.

So, the question is, do tide tables reflect the new normal? Are they updated every so many years to take into account the real high tide levels?
Whereas in Norway and parts of Scotland we have the opposite problem as the land rebounds after the last ice age and sea level is actually dropping. So much for global warming causing global sea level rises. In some places this is very evident by the appearance of raised beaches, often in terraces, where banks of stones mark the previous sea level sometimes as much as a meter or more high.

This land rebound is part of the reason why London is sinking, the UK pivots around Manchester (roughly).

Are you actually sure it is the sea rising and not the land sinking? The Camargue in France has seen a sea level rise in the order of metres but this is nothing to do with the Med rising and entirely due to the land sinking

In the general scheme of things though 0.5in (13mm) of sea level rise a year is nothing to be {overly} concerned about as that is about the same as a ripple. The increase in yearly flooding is more likely due to weather than sea level rise (at that kind of rate).

In answer to the original question:
You have High tide and Low tide
The Highest High Tide and Lowest Low Tide occurs 2 days after Full and New Moon. This is Springs (and nothing to do with the season)
The Lowest High Tide and Highest Low Tide occurs 2 days after the half Moon and is called Neaps.
At certain times of the year and certain points in the Earth/Moon cycle there are particular tides called Highest Astronomical and Lowest Astronomical Tide. LAT is usually also called Chart Datum as this is the theoretical lowest water level experienced in a particular region (that is water level will never go below this), some areas though continue to use Mean Sea Leve being the average of High and Low tides (therefore water depth can go down as well as up unlike using LAT where it can only go up).
The Tidal Bulge is always moving so tides are constantly in motion around the planet. Different sides of oceans will experience High and Low tides are different times, even a few miles along the coast will result in slightly different High and Low Tide times (Fort William is 8 minutes later than Oban some 50km SW down Loch Linnhe for instance).
Avonmouth near Bristol has a tidal range of 14.5m at Springs and the Med lucky to see a metre.
Tides can be insanely complicated or stupidly easy depending on how detailed you want to get.
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Old 11-08-2019, 11:55   #22
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Re: Questions on neap and spring tides. Is anyone able to help?

Invest in an Almanac or at very least a set of tide tables. If you're sailing anywhere with any amount of tide it's crucial to get your head around the concept. The RYA Day Skipper course or something similar should make it a lot clearer.
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Old 11-08-2019, 14:08   #23
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Re: Questions on neap and spring tides. Is anyone able to help?

Quote:
Originally Posted by fif.ed View Post
I’m close undertaking my first ever passage!! ⛵️ and studying day skipper theory online.

I’m confused about tide phases.
Are we always in a spring or neap tide phase? And it alternates between one and the other?

Or do spring tides only occur for one day when there is a new moon or no moon. And then neap tides occur for one day when it is half way through the cycle?

If so, what phase of tide are the rest of the days in the cycle? ��

Thanks
There is a gradual transition from springs to neaps and back again... you can see it here...
https://www.tide-forecast.com/tides/...ontt-Chile.png

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

with 'springs' occuring on the 15th/16th of this month. For the days before that the tidal range is slowly ramping up.
I would refer to the days after spring tide as 'a couple of days after springs' and in the same manner talk of 'a few days before neaps' or 'coming up to springs'.

Spring tides typicaly occur at or just after the time of new and full moons when the sun and the moon are acting together.

What you will see in the link above and in the pic below is that each day there is a higher high water and a lower high water... same with low water heights.

This is quite important.... what you do not want to do is run aground just after springs at higher high water... if you do you will be stuck there for some time...

This is a very complex subject... above is the very simple view... below is a 'tide machine' used in the good old days for calculating tides.
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Old 11-08-2019, 14:23   #24
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by El Pinguino View Post
There is a gradual transition from springs to neaps and back again... you can see it here...
https://www.tide-forecast.com/tides/...ontt-Chile.png

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

with 'springs' occuring on the 15th/16th of this month. For the days before that the tidal range is slowly ramping up.
I would refer to the days after spring tide as 'a couple of days after springs' and in the same manner talk of 'a few days before neaps' or 'coming up to springs'.

Spring tides typicaly occur at or just after the time of new and full moons when the sun and the moon are acting together.

What you will see in the link above and in the pic below is that each day there is a higher high water and a lower high water... same with low water heights.

This is quite important.... what you do not want to do is run aground just after springs at higher high water... if you do you will be stuck there for some time...

This is a very complex subject... above is the very simple view... below is a 'tide machine' used in the good old days for calculating tides.


Thanks so much! So how do you know what the specific tidal height is in a specific area of a bay, for example? Because I only understand how to apply these tide variations and valuations to the vague figure given in the training almanac.

For example, if a spring tide means a subtle increase in depth by a meter... well thatís useful information... but only if itís totally precise about the spot. The depth could vary by a meter anyway if you were in a slightly different spot in the bay.

I donít understand how it can be that precise?
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Old 11-08-2019, 14:38   #25
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Re: Questions on neap and spring tides. Is anyone able to help?

Quote:
Originally Posted by fif.ed View Post
Thanks so much! So how do you know what the specific tidal height is in a specific area of a bay, for example? Because I only understand how to apply these tide variations and valuations to the vague figure given in the training almanac.

For example, if a spring tide means a subtle increase in depth by a meter... well thatís useful information... but only if itís totally precise about the spot. The depth could vary by a meter anyway if you were in a slightly different spot in the bay.

I donít understand how it can be that precise?
Simple answer to that.... it isn't.

Its a 'prediction'...

Depending on the area it can vary quite considerably in time and height just a few miles from either the standard or secondary port that you have to use.... local knowledge is needed here.

Predicted tide heights at standard ports can be influenced to a considerable degree by the weather. Where I used to sail ( Port Phillip, Australia ) an extended period of high barometric pressure coupled with low or no rainfall in the catchment would see both high and low waters lower than predicted... to such a degree that having hauled your boat you would not get enough water to splash her again...
Likewise in winter... prolonged SW gales combined with an extended period of low barometric pressure and heavy rain inland would see far higher tides.

A similar situation occurs in the River Plate ( that tide machine above is in a museum near Buenos Aires ) where the wind has a huge effect on tide heights.
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Old 11-08-2019, 14:46   #26
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Re: Questions on neap and spring tides. Is anyone able to help?

When the sun, moon and earth are inline it increases the gravitational force thus pulling (springing) the water and making tides more radical. At least that's what I was told. Neap is the opposite. Least gravitational force. Other factors are at play such as melt water and rivers influencing the tides especially in the PNW.
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Old 11-08-2019, 14:48   #27
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Re: Questions on neap and spring tides. Is anyone able to help?

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Simple answer to that.... it isn't.



Its a 'prediction'...



Depending on the area it can vary quite considerably in time and height just a few miles from either the standard or secondary port that you have to use.... local knowledge is needed here.



Predicted tide heights at standard ports can be influenced to a considerable degree by the weather. Where I used to sail ( Port Phillip, Australia ) an extended period of high barometric pressure coupled with low or no rainfall in the catchment would see both high and low waters lower than predicted... to such a degree that having hauled your boat you would not get enough water to splash her again...

Likewise in winter... prolonged SW gales combined with an extended period of low barometric pressure and heavy rain inland would see far higher tides.



A similar situation occurs in the River Plate ( that tide machine above is in a museum near Buenos Aires ) where the wind has a huge effect on tide heights.


Oh my, so these calculations can be fairly vague and inaccurate anyway? Feels like yo can never know enough
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Old 11-08-2019, 15:04   #28
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Re: Questions on neap and spring tides. Is anyone able to help?

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Originally Posted by fif.ed View Post
Thanks so much! So how do you know what the specific tidal height is in a specific area of a bay, for example? Because I only understand how to apply these tide variations and valuations to the vague figure given in the training almanac.

For example, if a spring tide means a subtle increase in depth by a meter... well thatís useful information... but only if itís totally precise about the spot. The depth could vary by a meter anyway if you were in a slightly different spot in the bay.

I donít understand how it can be that precise?
Putting aside that the prediction can be off due to excessive rain, extreme barometric pressure, prolonged winds or a large distance from the tide station for now. In the bay you postulate the height of the water above or below the datum will be the same everywhere. Let's say at noon the tide was a plus 10 feet and at 6 pm it will be 0 feet. If it is 3 pm the tide will be close to a plus 5. So any depth marks on your chart you add 5 to and so increase the depth marked on the chart by 5.

If you intend to anchor you will know that at 6 pm the depth will have decreased by 5 feet. So you look at your fathometer subtract 5 and see if the depth will still be adequate at that time. At midnight lets say the tide is back at plus 10. You have to add 5 feet to what your fathometer says at 3 pm to calculate your rode for the worst case scene of maximum depth.

By the way spring tide means a range. The high water will be higher, but the low water will be lower. Spring tides can have negative numbers, so the numbers on the chart can be less than what is shown.

Also look up the rule of 12's for estimating tide height.
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Old 11-08-2019, 15:56   #29
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Re: Questions on neap and spring tides. Is anyone able to help?

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Predicted tide heights at standard ports can be influenced to a considerable degree by the weather.

To put that into numbers for the OP:


Tide Height and Air Pressure - Franks-Weather - The Weather Window


A rough guide is that a change in pressure of one hectoPascal (one millibar in days gone by) will change the sea level by one centimetre. Tide tables assume a standard pressure of 1013 hPa. This means that a pressure of 1040 hPa, pretty high but not abnormally so, could give a sea level lower by nearly 30 cm than expected. That could make the difference between crossing the sill and ignominiously hitting it.
The lowest pressure recorded around the British Isles is about 925 hPa which would give sea levels nearly a metre above tide table predictions. This can be an important factor in storm surge conditions when the East Coast is threatened. Unless air clearance is critical, a skipper is unlikely to worry overmuch about too much rise of tide. The highest pressure around the UK is about 1050 hPa which would give sea levels about 40 cm lower.
In a nutshell, worry about the pressure effect if the pressure is higher than 1020 hPa and your depth is getting critical.
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Old 11-08-2019, 16:28   #30
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Re: Questions on neap and spring tides. Is anyone able to help?

Then there are the King tides. Ask all those that had their 4WD's swamped at the Coorong Surf fishing contest (Sth Australia) a few years ago what THAT means!!!!
(One in early Jan & the other in early July?)


https://www.abc.net.au/news/2007-01-...-beach/2176576
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