Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-01-2016, 19:33   #16
Senior Cruiser
 
jackdale's Avatar

Cruisers Forum Supporter

Join Date: Mar 2008
Location: Calgary, AB, Canada
Posts: 5,048
Images: 1
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by SimonV View Post
Moon shmoon. It's simple if the tide is out, it will be back in about six hours. Simple.

Sent from my GT-N7105T using Cruisers Sailing Forum mobile app
Only if it is semi diurnal.
__________________

__________________
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203,204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline   Reply With Quote
Old 25-01-2016, 19:54   #17
Registered User

Join Date: Jan 2010
Location: Port Ludlow Wa
Boat: Makela,Ingrid38,Idora
Posts: 1,973
Re: Tidal Cycle? Help me out here!

A very good subject indeed. Local tables for areas of swift current in areas of strong geographic affects are surprisingly accurate. I was once motivated to stay on a mooring in Obstruction Pass in order to attend a family event. The bottom under the mooring was jagged boulders.(certain disaster) Leaving the mooring before the expected minus low was a safety issue. We corrected our depth sounder reading for transducer location using a lead line and interpolated the time from the tide chart that we would need to leave the mooring to insure a mere 12 inches between the rocks and the keel. We left on time and the error was 6 inches....low. Whew!!!!That was close. Science is cool huh? Perhaps the moon was a little early? Perhaps the slosh was a little slow?
__________________

__________________
IdoraKeeper is offline   Reply With Quote
Old 25-01-2016, 20:00   #18
Registered User

Join Date: Jan 2010
Location: Port Ludlow Wa
Boat: Makela,Ingrid38,Idora
Posts: 1,973
Re: Tidal Cycle? Help me out here!

A request for Jack...please explain the difference between Canadian chart datum and US chart datum. It can't hurt to remind folks of the difference when thinking about moorings, docks and anchorages.
__________________
IdoraKeeper is offline   Reply With Quote
Old 25-01-2016, 21:01   #19
Senior Cruiser
 
jackdale's Avatar

Cruisers Forum Supporter

Join Date: Mar 2008
Location: Calgary, AB, Canada
Posts: 5,048
Images: 1
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by IdoraKeeper View Post
A request for Jack...please explain the difference between Canadian chart datum and US chart datum. It can't hurt to remind folks of the difference when thinking about moorings, docks and anchorages.
Canada is Lowest Normal Tide, US charts (at least in the PNW) use Mean Lower Low Water. The difference can be as much as 1.5 meters.

Let's just all go to LAT (Lowest Astronomical Tide)

CHS charts are generally also metric. A few are still fathoms and feet.

Read the Title Block.
__________________
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203,204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline   Reply With Quote
Old 26-01-2016, 07:15   #20
Registered User
 
NewMoon's Avatar

Join Date: Jan 2010
Location: Holladay, UT
Boat: Nordic Tugs 37
Posts: 285
Images: 13
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by deblen View Post
The sun gets involved also especially during spring & neap. If the sun's pull is aligned with the moons pull,you get a spring.Conversely.if sun's pull is opposite the moon's,you get a neap. This happens twice per month roughly.
Maybe it's just another way of saying the same thing, but here's my understanding:

The sun's gravity is also quite influential. When sun and moon are pulling in the same direction from earth (new moon) we get spring (largest) tides. Also, when they are pulling on opposite sides of the earth (full moon).

When sun and moon are pulling at 90 degrees from each other relative to earth (half moon), we get neap (smallest) tides.

On the Inside Passage, further in toward the mainland especially, spring tides can be as much as 24 feet. Not Bay of Fundy, for sure, but impressive.
__________________
Richard Cook
Dream Catcher (Nordic Tugs 37)
"Cruising in a Big Way"
NewMoon is online now   Reply With Quote
Old 26-01-2016, 07:34   #21
Registered User

Join Date: Jun 2015
Location: Indiana
Posts: 194
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by a64pilot View Post
Lord, you guys are way over my head, all I know about the cycle is it goes out, where does it go? I don't know, seems to always come back though
I just read the entire thread and I'm with you...
__________________
Hoosiersailor is offline   Reply With Quote
Old 26-01-2016, 07:46   #22
Registered User

Join Date: Oct 2015
Location: Germany
Boat: 2ft wide dreaming chair
Posts: 311
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by Hoosiersailor View Post
I just read the entire thread and I'm with you...
over here weather forecast usualy includes tidal predictions, at least for the North Sea, the Baltic side just goes "ti-what?" (they have a 30cm difference low to high)
__________________
Simonsays is offline   Reply With Quote
Old 26-01-2016, 08:10   #23
Registered User

Join Date: Sep 2014
Posts: 114
Re: Tidal Cycle? Help me out here!

Thanks for ALL replies, I am the OP.

Before I posted you will be aware I was sure I was correct. This information is no secret! I just needed reassurance before I fire another email off to the publisher of the training booklet.

Raindog nailed it in post 2.

Spring & Neap tides would occur randomly if they do not follow the Synodic/Lunar month. My understanding is that Lunar month is another name for Synodic month.

During my correspondence with the same publisher he advised me of something else I feel is probably incorrect but have been unable to determine, perhaps someone can help.....

I think we are all in agreement that the Synodic/Lunar month averages about 29.53 days. A google determines this never varies by more than about 7 hours.

This period is made up of 4 phases of the Moon and interestingly the individual phases can vary by much more. However I have doubts about the publishers claim that a phase of the Moon can be as little as 5 days and as much as 9 days.

I may be wrong, he may be right. I have so far been unable to determine this.

Any ideas.

Mike
__________________
Mike1956 is offline   Reply With Quote
Old 26-01-2016, 08:25   #24
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 2,736
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by Mike1956 View Post
Thanks for ALL replies, I am the OP.

Before I posted you will be aware I was sure I was correct. This information is no secret! I just needed reassurance before I fire another email off to the publisher of the training booklet.

Raindog nailed it in post 2.

Spring & Neap tides would occur randomly if they do not follow the Synodic/Lunar month. My understanding is that Lunar month is another name for Synodic month.

During my correspondence with the same publisher he advised me of something else I feel is probably incorrect but have been unable to determine, perhaps someone can help.....

I think we are all in agreement that the Synodic/Lunar month averages about 29.53 days. A google determines this never varies by more than about 7 hours.

This period is made up of 4 phases of the Moon and interestingly the individual phases can vary by much more. However I have doubts about the publishers claim that a phase of the Moon can be as little as 5 days and as much as 9 days.

I may be wrong, he may be right. I have so far been unable to determine this.

Any ideas.

Mike
Sounds like hogwash to me. There are some variations caused by orbital eccentricity and such, but a glance at a phase calender shows phases occur roughly around the 7 to 8 day mark (well, for 2016 at least)

http://www.calendar-12.com/moon_phases/2016

Sent from my SGP521 using Cruisers Sailing Forum mobile app
__________________
Reefmagnet is offline   Reply With Quote
Old 26-01-2016, 08:42   #25
Registered User

Join Date: Sep 2014
Posts: 114
Re: Tidal Cycle? Help me out here!

I do accept that the phases of the Moon vary quite a bit. Assuming the average phase is 25% of the Synodic month +/- 7.3 days, the variation can certainly be 30 hours or more but I doubt as much as the publisher suggests. Just have been unable to put my finger on it!

Mike
__________________
Mike1956 is offline   Reply With Quote
Old 26-01-2016, 09:04   #26
Registered User

Join Date: Dec 2015
Posts: 378
Re: Tidal Cycle? Help me out here!

What is usually left out of the grade-school explanations of tides is that how the gravity of moon pulls the oceans to make peaks under the moon and opposite to the moon, and troughs at 90 degrees on either side is true only in the southern ocean, where the oceans are free to flow 360 degrees around the globe.

Everywhere else, what we experience as tides are enormous low-frequency waves that propagate northward.

In the roaring forties, high tide is beneath and opposite the moon. Everywhere else, the timing of high tide is dependent upon how long it takes for the wave to propagate northward. At any given longitude, high tide is later the farther north you go.
__________________
Jdege is offline   Reply With Quote
Old 26-01-2016, 09:19   #27
Registered User
 
TeddyDiver's Avatar

Join Date: Aug 2010
Location: Arctic Ocean
Boat: Under construction 35' ketch
Posts: 1,828
Images: 2
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by Mike1956 View Post
I do accept that the phases of the Moon vary quite a bit. Assuming the average phase is 25% of the Synodic month +/- 7.3 days, the variation can certainly be 30 hours or more but I doubt as much as the publisher suggests. Just have been unable to put my finger on it!

Mike
Well if the publisher is using "wrong" month they surely get more variation too
__________________
TeddyDiver is offline   Reply With Quote
Old 26-01-2016, 09:30   #28
Registered User
 
deblen's Avatar

Join Date: Oct 2014
Location: Grand Manan,N.B.,Canada N44.40 W66.50
Boat: Mascot 28 pilothouse motorsailer 28ft
Posts: 1,400
Images: 1
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by NewMoon View Post
Maybe it's just another way of saying the same thing, but here's my understanding:

The sun's gravity is also quite influential. When sun and moon are pulling in the same direction from earth (new moon) we get spring (largest) tides. Also, when they are pulling on opposite sides of the earth (full moon).

When sun and moon are pulling at 90 degrees from each other relative to earth (half moon), we get neap (smallest) tides.

On the Inside Passage, further in toward the mainland especially, spring tides can be as much as 24 feet. Not Bay of Fundy, for sure, but impressive.
You are correct & I was wrong in my post #12.
I said a neap occurs when sun & moon are pulling against one another.
Actually,as you say,a neap is when sun & moon's pull are at 90 deg. to one another. We call them dead tides locally as opposed to full tides(springs).
There are 2 full tides per month(at full & new moon) & 2 neaps per month. In practice,this means a week of spring,week of neap, week of spring & week of neap.

Link to Saint John,N.B. tide tables-SJ is about 1/2 way up the bay.

http://www.waterlevels.gc.ca/eng/station?sid=65

Another important point when traveling in unfamiliar tidal waters is local knowledge.
Tide tables are helpful but asking the locals is wise.

Cheers/ Len
__________________
My personal experience & humble opinions-feel free to ignore both
deblen is offline   Reply With Quote
Old 26-01-2016, 10:29   #29
Registered User

Join Date: Dec 2015
Posts: 378
Re: Tidal Cycle? Help me out here!

Quote:
Originally Posted by Jdege View Post
Everywhere else, what we experience as tides are enormous low-frequency waves that propagate northward.
A followup:

Animations of models of the tides of the oceans
__________________
Jdege is offline   Reply With Quote
Old 26-01-2016, 12:33   #30
Registered User

Join Date: Dec 2013
Location: SF Bay
Boat: 36' Hartog ketch
Posts: 30
Re: Tidal Cycle? Help me out here!

The thing that has me baffled, and perhaps someone here knows, is how the tides have switched times. Here in SF, when I was a lad, the the extreme low tides in the early morning were followed by the 'king tides', around noon or so. Now that I have returned to the bay area, after 25 years, the king tides are early and followed by the extreme lows.

When did this happen?

Ed
__________________

__________________
ThresherMan is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Need help with tidal calculation and passage planning dokondr General Sailing Forum 7 31-03-2014 06:11
Tidal prediction freeware Hud3 Navigation 7 17-02-2008 08:15
tidal stream (direction) information pete33458 Seamanship & Boat Handling 15 08-08-2007 19:14
Tidal Prediction Website GordMay The Library 0 05-03-2006 06:42



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:13.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.