Understanding tides, bit of help please

[GrandWood]

Looking at this tide chart for the Townsend canal, I’m assuming that slack tide there is no current, then when it transitions to Ebb that is the time the tide starts going out, then the following slack is the peak of low tide.

Thanks for any input to understand what’s happening with the current, my understanding is when there is an Ebb tide in the canal the current flows north towards Port Townsend, just looking to get the timing right as it seems from 10:48am to 2:18pm would be the best time to go from Puget sound to Port Townsend through the canal.

 

[SteveK]

First off the photo is not a tide table, it is a current table. The low and high tides of course are related to the currents. You need to look at the tide table along side of current table to see the relationship.
Slack current is between high and low tides, but not necessarily equal times. it can be short or several hours depending on the rise and fall.
If you want to use currents to choose best travel times, then about the slack depart in the direction of the next current using it to add to your speed over water.

 

[Hippocampus]

Anytime one has a large body of water and a smaller body of water connected by a canal the tide chart will not be consistent with the current chart. Other examples abound. The Cape Cod canal is an example in my neck of the woods. Generally speaking the smaller shallower body will empty or fill faster so set up a current. Same happens between junctions of multiple tidal rivers where flow rates maybe different.

 

[twistedtree]

Looking at this tide chart for the Townsend canal, I’m assuming that slack tide there is no current, then when it transitions to Ebb that is the time the tide starts going out, then the following slack is the peak of low tide.

Thanks for any input to understand what’s happening with the current, my understanding is when there is an Ebb tide in the canal the current flows north towards Port Townsend, just looking to get the timing right as it seems from 10:48am to 2:18pm would be the best time to go from Puget sound to Port Townsend through the canal.

When it says ebb and flood, I think those are the max ebb and flood currents. In this case I think you are correct that the ebb flows towards PT, but always good to confirm. In some locations the flow direction is counter intuitive.

And as has been pointed out, although tide levels and currents generally correspond, that’s not always the case, so again should be confirmed.

Some charting programs, Coastal Explorer for example, show both current and tide stations on the charts and with one click you can see what’s predicted.

 

[mvweebles]

A bit of semantics.

Tides are water filling and emptying and therefore measure vertical water level. Currents are water flow caused by tides and therefore go horizontally. Technically, there is slack current (or slack water) where water is not flowing in either direction, but not slack tide (typically called high or low tide). May sound like splitting hairs but it's an important distinction.

But the brain teaser comes when you figure out that for most navigable bays of any size (SF Bay for example), slack current does not coincide with high or low tide.

I took a quick look at tides and currents for Golden Gate Bridge. Low tide is -1.3ft at 0816. But slack water (transition from ebb to flood) doesn't occur until 0948. Said another way, there is a 1-1/2 hour period (0816 until 0948 at GG Bridge) where SF Bay is filling (rising tide) but water is draining out (ebb current).

I had the good fortune to be from San Francisco where the Army Corps of Engineers constructed The Bay Model in the 1950s before computer modeling. It was a scale model complete with tides and currents of the entire SF Bay the size of a basketball court that accurately showed effect of tides and currents (what would happen if there was an oil spill in Richmond for example).

I believe the model is still open in Sausalito. It's a great museum. Was helpful for me

Peter

 

[Bmarler]

Looking at this tide chart for the Townsend canal, I’m assuming that slack tide there is no current, then when it transitions to Ebb that is the time the tide starts going out, then the following slack is the peak of low tide.

Thanks for any input to understand what’s happening with the current, my understanding is when there is an Ebb tide in the canal the current flows north towards Port Townsend, just looking to get the timing right as it seems from 10:48am to 2:18pm would be the best time to go from Puget sound to Port Townsend through the canal.

Any time near or after slack is ok. Ebb is definitely north towards port Townsend. Max ebb runs about 3 knots, so be sure you maintain enough forward throttle to ensure steerage.
If you waited till about 1 to go through, there would be lots of depth, slower water, and still enough time on the ebb to help carry you to port Townsend.

 

[RT Firefly]

Greetings,
Perhaps this ditty will clarify...

 

[sjisailor]

+1 to the other explanations. Just want to add that slack current does not generally align with high or low tide -- although those points are where the tide is lowest or highest they are NOT usually aligned with the exact time when the current shifts direction (water sloshes, after all). Slack may differ from high/low by an hour or two.

A good thread with charts and explanations is here: Slack tide length

Related, at slack tide/current, it's not the case that there is NO current, only that ebb and flood are roughly equal. Locally, there may be currents in arbitrary directions, whirlpools etc. to watch out for, minute to minute.

 

[Portage_Bay]

A good way to phrase it to keep your head in the right place is for currents use "slack before the ebb" and "slack before the flood". "Slack tide" mixes the two. Even worse terminology I too often hear is "high slack" or "low slack"

OP, as you gain more confidence and experience you will be ready to travel further. Fully understanding tides and currents will be important. Deception Pass, Agate Pass and Tacoma Narrows are some local examples. When you are ready to venture to BC and Ak its even more important.

 

[AlaskaProf]

Coastal Explorer! Real-time graphics explain it all. Cheap, perpetually supported, and user-friendly.

I sold the boat three years ago and still consult it at home computer for the fun-of-it. (see screen grabs above).

 

[NWboater2]

I get that “slack” is too vague in many contexts but how is high slack “even worse”? It’s slack before ebb, said more pithily. Plain as day.

 

[klee wyck]

Looking at this tide chart for the Townsend canal, I’m assuming that slack tide there is no current, then when it transitions to Ebb that is the time the tide starts going out, then the following slack is the peak of low tide.

Thanks for any input to understand what’s happening with the current, my understanding is when there is an Ebb tide in the canal the current flows north towards Port Townsend, just looking to get the timing right as it seems from 10:48am to 2:18pm would be the best time to go from Puget sound to Port Townsend through the canal.

I think when beginning to learn the vagaries of tide and current, sometimes a graphic display beats a tabular display so that you can see the speed of the current over a range of time rather than just looking
for s specific time for absolute slack which really doesn't exist in my experience.
Every tidal cycle results in a unique shape to the current graphs. Some cycles go from slack to roaring in minutes and others build gradually.
Looking at a graphic display gives you insight into how long the decent window may last in a given tidal rapid.
I prefer running against a slight head current to running down a fast current behind me in terms of steering control.
I have attached a graphic display of the current in the PT Canal on the 28th. You can see that during the afternoon hours you will always have a flood against you, but it will never exceed about 2.7 knots. Good going for several hours. You can see the ebb before that gets over 4 knots and that is a bit steep at peak for my tastes.
You should have an easy ride if you are heading toward PT that afternoon.
For me, I would plan leaving Poulsbo between 11:00 and noon to ride the morning ebb all the way to the Canal and then thru the Canal early in the flood. Sets up perfect for a slow boat.

 

[Portage_Bay]

I get that “slack” is too vague in many contexts but how is high slack “even worse”? It’s slack before ebb, said more pithily. Plain as day.

Because as others have said high and low do not necessarily happen at the same time as slack. Sometimes that time difference is important. High slack infers high and slack happen at the same time. Confusing to boaters just learning about tides and currents.

For example high at Yokeko Pt near Deception Pass is at 21:23 this evening. Slack was at 19:13. At 21:23 current was 5.2 kts ebb. To tell a novice boater to run the pass at high slack might not end well this evening.

I'm using OpenCPN on a tablet with a fat thumb so things might be a bit off. But the concept is valid.

 

[Crusty Chief]

That’s all great when you’re up in the PNW (wait till you get to Alaska), that all goes out the window as you head south. Local knowledge is what makes the difference. I had a hard time wrapping my head around when to enter the bar at El Salvador ( there we were looking for most available water under our keel, and even more so when we entered Panama further south. Do your homework, make sure you understand current and tides. Otherwise, you’ll need your depends, LOL

 

[NWboater2]

Agree it’s critical for anyone using the information to transit a rapid or bar to understand that high tide is not the same time or concept as that point on a current graph where the current stops flowing one way, pauses for a a few or maybe more minites and slowly starts going the other way.
Disgree that the word “high” as a modifier of slack— answering “which of the two kinds of slack am I dealing with?” —would lead to confusion that “slack before ebb” would not.
That novice boater might just as easily think “ebb… yeah that’s when the tide starts going out so I’ll go at high tide” and be in the same pickle.
Also I can’t say I’m positive but I thought the, or at least a, technical term was high slack water? Isn’t that used in some tables and texts?
Either way OP sorry for the drift.
Id hit that canal at the very end of the northbound current, caused the outgoing tide. That lets you ride that current all the way up from the south. If you miss your timing it’s no problem to go around. Good luck!

 

[NWboater2]

Or high water slack?

 

[psneeld]

This is one of the things that makes more sense with experience.

When I was teaching captain's licensing, a life long longliner fisherman was in a class and he stumbled across a small place near the James River (Norfolk area) where the current and tide made no sense to him or me.

We studied it for hours an realized the geography made this area an anomaly by a country mile buy eventually both of us could see why.

This topic is really misunderstood by newer boaters and even old salts cruising along will be surprised by current direction or strength without tidal documentation.

I went into mental battle with my last marina manager (25 years as a city marina manager) about tides. He was using a tide chart for a geographic point way up the bay. All you had to do is look at the wet pilings to see the tide had changed hours before. Along came my friend and marina resident who was a nuc sub captain... I shouted to his about he tidal stage...he glanced down and said it had changed hours ago like I told the manager. So experience is one thing....but paying close attention to detail is the other.

Like weather, learn the basics and every day when on the water, take notice of tide and tidal current and compare it to documented information. Be wary of locally published/internet "tide charts' as they are often incorrect and try and use NOAA ones or ones well proven accurate.

While in many places tide and tidal current is not a big piece of important navigational information, some places it's huge.... and one thing the new boaters that plan on cruising with minimal experience need to pay attention to. I say this as an assistance tower who met a lot of boaters sitting high and dry who "thought" they were knowledgeable or good navigators.

 

[Hippocampus]

Virtually all nav programs used on MFDs have those little current arrows. Tap on the one closest to your area of interest and you’ll get a banner on the bottom of the screen. There you can move the cursor forward and see what the current will do in the future.

Before the days work I go through that exercise for the entire path I expect to travel during the upcoming day. Might even do several days if I’m also thinking about weather windows or running 24/7 with crew. Now being under 5’ of draft tides are of much less interest but currents rule the day. You can’t figure out expected days work without considering current. You can’t adjust your SOG to make best use of currents without knowing them well in advance of getting to that spot.

So pretty much don’t think about tides except when having to deal with fixed piers. Do think about current a lot even when not dealing with pinch points like canals.

 

[Bmarler]

Or high water slack?

Slack water high could be the name of a maritime high school…

 

[Bmarler]

I think a lot of us come from slow boat backgrounds. Currents are a tool to be used to our best advantage.
It seems every area will have an anomaly though. Like the long boring colvos passage. Current always seems to go north, just at different speeds.

 

[SeaDogAK]

Virtually all nav programs used on MFDs have those little current arrows. Tap on the one closest to your area of interest and you’ll get a banner on the bottom of the screen. There you can move the cursor forward and see what the current will do in the future.

Before the days work I go through that exercise for the entire path I expect to travel during the upcoming day. Might even do several days if I’m also thinking about weather windows or running 24/7 with crew. Now being under 5’ of draft tides are of much less interest but currents rule the day. You can’t figure out expected days work without considering current. You can’t adjust your SOG to make best use of currents without knowing them well in advance of getting to that spot.

So pretty much don’t think about tides except when having to deal with fixed piers. Do think about current a lot even when not dealing with pinch points like canals.

At least in SE Alaska, I find the little current arrows on Navionics to be so inaccurate that they are close to useless.

 

[Bmarler]

At least in SE Alaska, I find the little current arrows on Navionics to be so inaccurate that they are close to useless.

In that area there’s no substitute for local knowledge. I grew up in Sitka and fished there with my family. You never stop learning…

 

[ofer]

I feel better now. i am fairly new to homer ak and was trying to figure tides mainly for fishing halibut. nothing made sense to me. so now i just get over to the grounds throw anchor wait for the water to stop swirling past the prop and then throw my lines in.

 

[psneeld]

At least in SE Alaska, I find the little current arrows on Navionics to be so inaccurate that they are close to useless.

Agreed....and it's not just SE AK..... thats why I posted one should both study charts/tables but use active observation and experience which trumps all....mainly because there aren't nearly as many actual current stations as tide stations. Many of those chart arrows might be calculated/estimated as opposed to tables of recorded data over hundreds of years like the tide stations.

 

[GrandWood]

Any time near or after slack is ok. Ebb is definitely north towards port Townsend. Max ebb runs about 3 knots, so be sure you maintain enough forward throttle to ensure steerage.
If you waited till about 1 to go through, there would be lots of depth, slower water, and still enough time on the ebb to help carry you to port Townsend.

Thank you much appreciated

 

[GrandWood]

Greetings,
Perhaps this ditty will clarify...

lol, I’m all squared away now, thank you

 

[GrandWood]

I think when beginning to learn the vagaries of tide and current, sometimes a graphic display beats a tabular display so that you can see the speed of the current over a range of time rather than just looking
for s specific time for absolute slack which really doesn't exist in my experience.
Every tidal cycle results in a unique shape to the current graphs. Some cycles go from slack to roaring in minutes and others build gradually.
Looking at a graphic display gives you insight into how long the decent window may last in a given tidal rapid.
I prefer running against a slight head current to running down a fast current behind me in terms of steering control.
I have attached a graphic display of the current in the PT Canal on the 28th. You can see that during the afternoon hours you will always have a flood against you, but it will never exceed about 2.7 knots. Good going for several hours. You can see the ebb before that gets over 4 knots and that is a bit steep at peak for my tastes.
You should have an easy ride if you are heading toward PT that afternoon.
For me, I would plan leaving Poulsbo between 11:00 and noon to ride the morning ebb all the way to the Canal and then thru the Canal early in the flood. Sets up perfect for a slow boat.

Thank you, much appreciated, we were thinking of heading out at 7am to hit the canal around noon-1oclock. Thinking the current would shoot us through the canal, our speed on our boat cruising around the bay today is 6knts at1600rpm. I for sure want to go thru the canal safely without and suprises

 

[RedRascal]

I see that max ebb is at 10:48 and slack is at 2:18. If you go through at noon you will have some current giving you a push. One thing to consider with a new to you boat is if Murphy shows up at the wrong time while transiting the canal it won't take long with current to position you where you don't want to be. It's back to 7th grade algebra problems like if my boat goes dead and the current is 1.5 knots how many seconds do I have before I am on the rocks 200' away. It wouldn't hurt to practice steering the boat with one engine before getting in there.

 

[GrandWood]

I see that max ebb is at 10:48 and slack is at 2:18. If you go through at noon you will have some current giving you a push. One thing to consider with a new to you boat is if Murphy shows up at the wrong time while transiting the canal it won't take long with current to position you where you don't want to be. It's back to 7th grade algebra problems like if my boat goes dead and the current is 1.5 knots how many seconds do I have before I am on the rocks 200' away. It wouldn't hurt to practice steering the boat with one engine before getting in there.

We are making the trip on one engine, starboard engine is seized, hopefully be able to get it swapped out there in june, if not while I’m there, then I’ll have to wait till fall. Have been practicing with single port engine docking, learning the effect of prop wash. I lose the engine while in the canal, I’m up a creek for sure no matter what the currents doing. Maybe better to go around, your giving me the hee bee gee bees, lol

 

[RedRascal]

Well shoot, I didn't know Murphy already took out the starboard engine. If it was me I'd just favor going through about 30 before slack. One other thing to be prepared for is larger opposing traffic. Just study the chart for coming through on the right 1/3 of the canal then if you meet something bigger coming through you won't have to scramble to see how far over you can go. Enjoy your cruise.