Tides and Forward Progress

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From another thread Marin's friends seem to think one's progress as affected by tidal currents does not average out. I think it's obvious that it can be no other way given enough time underway in tidal waters.

With the exception of river influence tidal currents spend 50% of their time going one way and 50% of their time going the other way and when their velocities aren't the same other tidal current will balance that out so if one traveled over time their progress would average out so they would be running with the current half the time and bucking it half of the time.

However People's notions about it dosn't seem to mach up. I think it's like rainy days. Sunny days come and go but if it rains on the weekend people will be whining about the rain big time. And they won't be inclined to forget it for quite some time. When we run w the current we think or say "oh thats nice" but when we buck it for hours the effect of the current has much more emotional impact. And when the trip is over and a year has past we tend to think the current was against us much more than with us. I submit that that is true no more than an old wives tale.
 
In our area, with long deep channels, the tides change from the edges in towards the centre. The main body of flow in mid channel slows down and reverses at a slower rate than the shallow water at the edges. Ever see those long, thin foam lines parallel to the shore? That's the line of opposing currents which you can feel through the seat of a kayak when you cross it. Sometimes sticks will spin in circles in the foam.

Knowing this, you can milk the main flow mid channel for an extra bit, or scoot closer to shore if that's an advantage. So, in other words, it doesn't have to be 50/50 :)
 
Eric- There are the 'doers' and the 'cut and paste' posters.
Why do you want to waste your time with it?
 
Anode,
Peraps there's something to learn. There's probably 100 guys here that will learn from MurrayM's input. Frequently I move around in a channel to find the best water and my looking at this question in simplistic terms isn't reality. Just like the gas engine thing I like to explore. But you're completely free of all this aren't you?
 
You're 100% correct. Using Marin's logic the Sound would soon be empty and the bay's all dry.

While I would say that running against a river outflow would affect you're progress, it still is invalid because most of us RETURN from our journeys eventually, so any extra fuel would be recovered on the home trip.

Another thing would be the prevailing winds. They alter the times I like to head out. Sometimes I'd rather buck a current than deal with deal with quartering seas.

It's all about choices.
 
Knowing this, you can milk the main flow mid channel for an extra bit, or scoot closer to shore if that's an advantage. So, in other words, it doesn't have to be 50/50 :)

I do this a lot if know the tide is changing under me and I'm gonna get caught in it. Also, cutting the inside of a corner will put you across the tide longer.
 
When I put the camper on the truck and head out on a trip it is always uphill. That's just life.
 
When I put the camper on the truck and head out on a trip it is always uphill. That's just life.

That's because it's downhill into both Smithers and Prince Rupert ;)

Howdy neighbour, from Kitimat :)
 
I believe Marin is right and I'll attempt to prove it mathematically.

Imagine cruising a 2 NM course, round trip at 6 kts with no current. Each leg will take 20 minutes (2/6=.333x60=:20) for a :40 round trip.

Now cruise the same course with 2 kts of current with you and against you. Leg 1 is into the current yielding a 4 kt speed over 2 miles and it takes you 30 minutes. (2/4=.5x60=:30)
Leg 2 is completed at 8 kts with the push from the current and takes you 15 minutes.(2/8=.25x60=:15) Adding leg 1 and 2 is :30+:15=:45.

The same course traveled with the 2 kt current took 5 minutes longer. The reason is that when the current is helping you, you have less time to benefit from it. When it slowing you down, the effect of the current hits you over a longer span of time.

That's this engineer's take on it anyway.
 
On the east side of Princess Royal Island, if you time it right, you can travel with the current on the flood, keep going in the same direction, and keep going with the current on the falling tide.

We got there on a calm day on a rising tide and there was a weird band of jumpy little wavelets from shore to shore. On the chart there was a notation that read, "Tides Meet".
 
That's this engineer's take on it anyway.

WHAT?

OK... when would take a 2 NM trip... and go so slow that THE TIDES are a problem for you. (you're making trawlers look bad around the world)

We originally were talking about maximum range and accounting for the tides on long (Inside Passage types of runs)

Here's another for you (engineering problem)

I get up in the morning and notice that if I wait 2 hours to get started... I can catch the Slack tide ahead of the flood... the flood itself... and then the slack before the Ebb tide starts.

I can take advantage of all three, run for 6 hours and never have a problem. (plus have an extra two hours to enjoy my coffee) :)

Each day, there are two high tides and two low tides (about 12 hours, 25 minutes apart). Therefore... at worst, I'd have to wait 4 hours (& 12 minutes) to miss whichever I wanted to avoid and take advantage of the other.
 
You're 100% correct. Using Marin's logic the Sound would soon be empty and the bay's all dry.

Of course it would. You guys need to learn to read better. I never said the overall flows don't cancel each other out. Of course they do. My dog knows that.

I said that in running a boat through the maze of islands and channels along this coast, the current effects on the boat will not always cancel themselves out. Anyone who's actually run a boat around here-- and I'm beginning to think some of you haven't or if you have you've not been paying attention to what's going on around you-- knows that when you follow a winding course through the islands you will encounter all manner of local currents, some helping, some hindering your forward progress even though the overall flow is ebbing or flooding.

And, depending on your route, you can encounter more adverse current than helpful or neutral current, or it can be the other way around. This happens to us every time we go to destinations in the islands. The fact most of you don't seem to realize this is pretty amazing, frankly. Everyone we boat with is well aware of it.

The same is true going up the Passage. So you can't assume that all the local current effects on your way north or south will cancel themselves out. According to the people I know who've done it, as opposed to speculating about it from the couch in front of the TV, the current effects on their boats do not equal out on these trips and some of them have the log and fuel consumption records that show this.

One person here who seems to have a grasp of this local current concept is Murray. What he's experienced with varying current strengths and probably directions in different channels is what I'm talking about.

How the current will effect you depends on the route you take and what the current does locally along that route. And these effects will not always cancel themselves out.

My dog knows that, too.
 
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The same is true going up the Passage. So you can't assume that all the local current effects on your way north or south will cancel themselves out.

But you also cannot assume that it's harder to get UP the Passage, than it is coming back.

Traveling long enough, and choosing your departures and arrivals will easily null out with just a little forethought. I can get there without EVER bucking a tide if I chose, but I also understand how tides, currents, ebbs and flows can work to my advantage.

My dog knows that, too.

My dog isn't allowed to advise me on matters of navigation.
 
But you also cannot assume that it's harder to get UP the Passage, than it is coming back.

I never said that. I'm at the bottom of it so to me a trip along the Passage is "up." If I lived in Price Rupert a trip would be "down" and I would have used that term. This all started when I said in another thread that our boat barely had the range to get up the Passage to Prince Rupert, but because of the current effects and winds we probably wouldn't get anywhere near that far. But then someone said the current's not a factor because it cancels itself out and that, in this case, is wrong for the reasons I've stated.


My dog isn't allowed to advise me on matters of navigation.

You might want to talk to him about it. Particularly about local currents. Could be you might learn something.:)
 
Here's another variation on our local currents; during heavy fall rains there can be so much fresh water flowing on top of salt water that the surface flow in long channels can actually be opposite of the incoming tide. You know it's raining hard when seagulls are taking fresh water baths in the middle of two mile wide channels.
 
Sometimes you can have it both ways, depending very much on your cruise plan. When I was in Jersey City on the lower Hudson, our tide averaged about 3-4 knots. If I was just taking a day trip I would cruise upriver
towards Croton-Harmon on a rising tide or go the other way under the Verrazano and out towards Sandy Hook on a falling tide. The trick was to coincide your return with the tide swing. Not very practical if you are going to your favorite fishing spot, but it was neat to have a favorable tide both ways while just messing about.
 
FlyWright is absolutely correct. And Marin won't even give him credit even when it's to his favor?????

FlyWright I wonder if this "time each way" factor (not theory) is significant enough to be noticeable in seat of the pants real life activities like Marin's friends that profess to know from experience. To know this it would seem to me it would have to affect overall cruising time very significantly.

For all practical purposes one is being slowed or sped along basically all the time but of course most of the time it's not enough tide to be aware of unless one is doing high tech navigation. And if this time each way factor (TEW) the wind will also play it's part in much the same way. I've always thought going both ways in calm water (whereas going 6knots is going 6knots) would/could not be the same or come out equal. Bucking the tide must have it's price. But I failed to transfer that over in this case or perhaps that's what drove me into this question.

So as far as what's right FlyWright has proven that bucking tides does not come out even or put another way ..... a wash.

So Anode you see ther'e are things to learn after all.

But I doubt that Marin's friends can know this without applying the same armchair theories that we did and then of course they wouldn't have needed to travel 2000 miles over water to know that. But perhaps someone can shor how that information should come to pass through normal navigational proceedures. Perhaps there's more to learn yet.
 
There area few of us dock queens that have left the dock and because of slow deep draft we do pay attention to the current and tides. :D

Many electronic charts have tide/current calculator and simulations. After plotting the course I always go back and simulate the tide and current for narrow channels and marinas with a 5’9” draft. There are many channel and marinas we can not enter at low tide, and/or go thru as the current is swifter than the Eagle’s head way. I clock the Eagle at 14+ knots going through some narrow passages. Deception Pass is 5 kts. Tacoma Narrow is 4 knts, agate passes is 3 knts. In the San Juan there are several that are 6.0+ knts. When we go thru narrow/shallow/swift passages/channel I like to follow a sail boat. Sail boat make great bottom finders and they are slow. :thumb::D

The general rule when running a river/current is to stay to the out side as the depth is probable deeper as the current has gouged out. Might be Ok to cut the corner if you know the area and/or shallow draft. Anyway I do not cut corners. :flowers:

Just north of Campbell River the tide changes, so if you time it right you can ride the incoming tide and then ride the out going tide. The current is quite swift through there, 7.0 knts and rather large whirl pool. Looks rather daunting looking down into a whirl pool several ft deep. Suck you right up! :eek:

I also simulate using the tide current on best time to depart and/or arrive. However, once out in the open Puget Sound the current tide is not that much, 0.5 to 1.0. So knowing tide and current charts can be very important especially with a slow deep draft boat.:socool:
 
But then someone said the current's not a factor because it cancels itself out and that, in this case, is wrong for the reasons I've stated.

Just because you stated it, doesn't make it so.

All things being equal... if you sailed around the world for a hundred years, day an night... to the same destinations and back, they would most definitely cancel out. That being said, ruling out departure times, river crossings and narrows, the same would apply. (contrary to your position)

It's moot because I can gain benefit of EVERY tide if I choose. And you... for the sake of being right... can buck the tide every time if you so choose.

You might want to talk to him about it. Particularly about local currents. Could be you might learn something.:)

He's asleep on the couch. It's hard enough listening to you explain it. You seem to be a pretty smart guy... but certainly are hard-headed. :)
 
Might be Ok to cut the corner if you know the area and/or shallow draft. Anyway I do not cut corners.


Possession Pt is a good example of that. If the tide is just starting to flood, the deeper water feels it first there. Closer to shore (still well over 60') the currents swirl around, but don't run against ya as quickly.


The current is quite swift through there, 7.0 knts and rather large whirl pool. Looks rather daunting looking down into a whirl pool several ft deep. Suck you right up!

I used to like to do that. Felt fun on my go faster boats. BUT... I as drove across Deception Pass every day... One day, I'm sitting there enjoying the view looking down from the bridge and was looking down in these whirlpools from above to get an idea of how deep they would really get (some were a couple of feet across and appeared 6-8 feet deep at max!). When SUDDENLY... a freaking pole pops up out of one, dances in the air for a minute and then spins back under the surface.

I had an epiphany that day and realized that my boat wasn't the only thing in those holes. :) I steer clear of them now. Lots of junk in them.
 
it all depends on what the voyage is... some it averages out and some it doesn't.

without constraints put on what one calls "averages" out (like a lifetime of boating versus a 25 mile up and back)...makes the discussion impossible to come to a conclusion.

to argue otherwise makes me laugh till my eyes water...:rofl:
 
WHAT?

OK... when would take a 2 NM trip... and go so slow that THE TIDES are a problem for you. (you're making trawlers look bad around the world)

We originally were talking about maximum range and accounting for the tides on long (Inside Passage types of runs)

Here's another for you (engineering problem)

I get up in the morning and notice that if I wait 2 hours to get started... I can catch the Slack tide ahead of the flood... the flood itself... and then the slack before the Ebb tide starts.

I can take advantage of all three, run for 6 hours and never have a problem. (plus have an extra two hours to enjoy my coffee) :)

Each day, there are two high tides and two low tides (about 12 hours, 25 minutes apart). Therefore... at worst, I'd have to wait 4 hours (& 12 minutes) to miss whichever I wanted to avoid and take advantage of the other.

not everywhere....:socool:
 
Ok, my experience here with an apx 64 NM journey from Point A to Point B (made this trip twice each way)... On the way from A to B, it is possible to time the journey such that I can have the current with me the entire way. It is not possible to have the current with me the entire way going to opposite direction. Sure I can leave at the right time to have it with me at the START when I leave point B, but at some point the current is going to change and be against me. I am sure someone can explain this better than I can, but in my simplistic terms, this is because the current changes from ebb to flood later as I get farther from the golden gate bridge. Which is to my benefit when I am riding the flood, but when I am riding the ebb I am eventually going to get to a place where the current direction has already changed to a flood and be against me. If we cruised faster we would probably have the opposite problem where we'd outrun the flood on the way up river...
 
I believe Marin is right and I'll attempt to prove it mathematically.

Imagine cruising a 2 NM course, round trip at 6 kts with no current. Each leg will take 20 minutes (2/6=.333x60=:20) for a :40 round trip.

Now cruise the same course with 2 kts of current with you and against you. Leg 1 is into the current yielding a 4 kt speed over 2 miles and it takes you 30 minutes. (2/4=.5x60=:30)
Leg 2 is completed at 8 kts with the push from the current and takes you 15 minutes.(2/8=.25x60=:15) Adding leg 1 and 2 is :30+:15=:45.

The same course traveled with the 2 kt current took 5 minutes longer. The reason is that when the current is helping you, you have less time to benefit from it. When it slowing you down, the effect of the current hits you over a longer span of time.

That's this engineer's take on it anyway.

Flywright has got his head in the clouds again. He only recently retired from flying. He forgets the physics is different for a boat than an airplane. On boat calculations you have to carry your knot.:D

Why is it on a timed measured mile boat speed run do you have to run in both directions and average the two legs for true speed? I wonder.
 
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Eric--- I didn't credit FlyWright because I didn't see his post until just now. And he makes sense to me. It certainly explains why when we have the currents mostly with us on a run into the islands, the trip is really short (comparatively speaking), while when it is mostly against us the trips take forever even though the actual SOG differences are not that great. It's because of the extra time we are bogged down going slow.

This next is really long, even for me, but I'm waiting for a computer so have a bit of time. Please skip it if the length is too intimidating.

There is another aspect affecting why positive and negative current effects don't mirror themselves on a trip up (or down) the Inside Passage that I'm amazed nobody from here seems to know about since nobody's mentioned it (unless somebody does while I'm writing this.)

It's a very complex concept so I will attempt to break it down into its simplest components for those to whom the behavior of water continues to be a mystery. It may seem overly basic to some but apparently that's what's needed here for some folks.

The moon, gravity,earth's rotation, and a bunch of other stuff cause the water in the oceans to move around. When it gets pushed in our direction up here along the northwest coast the level of the water goes up. When it gets pushed in someone else's direction the level of the water level along our coast goes down.

When it's pushed in toward us the level of the water when it's as far up as it's going to go is called high tide. When the water is pushed away from us and it's reached the lowest point it going to go, that is called low tide.

The difference between the height of the water at high tide and low tide is called the tidal range.

So far, so good, right?

Now when the water is going out as it's pushed away from us, or is coming in as it's pushed towards us, that movement of water going in one direction or the other is called current.

Now it starts to get a little tricky so I'll write slower to make sure people can follow along.

The tidal range varies. Yes, I can tell from your reactions that it's hard to believe, but it does.

It varies day by day, week by week. Some days there might be a real big tidal range, the next day, not, or there could be big tidal range between low tide and high tide but a small range between that high tide and the next low tide.

Some parts of the month might see high tidal ranges, other parts of the month might see relatively low tidal ranges. And in this part of the world, with four tides a day, there can be high tidal ranges and medium or low tidal ranges within a single 24 hour period.

Now, because the tidal range is always varying, it follows that the current varies, too, since the current is created by the water action that's causing our high and low tides. So when the tidal range is large, the current is what we call, what do you think class? SomeSailor? That's right, strong.

When the tidal range is small, the current is what we call weak. Very good.

I'll give you a minute to wrap your head around this always varying tidal range business and how it affects the current.






Okay. Now this will seem unrelated but it will all come together in the end. It takes an eight-knot boat, running every day, all day, only in the daytime, in May (relevant only because of the length of the days) ten days to go between Bellingham and Ketchikan (or the other way if you prefer). This is assuming no weather or mechanical delays.

I know this because we know a fellow who used to run an eight knot charter tour boat between Bellingham and Ketchikan in May for a number of years for the summer season and then back again in October. He told us that on those occasions where he had decent weather the whole time and could run every day, it took ten days.

But most recreational boaters will take longer than that. They have weather delays, they visit places, and so on. So they may take two or three weeks or a month or even more to get up (or down) the Passage.

So now we're going to put all this together. It's a hard, complex thing to grasp but I'll do my best and write really, really slow.

We have tidal ranges that are varying all the time. This means that the currents are varying all the time. Some parts of the week or month might see stronger flood currents during the day than ebb currents. At other times, there might be stronger ebb currents during the day than flood currents.

So a person running a boat up (or down) the coast over a ten day or two week or even one month period of time is not going to see mirrored currents every day. If they did, what SomeSailor and others believe would be correct.

But depending on when our boaters goes, depending on where the tide cycle happens to be, depending on how much his plans are messed up by weather or other delays, our boater can spend more time bucking adverse currents than being pushed along by following currents.

Or it could be the other way around.

Which is one reason why, in taking a boat up (or down) the Inside Passage, you cannot count on, and most likely will not experience, the effects of currents going against you being balanced out by the currents going with you.

If you're lucky you might spend more time in following currents than adverse currents. But if the adverse currents are consideraby stronger than the following currents, which they can be, this can negate and even remove the advantage of the extra time in the following currents. And of course it could happen the other way.

Couple this varying current strength business with the geographic effects on local currents which I talked about before--- and the calculations that FlyWright did for us--- it becomes very obvious--- at least to me and the people I boat with--- that you can very easily spend more time going up (or down) the Passage than you throught you would and burn more fuel than you thought you would.

It's true you could spend God knows how long calculating every current in every channel at every time of the day for entire window of time you think you might be enroute so you can determine exactly how long it will take you and how much fuel you will use. Which would take forever since much of the local area current information is not in the books and may not even exist.

But I've never met anyone who does that and we won't if the day comes we take our boat up (and down).

Everyone we know or have talked to who has done the Passage does fairly basic calculations based on the distances and the rather skimpy current detail that's available for the Passage, particularly the middle part, arrives at "it will take us about this long and we'll use about this much fuel" figures, and goes. And in all the cases we know of personally, it always took longer and always required more fuel than the boater figured, which they all atributed to the effects of the currents they encountered along the way.

If you want to talk about a round tripto Alaska and back, it's possible that whole run could end up without, or with a very small, impact from the currents, assuming both runs were made under similar tide and tidal range schedules.

But I've been talking about a one-way run as it relates to the range of our boat and why we can't make it on one load of fuel even though we theoretically could (barely).

Our dog, a Little River Duck Dog aka Nova Scotia Duck Tolling Retreiver, the official dog of Nova Scotia, has a maritime heritage that goes back hundreds of generations. So this whole tide-current-variation business is in his genes and is part of his inherent instinct. Which is why he was able to explain it to my wife and I so succinctly. If you don't have a water dog but have something like a dachshund or a Scotty or something, he or she may not be of much value in this regard.

But prior to Albi spelling all this out for us, I spent a few years crewing on a co-worker's racing sloop here in Puget Sound. And in my opinion there is no better way to gain an appreciation, if not an understanding, of what the currents are like in this area, particularly how local currents can affect one's progress, than challenging them with a sailboat, particulalry in a point-to-point, long distance race when you are actually measuring the effects of the constantly changing currents against the shoreline and the other boats in the race.

The only other thing that will give one the same or better appreciation and eventually knowledge is, in my opinon, kayaking (which I have never done).
 
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Ok, my experience here with an apx 64 NM journey from Point A to Point B (made this trip twice each way)... On the way from A to B, it is possible to time the journey such that I can have the current with me the entire way. It is not possible to have the current with me the entire way going to opposite direction...

Jennifer, I made the same point a day or two ago on another thread.
 
This seems to be a discussion between Pacific Northwest boaters, a place I know nothing about.

I can tell you though that here on the east coast it is possible to have the tidal current with you, or against you, for an entire day even if traveling 150 miles or so.

It’s all in the timing, moon phase, location, and karma. On days when it’s with me I feel like buying a lottery ticket, but then we are in a too remote location to do so.

Mike
 
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This seems to be a discussion between Pacific Northwest boaters, a place I know nothing about.

buying a lottery ticket, but then we are in a too remote location to do so.

Mike

Mike-- I believe what I have been talking about as it relates to the northwest coast would applicable to any other place with similar tidal ranges and geography. Perhaps Maine and the Maritimes, Scandinavia?

What makes this area unique is the very complex system of inside water channels, passes, fjords, and islands that can conspire to make water go in directions that you would not expect it to be going. If you call up Google Earth and take a look at this coastline (if you are not already familiar with it's appearance) you will see what I'm talking about.

The volume of water that gets exchanged along the coast four times a day is staggering. I've seen the figures but can't recall them and couldn't find them with Google. But when you combine that volume of water leaving and returning with the almost countless islands and waterways that affect its path, it's no wonder the local currents here do all sorts of things you would never expect.

It's fascinating--- to me anyway--- and is one of the things I love best about boating here either in our cruiser or our 17' fishing boat. My wife and I find it exciting to be out there amidst all the currents and eddies and tide rips. And it's why, I think, the ocean life here is so plentiful and diverse.
 
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