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Old 12-18-2012, 05:22 PM   #21
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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.


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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.
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Old 12-18-2012, 05:49 PM   #22
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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...
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Old 12-18-2012, 05:52 PM   #23
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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....
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Old 12-18-2012, 06:11 PM   #24
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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. 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...
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Old 12-18-2012, 07:22 PM   #25
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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.

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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Old 12-18-2012, 07:26 PM   #26
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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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Old 12-18-2012, 07:33 PM   #27
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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.
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Old 12-18-2012, 07:39 PM   #28
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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.

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Old 12-18-2012, 07:51 PM   #29
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Old 12-18-2012, 07:55 PM   #30
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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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Old 12-18-2012, 07:56 PM   #31
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Jennifer, I made the same point a day or two ago on another thread.
Of course, the simplistic mathematical analysis assumes random and equal exposure to currents in both directions. We often have the ability to choose departure time, so we can make it work in our favor if we pay attention to the details.

(OK, as Moonstruck's comment suggests, us retired guys might have more options than you working stiffs, but I digress.)

Don, as far as I know, the math in aviation is the same as the math in boating, but the boating numbers are WAAAAYYYYYY smaller. On your fast boat, if you carry the knot it can get lost in all that extra speed of yours. On my slow boat, an extra knot can mean an added 15% speed advantage!!
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Old 12-18-2012, 08:12 PM   #32
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Of course, the simplistic mathematical analysis assumes random and equal exposure to currents in both directions. We often have the ability to choose departure time, so we can make it work in our favor if we pay attention to the details.

(OK, as Moonstruck's comment suggests, us retired guys might have more options than you working stiffs, but I digress.)

Don, as far as I know, the math in aviation is the same as the math in boating, but the boating numbers are WAAAAYYYYYY smaller. On your fast boat, if you carry the knot it can get lost in all that extra speed of yours. On my slow boat, an extra knot can mean an added 15% speed advantage!!
OK, you guys have convinced me. I've been thinking I was cruising at 27 knots, but I was really backing up.
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Old 12-18-2012, 08:25 PM   #33
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Oh, another thing about all that fresh water I was talking about earlier riding on top of the salt water, well, it's less dense so the waves get steeper and closer together forcing one to slow down. This of course plays havoc with time estimates newly calculated to account for increased speed for any given RPM resulting from reduced friction on the hull comparative to 100% salt water as would be found further off shore.

Eegad...talk about whirlpools to nowhere!
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Old 12-18-2012, 08:57 PM   #34
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OK, you guys have convinced me. I've been thinking I was cruising at 27 knots, but I was really backing up.
Have you never wondered what that white streak of foamy water was stretching out ahead of your bow was?
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Old 12-18-2012, 09:11 PM   #35
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OK, you guys have convinced me. I've been thinking I was cruising at 27 knots, but I was really backing up.
Current effects have a smaller impact on fast boats. In my boating area, two-knot currents (plus or minus) are common so there can be a four-knot difference depending on boat and current directions. For a 27-knot boat, that's only a 15 percent difference in speed going with versus against the current. For a 6.3-knot boat like the Coot, there is a 63 percent difference.

Took a lot of water over the Coot's deck and pilothouse today. Current was going opposite the wind, and I hadn't imagined the effect of fresh on top of salt water due to run-off from recent rains to add to the steep waves (many were breaking) in Carquinez Strait.

Demarcation of current was very obvious in certain areas. At the location of the former railroad-ferry dock in Benicia (where the world's largest railroad ferries once operated), there was a very long and thick foam line, as well as a large patch of foam where the bottom depth suddenly changes. In some spots the foam was nearly a half-foot thick.
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Old 12-18-2012, 09:22 PM   #36
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Mark, with all that fresh water flowing down the Napa, you probably don't even need to rinse off after returning to your slip!! Ahhh, the benefits of freshwater trawlering!!

Did you get a pic or model number of your VHF Radio?

Moonman, your boat probably goes faster in reverse than many of our boats go in forward! I make fun, but secretly I'm just envious as hell!! I gotta come east someday for a fast boat ride!!
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Old 12-18-2012, 09:25 PM   #37
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Chip, How's that beautiful boat you rebuilt running? You've had several months with her by now. Any surprises since you launched?
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Old 12-18-2012, 09:27 PM   #38
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Did you get a pic or model number of your VHF Radio?
No, forgot about it. Also had my hands full steering through the waves and current swirls. And I even flubbed taking the picture of The Real McCoy car ferry parked alongside Mare Island. Under repair again?
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Old 12-18-2012, 09:48 PM   #39
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I almost never alter plans as in courses or layovers because of tides or current. I just plow on at 2 knots if needed but there are times in the San Juans where that philosophy would leave me dead in the water at 6 knots ... but it hasn't happened yet. My previous boat could throttle up to 8.5 knots but 6.4 is about it for Willy. To me any time underway is good as long as I'm making 2 knots.

Marin I read your entire long post and yes if you spent a lot of time studying currents and altered your course much of the time you could I'm sure raise your speed above normal cruise and if it's that important to you then OK w me but I would rather enjoy the scenery. But if you don't play games w currents and stop when the current is high/fast you will make less time underway that what you would deduct w cruise speed and distance.

Marin said "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."

The above is "on the street" results from the effects of currents that FlyWright points out. And the winds will further increase the time required to go from point A to B. My interest in this is only academic but the two trips to Alaska that I can recall how long the trip took was 22 days and 33 days. The latter was anything but a direct route trip but we could probably do the run in about 15 days without any problems whatsoever. At 17 knots the Ak State ferries take 37 hrs to go Bellingham to Ketchikan on the most direct route planed to dance w the tides and currents and running 17 knots except while passing Bella Coola and Campbell River.

Everything involved in it is complicated but the question asked is answered beyond a doubt so we will get back most to much of the distance lost when bucking tides but (over the long haul) never all of it unless a great effort is made.

I read all of Marin's post and am still trying to figure out what he actually said but I kept on saying ... yes ... yes ... yes until he got to the dog stuff. I don't get the doggoned dog stuff.
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Old 12-18-2012, 10:05 PM   #40
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Greetings,
Mr. Eric. Woof, woof woof. Arf, woof woof woof. Aruuuuu...woof woof. Understand now?
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