Understanding tides, bit of help please

[SteveK]

I agree with 30 up to 60 before slack to start going through.

 

[Bmarler]

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

There no reason to fear going through the canal, it’s well marked and easy to transit.
If I were limping on one engine I’d definitely prefer to go through vs around.

 

[GrandWood]

Want to thank all of you for the informative chat, we made it to PT, left poulsbo at 10am, hit he canal at 2:40 pm, speed went from 7.5 knots to 3.8 as we entered the canal, so we were a bit after slack, had to give a bit more pwr to motor thru as the current was moving us side to side. No traffic, and we stayed right in the center. 6 hr trip, off of port orchard we hit some decent size waves hitting the beam(side) and stuff was flying around the cabin, rained the whole trip, and pretty choppy most of the way, just as we tied up in PT the sun comes out, beautiful evening here now.

I had a blast and really enjoyed the whole experience, first real cruise done, and am looking for many more to come.

Think we will spend most of the rest of this year and winter from here to olympia, and venture to BC coast next season.

Once again, thanks to all, much appreciated

 

[Portage_Bay]

Congrats on a successful cruise! You mention cruising to Olympia. You'll want to take the lessons learned here and think about your passage through the Tacoma Narrows enroute to Oly. Currents of 4 to 5 kts are common, sometimes faster. And there is Deception Pass, another rite of passage for those learning currents in the local area.

A blog you may find interesting Sailing with Puget Sound’s tides and currents
A detailed study of tides and currents in Puget Sound. Starpath's Tidal Currents of Puget Sound
A visualization of Tacoma Narrows currents. Surface Currents at Tacoma Narrows
A publication I have found very useful. Tide Prints The price they are asking for it is outrageous. I can't see the value in that. But if you can find a used copy at a better price it's worth having on your chart table when cruising Puget sound.

 

[GrandWood]

Congrats on a successful cruise! You mention cruising to Olympia. You'll want to take the lessons learned here and think about your passage through the Tacoma Narrows enroute to Oly. Currents of 4 to 5 kts are common, sometimes faster. And there is Deception Pass, another rite of passage for those learning currents in the local area.

A blog you may find interesting Sailing with Puget Sound’s tides and currents
A detailed study of tides and currents in Puget Sound. Starpath's Tidal Currents of Puget Sound
A visualization of Tacoma Narrows currents. Surface Currents at Tacoma Narrows
A publication I have found very useful. Tide Prints The price they are asking for it is outrageous. I can't see the value in that. But if you can find a used copy at a better price it's worth having on your chart table when cruising Puget sound.

Thank you for the links, I will make use of those.

 

[Ken E.]

I'm late to this party but I've always been perplexed how slack current was not the same as slack tide. The most extreme example of this that I've witnessed was on the west side of Price of Wales Island in SE AK, Tlevak Narrows at the north end of Cordova Bay. Slack current was different from slack tide by a couple hours. I suspected that there was a mistake or typo in the tables. I found the following at the NOAA website which offers a good explantion.

What is the relationship between “Tides” and “Tidal Currents”?
The vertical rise and fall of the tides, created by the gravitational force of the Moon and Sun acting on the oceans water, also creates a horizontal motion of the water in the bays, harbors and estuaries. These are tidal currents. In general, as the tides rise there will be a current flowing from the oceans into the bays, harbors and estuaries; this is termed a "flood current". As the tides fall, there will be a current flowing toward the oceans; this is termed an "ebb current". There are also periods when there is little or no horizontal motion of the water; this is called "slack water".

Many professional and recreational users of tide and tidal current information have a "rule of thumb" to assume a relationship between the times of high/low tides and the times of the currents: that the times of slack water will be at the same time as the high and low tides, and that the flood and ebb current will occur between the high and low tides. Unfortunately, this assumed "rule of thumb" does not hold for most locations.
The relationship between the times of high/low tide and the times of slack water or maximum current is not a simple one. There are three "base case" conditions. The first is a "standing wave" type of current. In a standing wave, the times of slack water will be nearly the same time as the high and low tides, with the maximum flood and ebb current occurring mid-way between the high and low tides. The second is a "progressive wave" current. In a progressive wave, the maximum flood and ebb will occur around the times of the high and low tides, with the slack water occurring between the times of high and low tide. The third case is a "hydraulic current". In a hydraulic current, the current is created by the difference in height of the tides at two locations joined by a waterway. The current will be at its maximum flood or ebb when the difference in the two heights are the greatest. The slack water will occur when the height of the tide at the two locations in nearly the same.
Hydraulic currents occur at a limited number of locations. Some examples would include:

• Chesapeake and Delaware Canal, which connects Chesapeake Bay and Delaware Bay
• Cape Cod Canal, which connects Cape Cod Bay and Buzzards Bay
• East River in New York, which connects Long Island Sound to New York Harbor
• Certain sections of the Intra Coastal Water Way (ICWW)
• Between barrier islands which create different tidal conditions on opposite sides of the island

Progressive currents are most common at the oceanic entrance to many bays and harbor. Standing wave conditions are most common at the head (most inland point) of larger bays and harbors. Most areas of the coast will fall somewhere in between a progressive and standing wave current. [See example here (jpg)] The exact relationship between the times of high and low tides and the maximum current or slack water is unique to each location and cannot be determined from a generic "rule of thumb".
Because the tidal currents are created by the same forces which cause the tides, the currents can be predicted in much the same way as the tides. Observational data on the currents at a location can be analyzed using the same methods employed to analyze tides, and the results of that analysis can be used to generate predictions of tidal currents. However, because the relationship between tides and tidal currents is unique to each location, tide predictions and tidal current predictions are generated separately.

• Tide predictions provide the times and heights of the tides, available from the NOAA Tide Predictions service
• Tidal current predictions provide the times and speed of maximum current and times of slack water, available from the NOAA Current Predictions service.

It is up to the customer to use the correct type of predictions for their activities.

 

[dhays]

Portage Bay gave some great suggested resources. Here is a publication that I bought and despite having sailed Puget Sound since childhood, I will still use as a reference. I think it is well worth the cost.

Tidal Currents of Puget Sound

This is really three publications in one, "Tide Prints", "Tidal Current Charts, Puget Sound, Northern Part" and "Tidal Current Charts, Puget Sound, Southern Part". Portage Bay referenced "Tide Prints" which shows surface current every 3 hours throughout the tidal cycle. If I recall, this was done through a research grant by the University of Washington back in the 1970's and was done using aerial photographs and likely a bunch of young grad students with good eyes and lots of patience. It has a separate sheet for each 3 hour period based on the high tide time at Seattle. If you are a sailor, or have a slow boat, this can be an interesting and useful resource.

The other two publications included, "Tidal Current Charts, Puget Sound" are NOAA publications the last edition being from 1973. These are hourly current charts based on a the time of the max flood or max ebb at a reference location. For the Northern Part the reference is the current in Admiralty Inlet off Bush Point. For the Southern Part, the reference is the current at the northern end of Tacoma Narrows. The charts show the direction and speed of the currents at all the current stations (some have changed over the years). To get the actual speed speed you have to take the max flood or ebb current at Bush Point, and then use that to look up a conversion factor for the speed that is listed in the chart. I still have 50 year old copies of these original charts. I bought the Tidal Currents of Puget Sound linked above because my old current charts were falling apart and the binding staples were rusting out. This is from the decades of use they had in the cockpit of sailboats.

The Deep Zoom website uses the same NOAA information for its predictions so gives the same results as the Tidal Current Charts, just without having to do the work. I use Deep Zoom a lot, but keep the current charts on the boat as well so I'm not dependent on required connectivity.

 

[MichaelD]

There’s this
Tides & currents in the Salish Sea

 

[old salt]

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.

To complicate matters a bit, the PT Canal seems to run a bit earlier than the tables would indicate. That means the flood and ebb begin, in reality, sooner than the current table would indicate. I have observed this over the past ten years. I use this program for the most part: WWW Tide/Current Predictor - Site Selection .

You will find the Canal depths to be a bit less than indicated at the south end. I went through with a 5 foot draft on June 5th at a minus 2.5 feet (at 7 knots rung up) and found the shallowest spot to be 7,5 feet under the keel. The current flow is straight up and down the canal except at the south end, where there are confused currents (swirls and boils) right as you enter the south end heading north and for about the next 200 yards. On the ebb, you may encounter the same conditions on the north end of the canal, well before you reach the two day marks. The swirls and boils at the north end extend north about 500 yards on average on a strong ebb.

 

[JDCAVE]

In Canada, there are the CHS Sailing Directions guides that are full of local knowledge and information. They specify the direction of and offset of tides and currents at key locations. You especially need to refute to these for the north coast of BC, as there are very few current stations for most inlets and passages.

They are fee to download. I have the lastest versions on my Nav computer.

https://www.charts.gc.ca/publications/sailingdirections-instructionsnautiques-eng.html

Jim

 

[SteveK]

I use current atlas on phone as a visual reference