Utility of tide tables in complex geographies

bmbaum

New Member
Joined
Sep 6, 2022
Messages
1
Location
Victoria, B.C.
Please correct or confirm my understanding of this. My current understanding is that in open ocean, the tidal current will be slack pretty much at low and high tide, with little delay, and the fastest tidal currents will occur in between high and low tides (at the inflection points in the tidal chart). Thus, currents are easily predictable from the tidal chart. However, the deeper you are into a channel or complex island system, the more the currents are delayed from the tides, and they become less intuitive. For example, I was kayaking through Porlier Pass in the Gulf Islands this past weekend, and apparently there is almost a 5 hour delay between the low tide and the next slack current according to the tables. For an area like this, are tide tables pretty much useless for current predictions?
 

Tangler

Paddler
Joined
Sep 5, 2016
Messages
131
Location
Nanaimo, BC
The currents are linked to the tides in all areas but it can be complicated.
In those areas it is easier to use the current tables.
Info on the charts for that area will tell you which ones to use.
 

AM

Paddler
Joined
Jan 30, 2006
Messages
1,056
Location
Vancouver
The currents are linked to the tides in all areas but it can be complicated.
In those areas it is easier to use the current tables.
Info on the charts for that area will tell you which ones to use.
100% what Tangler said. Use the Current Tables.

Other resources I have use to supplement the above:

Current Atlas (for a synoptic view of what’s happening on a given tide)
Sailing Directions manual (for verbal descriptions of areas of major current)
And my favourite…local knowledge!

Cheers,
Andrew
 

Peter-CKM

Paddler
Joined
Dec 1, 2011
Messages
671
Location
San Francisco, CA
...Thus, currents are easily predictable from the tidal chart. ...
Nope. Not easily predictable.

In open ocean, tidal currents are nominal. If I was paddling off shore off of the San Francisco area (my home territory), I would not notice a current caused by tides. But we do have an along shore current of a half knot or so caused by other factors (temperature, salinity, wind, etc.) - part of the North Pacific Gyre.

In most areas with tidal currents, the slack currents occur some time after the high and low tide. For San Francisco Bay, if we have a high tide at noon, the high slack tide will be around 12:30 to 1pm. Similar delay after low tide when you would have low slack. The delay varies by locations, so local tide books are your friends in figuring this out.

The more there are constrictions with large volumes on the far side, the more the currents you will have (along with the larger the difference between tide heights). Our strongest currents are at the mouth of the bay, pretty much under the Golden Gate Bridge. We can get currents there up to 4.5-5.5 knots. Most of our currents are much less than this.

The further inland or closer to sea from the place the tide height was calculated, the later (or earlier) the high and low tides will be, with corresponding delays for high and low slack tides.

In summary, currents are very challenging. Tide and current books are your friends.
 

kayakwriter

Administrator
Joined
Feb 27, 2006
Messages
1,167
For an area like this, are tide tables pretty much useless for current predictions?
Actually, as you've discovered, tide tables are worse than useless for current predictions; that's why they have them separately in the Tides & Currents book - and they not only have the times for slack water but of peak flood and ebb. Free downloadable PDF here. Don't forget to add an hour to the times shown in the book if it's during a period of daylight saving time!
 

cougarmeat

Paddler
Joined
Sep 17, 2012
Messages
1,014
Location
Bend OR USA
My paddling partner buys Ports and Passages each year. It covers both the Vancouver Island waters and the San Juans. It requires a bit of tinkering because you are given the max/slack for a current/tide station, then a table of adjustment times, plus or minus, near (hopefully) your desired location.

Remember, it's a prediction, not a statement of fact.

I use AyeTides at home. Today, at Dionisio Point, it shows a 14 ft high Tide at 5:30 pm and a 4.2 knot Ebb at 6:30 pm.
 

eggabeewa

Paddler
Joined
Dec 12, 2019
Messages
41
Location
Greater Vancouver, BC
An interesting observation from this discussion is that the complexity of the waterways of this area (Puget sound to Salish Sea) is really quite unique in the world. I've always considered it normal to need tide and current charts for accurate predictions. After thinking about it though I realized that most of the world has such open coastlines that currents are quite simply related to tides. The only other similar areas that come to my mind are maybe Chile, Norway and Alaska.
 

AM

Paddler
Joined
Jan 30, 2006
Messages
1,056
Location
Vancouver
An interesting observation from this discussion is that the complexity of the waterways of this area (Puget sound to Salish Sea) is really quite unique in the world. I've always considered it normal to need tide and current charts for accurate predictions. After thinking about it though I realized that most of the world has such open coastlines that currents are quite simply related to tides. The only other similar areas that come to my mind are maybe Chile, Norway and Alaska.
Indeed. It therefore isn’t surprising that the Royal Canadian Navy has a strong reputation for navigation. It trains all its officers on this coast (using the Gulf Islands and Salish Sea for its exercises) and accepts students from other navies around the world. Hence the presence of Orca-class craft in local waters: these are the basic navy training vessels that run loops around all the islands and through all the narrow channels.

Cheers,
Andrew

 
Top