Re: [Paddlewise] Tudes and Current Speed

Craig: I think that the rules work best for tides and current through a 
large bay but fails at a really constricted entrance. I always thought 
the rule of 3rds was for tide height and the 50/90 for currents. As far 
as Deception Pass goes I suspect current speeds reach 90% of full speed 
within 1 hour of slack.B  I agree that it seems to be flowing out in one 
place while flowing in somewhere else. No way in a small boat to be all 
over the place.

I think I'll take the Zodiac and a GPS over there this summer as a 
project and find out. This question has nagged at me for 20 years at 
least. Paddling back and drifting through would be a pain in the butt 
in a kayak but a piece of cake (and probably fun) in a Zodiac.

Rob: There is also a rule of 3rds for current. 33% at the end of the 
first hour 66% at the end of the second and the rest at the end of the 
3rd hour. Doesn't work well around here in most places I've been.


Rob: The sheer volume of water from Puget Sound and the southern 
Georgia Strait collides with the flood that usually sets against 
Vancouver Island. Most times I've been out the mouth of JDF it was this 
way. The ebb was still going strong while the flood was starting, 
albeit in mid channel. The one time I've been through the mouth of Icy 
Strait, we planned on the flood not helping us for 90 minutes prior to 
published flood. Sure enough, the rips in the Inian Islands were still 
going off. That's one time, though, hard to make a claim based on that, 
however looking at the chart for Icy Strait, there was no way all that 
water in there was going to come out nice and uniform.


Craig: No but 90 minutes seems a bit long. I always give myself 30 
minutes for slack water at any pass in a slow boat (like a sailboat or 
a fishing boat) and that seems to work. I bet the tugboat drivers could 
add a lot to this discussion. All the guys I knew have long since 
retired so I might have to chat one up some day given the chance.

Rob: All the shipping I've seen are out in the lanes in mid channel. It 
wouldn't surprise me to be more uniform out there where the West 
Entrance buoy is. My observations are based on numerous trips from Neah 
Bay to Cape Flattery and watching the ebb near shore continue for up to 
90 minutes after the flood was supposed to begin. I've eddy hopped back 
several times until I asked the question to the Armchair Sailor guy.


Craig: Yes, they all develop over time (of course) but I think that the 
time is a lot smaller than any of the rules would make us believe. Bob 
Burnett has been doing a lot of playtime in Cattle Pass lately with 
newbies so I would expect him to be pretty aware of how current speeds 
develop. I'll try to ask him.

Rob: Having padled there numerous times I wouldn't say it goes off full 
tilt very quickly, but I agree with your supposition that it develops 
more fully sooner than the rules of thumb would imply. I think you are 
right, that areas with tighter constrictions and more convoluted 
bathymetry can defy the *rules.*

Rob: I have a new one for ya, Craig. The WA side of JDF from Port 
Angeles to Cape Flattery often experiences a double ebb; a very short 
and weak flood; or, sometimes more *normal* conditions. It makes surf 
prediction at Crescent Bay and other breaks difficult, for one thing. 
It ranges from diurnal to the more NW standard of semi-diurnal tides. 
In my opinion the anomalies there are are more PHD worthy than current 
differential in tight embayments. Next time you see a Captain Jack's 
Almanac, look it up.

Cheers,

Rob G





-----Original Message-----
From: Craig Jungers <crjungers_at_gmail.com>
To: rcgibbert_at_aol.com
Cc: paddlewise_at_paddlewise.net
Sent: Wed, Oct 28, 2009 9:04 am
Subject: Re: [Paddlewise] Tudes and Current Speed


On Wed, Oct 28, 2009 at 8:14 AM, <rcgibbert_at_aol.com> wrote:


I usually avoid the rule of 3rds and stick with David Burch's 50/90 
rule. That being at the end of the first hour after slack the current 
is 50%, the second 90% and the 3rd 100%. It reverses the same way. It 
is a pretty good guide, but not a tack driver for all places. Deception 
Pass has 2 inlet/outlet features at Canoe Pass and Deception Pass 
proper. The time for slack varies all over the general area and in some 
places it still ebbs while others the flood begins. I wouldn't say it 
goes full on just after slack, all the times I've been there it seems 
to me to take on a noticeable ramp up period, but less than the 50/90 
rule would imply, perhaps due to the features you've noted and others 
we both are overlooking.


I think that the rules work best for tides and current through a large 
bay but fails at a really constricted entrance. I always thought the 
rule of 3rds was for tide height and the 50/90 for currents. As far as 
Deception Pass goes I suspect current speeds reach 90% of full speed 
within 1 hour of slack.B  I agree that it seems to be flowing out in one 
place while flowing in somewhere else. No way in a small boat to be all 
over the place.

I think I'll take the Zodiac and a GPS over there this summer as a 
project and find out. This question has nagged at me for 20 years at 
least. Paddling back and drifting through would be a pain in the butt 
in a kayak but a piece of cake (and probably fun) in a Zodiac.


There are 2 areas that I have been that have a noticeably similar 
current dissimilarity to published guides, the mouth of the Strait of 
Juan de Fuca and the mouth of Icy Strait. A yachtie who owns armchair 
Sailor in Seattle, informed me that closer to shore in JDF on the US 
side the water *usually* ebbs longer than it floods.

That doesn't surprise me either. Tidal flow is calculated and 
represented as linear but, like all hydraulics, it's more chaotic. The 
linear representations work fine as an over all view and most clients 
of tidal data don't much care about anything more granular. Most of 
them not being kayakers.


The sheer volume of water from Puget Sound and the southern Georgia 
Strait collides with the flood that usually sets against Vancouver 
Island. Most times I've been out the mouth of JDF it was this way. The 
ebb was still going strong while the flood was starting, albeit in mid 
channel. The one time I've been through the mouth of Icy Strait, we 
planned on the flood not helping us for 90 minutes prior to published 
flood. Sure enough, the rips in the Inian Islands were still going off. 
That's one time, though, hard to make a claim based on that, however 
looking at the chart for Icy Strait, there was no way all that water in 
there was going to come out nice and uniform.


No but 90 minutes seems a bit long. I always give myself 30 minutes for 
slack water at any pass in a slow boat (like a sailboat or a fishing 
boat) and that seems to work. I bet the tugboat drivers could add a lot 
to this discussion. All the guys I knew have long since retired so I 
might have to chat one up some day given the chance.


Cattle Pass between San Juan and Lopez islands is another tight 
opening, relatively speaking, that seems to have a quicker max, but it 
still develops over time.


Yes, they all develop over time (of course) but I think that the time 
is a lot smaller than any of the rules would make us believe. Bob 
Burnett has been doing a lot of playtime in Cattle Pass lately with 
newbies so I would expect him to be pretty aware of how current speeds 
develop. I'll try to ask him.


There is a PhD in here somewhere. :P


Craig Jungers
Moses Lake, WA
www.nwkayaking.net
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