|Topic Review (Newest First)|
|03-30-2010 10:36 AM|
Originally Posted by olgriz View Post
|03-30-2010 01:52 AM|
Those conditions can be intimidating to say the least. Here in SF bay, we get a lot of SC advisories for winds 25-35—add 4 knot contrary tide and you get a short, steep chop of 6+ feet. Most bay sailors would call that a fun day but it requires different tactics. First, reefs are good! Small jibs or blades are good! But with that rig you can't point well so you have to bear off—which is good. I would try to avoid taking the waves on the beam though. If you're going to weather, I think 45-50° would be an acceptable angle as long as the wave direction works as it would allow you to maintain enough boat speed to maneuver through the waves. Just my 2¢ worth.
As we sit in the cockpit with cocktails, it's strange that we first remember those treacherous days rather than the lazy warm ones.
|03-29-2010 09:27 PM|
Originally Posted by JimHawkins View Post
The OP has quoted the tide turn time, assuming that it is directly related to the tidal current. Unfortunately, it seldom is. I sail in the Gulf Islands in Canada. We have extreme currents and excellent tools to understand them. These include many current stations which are listed in the tide tables and a very nice current atlas which provides a visual representation of the larger back eddies, etc. Sometimes when the current is flooding, the current will be going exactly the opposite to what you'd think because it's hitting an underwater obstruction causing an upwelling and water moving in the ebb direction!
Does NOAA not publish at least current predictions that provide times of turn and maximum current at important passages? If so, it's instructive to look at tide turn vs slack current times. They can be hours different due to local topography (large basins behind narrow channels, influence of rivers, etc.
We even have one area in Johnstone straight that will sometimes just decide not to ebb sometimes, apparently. It has the current going one way on the surface and another way down deep. It's all detailed in the current atlas.
|10-04-2009 02:05 PM|
|KrabKrusher||Hard to say without being there, but it sounds as though you did ok (except for not bringing the dinghy on deck before you left port). Coastal waves are often steep and out of step. Using teh engine is good. If you start hearing teh low oil pressure alarm it likely means the oil pump is sucking air becasue of the heel.|
|10-04-2009 02:02 PM|
|KrabKrusher||Hard to say without being there, but it sounds as though you did ok (except for not bringing teh dinghy on deck before you left port). Coastal waves are often steep and out of step.|
|10-03-2009 04:00 PM|
There are a series of books called tidal atlases issued amongst others by the Admiralty for places all over the globe. These provide a series of flow directions and intensities at different points of the tidal range. Whether there is one for your specific spot I couldn't say.
Alternately, I have always found that in spots were currents/tides present a problem, a decent marine chart will contain tidal diamonds that give a sound indication of the flow dynamics. In my general experience if there is no tidal diamond then there is generally no real cause for concern.
Having said that, there are places where I sail (3.2m tidal range at times) where the tidal drift even out in the open is considerable and has to be acknowledged.
So it is a bit of a moving target.
|10-02-2009 02:03 PM|
Not sure where you sail. but at least here in the puget sound region up into BC Canada...........There are two books I can think of off the top of my head, one covers puget sound proper, ie from about Port townsend and north whidbey island south to Olympia. Another one or two do the San juans, and up farther north into BC. They have charts with tidal currents, how they generally run etc at different times of the flood vs ebb tides. Of course they show +/- 3 hrs from max ebb or flood. Sometimes there are only 5 hrs or a length of 7! so you need to interpret the book charts a bit based on directions given. Also the shown tide currents are based on a say 8' swing, where as we around here can range from a 4-16' swing of the tide. So what may show as a 4 knot current, during a 16' max sing, the current may really be 6-8 knots thru a given channel.
I know of one channel that basicly runs opposite of the flood or ebb, due to filling or lack of north and south of the channel.........these books help.
WInds can also vary based on local topography, hence why Puget sound is broken up into about 6 wind forecast area's. I'm consider the northern part of Puget sound, BUT, I find with a North wind, the forecast for Admirality inlet is close to what I get for wind speeds that are usually a bit higher, as they typically are thru AInlet, as there is a funnel effect thru their, and does not just fan out really quick in the area I am, just to the south of this funnel. It takes about another 3-5 miles south to lower this topagraphy effect on the wind.
So it helps to learn and understand some of the local stuff. Puget Sound in general is hard to weather predict, as the computer models are "JUST" beginning to show the Olympic mtns as being there etc. so the winds and even rain shadows are not showing up always correct in forecast etc too.
|10-02-2009 12:47 PM|
|JimHawkins||I believe currents don't always match tides exactly. Can someone more experienced chime in here, and maybe say how to predict currents for a given area at a given time?|
|10-02-2009 10:43 AM|
Thanks for taking the time to pull the data. You are correct that Mt Desert Rock was the buoy closest to my position at the time (about 15 nm to the SE I would guess). I had tried the GOMOOS website for exactly this info, but kept pulling blanks on wind for some reason. Frankly, it helps confirm a thought I had yesterday after I had posted my summary: Another takeaway for me is that the NOAA broadcasts and other data points are all useful as broad indicators of wind and wave conditions, but that one has to be constantly aware of potentially significant local variances - especially in the type of highly variegated coastal waters in which we sail. I was outside the mouth of Jericho Bay at a time when the tide was starting to reverse - looking back on it and with the benefit of this info, I can only conclude that the sea and wind conditions were much more localized than I assumed at the time. Rather than beating up into the harsher conditions, I may well have been better off staying my course while temporarily moving to a close reach - it sounds like it would have been a friendlier point of sail and may have been a quicker route to more manageable conditions.
|10-02-2009 07:02 AM|
Originally Posted by AndrewMac View Post
First, I just want to clarify that I don't doubt that you experienced significantly stronger winds and higher seas than I did that day. I was still very much in the protection of the Boothbay pennisula. We had sailed out Fisherman's Passage, and turned around out by the Damariscotta River entrance buoy (where it started to get really windy). Most of the time we were inside of Squirrel Island.
That said, here are the data from the GOMOOS buoy located north of Mount Desert Rock (the closest one to where you were), for the period in question on Friday September 25:
Time Direction Knots
8:00 AM NNW 16.9 19.9
8:10 AM NNW 19.6 23.2
8:20 AM NNW 16.8 20
8:30 AM NNW 17.9 21.2
8:40 AM NNW 19.1 23
8:50 AM NNW 20.1 24.2
9:00 AM N 20.6 25.3
9:10 AM N 22.3 26.8
9:20 AM N 21.8 26.8
9:30 AM N 21.1 24.6
9:40 AM N 22.3 26.3
9:50 AM N 22.3 25.4
10:00 AM N 22 25.7
10:10 AM N 22.3 26.3
10:20 AM N 21.4 24.1
10:30 AM N 21.2 26.1
10:40 AM N 22.6 26.8
10:50 AM N 20.9 26.8
11:00 AM N 22.1 25.2
11:10 AM N 20.3 23.8
11:20 AM N 19.4 22.3
11:30 AM N 21.7 25.4
11:40 AM N 22.2 26.7
11:50 AM N 22.7 28.3
12:00 AM N 22.6 26.4
12:10 AM N 24.5 30.5
12:20 AM N 23.6 30.5
12:30 AM N 22.6 26.2
12:40 AM NNE 22.8 27.1
12:50 AM N 20 23.8
1:00 PM N 21.4 25.2
1:10 PM N 23.1 27.5
1:20 PM N 21.5 26
1:30 PM N 18.9 23.4
1:40 PM N 20.1 23.4
1:50 PM N 19.7 26
2:00 PM N 19.5 23.7
FWIW, I often find that it seems like the buoys under-report the conditions! And indeed, the conditions where you were may very well have been stronger.
But to ease your mind, you might confirm that your instrument system is reading in knots and not miles per hour or some other unit (e.g. 20 knots is about 37 kph, meaning kilometers per hour).
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