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Sea Slacker
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Discussion Starter #1
Yesterday on a daysail I am running almost downwind (wind was from NNE) just past the Sandy Point shoal light west of the ship channel, going south towards the Bay Bridge, for no particular reason at all. My GPS shows SOG of 5.5-6 kts and I wonder how good of a sailor I must be to get that much speed out of that little wind, and that I must finally be doing something right.

Perhaps a quarter mile to the bridge I decide that there is nothing to do on the other side and I'd better turn around. Well. I head up, tack through the wind and - well, the bow is pointing north-west, sails are full, but the GPS tells me I am making about 0.5 kts south-west, towards the sandy point :eek: Oops, I guess those 6 kts were not all my sailing skill :laugher

So, had to start the engine and got all of 3.5 kts motor-sailing.

I guess what I wonder about is - is this the normal state of things near the bridge or was I lucky? I guess if not for the engine, I'd be pretty well committed to going under the bridge and continuing south :)
 

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That's about right. Happens all the time with wind and current. At least you made it back.
 

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Tartan 37
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Never seen that much current there and I have sailed that area pretty regularly. Interesting, I will sure take more notice next time, thanks for sharing.
 

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Relates to tidal flow and the narrowing of the land masses at the bridge. Bucking the tide is never pleasant and can cost you speed going against the flow of water. Think of the width of the Bay miles north of the Bay Bridge and then envision all of that water flowing south (or north) being forced into a narrowed passage, the opening between Kent Island and the mainland. IN order for the same volume of water to pass through the narrowed opening it has to speed up. I've never noticed as much tidal surge as you describe but it could easily be 2+ knots. Great when it's working with you...terrible when it's against your travel.

MGM
 

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Brak,

The area around the bridge can get pretty squirrely with both wind and tide. The land pinches in as stated above, accelerating water through. Same thing happens to the wind and then throw the bridge obstruction into it and it can be quite a chore getting through under sail.

Besides that, though, there's been an unusually strong current. I was out on Tuesday and noticed a strong southerly current when the tide was supposed to be coming in. I think the bountiful rain throughout the Chesapeake bay watershed had a lot to do with it, judging by the coffee color of the water and the debris floating in it.

Even the marine forecasts have been describing abnormally high tides. My boat was riding quite high relative to the docks.
 

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Even the marine forecasts have been describing abnormally high tides. My boat was riding quite high relative to the docks.
Yeah, the tide has been unusually high for a while. I think all that extra rain water that was held in by wind and barometric pressure is finely draining out. The boost in current would be most noticeable at narrower pinch points like the Bay Bridge.
 

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Hey, JRP, what is the effect of barometric pressure on the amount of water in the bay, other than the creation of wind?
 

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Hey, JRP, what is the effect of barometric pressure on the amount of water in the bay, other than the creation of wind?
Pain,

When a big dome of heavy high pressure sets up off the u.s. mid-atlantic east coast, not only does it's anticyclonic rotation send southerly winds pushing up the Bay, but it also "displaces" some of the water that's under it. That water gets "displaced" to areas where the barometric pressure is less.

It's the fair-weather analogue to the storm surge from a low pressure system that passes overhead, but usually not as dramatic.

Last weekend and during the previous week (during that period of high water), while the weather was generally fair, the barometric pressure was flirting with "low pressure" territory. So there must have been a steep pressure gradient between the high pressure off-shore and the Bay area. Which would feed those southerly winds and also invite the water displaced by off-shore high pressure.
 
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