PeterB Posted October 21, 2008 Share Posted October 21, 2008 Four of us converged on Pavilion Beach around noon on Sunday , with remote hopes of catching some surf somewhere off of Plum Island . We had ventured from our inland homes where winds were mild, and weather was brisk but fair. Marine forecasts were for 7-10 foot seas (!) and 20-30 knot winds , and cautionary word had filtered to us by cell phone from various friends , but having lost out on past paddling opportunities by being Marine forecast idealogues , we wanted to get a “nowcastâ€: see for ourselves and make the call from the beach. Arriving at Pavilion, from the tip of Plum Island all the way to Rockport was a near unbroken mass of breaking waves , winds felt @ 20 knots, and it was biting cold. What to do? “When the proper man does nothing (wu-wei) his thought is felt for ten thousand miles†-Lao Tse We repaired to the Choate Street Pub for an Ipswich Ale, and then went our merry ways. Quote Link to comment Share on other sites More sharing options...
jdkilroy Posted October 21, 2008 Share Posted October 21, 2008 The wiser man will return to paddle another day ... Hey Peter, Laura and I were over at Plum on the Merrimack side while the spring ebb was near max. We put in on the NE end of the island at the public launch and paddled out to the mouth between the breakwaters. There was a 5 ~ 10 kt onshore wind and the standing waves mixing with the S'ly swell at the mouth was really something. We were flying past the #3 can in a flash when we decided to claw our way back into the river. That was our first time at Plum and we paddled away with a healthy respect for the forces at play there. Sounds like the Pub was the place to be. Jon Quote Link to comment Share on other sites More sharing options...
risingsn Posted October 21, 2008 Share Posted October 21, 2008 Four of us converged on Pavilion Beach around noon on Sunday , with remote hopes of catching some surf somewhere off of Plum Island . We had ventured from our inland homes where winds were mild, and weather was brisk but fair. Marine forecasts were for 7-10 foot seas (!) and 20-30 knot winds , and cautionary word had filtered to us by cell phone from various friends , but having lost out on past paddling opportunities by being Marine forecast idealogues , we wanted to get a “nowcastâ€: see for ourselves and make the call from the beach. Arriving at Pavilion, from the tip of Plum Island all the way to Rockport was a near unbroken mass of breaking waves , winds felt @ 20 knots, and it was biting cold. What to do? “When the proper man does nothing (wu-wei) his thought is felt for ten thousand miles†-Lao Tse We repaired to the Choate Street Pub for an Ipswich Ale, and then went our merry ways. ...and discretion is the better part of valor Quote Link to comment Share on other sites More sharing options...
EEL Posted October 22, 2008 Share Posted October 22, 2008 [quote name='PeterB' date='Oct 21 2008, 05:19 PM' post='28136We repaired to the Choate Street Pub for an Ipswich Ale, and then went our merry ways.Which doubtless beats a chopper ride by a wide margin. Ed Lawson Quote Link to comment Share on other sites More sharing options...
PeterB Posted October 22, 2008 Author Share Posted October 22, 2008 The wiser man will return to paddle another day ... Hey Peter, Laura and I were over at Plum on the Merrimack side while the spring ebb was near max. We put in on the NE end of the island at the public launch and paddled out to the mouth between the breakwaters. There was a 5 ~ 10 kt onshore wind and the standing waves mixing with the S'ly swell at the mouth was really something. We were flying past the #3 can in a flash when we decided to claw our way back into the river. That was our first time at Plum and we paddled away with a healthy respect for the forces at play there. Sounds like the Pub was the place to be. Jon John, Did you mean that you were at the mouth of the Merrimack during max ebb on Sunday? If so, high tide was 3:04 PM, so to be there at max ebb it would have had to be a few hours after that, either that or early am. In any event, the mouth of the Mac at ebb can be a daunting place. When we were there in August, paddling aganst a 3+ knot current was a trial , because there were no eddies: along that jetty it's just a sluiceway, and we couldn't get out in the middle and use any waves because of the heavy boat traffic, so it was a pure slog to paddle against the current. Quote Link to comment Share on other sites More sharing options...
Bill Gwynn Posted October 22, 2008 Share Posted October 22, 2008 Max ebb on Sunday the 19th at the mouth of the Mac was at 1730 with current at 1.4 knots. I don't believe the Mac ever ebbs more than 2 knots, the flood can exceed 3 knots. This info come from NOAA's Tidal Current Predictions. That being said, I am positive there are areas that do exceed the current predictions due to underwater topography. Plus, it sure as hell feels like a lot more when trying to make headway against max ebb. It's one of those paddles I love to hate. Quote Link to comment Share on other sites More sharing options...
jdkilroy Posted October 22, 2008 Share Posted October 22, 2008 We were there late afternoon on the 16th. Max ebb was in the 1600's and somewhere near 2 knots... but I have to agree with Bill; it felt like considerably more than predicted. We weren't so much taken by the actual conditions as much as the lack of expectation of them. The entire setting seemed rather tame at the outset. I can tell you that I paddle in and around the Piscatiqua routinely where the currents can be vigorous and fickle and I was instilled with a healthy respect for the mouth of the Merrimack that day. We did have fun ferrying back and forth within and enjoyed the multitude of seals that converged on the inner sand bank west of the day marker on the SW'n tip of Salisbury beach. It was a fun and educational day all in all. By the way; my Cetus has finally hit the eastern US shores; hoping to pick up in a few days... Jon Quote Link to comment Share on other sites More sharing options...
PeterB Posted October 22, 2008 Author Share Posted October 22, 2008 Max ebb on Sunday the 19th at the mouth of the Mac was at 1730 with current at 1.4 knots. I don't believe the Mac ever ebbs more than 2 knots, the flood can exceed 3 knots. This info come from NOAA's Tidal Current Predictions. That being said, I am positive there are areas that do exceed the current predictions due to underwater topography. Plus, it sure as hell feels like a lot more when trying to make headway against max ebb. It's one of those paddles I love to hate. I'm surprised that flood can exceed the ebb. I thought that the ebb always was greater than the flood, especially at the mouth of a river such as the Mac , where the flood is countered by the current of the river, and ebb would be the combined force of the outgoing tide and the water backed up by the previous flood. The mouth of the Merrimack, at that jetty, would surely be one such spot that "exceeds current predictions". In any event, it can be a fun place. Or harrowing. Or everything in between. Quote Link to comment Share on other sites More sharing options...
Bill Gwynn Posted October 22, 2008 Share Posted October 22, 2008 I'm surprised that flood can exceed the ebb. I thought that the ebb always was greater than the flood, especially at the mouth of a river such as the Mac , where the flood is countered by the current of the river, and ebb would be the combined force of the outgoing tide and the water backed up by the previous flood. I agree that it counters what we would think. So...who can provide a logical explanation as to why the flood is stronger than the ebb? Quote Link to comment Share on other sites More sharing options...
Bill Gwynn Posted October 22, 2008 Share Posted October 22, 2008 I agree that it counters what we would think. So...who can provide a logical explanation as to why the flood is stronger than the ebb? Some thoughts... Looking at the current predictions for Oct 16th. The morning flood took 6 hours and 1 minute (slack to slack). The afternoon ebb took 6 hours and 34 minutes. So, roughly the same amount of water has to move from flood to ebb and the flood happens in less time, therefore more current. Quote Link to comment Share on other sites More sharing options...
EEL Posted October 22, 2008 Share Posted October 22, 2008 I agree that it counters what we would think. So...who can provide a logical explanation as to why the flood is stronger than the ebb? I did not stay at a Holiday Inn Express last night and will leave it to others to provide a scientific explanation. However, the following might be a factor. Where is the current measured? As I recall the predictions are based upon observations made at specific locations and depths. The current you see on the surface may not be the same as the current at a greater depth. Since the water coming in is colder with greater salinity, it is more dense. The fresh water flowing out will ride on the surface as the sea water forms a wedge as it flows in on the flood. So the current in the sea water wedge might be different than the current on the surface. Also, even a small change in location can substantially alter the direction and velocity of tidal currents. Check the tide currents around Hussey Sound near Portland for example. So the predictions tend to apply to a limited area of the flow and represent peak current velocity. Maybe when you have a mixing of fresh and slat water the variation in velocity over a tide period may not be a sine wave further complicating things in terms of predicting where is the water our kayak sits in is going and how fast. Just my superficial thoughts to limit hair hurting. Quote Link to comment Share on other sites More sharing options...
EEL Posted October 23, 2008 Share Posted October 23, 2008 Just to add to the confusion or knowledge, I looked at the current velocities for Portsmouth Harbor and found that for Portsmouth Harbor the ebb velocity is always greater than the flood velocity. I believe the location of the Portsmouth harbor station is off Wood Island. For Oct. 19, 2008 the mid day flood was 1.5 Kts and the dusk ebb was 2.2 Kts. However, the velocities south of Seavy Island were a flood of 3.75 Kts and ebb of 4.62 Kts while NE of Pierces Island the flood was 3.6 Kts and the ebb was 1.54 Kts. Note the huge difference in ebb velocity at locations not that far apart while flood velocity not that different. The Merrimack current velocities are based on correction factors applied to the Boston Harbor velocities and, as opposed to Portsmouth, at the Boston Harbor station some days the flood is higher than the ebb and some days the ebb is higher than the flood although they are often close. The correction factors for the entrance of the Merrimack river are flood 2.0, ebb 1.2 which would tend to make the flood faster than the ebb at that location for whatever reason. Ed Lawson Quote Link to comment Share on other sites More sharing options...
Bill Gwynn Posted October 23, 2008 Share Posted October 23, 2008 Just to add to the confusion or knowledge, I looked at the current velocities for Portsmouth Harbor and found that for Portsmouth Harbor the ebb velocity is always greater than the flood velocity. I believe the location of the Portsmouth harbor station is off Wood Island. For Oct. 19, 2008 the mid day flood was 1.5 Kts and the dusk ebb was 2.2 Kts. However, the velocities south of Seavy Island were a flood of 3.75 Kts and ebb of 4.62 Kts while NE of Pierces Island the flood was 3.6 Kts and the ebb was 1.54 Kts. Note the huge difference in ebb velocity at locations not that far apart while flood velocity not that different. The Merrimack current velocities are based on correction factors applied to the Boston Harbor velocities and, as opposed to Portsmouth, at the Boston Harbor station some days the flood is higher than the ebb and some days the ebb is higher than the flood although they are often close. The correction factors for the entrance of the Merrimack river are flood 2.0, ebb 1.2 which would tend to make the flood faster than the ebb at that location for whatever reason. Ed Lawson More confusion...The flood on the 19th in Portsmouth Harbor took only 5 hours and 42 minutes at a max of 1.5 knots. The Ebb that evening took 7 hours and 8 minutes with a max of 2.2 knots. That throws my theory of water moving in an amount of time effecting current right out the window. Now I am really intrigued/confused as to why this is. Quote Link to comment Share on other sites More sharing options...
spuglisi Posted October 23, 2008 Share Posted October 23, 2008 More confusion...The flood on the 19th in Portsmouth Harbor took only 5 hours and 42 minutes at a max of 1.5 knots. The Ebb that evening took 7 hours and 8 minutes with a max of 2.2 knots. That throws my theory of water moving in an amount of time effecting current right out the window. Now I am really intrigued/confused as to why this is. Bill, It appears that you're not the only one curious about it. I've just scanned this but it might offer an explanation. http://www.whoi.edu/science/cohh/whcohh/i/...inal_report.pdf Quote Link to comment Share on other sites More sharing options...
subaruguru Posted October 25, 2008 Share Posted October 25, 2008 It appears that you're not the only one curious about it. I've just scanned this but it might offer an explanation. Fascinating. The conclusion stating the differential pressures of flood/ebb are crudely visualized by me as filling and emptying a kid's squirt gun. It takes less time to fill, water sourced from a larger area at lower velocity on flood, but "squirted" at higher pressure (smaller orifice area effect) upon ebb. Ha. Quote Link to comment Share on other sites More sharing options...
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