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Drfit Models


adambolonsky

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I know that when the CG conducts SAR operations for lost boaters they use drift models based on wind direction, windspeed, and tidal current velocity and direction. Thus, were one of us to go missing in the fog or at night, the CG would want to know at what time we were last seen, and where. Calculating forward from that time, they'd factor in the wind speed and direction to assume how far, and in what direction we've drifted after a capsize or an accident. They'd then factor in the tidal speed and direction to arrive at an assumption of where we are. A kayak drifts faster than a body, of course, so I assume they'd factor that in also: whether they looking for a body, a kayak, or both.

So when Mary Jagoda and Sara Aranof drowned two weeks ago in Nantucket Sound, SAR had this to contend with: a noreast wind, thus offshore, blowing from Harwich southwest towards the middle of Nantucket Sound. The time, late afternoon, meant the tide was still going out. In the Sound, ebb tides flow east (?), towards Monomoy Island.

It was a also few days after a big moon, so the tide's velocity was increased. I'd assume then that Jagoda and Aranof were first blown southwest by the wind, then were pulled east, and fast, by the tide towards Monomoy's Handkerchief and Stone Horse Shoals, two truly horrifying places to be if the rip is up due to bigger tides. The water is rough, with standing waves and boomers.

The Shoals then spill off into the Pollock Rip and Channel --- deeper water where the current increases in speed when it wraps around south Monomoy Point. This is the approximate area where Jagoda's body was found, so too the kayaks after the 750 square mile, 51-hour search.

So the drift vectors were: southwest, into Nantucket Sound, where the fast tidal velocity then picked up the boats or bodies and began to pull them east.

Anybody else have a different analysis?

I bring this up for a couple reasons. There are hard currents that run in both Sandy Bay off Rockport and off and around Milk Island and Land's End, where a lot of NSPN stuff goes on. The currents run basically northwest and southeast, depending on the tidal ebb or flow. The flow is especially pronounced in the Avery Ledge area, between Straitsmouth Island and the Breakwater, so too in the open passage area northeast of Straitsmouth to Thathcers, Londoner Pole, and beyond.

Perhaps it's important we as a club discuss and are perhaps able to list or document the tidal direction for other popular NSPN areas. . In the event one of us goes misising in fog or at dusk, it'd be helpful, I think, if we as well as the CG and local harbormasters have a notion of where we or our boats or getting dragged by two alternatingly conflicting or mashalling vectors: that of the wind, that of the current.

If nothing else, knowing this will help us try to assume by ded reckoning where are should we find ourselves in Jagoda's or Aronof's terrifying situation because, sure, we may call oursevles "seakayakers", but that assumes an awful lot.

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Sunday October 12, 2003

Harwich Port MA

Wychmere Tide Station

Location: Latitude 41° 40.000’N Longitude 070° 04.000’W

Tide Table

High 01:56 3.8ft

Low 07:29 0.3ft

High 14:06 3.9ft

Low 19:55 0.1ft

Distance from Monomoy Point 7.7 NM

Chatham Roads Current Station

Location: Latitude 41° 38.6000’N Longitude 070° 01.700’W

The current at this station are classified as Weak and Variable

Flood Direction: NA

Ebb Direction NA

Distance from Monomoy Point 6.4 NM

Dennisport Tide Station

Location: Latitude 41° 39.000’N Longitude 070° 07.000’W

Tide Table

High 02:07 3.5ft

Low 07:42 0.3ft

High 14:17 3.6ft

Low 20:08 0.1ft

Distance from Monomoy Point 8.3 NM

Dennis Port, 2.2 miles south of, Current Station

Location: Latitude 41° 37.000’N Longitude 070° 06.900’W

Current Table

Slack MAX Speed

---- 03:11 0.3 kts Ebb

06:40 09:29 0.4 kts Flood

12:04 15:25 0.3 kts Ebb

18:55 21:46 0.4 kts Flood

Flood Direction: 093° Mag

Ebb Direction 285° Mag

Distance from Monomoy Point 6.6 NM

Monomoy Point, channel 0.2 miles west, Current Station

Location: Latitude 41° 33.000’N Longitude 070° 01.300’W

Current Table

Slack MAX Speed

---- 01:44 2.0 kts Ebb

05:12 09:16 1.5 kts Flood

11:55 13:58 2.0 kts Ebb

17:27 21:33 1.6 kts Flood

Flood Direction: 186° Mag

Ebb Direction 002° Mag

Distance from Monomoy Point 0.2 NM

Station BUZM3 - Search and Rescue Data - Date 10/12-13/03

Ave Wind Dir True 37° 35° 36° 19° 355° 332° 331° 327°

Ave Wind Spd Knots 22 24 25 19 17 15 16 14

Time every 6 hours 00 06 12 18 00 06 12 18

Water Temp 9-30-2003 61°F

Water Temp 10-26-2003 57°F

We can safely assume that the water temperature is 60 or lower on Sunday October 12, 2003

On Oct 12, 2003 at 15:00 hours the current was 0.3 knots ebbing 285° Mag as reported from the Dennis Port Current Station. This would be almost 270° at 16°00”W VAR Directly West. At 17:04 the current drops to 0.2 knots and again at 17:55 the current drops to 0.1 knots still maintaining the Ebb course of west. At 18:37 starts the slack time with no current.

So let’s assume an object is drifting west at 0.3 knots for two hours, 0.2 knots for one hours and 0.1 for ½ hour. That would be 0.85 knots in three and one half (3 ½ ) hours. Keep this in mind.

The wind is from the NNE dropping from 22 knots to 19 knots say it is blowing the surface water at .5 knots in one hour. Or 1.75 knots in 3.5 hours.

This would put the object about 41°37.918’N 70°05.298’W Or .85 NM west of Harwich Point and 1.75 NM south of shore. It is now 18:30 the object has been in the water for 3 ½ hours.

Dennis Port Current Station

Flood Direction: 093° Mag

Distance from Monomoy Point 6.6 NM - Over the next 5 hours the current starts and move east 093° Mag. From 19:07 to 19:36 (.50 hour) the current moves east at .1 knot. From 19.37 to 20:08 (.50 hour) the current moves east at .2 knots. Form 20.09 to 20:51 (.75 hour)at .3 knots. From 20:52 to 22:37 (1.75 hours) at .4 knots. From 22:38 to 23:18 (.75 hours) at .3 knots. From 23:19 to 23:49 (.50 hours) at .2 knots. And finely from 23:50 to 00:16 (.50 hour) at .1 knot. When this is all summed up you arrive at 1.445 or 1.5 NM east at 093° Mag.

Monomoy Point Current Station

Over the same 5 hour time period the current is moving south 186 Mag.

From 19:07 to 19:36 (.5 hours) The current moves south a 1.2 knots. From 19:37 to 20:08 (.50 hour) the current moves south at 1.4 knots. Form 20.09 to 20:51 (.75 hour)at 1.5 knots. From 20:52 to 22:37 (1.75 hours) at 1.5 knots. From 22:38 to 23:18 (.75 hours) at 1.0 knots. From 23:19 to 23:49 (.50 hours) at .5 knots. And finely from 23:50 to 00:16 (.50 hour) at .1 knot. When this is all summed up you arrive at 6.3 NM south at 186° Mag

Chatham Roads Current Station

The current at this station are classified as Weak and Variable

Flood Direction: NA

Ebb Direction NA

Distance from Monomoy Point 6.4 NM

With the wind from the north dropping from 19 knots to 17 knots the object would drift .5 knots for 5 hours or 2.5 NM south. Or at 41°35.677’N 70°03.243’W about 4.13 NM south of Harwich Point.

Let’s now assume that because the current is mild at Dennis Port Current Station, weak Chatham Roads Current Station and moderate at Monomoy Point Current Station an object at the surface would travel slowly eastward then toward the southeast and finely towards the south at an increasing speed toward Monomoy Point. Including the wind this might put an object at 41°37.918’N 70°05.298’W about 5NM south of Harwich Point and still 3NM NNW of Monomoy Point. It is now mid-night and this object has been in the water for 9 hours.

For the next 6 hours the current is ebbing running north average speed is about 1 knot. Wind remains out of the north. Object near the location of Rodgers Shoal until next flood current which would run south. Wind remains out of the north.

Current Station in the NSPN local area:

Cape Ann

There are only 3 current stations around Cape Ann.

Annisquam Harbor Light

Blynman Chanal Entrance Gloucester Harbor

Gloucester Harbor Entrance.

North Shore

Marblehead Channel

Nahant East Point

Pea island (Southeast of Nahant)

Bass Point (Southeast of Nahant)

North of Cape Ann

Plum Island sound Entrance

Merrimack River Entrance

Newburyport, Merrimack River

Readings from more specific area would help but as you can see the current stations are some distance apart. Local knowledge is all we can go on.

Analysis:

Although it was a revealing exercise doing this analyses I could not help but feel sorry for those involved with the Oct 12 incidence. As I looked over the wind and current info I felt lost for reasons why. If we could only have had an these two young women in an intro course .... Just a few minutes of caution about offshore winds .... I’m sadden about the tragedy.

Most Important

Hypothermia is the abnormal lowering of the internal body temperature. Exposure to the chilling effects of cold wind, or water can result in hypothermia. If a person is exposed to water temperature of less than 92 degrees Fahrenheit, hypothermia may occur. In water temperature of 60 degrees Fahrenheit and below, depending on how much body fat a person has, they could die from hypothermia in as little as 3 hours time, in the water.

Keep it safe out there.

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I don’t quite agree. High tide was around 2 pm. They launched at 3 pm and were reported missing in fog at 4 pm. The sun set two hours later and they were probably in heavy fog and total darkness by 7 pm. Wind and waves were the only indication of direction they had. Later they may have seen some illumination from the moon in the southeast.

Winds were NNE when they left Ayer Lane. I believe the report said they were last seen heading eastward along the shore before slipping into the fog. Without a compass or GPS I would have paddled along the troughs, wind & waves to my right, confident I would soon see the shore again. I think that’s what they did but the wind kept them out in the fog. An automobile horn might have provided the reference they needed. They probably paddled sideways to apparently light winds unaware they were moving southwesterly. Things only became worse as the waves height increased and winds backed to the NNW. It doesn’t make sense that they only drifted if they wanted to get back in.

They were likely both paddling to stay warm and stabilized, confounding the drift models. If one was towing the other with a bungee cord, the boats were connected bow to somewhere aft of the lead paddler and forced into the 15-20 knot wind. Paddling into the wind was the direction they needed to go but wetter and colder than going with it. More likely, they rafted together at some point for stability in unseen waves.

I would agree with Adam that wind drift was the dominant factor until the boats were swamped. It carried them out beyond Buddy’s calculated course into stronger currents. If they were paddling eastward in beam seas they had a fair chance of being near Rodgers Shoal and South Monomoy.

Buddy found a lot of relevant information regarding currents and wind. Adams point should be well taken about generating data on local conditions in case it’s ever needed. Tables regarding wind drift of kayaks in different configurations might be useful.

David bought a small compass for his PFD. I hope it glows in the dark.

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>David bought a small compass for his PFD. I hope it glows in the dark.

OK, I'll add one of those little high-intensity, LED flashlights, especially if I figure to be out anywhere near dark. Nope, It'll always be there... lots of good uses for it. I wonder how well it shows up in the fog, as a signalling device, or even in clear air.

Of course, I always have my triple-LED headlamp at least in a hatch, even at 9:00 AM. But I presume we are talking about situations where that does not help.

http://www.campmor.com/webapp/commerce/com...rrfnbr=26634962

http://www.campmor.com/images/lights/29657.jpg

--David.

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Following your lead, I stopped in at REI yesterday, after dark, to look for a little compass. I narrowed the field to the whistle, thermometer, magnifier and compass combinations. They have one for $4.50 and another nearly identical by Silva for $7.00. The compass card is on the Silva product is a little easier to read in the dark.

Does that LED light float?

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>Does that LED light float?

Doubtful... it's a dense little bugger. But it's got a hole for a tether. Maybe the compass and light can go on the same line.

I saw those combos too, but opted for a straight compass. Unfortunately, it also has a basically functionless plastic base that makes it much larger than necessary, though still quite small.

What I'm waiting for is a tiny barometer/thermometer. I'm impresssed how well you can foretell weather deterioration heading your way with one. Is it possible, from a technical standpoint? The smallest thing that Campmor has is a $60 watch with a barometer/altimiter.

http://www.campmor.com/webapp/commerce/com...rrfnbr=27738482

--David.

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Thanks for the info on tide stations, Buddy. I checked my Nantucket Sound charts. Ebbs do flow WEST in the sound, as you pointed out; this would have made Jagoda's and Aranof's initial drift (if it was indeed a drift) all the worse towards the southwest, where I guess the heavier incoming tidal currents, flowing east after the tide change, would have then pulled them out towards Monomoy Point, with the backing NW wind Don mentions helping.

This is all speculation, of course. What's probably more important is what one of us would expect and try to use to ded reckon were we to get caught in the fog or at night and more under the influence of tidal or wind drift. With a drastically diminished capacity to figure out by visual features where the hell we are, it might be tough too to maintain the peace of mind to factor in wave troughs, etc.

Yeah, yeah, yeah, bring a GPS, but for a daytrip who wants to? Cumbersome, distracting, and always ready to crap out due to battery depletion.

Currents run fairly hard in areas of Salem Sound, I noticed this weekend. Aside from the spinning rip that wraps around the southeastern edge of Bakers Island, where Marc Schlosser caught a big striper last year, there's also a current that looks like it runs south/southeast and north/northwest in what's known as Stinkpot Alley in the Salem Sound approach channel. One gets pulled toward Whale Ledge by it on the outgoing tide (?), towards Childrens Island (?) when the tide's on its way in...

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I usually carry a simple backpacker's compass in my PFD and another in my emergency drybag. But like David, I think the baseplate makes it cumbersome in a PFD pocket. Besides, my old Silva eventually leaked and corroded. Not carrying one at the present.

So after the Cape incident, I dug out a gadget bought but never really used: one of those miniture compasses that clip on your watch band.

The clip fits nicely on one of the straps on my PFD and it survived repeated dumpings and rescues at the cold water session. It is tiny (easy to carry) but has only the 8 principle points of the compass. Not enough to take degree headings, but if you know about where you are, at least you'll be heading in toward land rather than out to sea.

Just another redundancy. Not sure if it glows in the dark, though.....

Scott

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David,

I recently got a Timex Helix from Campmor. The battery quit in 2 months,the altimeter is reliable within a couple of hundred feet,if you can ever get it to recalibrate! The temperature function is useless as long as you wear it. But it did keep accurate time(till it quit)

I carry a carabiner watch on my PFD now,and a small clip on compass with thermometer. Gee,I really haven't missed the altimeter while kayaking!

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