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View Full Version : What are the hydrodynamics of a "rip"


Thad
08-19-2002, 01:16 PM
That is the question. I was going to the Opera House race at Nantucket in the 42' Alden Yawl FIREBIRD this past weekend. We finally got off the float Friday afternoon at 5 after a little rig tuning , changing the fuel filter, and stowing our gear and the gear for the owners family cruise to follow. (The owners wife did the stowing and a great job of it) The breeze was SW and freshened as the evening went along. We were headed outside the Cape for the Pollock Rip Channel.
The crew is Brian, me, and three of his lifelong friends -- only one a sailor, the other very pleasant and funny fellows who kept the tone light to the best of their considerable abilities. There were bilge pump problems but she is not really leaking that bad. We had a little hand pump and a bucket and a few buckets full over the side every few hours kept things in control.
We are ripping along! That is the thing to keep in mind, just ripping. Still in the Bay there is some chop with the breeze SW 15-20, but we are on a close reach SSE and driving with a high cut jib, main and mizzen.
Around 10 I pass the tiller to Brian's friend and go below for some rest. Friends have left an hour or more ahead of us and we can hear them calling but they can't hear us. Range is the thing. We are going something beautiful! blasting along. Truth be told she was creaking all over the place with the stress of sailing. Around the partners, from the bulkheads, lots of noise around me there in the bunk.
One o'clock I get up. Brian has hit the hay. Bob has the tiller and says "This is terrific!" The noises inside the boat are not heard in the cockpit. We can see lights from Provincetown over Race Point. Highland Light is off the starboard bow and we are closing with the bouy flashing ahead. Overhead the stars are shining bright even with the hazy atmosphere. Outside the Cape in 20 knots of wind SW the chop is minimal with no sea running. Now the stresses of the Bay are gone. One fishing boat shows well outside of us and a few car lights can be seen moving along the shore. After a couple of hours we have opened up Nauset Beach light, we are running about a mile off shore. Brian came up and bails and takes over the helm, I go back to the berth.
Back in the cockpit before dawn we can see fog making up and then we are in it just as the sun dawns over the rolling sea. We are riding the tide with the breeze still SW but 10-15 now and soon to go W in our favor. Depth is 40-50 feet and our circle of fog is maybe 100 feet. We see one little fishing boat at the edge of our visual circle as we cruise along. Our crew emerged with the dawn. Brian got the stove going for tea and coffee. All available eyes peeled we rolled along motor-sailing for the bouy and the East end of the Pollock Rip channel. We heard the groaner before we saw it in the mist. Then shortly we were in the rip and the question was raised.
What was raising the short breaking chop we drove through? We still had 40 feet of water, but the fisherman who gave the horn blasts were probably at the edge of the shoal. The shoal is mostly about 20 feet there with the channel 40. The tide was sweeping South and then West into Nantucket Sound around Monomoy Point at maybe 2 knots. We were going 8 over the ground at times with little effort, the sails luffing as we motored to windward though there was little wind. That little rip right past the bouy was the only clear evidence we saw of the motion around, with that one boat and quite a few birds, mostly gulls. Then we were through into the Butler Hole and bore off for Nantucket.
The Westerly held enough so we could sail much of the way through the Sound. Slowly the fog lifted and there passing off to starboard were Brian’s friends who had left ahead of us. In range the radio did work. They had been making 9 knots further out from shore and had layed to waiting for the tide to turn. We were that blip they had seen on the radar as they followed us through the rip. We motored into Nantucket, picked up a mooring and took in the scene on that hot August day on the Island. The crew went swimming.
Brian decided not to do the race after all (the family was coming), but we had one wonderful sail outside the Cape. It would have been fun to see more of the Pollock Rip than our circle of fog. I know Monomoy Island is too low to be much seen but we saw none of it, only the beautiful water, birds, and a couple of bouys.
I decided to forgo the race party since we didn’t race and took the noon ferry to Hyannis passing the 12 meters in their prestart maneuvers with the other classes stretched out to the East on their reaching leg, Brian's family met me at the wharf and I drove the car back to Marblehead, home before 5. 18 hours to Nantucket (95NM), two days round trip.

Ian McColgin
08-19-2002, 02:24 PM
Dern. Thought I answered this . . .

PolyGrip has fascinating currents that can run quite differently than predicted depending upon how much water has piled into Nantucket Sound.

The chop you saw is usual there - current making against the wind and all - but given how the current bends around, including some fantastic verticle roils, and how the waves form in different places and then interact, it's never a simple chop like you might see on the afternoon ebb in upper Buzzards Bay.

There's also the effect of sea swells. These are most noticable north of the hole along a sneaker channel running north. Fun between the breakers.

The Harwich sailors know this place best - the Stone(d) Horses. . . .

rodcross
08-19-2002, 06:52 PM
There's something else to be added here.

Starting in Gaspe, Quebec, and repeated a dozen times to Halifax and Bar Harbor, the advice was the same...'Don't go outside Cape Cod unless you choose to go 40-90 miles out. Only a fool risks staying close outside to the cape.'

You guys were lucky. Those are very dangerous waters and the charts don't help.

Cape Cod Bay, the canal, a little mashing in Vinyard Sound bring you to an easy reach to Nantucket.

What was the point?

Rod

Thad
08-19-2002, 08:16 PM
No more lucky than crossing a street. The forecast was good and believeable with the weather information available, and proved very accurate. Even if it had not been quite so accurate there were options along the way. The currant turn at Pollack Rip worked well with our schedule, more so than the Canal and Woods Hole, not an easy passage. Going on to Quicks Hole means you have to work your way back through Vinyard Sound. If you read Duncan and Ware you get a different perspective than the one you report. Have you read THE COMPLEAT CRUISER by LFH? The water along the Pollock Rip Channel is not that shallow and the beach along the Cape shelves evenly to the shore so you can monitor your position with the bottom. Brian had done his research, I had done my own and was comfortable with our equipment and the options. The fishermen out there at dawn fishing the rip were in much less capable sea boats than we, also enjoying the moment. One of our options was to carry on past Pollack Rip and go through the Great Round Shoal Channel. Overstated warnings are no more helpful than overstated recommendations, the way I see it. It was a great sail and we made the passage in good order. Do we need some other point?

Chris Coose
08-20-2002, 08:32 AM
Thad,
I've made that trip a few times outside and in.
Let's see, would I rather hit P-town with the rising sun and the breeze riding my back, as has been on the well planned trips, or would I rather be waiting in Refuge harbor at the top of the canal for a tide change?
I like that crossing the street business. A person can make a safe crossing if planned well, get pasted if he were to take it haphazardly or remain at the curb.
Thanks for writing that story. I took a friend up on a fishing trip to the islands this weekend. Rips and fishing go nicely together. I spent half the time watching the ocean work it's way in and around the islands. I was trying to imagine what it would be like if they had tide changes like here in Portland.

Thad
08-20-2002, 06:26 PM
The ebb tide there at Pollock Rip is the ebb out of the Gulf of Maine/Bay of Fundy (at it's outer widest reach) following the ebb West through Vinyard Sound. The coming tide flows East through the Sound and the Rip channel part of the tidal pressure from the East modified by the Gulf Stream and working toward Fundy again. I think. It is the ever interesting ocean, the ever changing wonderful ocean, even if we have made something of a mess of it.

[ 08-20-2002, 06:31 PM: Message edited by: Thad ]

rodcross
08-21-2002, 06:39 PM
All well and good. Cross the street if you choose.

My logs show 15 hours from Gloucester to Nantucket, with a stop in Edgartown for lunch, and that with a contrary tide in the canal. Great sail, by the way.

I had a novice on board. I was not going to explain to her mother that the weather reports and the Compleat Sailor said I would have no problem.

I say again, What's the point?...Especially as you didn't race.

Rod

Ian McColgin
08-22-2002, 09:25 AM
When I run to or from Boston, I choose inside v. outside by weather and tide.

For example: both were nice for the famed Calamari Cruise to Boston on that horridly short fall day when we went from DST to EST. Bright and clear and blowing blue stink just a smudge north of west. Under jib, forestaysail and double reefed fore (main and mizzen furled) Grana AVERAGED 11.5 kt from dropping the mooring in Hyannisport to those towers up near the hook before Race Point.

The beauty of this run could not be matched. We were making a party of it - crew of 8 - roaring along in relativly flat water a couple miles off the Cape, with the strange autum light playing on the water and, as the sunset, making us quite a sight from shore, judging from the calls I got from some lower Cape friends. Along the way, we had rather a lot of calamari salad.

As the sun set for a long night we rounded the Cape and faced into a strong wind and bucking sea. I also wanted to jog very slowly essentially P-town to somewhere near Minots at dawn. I just didn't want to wrestle my way into Boston against strong winds and an ebb in the dark.

So we spent the night piddling along in the grip of the uppitydownity. What the sea had given, the sea took back as we all returned the calamari to its rightful place.

None the less a wonderful sail. The wind clocked over to a bit east of north with the dawn sleat storm and we swept into Boston fueled by my infamous coffee and pancakes that served double duty as inside ballast.

We go outside sometimes just because it's really fun. No point. Just fun.

Scott Rosen
08-22-2002, 11:03 AM
Thanks for the nice stories and good writing, guys.

I still have a sense of wonder and slight fear when ever I encounter strong rips in deep water. Especially if the charts show a fairly level bottom. It's one of those pleasant mysteries you encounter on the water. I do a lot of cruising through The Race, which separates Long Island Sound from Block Island Sound. I've encountered very rough seas in otherwise calm conditions with no wind. There seems to be no rhyme or reason as to where you find the rips one day to the next.

Night passages are great. Night passages sailing solo are an unforgetable experience. If you've got confidence in your boat and your skills, I highly recommend it.

Ian McColgin
08-22-2002, 11:10 AM
Ah, the Race is awesome. I saw a hole in the water there. Not big enough to swallow my boat but I have heard of small outboards just vanishing.

No huge roils around the hole I sailed through. We're just easing along in a light breeze and all of a sudden we were in a maybe 3' trough. No surrounding upward waves, just a trough. Felt very happy to have the momentum to sail on through with a sort of drop down and somewhat slower rise back up. Treswierd.

rodcross
08-22-2002, 12:30 PM
There were two memorable rips on ALITA's trip out the St.Lawrence and around the southern tip of Nova Scotia. The greatest amount of water flowing through the smallest channel was the Richlieu Rapids between Sorel and Quebec City. The water was moving at 7 kts and so was ALITA. The GPS recorded 14kts over the bottom. I expected to see standing waves, but there were none. Instead, the water just boiled and roiled. I attributed the lack of standing waves to the fact that the depth in the rapids was 400 to 600 feet. You could see where the bottom came up as there would be a broad roller, but no crests... Sort of a Thank-you-ma'am. I don't think she ever went that fast before, unless when she was on a truck, that is. We covered over a hundred miles that day, in about 11 hours.

(By the way, every chance I had, I would study the charts and tide tables and predict (poorly) the flow of the river. Tide tables turned out to be nearly useless as the eddys were nearly as important as the general flow and the charts only noted the serious rips. By sheer luck, I happened to be in a bookstore near Montreal when I spotted a book titled "ATLAS DES COURANTS DE MAREE" published by the Department of Fisheries and Oceans of Canada, which had color graphics of the set and drift of currents, by the hour, from just after Montreal to beyond Quebec. To anyone planning to take the journey out or into the St. Lawrence: GET THIS BOOK!, especially if you're going upstream. It could make the difference between a 40 mile day and a 10 mile day.)

Cape Sable turned out to be much more daunting. All the advice said to stay within a quarter of a mile off shore or go offshore 15 miles - in between was 10 miles of maelstrom. I opted to take the close-to-shore route. We took a pounding for about two miles, then things calmed down. From me to the horizon was nothing but standing waves with a contrary wind knocking the tops back. Thats a lot of water flowing into the Bay of Fundy. A big power boat, out about 4 miles, must not have checked his tide tables and was heading against the flow. I hope he hadn't had calamari salad.

Stu Fyfe
08-22-2002, 02:15 PM
They choice of going around the Cape or thru the Canal is one I've made a few times myself. I've always enjoyed the trip outside. It is absolutely beautiful on a good day. True, if you get into trouble there's no where to pop into. If you don't like Pollock Rip you can always go through the small winding cut just between Stage Harbor and Monomoy. It's well marked and gives you a great view of a large Grey Seal colony on Monomoy. Saves you about 10 miles. As far as going thru the Canal, I hate having to go thru Woods Hole. In my opinion it's the most dangerous channel in Massachusetts. The current really rips through there and on a crowded weekend day all heel can break loose as sailing craft with their slower hull speed try to squeeze through at the same time. Like the Canal, if you can hit the tides right you'll fly thru. If not, forget it.
I've been through the Race a few times and Quicks Hole. They can be bad too. But there's something about Woods Hole!