Better Boating

Understanding The Tidal Currents in Woods Hole (With Daily Charts)

Without a doubt, the most popular post eva on My Buzzards Bay has been Understanding Cape Cod Canal Tidal Currents (with Daily Charts) It’s been viewed by about 10,000 of you and an average of 20 new viewers a day years after I first published it!

The post was very important for those of you who sail, have a trawler, or some other speed challenged vessel trying to make passage through the Cape Cod Canal.

This morning I was thinking about Woods Hole and its unique challenges. And while the canal tidal currents are challenging, most Buzzards Bay boaters will tell you their first run through Woods Hole was somewhat terrifying.

Hazard #1 – The Rocks

If you pass through the Hole frequently, you may have noticed rescue boats from Sea Tow and Tow Boats hanging out at either end like cabs waiting outside LaGuardia.

To understand why this is such a lucrative venue for rescue boats, look than no further than this guy – an experienced boat owner from Marion…

Here’s what the MV Times reported

Tow Boat US, Falmouth, owner Mark Brown, was first to respond after receiving the distress call. The 25-foot Nauset powerboat Grit and Grace had a five-foot tear in the keel, Brown said. Even though he was on scene within five minutes of the mayday, Brown said, the boater was in water well over his ankles due to the hull breach.

“We see people hit there all the time,” he said of the ledge, which he described as roughly an eighth of a mile from the Steamship Authority terminal.

There are rocks everywhere, some can always be seen and some are only visible at low tide. The two clear passages between the rocks are only a few hundred feet wide and with the current pulling you every which way, disaster is never more than seconds away.

Hazard #2 – The Tidal Rip Currents

There are a number of reasons for the wicked currents in Woods Hole.

From a big picture perspective, the upper Cape is pretty much the intersection of two massive sea currents – the Gulf Stream and the Labrador Current which is a subset of the North Atlantic Drift.

Thanks to the constantly fluctuating high and low pressure weather systems, these powerful sea currents constantly collide from the north and the south Atlantic in the middle of Vineyard Sound.

From a local perspective, the 250 square miles of sea water in Buzzards Bay empties and refills itself twice a day by rushing through Woods Hole.

20 Minutes Of Slack

The net effect of all of these hydrodynamics is an extremely short slack period in Woods Hole – about twenty minutes four times a day. In fact, slack currents are so rare that I’d never even seen one until one foggy morning in June when our Nantucket Flotilla serendipitously passed through…

Here’s how the Boston Sailing Center describes the currents…

[The current] routinely flows through at over 4 knots (80 or 90 percent of velocities in the Cape Cod Canal), and, according to Eldridge, will hit 7 knots on occasion. The full current on the nose makes transit slow and awkward. The full current from astern will cause things to happen at an alarmingly rapid pace.

Moreover, the current runs slightly cross-channel in the upper section called “The Strait” and more significantly cross-channel in the lower section called “Broadway”. As the current approaches full strength, it can literally pull hard enough on the buoys to tow them partially under, creating a distorted navigational picture.

More…

Remember that current is described by the direction towards which it flows, so the southeast flood runs from Buzzards Bay towards Vineyard Sound and the northwest ebb runs from Vineyard Sound into Buzzards Bay. The brief period of essentially slack current persist for about 20 minutes either side of the time the current turns.

Woods Hole Survival Strategies

While the Cape Cod Canal report was about making efficient passage, my advice on Woods Hole is literally about survival for your good ship and crew.

And unlike the canal where you get a favorable current half the time, the currents in Woods Hole are equally dangerous if they’re with you or against you so the only semi safe passage is in one of the very short 20 minute slack window.

The Daily Current Chart for August 15, 2020

If that’s your plan, you can click here to access today’s Daily Current Chart.

My survival strategy is speed and space!

With 4-7 knot currents pushing you toward the rocks, the only way to maintain control of the helm is to “put the pedal to the metal” and go so fast that you overcome the currents.

Of course with the main routes only a few hundred feet wide, you really don’t want to speed though if it’s crowded. In particular, watch out for slow moving sailboats and trawlers. Oh yeah, steer well clear of the huge ferries…

I will generally scan both ends before I enter The Hole. If I see a ferry, a slow boat, or just too many boats, I’ll back down and wait until the traffic clears.

There are two ways through; Broadway and The Strait. The ferries and bigger boats generally favor Broadway, but I tend to avoid it when the currents are rushing hard.

The problem with the Broadway route is that it involves a sharp turn by the day marker and depending on the currents, you can easily get pushed toward a rock outcropping.

For example, if you’re entering from Buzzards Bay and you have a Southeast Flood at your back you’re on easy street until you try to bang a right on Broadway. That 4-7 knot current at your back is now abreast abeam pushing you straight into oncoming vessels or worse – Red Ledge.

Similarly, if you’re entering from the Sound and you have a Northwest Ebb off your stern and try to hang a left, the current will keep pushing you straight; straight into the aptly named Devil’s Foot Island.

My preferred route is to run down the Strait toward the Steamship Dock and make a broad turn between the generally visible rock outcroppings in Great Harbor. There’s a lot more water to maneuver in, less currents, and generally less traffic.

Strategy for the Fog

The best strategy for the fog is to avoid it all cost. I am quite proficient in piloting by instruments – even in zero visibility, but not Woods Hole.

The problem is all those tall medal cans and nuns look like cruise ships on radar and there are dozens of them. It’s simply too nerve-wracking to stare at the radar screen trying to pick out the boats from the cans doing 20 knots.

Here’s my view from the helm of Vigilant the first and last time I venture through doing 20 knots in pea soup fog…

In fact, that was the only piece of land I saw during the entire passage.

The best strategy for a foggy day is to take a pass on Woods Hole and head down to Quick’s Hole or even Robinson’s and play it safe. NOTE: My friends on the Buzzards Bay Boater Facebook page advise against Robinson’s…

If you boat on Buzzards Bay and you want to visit Martha’s Vineyard or Nantucket, you have to pass through Woods Hole. Yes, it can be very challenging, but if you have a strategy and you stick to it, it’s really no big deal.

Categories: Better Boating

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