Jupiter transits Seymour Narrows, one of many important navigable tidal rapids along the Inside Passage from the San Juan Islands in Washington, through British Columbia, continuing into Southeastern Alaska. Described by George Vancouver in 1792 as “One of the vilest stretches of water in the world,” Seymour is today calculated to be the most dangerous rapid on earth using a formula that predicts the probability of flow being laminar or turbulent.. the Reynolds Number.
Timing is Everything
Mariners must time their navigation along tidal passages with dangerously narrow channels. Fortunately, accurate times of slack water—when seawater movement slows enough to allow boat passage—are well known and widely published in guides and on electronic charts.
The seas are propelled on the earth by the gravitational pull of the moon and sun, and the forces are strongest twice during the synodic month, at new and full moons, to which Jupiter’s Crew pays heed. In the Pacific Northwest we have semidiurnal tides—two high and two low tides per day—offering four times daily when slack water occurs.
Tidal heights along Jupiter’s way vary from 8 to more than 20 feet contingent on geography and lunar cycle, and these immense water movements create mighty currents within constricted channels.
Best Boats Beware
Jupiter and her crew love this stuff and indulge in all sorts of rules-of-thumb, formulae, computations, speculations, and wishful thinking. Fearless Jupiter argues that she has power enough to churn through rapids at times other than slack water, but turbulence rules the tidal realm, and the best boats best favor caution.
Fluid Dynamics
Naturally, there is a formula to determine the Reynolds Number for navigable rapids:
Low Reynolds numbers indicate smoother flow. Very high Reynolds numbers indicate turbulent flow with eddies, boils, standing waves, and chaotic water movement.
Major tidal rapids such as Seymour Narrows often exceed Re = 100,000,000.
| Rapid | Region | Peak Current | Approx. Depth | Estimated Reynolds Number |
|---|---|---|---|---|
| Seymour Narrows | British Columbia | 15–16 knots | ~100 m | ~800,000,000 |
| Skookumchuck Narrows | British Columbia | 16–18 knots | ~20–40 m | ~350,000,000 |
| Nakwakto Rapids | British Columbia | 18–20 knots | ~25–40 m | ~300,000,000 |
| Turnagain Arm | Alaska | 8–12 knots | ~20–50 m | ~200,000,000 |
| Sergius Narrows (Peril Strait) | Alaska | 8–10 knots | ~20–40 m | ~120,000,000 |
| Malibu Rapids | British Columbia | 8–9 knots | ~10–15 m | ~70,000,000 |
| Wrangell Narrows | Alaska | 4–8 knots | ~15–30 m | ~50,000,000 |
CONCLUSION: Think in sync so as not to sink.
Handheld Granola
Traveling at 30,000 feet between St. Louis and Seattle enroute to Jupiter, the crew is offered Alaska Airlines’ “proprietary” granola for breakfast, but, says the flight attendant unprompted, it’s actually good! Turned out to be true. Spotting a captive gourmand, chef discovers that the steward has mined the recipe from secret sources and is willing to share. Encrypted texts exchanged.
Preheat an oven to 325° and line a baking sheet with parchment. In a bowl stir up 3 cups of rolled oats, a handful of sliced almonds, some roasted sunflower seeds, and a pinch of salt.
Melt slowly together 1/2 stick of butter, 1/3 cup of brown sugar and 1/3 cup honey, stirring gently until it forms a highly viscous fluid with a low Reynolds Number. Blend in a teaspoon of vanilla extract off the heat.
Pour the wet ingredients over the dry and combine well. Smooth everything onto the baking sheet, spreading and pressing down firmly with a spatula. Bake for 20-25 minutes until golden. Cool completely then break apart into large flats. These can be further broken down to eat with a spoon, or simply handheld with coffee for early underway breakfast.
Alaska Airlines includes dried cranberries, and serves with milk and yogurt.
Can’t wait to try the granola recipe. Safe travels
Glad to see you back and on the water, continuing to pepper us with new vocabulary words. Those tidal rapids are really a sight to see… from afar. Glad to have passed through many without incident, though I was once going with the flow, when a barge like the one in your picture decided to go against the flow and that almost produced some very unpleasant side effects!
Bruce B, none of these rapids compare to some of your bicycle efforts!
A couple of years ago two long-distance Kayak paddlers from Olympia appeared at Butedale in northern BC where Jupiter was moored. They described in terrifying detail the existential threat boat wakes provide for sea kayaks.
There are unannounced, un-promoted and unseen paddlers moving north along the Inside Passage every summer, usually along shorelines, but occasionally making open water crossings. They also need to time rapids and currents, often at night.
This would make a fascinating story when you are ready.