Two gates on a passage have independent slacks, and the boat takes time to get between them. What to do when they will not line up.
Because each gate has its own slack at its own station, and those slacks are independent of one another. The boat also takes time to travel between them, so even two gates that turn at nearly the same moment cannot both be met at slack — you arrive at the second one an hour or more after leaving the first. On most days no single departure serves both, and the honest answer is which one to favour and what the other will cost.
Roughly fifty minutes later each day, because the tidal cycle is about twelve hours and twenty-five minutes rather than twelve. Two gates on the same passage drift at close to the same rate, so their relationship changes slowly — a pair that lines up conveniently this week will not next week, and a pair that conflicts today may be workable in a few days.
The least forgiving one, which is usually a matter of class rather than distance off slack. A rapid the sailing directions say to take at slack outranks a pass you can drive through, because being wrong about the first is a different kind of wrong. TidePush names the gate to re-time around rather than leaving you to work it out from a list of slack times.
No. The Yucultas and Gillard Passage take their prediction from the same station and turn within about ten minutes of each other, and they are still two things to time, because a boat needs the better part of an hour to get from one to the other. What separates two timed pieces of water is the travel between them as much as any difference in when they slack.
Often, yes. The recommended cast-off is chosen for the day as a whole — how long the passage takes and whether you are in before dark — which can leave every gate on a multi-gate route poorly served. TidePush also scans the day for the departure that gives the gates the easiest water and offers it with the cost attached, so you can weigh twenty minutes of extra passage against a rapid taken near slack.
In short: Each gate turns at its own time, and you cannot be in two places at once. Time the first one perfectly and you arrive at the second one late.
A passage with one gate has a simple answer: leave so that you arrive near the turn. A tide table gives you that, and so does any current atlas.
A passage with two gates does not, and the reason is that the two windows are INDEPENDENT. Each has its own slack at its own station, they drift apart through the month, and the boat spends real time getting from the first to the second. Whether they can both be met is a fact about the PAIR, and a table that knows about one gate at a time cannot express it.
12 routes in the library carry more than one gate, and on most days their windows do not line up.
Instead of a list of slack times, TidePush shows the chain: every gate in order, when this passage reaches it, how far off THAT gate’s own slack the arrival lands, and whether the windows can be reconciled at all. Where they cannot, it says so and names the gate to re-time the day around.
Coal Harbour to Sidney is the case that makes the point. First Narrows comes up in the first half hour and Active Pass some thirty-five miles later, and a boat cannot be early for one without being late for the other. On a typical August day the two ideal departures sit about an hour apart, so the plan is a compromise by construction and the card says which gate is bearing the cost.
In short: Even two rapids that turn at the same minute are separate problems, because it takes the better part of an hour to get from one to the other.
It is tempting to treat gates that share a current station as a single problem. The Yucultas and Gillard Passage are predicted from the same station and turn within about ten minutes of one another — and they remain two separate things to time, because the boat needs the better part of an hour to travel between them.
This is why the three rapids above Desolation Sound are counted as three and not one, and why the established practice is to take the Yucultas about an hour BEFORE slack at Gillard, so the building stream carries you through the set rather than stranding you between two of them.
In short: The recommended time is chosen for the day as a whole. On a route with several gates, a departure twenty minutes slower can put every one of them in easy water — so the app looks for that hour and tells you what it costs.
The recommended cast-off is chosen for the day as a whole: how long the passage takes, and whether you are alongside before dark. That is the right default and it is not always the right answer for the gates. On a multi-gate route it can leave every one of them poorly served without anything drawing attention to the fact.
So the day is also scanned for the departure that gives the gates the easiest water, and if one beats the recommendation it is offered with its cost attached — what the gates do at that hour, and how much longer the passage takes. It is an alternative rather than a correction, because the trade is the skipper’s to make.
Refuge Cove to Dent Island is the case that earns it. A cast-off chosen for the day can reach the three rapids well off their slacks, where a departure some twenty minutes slower puts every one of them in easy water.
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