Understanding Current Overlays
The current overlay shows predicted tidal current speeds and directions along your route. Understanding currents is one of the most important factors in passage planning in the Pacific Northwest, where tidal currents can exceed 5 knots in narrow passages.
What You See
Section titled “What You See”When the current overlay is active, arrows appear along the route showing:
- Arrow direction — the direction the current is flowing
- Arrow size — proportional to current speed (larger arrows = stronger current)
- Arrow color — indicates whether the current is favorable or opposing relative to your direction of travel:
- Green — favorable current, pushing you toward your destination
- Red — opposing current, pushing against your direction of travel
- Gray — slack water or negligible current
Current Impact Summary
Section titled “Current Impact Summary”At the top of the route detail page, the current impact summary gives you a quick assessment:
- Net effect — whether currents will overall help or hinder your passage
- Time delta — estimated minutes gained or lost due to currents compared to still-water travel time
- Favorable percentage — what fraction of your route has currents working in your favor
How It Works
Section titled “How It Works”BoatRoutes uses NOAA tidal current prediction data to model currents along your route:
- Station matching — We identify the current stations closest to each segment of your route
- Time estimation — Based on your departure time and boat speed, we calculate when you will reach each point
- Prediction lookup — We retrieve the predicted current speed and direction for each station at the estimated arrival time
- Impact calculation — We compare the current direction against your course heading to determine favorable vs. opposing effects
Understanding Tidal Currents
Section titled “Understanding Tidal Currents”Tidal currents in the Pacific Northwest follow a predictable pattern:
- Flood current — flows inland (generally north/east in Puget Sound) as the tide rises
- Ebb current — flows seaward (generally south/west) as the tide falls
- Slack water — a brief period of minimal current between flood and ebb, typically lasting 15-30 minutes
- Maximum current — the strongest flow, occurring roughly midway between slack water periods
Currents rotate direction approximately every 6 hours, with two flood/ebb cycles per day in most of our coverage area.
Strong Current Areas
Section titled “Strong Current Areas”The strongest tidal currents in our coverage area include:
| Location | Typical Maximum | Notes |
|---|---|---|
| Deception Pass | 6-8 knots | Transit at slack only |
| Active Pass | 5-7 knots | Between Galiano and Mayne Islands |
| Dodd Narrows | 6-8 knots | Near Nanaimo |
| San Juan Channel | 2-4 knots | Between San Juan and Shaw Islands |
| Rosario Strait | 2-3 knots | Between Fidalgo and the San Juans |
| Admiralty Inlet | 3-5 knots | Entrance to Puget Sound |
- In areas with strong currents, timing your departure to ride a favorable current can save an hour or more on a passage.
- Change your departure time by 2-3 hours and compare the current overlay — you may find a dramatically better or worse window.
- The current impact indicator turns from green (favorable) to red (opposing) as you shift your departure through the tidal cycle. Look for the greenest window.
- Even moderate currents of 1-2 knots make a significant difference for slower boats. A 1.5-knot current adds or subtracts 20% from a 7-knot cruising speed.