Understanding Tides and Currents in PWS
Prince William Sound experiences severe tidal fluctuations that present significant hazards to vessels of all sizes. Vertically, the tide can rise or fall over 15 to 20 feet in a single six-hour cycle. Horizontally, these massive volumes of moving water generate swift currents and standing waves, particularly in narrow passages, bay entrances, and shallow river deltas.
Critical Tidal Hazards
1. Tide Rips (Standing Waves)
Tide rips are highly turbulent areas of standing waves caused by strong tidal currents flowing over shallow bars, around sharp points, or through narrow passes (e.g., Valdez Narrows, Esther Passage, Canoe Passage).
- The Wind-Against-Current Effect: Tide rips become exceptionally dangerous when a strong wind blows against the direction of the tidal current. This forces the waves to stack up into steep, vertical walls of water that can easily swamp powerboats and capsize kayaks.
- Action: Study tide tables and schedule transits through narrow passages during slack water (the brief period when the water is not moving) or during a fair-tide transit.
2. Mudflats and Shallow River Deltas
Significant parts of the eastern and southern Sound (especially near Cordova, Orca Inlet, Boswell Bay, and river mouths) consist of low-angle mudflats and stream deltas.
- The Stranding Hazard: A high tide can cover these flats with several feet of water, giving a false appearance of safe passage. As the tide recedes, these areas go dry rapidly, stranding vessels on exposed mud or rocks miles from deep water.
- Action: Give low-angle shorelines and river mouths wide clearance. Never attempt to cut across shallow bays without extensive local knowledge and an active depth sounder.
3. Beaching and Shore Stranding
When visiting the shore, even for a few minutes, never leave your vessel unsecured or sitting just above the water line.
- The Tidal Swing: A rising tide can lift a kayak or small powerboat and drift it out to sea. Conversely, a falling tide can leave a heavy boat stranded high and dry on rocky reefs or mudflats, forcing an unexpected overnight stay.
- Action: Always drag small boats well above the high-tide line and tie them securely to sturdy shoreline anchors (trees, heavy logs, or rocks).
Tactical Rules for Anchoring and Coastal Navigation
- Always Carry a Tide Book: Do not guess the tide stage. Note the high and low tide times and heights for the day.
- Calculate Anchor Scope: When anchoring in sheltered coves, calculate the total depth range (including the maximum high tide) to ensure you have sufficient scope (anchor line length). Aim for at least a 5:1 or 7:1 ratio of line to water depth, and allow plenty of “swing room” for wind shifts.
- Calculate Low-Tide Clearance: Ensure that your selected anchorage has enough depth at the absolute lowest tide so that your vessel’s hull or drive units do not settle onto a rocky bottom.
- Carry Shore Survival Gear: When going ashore, always carry your personal survival kit and a means of communication (handheld VHF radio or satellite messenger) on your person, in case your vessel drifts away or you are temporarily stranded by a sudden tidal change.