Where is Unimak Pass? The simple answer is at the west end of the Alaska Penninsula and the east end of the Aleutian Islands.
Sometimes a graphic makes orientation clearer.
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with a closer image...
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Unimak Pass is the gateway between the North Pacific Ocean and the Bering Sea. More than 4,000 commercial ships pass through this waterway every year... take a look at the marine AIS - note the commercial ships lined up following each other west from the Gulf of Alaska to pass west through Unimak enroute on a great-circle voyage to the orient...
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So now that you have your bearings lets discuss why this can be a very dangerous location... besides the obvious ship-to-ship collision risk...
The tidal current can flow through Unimak Pass at more than 5 knots. Add Alaska gale/storm weather and you have extremely large forces meeting in a small region... UNIMAK PASS!
What happens when weather from the NW comes into contact with tidal current from the SE?
A collision of sorts - powerful winds force seas from the NW towards the SE while 5 knots of tidal current flows towards the NW and it all comes together in Unimak Pass and the sea begins to 'boil' with waves crashing into each other and it looks like inside of a washer machine... except you could be there in your yacht... and it is not going to become extremely dangerous.
So how to avoid this danger?
1. Know the forecast weather, Plan your transit during calm weather if at all possible.
2. You must know your boat's intended direction of travel & speed to calculate an ETA be it approaching from the Bering Sea or from the Pacific Gulf of Alaska, Adjust your speed to arrive and transit during a safe period. NEVER GO INTO WEATHER ESPECIALLY INTO THE CURRENT ALWAYS GO WITH THE CURRENT AND WITH THE WEATHER. Consider adjusting your speed or anchor until a favorable tidal current change.
3. Be sure to carry the Unimak Pass tidal predictions for the dates you intend to transit.
and
4. KNOW THE DIRECTION OF EBB (118T) AND FLOOD (280T) currents.
5. HOW LONG IS IT GOING TO TAKE YOU TO TRANSIT UNIMAK PASS TO BE CLEAR OF THE DANGER?
NOT ALL TIDE BOOKS CONTAIN CURRENT and DIRECTION information so choose your publications wisely. Coast Pilots are another source of good local information.
Examples: 20161019-1200 forecast weather 330@31kts
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WHAT TECHNIQUES CAN YOU USE TO MINIMIZE THE FORCE OF CURRENT AND WEATHER? You may consider using the leeward of UNIMAK ISLAND to minimize forces. IN THE FINAL ANALYSIS IT WILL ALWAYS BE BETTER TO STOP, WAIT FOR A FAVORABLE TIDE WITH REDUCED CURRENT AND FAVORABLE WEATHER.
STAY SAFE!
Questions?
I can help!
Voyage Adviser
Email: voyageadviser (at) gmail (dot) com
Sometimes a graphic makes orientation clearer.
with a closer image...
Unimak Pass is the gateway between the North Pacific Ocean and the Bering Sea. More than 4,000 commercial ships pass through this waterway every year... take a look at the marine AIS - note the commercial ships lined up following each other west from the Gulf of Alaska to pass west through Unimak enroute on a great-circle voyage to the orient...
So now that you have your bearings lets discuss why this can be a very dangerous location... besides the obvious ship-to-ship collision risk...
The tidal current can flow through Unimak Pass at more than 5 knots. Add Alaska gale/storm weather and you have extremely large forces meeting in a small region... UNIMAK PASS!
What happens when weather from the NW comes into contact with tidal current from the SE?
A collision of sorts - powerful winds force seas from the NW towards the SE while 5 knots of tidal current flows towards the NW and it all comes together in Unimak Pass and the sea begins to 'boil' with waves crashing into each other and it looks like inside of a washer machine... except you could be there in your yacht... and it is not going to become extremely dangerous.
So how to avoid this danger?
1. Know the forecast weather, Plan your transit during calm weather if at all possible.
2. You must know your boat's intended direction of travel & speed to calculate an ETA be it approaching from the Bering Sea or from the Pacific Gulf of Alaska, Adjust your speed to arrive and transit during a safe period. NEVER GO INTO WEATHER ESPECIALLY INTO THE CURRENT ALWAYS GO WITH THE CURRENT AND WITH THE WEATHER. Consider adjusting your speed or anchor until a favorable tidal current change.
3. Be sure to carry the Unimak Pass tidal predictions for the dates you intend to transit.
and
4. KNOW THE DIRECTION OF EBB (118T) AND FLOOD (280T) currents.
5. HOW LONG IS IT GOING TO TAKE YOU TO TRANSIT UNIMAK PASS TO BE CLEAR OF THE DANGER?
NOT ALL TIDE BOOKS CONTAIN CURRENT and DIRECTION information so choose your publications wisely. Coast Pilots are another source of good local information.
Examples: 20161019-1200 forecast weather 330@31kts
WHAT TECHNIQUES CAN YOU USE TO MINIMIZE THE FORCE OF CURRENT AND WEATHER? You may consider using the leeward of UNIMAK ISLAND to minimize forces. IN THE FINAL ANALYSIS IT WILL ALWAYS BE BETTER TO STOP, WAIT FOR A FAVORABLE TIDE WITH REDUCED CURRENT AND FAVORABLE WEATHER.
STAY SAFE!
Questions?
I can help!
Voyage Adviser
Email: voyageadviser (at) gmail (dot) com