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Old 31-01-2021, 15:55   #1
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Running Delaware Bay in Current - Waterway Guide Wrong

A recent post regarding NOAA current diagrams really made me start thinking about navigating current in the Delaware. Heading northbound is not much of an issue since if you hit the entrance at the start of flood current you can easily ride the current all the way to the C&D canal. But this post is about traveling southbound starting at Chesapeake City, which is the popular stopover prior to a run down the Delaware.

This is directly from the Waterway Guide:
Quote:
Tital rise and fall is in the 5- to 7-foot range, and tidal currents can run up to 3 knots. A good rule of thumb is to head northward from Cape May when the tide is low, and head south from Chesapeake City when on the C&D canal at high water. This scheduling is especially important for sailboats equipped with auxiliary engines of limited horsepower.
I have attached a diagram below that shows if you are in a sailboat travelling southbound at approximately 6 knots, it is only possible to remain in good current about half the trip. But I decided to test the "rule of thumb" found in the Waterway Guide by building a route in Expedition running 66.5 NM from Chesapeake City to the Delaware Bay Entrance. Assumptions: motor continuously at 6 knots through the water, no affects of wind, Delaware Bay currents applied, and route is along main channel.

I ran about 20 optimization runs and found that the minimum time to run south from C City corresponds with departing at C City at LOW tide. The maximum time corresponds with departing C City at HIGH tide (opposite of what is said in the Waterway Guide. Runs starting before or after high and low tides have run times that fall in between the two runs starting at high/low tide.

Here are the two relevant results Departing at High and Low tide 31 Jan:
Depart 12:19:00 Route 66.6 NM Time 11h 47m 50s Avg Speed 5.64kt Finish 2/1/2021 12:06:50
Depart 18:38:00 Route 66.6 NM Time 10h 06m 07s Avg Speed 6.59kt Finish 2/1/2021 04:44:07

Delta was 1h 41m 43s

All thoughts on this are welcome.
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