Using Currents when Planning a Trip

August 2, 2017

Not long ago vessels used to depart "on the tide".  Mariners have long used tide calendars and current charts to find ways to get a free boost from nature.

Closely watching weather forecasts helped avoid headwinds or adverse sea conditions, with an occasional boost from tailwinds or waves.   SONY DSC Boaters were spoiled by years of cheap fuel and bigger engines, which made using tidal currents less important. Then higher fuel prices made everyone more conscious of how careful scheduling and routing to take advantage of tides, currents, and predicted winds would save both money and time. Now we have less expensive fuel again, but need to remember what we learned about using the current in our favor.  

Remember that tide is the vertical travel of the earth’s water and current is the horizontal travel of the water as it moves from low to high tide and back again. We want to either take advantage of or avoid those currents that will hinder or accelerate our headway.  

Traveling with or Against the Current: 

The chart below indicates the effect current will have on a boat at different speeds traveling against and with the current.   Note that Speed Made Good WITH Current showing Fuel and % GAIN

Boat Speed + 1 Knot + 2 knots + 3 knots + 4 knots
4 Knots 5 Kn=20% 6Kn=33% 7 Kn=43% 8 Kn=50%
6 Knots 7Kn=14% 8 Kn=25% 9 Kn=33% 10 Kn=40%
8 Knots 9 Kn=11% 10Kn=20% 11 Kn=28% 12 Kn=33%
10 Knots 11 Kn=9% 12Kn=17% 13 Kn=24% 14 Kn=29%

  Speed Made Good AGAINST Current showing Fuel and %  LOSS

Boat Speed - 1 Knot - 2 knots - 3 knots - 4 knots
4 Knots 3 Kn=33% 2Kn=100% 1 Kn=300% 0 Kn !
6 Knots 5Kn=20% 4 Kn=50% 3 Kn=100% 2 Kn=200%
8 Knots 7 Kn=14% 6Kn=33% 5 Kn=60% 4 Kn=100%
10 Knots 9 Kn=11% 8Kn=25% 7 Kn=43% 6 Kn=67%

Another tip to save fuel is to SLOW DOWN !

In a displacement vessel, even a small decrease in boat speed will save fuel. Data shows that reducing power as little as 10% from full throttle will save 20%. Depending on your boat and hull shape, cutting speed by one to two knots can cut consumption by 30% to 50%.

 For a good article on fuel efficiency, Click Here  
Capt. Rick Delfosse


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