Join Date: Feb 2007
Location: New Jersey
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Re: Course to steer at a given speed.
To answer your question if you are calculating the CTS from a known current and a known boat speed. the current triangle is a snapshot of an hour.
Plot your DR course..Or desired course to your destination. Then plot the Set and drift of the current from your starting point ( currents are always given in "True" direction) That current line is an hour long..( use miles to represent kn. ) now plot a line from the end of the set and drift line....that represents your boat speed for an hour..and swing it back to your desired track. Plot the point where it intersects and then measure the distance from the starting point along your DR. That new distance will represent your true speed or the speed you will make good..( how far you will have gone in an hour)
You can then figure out how long it will take to make the entire trip, given your speed made good.
Of course, this is all assumes that your boat speed and the strength and direction of the current all remain constant, which is rarely the case, especially if you are sailing. But I think this is the answer to the question you are asking?
IF you're sailing with a current setting you, you may also want/need to add a few degrees of leeway into the formula depending on the strength of the wind.
You can decide what you want to use as a Course to steer..( true, mag, compass etc. ) and make the appropriate calculations...just remember that currents are given in True degrees.
Last edited by tempest; 12-06-2012 at 12:27 PM.