The current isn't always perpendicular to the wind... in fact 99% of the time it won't be, so the pythagorean theorum falls on its face. Also, knotaloud's equations should have been written
vresultant^2 = (4kt)^2 + (3kts)^2
rather than what you had, since the ^ is often used to express raising something to an exponent. Merely having the number outside the parentheses is usually assumed to mean multiplication.
Also, the current is not always going to be the only thing affecting your course. Leeway also affects your course, and may, in many cases, offset the set of the current to some degree, so basing your calculations on just the current's speed, which also may not be perpendicular to the line of travel, is less than accurate.
BTW, "T=D/V" is Distance = Velocity * Time, not Destination
Finally, I generally recommend doing the calculations graphically, since it is far more difficult to screw them up by doing them graphically.
Also, it can be done right on the chart. Any calculations for set and drift are going to be estimates...and a graphic solution generally will get you in the ball park, without a lot of math.... and the extra precision of the mathematics-based solutions is generally both unnecessary and inaccurate—it is like measuring with a micrometer and then marking with a piece of chalk... why bother—doing the calculations graphically is simpler and faster as a general rule...
And often, like in many other things where time is of the essence, a good answer in navigation right away is better than a perfect answer that takes four times as long... since there are often times you need to have idea of what to do immediately...and the extra time the equations take can put you closer to danger by delaying any decision you make.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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