In navigation we need to be able to easily solve simple math problems involving speed, time, and distance. I always used to instruct my students: "Just memorize Distance = Speed X Time." Many books talk about using 60D = S x T and call it 60 D Street as a memory aid. Then, I had a sailing student who taught middle school math and he showed me triangle math. I thought this was pretty cool at the time and I still use it today.

Here is the math triangle. To use it simply put your finger over the letter you are solving for. If you want to know S for Speed, then putting your finger over S gives D/T (distance divided by time). If you want to solve for D then covering it up you have S x T or speed x time.

Let's talk about the units of measurement we'll be using in nautical navigation. Distance is always going to be in nautical miles and tenths of a nautical mile. Time will be in its usual hours and minutes. Speed will always be in knots and tenths of a knot. Remember, a speed of one nautical mile per hour = one knot. So, going at one knot for one hour we would cover a distance of one nautical mile.

D (distance in nautical miles) = Speed (knots) x Time (hours)

But, what if we are traveling at 5.5 knots for 1/2 hour?

S = 5.5 knots (nautical miles per hour) x .5 hours = 2.75 nautical miles. We usually round to the nearest tenth in nautical navigation so we could either drop the trailing 5 or round up to 2.8

The only tricky thing about our equation is that time comes in two varieties; hours and minutes. It's not a simple decimal system like speed and distance. There will be many times when you need to convert minutes to hours and vice versa. Converting hours to minutes; multiply by 60. Converting minutes to hours divide by 60.

**Example**. What's our distance run if we are going 6.2 knots for 23 minutes? We know from our triangle that since we are looking for D we are going to simply multiply speed times time. But, the formula calls for time in hours so we first convert the 23 minutes to decimal hours:

23 minutes/60 minutes per hour = .38 hours. Now we can plug this into our equation to get distance:

D = 6.2 knots x .38 hours = 2.4 nautical miles.

Just make sure a couple of hand held calculators are a regular part of your boat's equipment!

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