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"You need to clearly define 'speed to use' and 'given speed'" -Andrew Seligman

I re-read my post and I think you are right. Okay, one more time. :)

This time I'll use an example I am working on now. It's problem # 2-1 from "100 Problems". We start with our last fix of 40°55'S, 176°05'E at 1600 UT Dec. 17, 1993. Our course is 70° true, speed of advance is 7 and a half kts.

About 13 hours later, on Dec. 18 at 0541 UT, we get a Sun-Moon fix. Now, our DR position for this time is 40°20'S, 178°13'E. However, our fix puts us at 40°35'S, 178°18'E, ~16nm SSW of our DR. Our set is 166°, drift is 1 point 2kts. (16nm divided by 13 point 6 hours.)

So, in order to maintain a course of 70° true with a speed of advance of 7 and a half kts. and a set and drift of 166°/1.2kts., we must steer to 61° and will make good a speed of 7 point 45 kts. (over the ground).

But, whereas before, when we were on a heading of 70°, the set was coming from a bearing of 276°. On our new course of 61°, the set will be coming from a bearing of 285°...more towards the bow.

Now, my question is: Will this change in bearing of the set decrease our speed of advance in the same way it has slowed our speed made good so that our calculation of course to steer at a given SOA will need to be adjusted?

I really hope that makes sense.

Thanks "in advance"...get it? Uh haha... no?
-Sean ;)
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