Use of deviation on running fixes

[StuM]

Originally Posted by jackdale

Bowditch (Amercian Practical Navigator) and Chapman Piloting call it a bow and beam. I am not familiar with "four point bearing fix".
Yes, it is a special case of of doubling the angle on the bow.

May be an Australasian thing.

That's what Jeff Toghill called it in his "Manual of Yacht Navigation" and other sailing/navigation publications and he is considered "the authority" for the southern hemisphere.

(It's also sometimes called the "four point fix").

Are you familiar with the other variation of the "four point/bow and beam" and "doubling the angle" fixes known as the "special angles fix"?

That uses the fact that the distance traveled between certain pairs of angles will be the distance abeam when you pass the object (rather than the current distance to the object which you get from the other two fixes).

Common pairs of angles:
16 : 22 , 21 : 32, 25 : 41, 32 : 59, 37 : 72, 40 : 79

i.e. If you cover say 2NM while the angle off the bow of an object ahead changes from 16° to 22°, then you will pass 2NM off the object.

[conachair]

Ais targets can sometimes be a handy source of an accurate bearing to double check for deviation on a hand bearing compass.
And deviation sometimes gets worse as you get older....... Those nice new glasses you now need

[jackdale]

[QUOTE=StuM;2329569]May be an Australasian thing.

That's what Jeff Toghill called it in his "Manual of Yacht Navigation" and other sailing/navigation publications and he is considered "the authority" for the southern hemisphere.

(It's also sometimes called the "four point fix").[QUOTE]

Like a "boom vang" versus a "kicking strap."

Originally Posted by StuM

Are you familiar with the other variation of the "four point/bow and beam" and "doubling the angle" fixes known as the "special angles fix"?

That uses the fact that the distance traveled between certain pairs of angles will be the distance abeam when you pass the object (rather than the current distance to the object which you get from the other two fixes).

Common pairs of angles:
16 : 22 , 21 : 32, 25 : 41, 32 : 59, 37 : 72, 40 : 79

i.e. If you cover say 2NM while the angle off the bow of an object ahead changes from 16° to 22°, then you will pass 2NM off the object.

Yes.

[jackdale]

Originally Posted by conachair

Ais targets can sometimes be a handy source of an accurate bearing to double check for deviation on a hand bearing compass.
And deviation sometimes gets worse as you get older....... Those nice new glasses you now need

Just make sure you new glasses do not have magnetic clip-on sunglasses. That introduces deviation when using a hand bearing compass.

[conachair]

Originally Posted by jackdale

Just make sure you new glasses do not have magnetic clip-on sunglasses. That introduces deviation when using a hand bearing compass.

Wouldn't blindly trust anything, not even raybans