Which one is the hazard?

[bilbobaggins]

Diverging from the interesting 'AIS' thread, may I raise another topic?

While approaching the streams of shipping between, say, the Off Casquets and the Ushant TSSs ( or any similar non-TSS stretch ) and with multiple ships in view, just how do you determine which ones need close attention and a good 'pointing-at' with the trusty hand bearing compass - and which don't?

I find I'm able to decide visually 'Not that one. Not that one. Nor the other one. That next one needs keeping an eye on. That far one, also, looks as if it may get close... Now, where's my HBC?" That's proven quite reliable, in practice.

I've been doing this a fairly long time, and have a sound and well-practised background in 'thinking vectors'. However, what goes on in your mind, and how would you explain it to someone else?

 

[snowleopard]

Unless you have a very good HBC, there's no point in using it until an approaching ship is within a mile. If the ship stays in the same pane of the windscreen as we approach then I need to start thinking about taking action.

 

[Sandyman]

Unless you have a very good HBC, there's no point in using it until an approaching ship is within a mile. If the ship stays in the same pane of the windscreen as we approach then I need to start thinking about taking action.

Even with a good HBC its not much good in a touch of roughers.
Switch the AIS on. Put cursor over ship & hit info button. Bobs ya Uncle.

 

[Robin]

Diverging from the interesting 'AIS' thread, may I raise another topic?

While approaching the streams of shipping between, say, the Off Casquets and the Ushant TSSs ( or any similar non-TSS stretch ) and with multiple ships in view, just how do you determine which ones need close attention and a good 'pointing-at' with the trusty hand bearing compass - and which don't?

I find I'm able to decide visually 'Not that one. Not that one. Nor the other one. That next one needs keeping an eye on. That far one, also, looks as if it may get close... Now, where's my HBC?" That's proven quite reliable, in practice.

I've been doing this a fairly long time, and have a sound and well-practised background in 'thinking vectors'. However, what goes on in your mind, and how would you explain it to someone else?

Funny I just said much the same on the AIS post!

Generally if crossing around 90 degs at yacht speeds the problem ones will never be the ones you first see off the bow but will be just coming over the horizon way out on the beam. I monitor them from my favourite cockpit perch, one each side of the wheel, backrest on the dodgers, armrest on the bimini/canopy/gantry frame. The perch is relevant because you need to maintain a constant position. I line the target up with something convenient like a dodger eyelet, stanchion or the like to see if it stays lined up, but making sure to check we are actually on course at the time in any seaway.

Closer in when you can see the aspect of the ship proper I can judge things visually quite well rather like knowing when to cross a main road with trucks coming at intervals. It is even easier at night with the ship's lights and steaming lights on their masts that go from separated to in line to separated.

I have a very good handbearing compass as well as good compass binos but rarely need either in practice.

 

[Genoa]

A key aspect to your question is explaining what we take for granted to another person.

I start with the "bunny rabbit in the middle of the road. If it just kept on running it would live, but it stops and looks at your headlights at the last minute. You can't break so you hit it." Funny the kids went off me for a while ... Called me a male bunny boiler ....



But explaining it normally means starting with a point where both vessels have colided, then ask, where would both have been 15 mins before, 30 mins, 1 hour before and if you draw it, it is easy to show the concept of the bearing not changing. Then talk about perspective and paralax error (transits on masts etc)

 

[VO5]

It is a skill which is acquired over time with watchkeeping experience.

I think the starting point is to learn to identify aspect.

Aspect implies direction with regard to the shape the other vessel presents to the observer.

The next part is determining an idea of the other vessel's speed relative to your own and combining this with heading.

So it is a cluster of skills, not just one, which are acquired over time both for day and night sailing.

The general rule of a bearing NOT SIGNIFICANTLY CHANGING presenting a risk of collision is valid. If the bearing is falling away astern (drawing aft) the vessel will cross behind you. If the bearing is gaining forward (drawing forward) the vessel will cross in front of you, given in both cases that course and speed is maintained.

The most important thing to remember is when an alteration of course is required when risk of collision exists, is that any alteration of course must be SUBSTANTIAL, meaning, the other vessel is left in no doubt that you are taking action.

A substantial alteration of course is not 5 or 10 - but 25 or 30 or even 40 degrees so that the change in direction can be seen to be SIGNIFICANT.

 

[VO5]

Now a tip about night vision for those of you who are under sail at night.

If you are obligated to shine a powerful torch on your sails to alert a nearby vessels or vessels of your proximity, then shut one eye when you flash the light. Close the eye you opened when the light was on and open the other eye.

This way you will not be blinded and preserve perfect night vision.

When on the helm avoid the light illuminating the compass card from being too bright. I have mine on a dimmer, but you can soften the effect by coating the little bulb with a very thin coat of red nail varnish sparingly applied.

 

[sarabande]

if I may interpose, please.

The use of red light to 'preserve' night vision is an erroneous assumption.

See here pls:
http://stlplaces.com/night_vision_red_myth/