Freighters vs. Sailboats

[cappy208]

Originally Posted by Paul Elliott

Cappy208, I figure that the 6-kt vessel can be no more than 24.4 degrees off the bow of the 20-kt vessel (for them to collide). The math is arcsin(6/20), which gives the widest possible angle. The largest angle for a 4-kt boat and a 20-kt ship will be 11.5 degrees, I think the point here is that "fine" or not, aiming for the ship's stern in these cases (assuming that you can even see it) will probably not give you the desired clearance. For that matter, turning 180 degrees may not help either -- you have to figure the angles. In most of our crossing situations, I end up telling the crew "we couldn't hit him if we tried", and I'm right.

I've seen a few close crossing situations on San Francisco bay, and these seem to be caused by the pleasurecraft seriously underestimating the speed of the oncoming ship. (Yes, this has been said here before.) In some of our races if you get the five-blasts from the ship's horn you're automatically disqualified (if you survive ).

It's the "survive" part I am trying to help!


But seriously,

In Rapid Radar Plotting we are taught that there is a "allowable window of error' ( Not that we should depend on it!) But the error is to allow all the tangibles which happen. (like poor plotting conditions, (even a violently oscillating yacht chrt table))

My point is..... it is NOT just that a vessel which is directly ahead that is the threat. there is a heck of a lot wider margin than 'Directly ahead' that needs to be worried about.

[Lodesman]

Originally Posted by cappy208

Ok. I am taking this to task, because even a society approved instructor, (an experienced seaman) needs to see how the 'other half lives'.
...
The corresponding attitudes are: 20 knot vessel has a target 30 degrees off their stbd bow (most definitely NOT fine on the bow) And the 6 knot vessel has a target at about the port beam. NOTE, neither are 'fine on the bow' of ANYONE.

Need to work on your relative motion Cappy. In your example the "6 knot vessel" is actually going 10 kts. If a 6kt vessel was 30 degrees on the bow of a 20 kt vessel at 6NM, they will pass at about 1.5 miles.

[cappy208]

Originally Posted by Lodesman

Need to work on your relative motion Cappy. In your example the "6 knot vessel" is actually going 10 kts. If a 6kt vessel was 30 degrees on the bow of a 20 kt vessel at 6NM, they will pass at about 1.5 miles.

OOOOOOH. Is the emphasis correct??


I see you are looking at this. so..........

at six miles. (with the inherent error of RRP, AND human interpolation)


is 1.5 miles acceptable?

Is the yacht even able to compute this measurement?

Is this acceptable in 12' seas?


Add to this the yacht crew fatigue. and affects from the seaway.

Or.......... to ensure a safe passage should the yacht just alter course 10 degrees ........... for 15 minutes....... to ensure a greater CPA. ?????

I am not going to enter your discourse about whether to 'run away' from your voyage. But I will enter the discussion about staying alive.

I used a card, with stipplings on the edge to make the lengths used in my pics. I carefully measure my one mile, two mile, an (most importantly) .6 mile marks. Maybe the pics distort. Maybe the images are rough. (sorry, I am just an ordinary sailor like Y'all) But, this is what I expect when I am on a yacht on a bouncing, tipsey, rounded chart table. But, the concept is fairly accurate (as far as the original poster made the claim about how "Freighters Vs Sailboats" is concerned,


The funny thing is:

You GET it. Why argue? The semantics are irrelevant.


I pointed out your earlier post. It was an INCOMPLETE post. Yet you stand by it. When you speak in "absolutes" you must make sure that every (and i mean every one) situation in covered.

Maybe your interpretation of: "fine on the bow" is between 30 degrees either way. That would be a huge 'teaching' example. ( I don't agree)

[cappy208]

As I mentioned, the 6 knot vessel plot looks AMAZINGLY different.


This is the true dichotomy of this topic.

Here is the same plots of the intercept (but from the 6 knot vessels view)



It is amazing how different the plot is! Never mind that the different sailors are (mostly) ignorant of the others perception!

Not that one is any more valid. But this just shows how different the outlook is to the different speeds and courses.







PS. I HOPE they uploaded right way up this time!

[cappy208]

done, although there will be scheitte!

[sabray]

Alter course . You guys are making this way to hard. Maybe fun but I just cut back till I know I am not in the way and the big guys know what I am doing. Chit chat on 13 even if they think I am a dolt. I confirm you see me. I am going 1 whistle to tug named warped wench. Warped wench will usually confirm one whistle.they like whistling.. Damn near 50 and hair is starting to grow in my ears but the tugs and I still whistle at each other.

[cappy208]

Now, to get to the real root cause of the dilemma.....

How much would the 6 knot vessel (in these particular situations) have to alter course to safely pass (oh my gahd) astern of the 20 knot ship?) PS.... this is 'aiming at the stern'.........

[cappy208]

In RRP. how much are we allowed in overage to be considered 'good enough'?
At what point is this considered to be overkill? Yet you want every one to adhere to the Colregs as a finite 'edge' to lean on. There IS (at least for uninspected yachts) a window of leeway allowed as far as competence is concerned. The leeway seems to be what the dilemma is about.

[cappy208]

The sad thing is..... about 50% of the viewers will simply shrug their heads at these posts and...... look at the next post

[Stu Jackson]

What's "stand off"???

[sabray]

In 30 years I have never found myself confounded by how far away I need be. Surprised once. No issue. I cannot relate to most of the colreg stuff and way to behave.
I call on 13 monitor 13. We decide how we will pass . We agree its 1 or 2 whistles. We pass. If my shorts are hiked up I might get 2 whistles with a vibrato.are you really experiencing this level of risk?

[Lodesman]

Originally Posted by cappy208

OOOOOOH. Is the emphasis correct??

is 1.5 miles acceptable?

Is the yacht even able to compute this measurement?

Is this acceptable in 12' seas?

Or.......... to ensure a safe passage should the yacht just alter course 10 degrees ........... for 15 minutes....... to ensure a greater CPA. ?????

I pointed out your earlier post. It was an INCOMPLETE post. Yet you stand by it. When you speak in "absolutes" you must make sure that every (and i mean every one) situation in covered.

Maybe your interpretation of: "fine on the bow" is between 30 degrees either way. That would be a huge 'teaching' example. ( I don't agree)

Snarkiness isn't going to help you.

No.

Yes.

10º for 15 mins will have the same effect as a fly's fart has on a hurricane.

Incomplete? Absolutes? You have me stymied. I have no idea what you are on about. TonyB's advice was absolute - "no matter what happens, you can just point at the stern"; I simply pointed out that doesn't always work or make sense. Obviously not that simple, since so many including experienced mariners didn't get it. (Still don't get it?) Stand by it? Heck yeah! Even your example has only served to prove my point - a relatively slow vessel (6 kts vs 20 kts) can not be in a risk of collision just 30º off the bow of the fast vessel.

I don't believe I've ever said that 30º is 'fine' - all my examples were 10-12º on the bow - that is 'fine'. Rather than trying to interpret, if you have a question about something I write, just ask.

[cappy208]

Originally Posted by sabray

.are you really experiencing this level of risk?

Yup.

I especially like the 'vibrato' comment though! it makes me think things. Have a good nap. Hey. aren't there some loose Kerfunkles you have to attend to?

[cappy208]

Good thing you said that.....



Give me time to re do those plots, and a small course change becomes HUGE.

This is where trial maneuver is so instrumental.....

[cappy208]

Originally Posted by Lodesman

Yes.

That is what I am being Qixiotic about.

You keep saying absolutes, as if all are equal. It ain't so.

Not only that, the 'rules' we work under are only applicable if 'all' participate. Sadly this is not true.