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Old 04-06-2010, 09:58   #166
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I am familiar with North and Head up but what is "True" in regards to chart plotter/radar orientation?
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Old 04-06-2010, 10:18   #167
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I am familiar with North and Head up but what is "True" in regards to chart plotter/radar orientation?
true north (as opposed to magnetic north)
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Old 04-06-2010, 10:25   #168
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I set my system to default at Heading Up, but toggle frequently to North Up when I'm using a chart book. I prefer to enter a harbor under North Up.

My default MARPA alarm is set to identify any target within .5 nm as a "dangerous target." I'll usually set up a radar watch zone at 3 nm, even for naval vessels. At sea, I have the system automatically track any target within the 3nm radar range to show CPA and TCPA.

Once, at night off San Diego, we had a US Navy warship vector us off due to training exercises, and we couldn't even find him on radar. I'd sure like to know how many watts they were transmitting on their VHF, because it sounded as if the warship was within a hundred meters.
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Old 04-06-2010, 11:54   #169
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I am familiar with North and Head up but what is "True" in regards to chart plotter/radar orientation?
True motion means the vectors show the actual heading and speed of radar contacts. Relative means the vectors show the relative path and speed of contacts to your ownship.

True or magnetic north is usually dependent on the input to the machine - larger ships with gyrocompasses can use true north; if you only have a compass input, you'd have to use magnetic.
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Old 04-06-2010, 12:12   #170
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Unfortunately I think you can find your answer here: USS Cole Bombing
My story predates the Cole bombing by nearly a decade, we are an ally, and Cole was alongside not at sea. It's possible the USN paranoia stems from the USS Stark incident (hit by an Exocet from an Iraqi plane) or possibly to keep other vessels safe, stemming from the USS Saratoga incident (accidentally fired two SeaSparrow missiles at a Turkish ship in 1992.) My gut feeling is that young JGs will do anything to avoid calling the Old Man, including calling other vessels and asking/demanding outrageous passing distances.
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Old 04-06-2010, 12:12   #171
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Once, at night off San Diego, we had a US Navy warship vector us off due to training exercises, and we couldn't even find him on radar. I'd sure like to know how many watts they were transmitting on their VHF, because it sounded as if the warship was within a hundred meters.
I had that exact thing happen to me too off of SD harbor. We could see the vessel visually, he was only about 300 meters away, but could not pick him up on radar.
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Old 04-06-2010, 12:44   #172
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I am familiar with North and Head up but what is "True" in regards to chart plotter/radar orientation?
Think of True motion radar presentation as a “bird’s eye” view of what is happening.

The land stays still and your vessel and others move at their respective direction and speed. When your vessel gets to about 2/3rds away from the centre, the screen resets itself.

It is important for you to be “ground stabilized” in this presentation, meaning the radar has adjusted for current by selecting a known piece of land target and telling it… this is a fixed target.

This type of radar is handy when you are in a river estuary scenario like approaching Brisbane with lots of twists and turns as you can see exactly what the other vessel is doing when it turns.

In the fog in coastal waters, I have switched to it often when I am dealing with many targets with multilateral considerations who are all making course changes and I am navigating a high speed vessel (like a hovercraft) thru them.
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Old 04-06-2010, 12:56   #173
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Think of True motion radar presentation as a “bird’s eye” view of what is happening.

The land stays still and your vessel and others move at their respective direction and speed. When your vessel gets to about 2/3rds away from the centre, the screen resets itself.
I was aware of ECDIS/chartplotters that did this, but not radars - what radar models do this? Any that would be seen on modest cruising boats?
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Old 04-06-2010, 13:11   #174
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Rule 8 Action to avoid a collision.

Rule 8 Action to avoid a collision.


(a) Any action taken to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

(b) Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course and/or speed should be avoided.


What do you consider a “minimum” course change in an open water situation?


(c) If there is sufficient sea room, alteration of course alone may be the most effective action to avoid a close-quarters situation provided that it is made in good time, is substantial and does not result in another close-quarters situation.


What type of scenario is it considered safe to turn to port?


(d) Action taken to avoid a collision with another vessel shall be such as to result in passing at a safe distance. The effectiveness of the action shall be carefully checked until the other vessel in finally past and clear.


This puts the onus on all vessels to maintain a safe CPA


(e) If necessary to avoid collision or allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion…back to safe speed


(f)

(i) A vessel which, by any of these Rules, is required not to impede the passage or safe passage of another vessel shall, when required by the circumstances of the case, take early action to allow sufficient sea room for the safe passage of the other vessel.

(ii) A vessel required not to impede the passage or safe passage of another vessel is not relieved of this obligation if approaching the other vessel so as to involve risk of collision and shall, when taking action, have full regard to the action which may be required by the Rules of this part.


(iii) A vessel, the passage of which is not to be impeded remains fully obliged to comply with the Rules of this part when the two vessels are approaching one another so as to involve risk of collision.


This means that the requirements “not to impede” are complimentary to other requirements of the Steering and Sailing Rules.


Can anyone give us some examples of yachting scenarios where this rule is not understood?
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Old 04-06-2010, 13:28   #175
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Originally Posted by Lodesman View Post
I was aware of ECDIS/chartplotters that did this, but not radars - what radar models do this? Any that would be seen on modest cruising boats?
Hi Lodesman

My own small radar on Star Gazer has True Motion.

This is a Ratheon HSB series CRT display, quite old (1999) but with a mini ARPA and all the bells and whistles, pretty amazing except for screen size

I have not looked at any new small boat Radars but my guess is they still have that function
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Old 04-06-2010, 14:51   #176
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Rule 8

We tell out students to: "Do it big, and do it early."

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What type of scenario is it considered safe to turn to port?
To avoid creating another risk of collision and to avoid hazards.

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This means that the requirements “not to impede” are complimentary to other requirements of the Steering and Sailing Rules.

Can anyone give us some examples of yachting scenarios where this rule is not understood?
I once had a student asked why an deep sea vessel gave him 5 blasts while he was sailing in Rosario Strait east of Orcas Island. He was in a a Traffic Separation Zone. TSS's are not always well understood by pleasure craft boaters.

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Old 04-06-2010, 15:12   #177
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Well, you learn something new every day. I personally can not see how it's advantageous to have ownship move across the screen, but I guess I might change my mind after using that feature. You said:

Quote:
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It is important for you to be “ground stabilized” in this presentation, meaning the radar has adjusted for current by selecting a known piece of land target and telling it… this is a fixed target.
Does this mean you have to reselect land targets to stabilize the picture as you drive away from the previous one?
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Old 04-06-2010, 15:52   #178
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What do you consider a “minimum” course change in an open water situation?
Well the absolute minimum is that which is required to allow minimum desired CPA. This usually does not satisfy the requirement to be readily apparent. If power-driven visual in a crossing situation, I like to at least go from showing my stbd bow to showing my port; I then slowly trim my course back to pass well astern of the stand-on vessel, but not so far off my track. Head-on a change of 10-15° suffices; overtaking by nature usually requires a minimal course change and in all other cases an alteration of 30° usually does the trick. Sailing, if I can make a readily-apparent course change on the same tack, I will, otherwise a tack or gybe should be readily apparent.

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What type of scenario is it considered safe to turn to port?

There's a rather large list here. The rules tell you where a turn to port shall be avoided.

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This means that the requirements “not to impede” are complimentary to other requirements of the Steering and Sailing Rules.
"Not to impede" is so poorly understood as to be practically worthless in the Rules. Take a look at where it is used - narrow channels, traffic separation schemes and vessels constrained by draught. IMO the implication therefore is that you shall not force a vessel that is effectively limited to navigating within the deep part of the channel, out of the deep water. If a steering and sailing rule begins to take effect, as long as the vessel that shall not be impeded can take avoiding action without leaving the confines of the traffic lane or narrow channel, then you have satisfied the requirement to not impede. I know this will generate debate.

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Can anyone give us some examples of yachting scenarios where this rule is not understood?
I think it's self-evident there are varying levels of understanding of all the rules, not only in yachting circles but amongst the pro's too.
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Old 04-06-2010, 16:09   #179
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Can anyone give us some examples of yachting scenarios where this rule is not understood?
I had this happen last weekend. I was on starboard tack, the other boat was on port, and we were headed straight at each other. He had a deck-sweeper genoa, and I couldn't tell whether he saw me or not. I held course and speed, but at 100 meters I gave him one short blast, which technically meant I wanted to pass port to port, but which really meant I wanted to make certain he knew I was there. At that point he yelled, "I see you."

As I understand it, the proper response at this moment would have been 5 blasts, which in that particular case means, "Hey, Jerk, I don't care if you're racing, I'm on starboard and you're on port, so pay attention to COLREG Rule 8 (b)."
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Old 04-06-2010, 18:41   #180
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Bash,

Technically, one short blast has no meaning for a sailing vessel (unless you want to give Capt Ralph the justification he needs to run you down)

Personally I think the manoeuvring signals should be used by all vessels and wonder what the reasoning is for that restriction in the Rules, but I'll wait until we get to Rule 34 to discuss it.
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