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Old 28-09-2012, 08:34   #451
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Re: Freighters vs. sailboats

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Originally Posted by goboatingnow View Post
(1.b) many sailors have the experience that despite being the stand on vessel, they find there is no action by the give way vessel. A vessel that is closing at significant speed. This inaction may be unintentional , they didn't see us, or deliberate. The resulting close quarters situation may leave the sailboat with no safe exit strategy.
It's often a matter of perception. On the bridge of the freighter they've determined that the CPA of the sailboat is .5nm, and therefore no action is required. Meanwhile, the sailboat owner is convinced that the behemoth is aiming directly at him even though the CPA also shows as .5nm on the sailboat's radar.

I'll never forget, many years ago, crewing for a far more experienced skipper through the shipping channel off Santa Barbara. I wanted to make a course change to avoid a ship, and the skipper responded, "You couldn't hit that ship if you wanted to." Guess who was right.

Again, this is where a simple ship-to-ship call on the radiotelephone goes a long way toward relieving anxiety.
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Old 28-09-2012, 08:54   #452
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Re: Freighters vs. sailboats

@Cappy208

Wait till I am back on my boat - will collect Dutch colregs which are obligatory on board in the run of next week.
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Old 28-09-2012, 08:55   #453
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Re: Freighters vs. sailboats

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It's often a matter of perception. On the bridge of the freighter they've determined that the CPA of the sailboat is .5nm, and therefore no action is required. Meanwhile, the sailboat owner is convinced that the behemoth is aiming directly at him even though the CPA also shows as .5nm on the sailboat's radar.
Thunk. I coulda had a V-8!

Good post. I never thought of explaining it that way! That is EXACTLY what I have been trying to get across about the perception of an encounter like this.

The only problem, most yacht radars are incapable of giving an accurate CPA due to heading oscillations. ARPA and MARPA require a steady heading for several minutes to let the computer figure out CPA and TCPA. The only way to get a bearing line observation is by noting the heading.
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Old 28-09-2012, 09:07   #454
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Re: Freighters vs. sailboats

This appears to be the dilemma. How to both educate and eliminate this behavior from ALL involved.


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We have heard a number of professional mariners say that they don't maneuver sooner than 4-5 miles, or sometimes 2-3 miles, or maybe not at all, because they can't predict what the hell we will do, and the maneuver will just be wasted if it is done so far ahead.
and combined with this next post from Bash:

Quote:
Originally Posted by Bash
It's often a matter of perception. On the bridge of the freighter they've determined that the CPA of the sailboat is .5nm, and therefore no action is required. Meanwhile, the sailboat owner is convinced that the behemoth is aiming directly at him even though the CPA also shows as .5nm on the sailboat's radar.
It is perceived that Merchies don't alter. The perception that What IS a satisfactory meeting, is looked at as UN satisfactory by the SV at a distance FAR removed from the Merchies capabilities, combined with the
radical maneuver by the SV puts the Merchie at odds both with how to avoid, along with the next time the Merchie will just give up and keep on the straight and narrow.
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Old 28-09-2012, 09:25   #455
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Re: Freighters vs. sailboats

@Dockhead: You need to do some more research about what 'stabilized' means. I think you will be disappointed in your newfangled RADAR from what it appears you are expecting.

I have never heard of a gyro stabilized RADAR, that removes heading oscillations of the kind that make ARPA and MARPA accurate like you are expecting.

Stabilizing refers to the data input, and the relationship of travel through the water, OR over the bottom. It is NOT about your heading movement.
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Old 28-09-2012, 10:50   #456
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Re: Freighters vs. sailboats

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Originally Posted by cappy208 View Post
@Dockhead: You need to do some more research about what 'stabilized' means. I think you will be disappointed in your newfangled RADAR from what it appears you are expecting.

I have never heard of a gyro stabilized RADAR, that removes heading oscillations of the kind that make ARPA and MARPA accurate like you are expecting.

Stabilizing refers to the data input, and the relationship of travel through the water, OR over the bottom. It is NOT about your heading movement.
Gyro stabilised compasses are used on a lot a sailboats. The primary use is to provide better heading information for the autopilot, but the more accurate heading information also helps with MARPA.

The compasses vary from a simple gyrostabilised addition to the heading information from the fluxgate compass to high frequency very accurate and expensive instruments. Providing the processing power of the radar is sufficient each step will improve the MARPA accuarcy as a direct result of better heading information.

Many users have noted a noticicable improvement in MARPA when Raymarine switched from a simple fluxgate compass to a very basic, but gyro stabilised heading information in their autopilots.
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Old 28-09-2012, 11:18   #457
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Re: Freighters vs. sailboats

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I know I'm going to get the hammer for saying this, but one thing we as yotties should be aware of is that on many merchants, the "officer of the watch" and the helmsman are drunk on their asses. Every time a freighter runs aground or hits something here in the baltic - the helmsman is drunk. And not just a single glass of wine either. We're talking drunk as in almost passed out.

Yes I know a lot of yotties also drink (and heavily) while sailing. I don't. Sundowners and alcohol only come out after we're tied up for the night.

Well, here's one hammer

That was a pretty generalised statement Carsten, you know the Baltic, how many ships are transiting the Baltic at any one time, and how many incidents are there due to the watch keeper being drunk.
You have more chance of being hit by a drunk driver than by a ship being conned by a drunk watch keeper.

For what its worth, I work for a company that has a zero tolerance D&A policy, my contract forbids me from drinking alcohol from the moment I leave my house to join the ship, to the moment I get home again.
We are subjected to random D&A testing.
I've just spent the last two years working in the Baltic, in some pretty arduous conditions. During that time we ran 8000 anchors for a pipe lay barge, working in and around traffic separation schemes, and other busy area's, some times with less than a meter under the keel, in thick fog, and ice. During that time, we stopped work for 8 hrs in every 5 weeks to take bunkers and stores. During that 2 year period, there was not one single incident, not even a personnel injury to crew, nor one yacht run down.

You'll find the majority of merchant ships are dry.
Of course there are a few incidents involving drink, but they are very few.
The penalties being caught are harsh, all the prosecutions in the UK have led to heavy fines and prison sentences.
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Old 28-09-2012, 11:23   #458
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Re: Freighters vs. sailboats

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Originally Posted by noelex 77 View Post
Gyro stabilised compasses are used on a lot a sailboats. The primary use is to provide better heading information for the autopilot, but the more accurate heading information also helps with MARPA.

The compasses vary from a simple gyrostabilised addition to the heading information from the fluxgate compass to high frequency very accurate and expensive instruments. Providing the processing power of the radar is sufficient each step will improve the MARPA accuarcy as a direct result of better heading information.

Many users have noted a noticicable improvement in MARPA when Raymarine switched from a simple fluxgate compass to a very basic, but gyro stabilised heading information in their autopilots.
Two things happened when I went to respond to this post. The first is: what was visible on the forum was 3 lines. But the whole post showed up in the quote. Not everyone (unless they press the quote button) will be able to see. This may be a forum glitch. edit: but now, your whole post shows up????

The second issue. The dampening of heading data is what is being referred to. This would be NO problem, until the user is out of the heavy seas, and forgets to change the settings back. Then a simple thing like harbor entry by RADAR becomes a nightmare. When ANY vessels heading is being batted around 10 degrees on each side of heading (20 degrees of yaw) it will make any intercept data just about as useful as the wobbly relative trail smear in rough weather. BUT, even the trail is useful in a general way. And the ebl usage ON a specific heading, when compared to later sight ON the same specific heading is what is needed.

Or, as Dockhead said: A HBC could be used visually.
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Old 28-09-2012, 11:30   #459
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Re: Freighters vs. sailboats

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..............
Here is a guy who thought "We can make it".<iframe width="640" height="360" src="http://www.youtube.com/embed/_tUoUxzt9sI?feature=player_detailpage" frameborder="0" allowfullscreen></iframe> Whether this happened inshore, or offshore, it is an excellent example of tunnel vision which seems to be the greater issue. if any of you look all the way at the end of the video, you can see the escort/assist tug following. Note that other SVs were already there, having been aware. But look closely at the SV coming around the stern of the ship. He doesn't see the escort tug that is tethered TO the ship with about a 33 M wire! Surprise!
Yikes.... good eye. I've seen that video numerous times,, and never caught that.

So, how does COLREGS cover that situation? Is the tug a towed vessel? Hardly, I would think. Is it more than 200 meters behind? Tough to judge from the video. Rule 24 does not seem to applicable.

Thoughts?
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Old 28-09-2012, 11:36   #460
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Re: Freighters vs. sailboats

The tug is under the direction and control of the SHIP. the extension of the TUG is included in the vessels keeping clear.

When a Tug and tow (at least as far as US case law goes) are connected the TUG is both legally and financially responsible for the barge (or whatever is being towed). When ship assist work is done, the tug is responsible for any damages it may do in the course of her work. BUT, when the ship is directing the tug, as in this case, the ship is responsible if the ship (pilot) orders the tug to do something that causes damage.
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Old 28-09-2012, 11:36   #461
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Re: Freighters vs. sailboats

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The second issue. The dampening of heading data is what is being referred to. .
Dampening is quite different. Dampening averages the data. Gyro stabilisation is not a simple averaging of the data. It is using a gyroscope (or in some cases just a gyro stabilised compass) to provide more accurate heading data.
With effective gyro-stabilisation heading information is more accurate and the dampening, or averaging, can be reduced.

I agree the HBC is an essential tool and generally much better than than the more sophisticated alternatives.
A good pair of binoculars also deserve a mention especially at night.
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Old 28-09-2012, 11:48   #462
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Re: Freighters vs. sailboats

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The tug is under the direction and control of the SHIP. the extension of the TUG is included in the vessels keeping clear.

When a Tug and tow (at least as far as US case law goes) are connected the TUG is both legally and financially responsible for the barge (or whatever is being towed). When ship assist work is done, the tug is responsible for any damages it may do in the course of her work. BUT, when the ship is directing the tug, as in this case, the ship is responsible if the ship (pilot) orders the tug to do something that causes damage.
I guess my question is how do other boats in the vicintiy know the tug is tehtered? If normal procedure is to go behind the stern when crossing, in that busy channel that would be obviousy not wise in that situation.
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Old 28-09-2012, 11:49   #463
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Re: Freighters vs. sailboats

Let me put it this way. When your vessel is heading 045 The compass reads (well, should read!) 045. When you yaw, it will read whatever course the head of the vessel is on.

There is no alteration of the heading output for any nema output that somehow slows the swing down.

ARPA requires by definition a certain number of target sweeps to lock onto a target for tracking. Then it requires more sweeps to finalize the computers program. Each time the heading it altered, the computer has to restart the computation.

You mention the computers processor. IIRC, ANY full ARPA radar has to meet specific technical requirements. MARPA doesn't. This may be the problem. MARPA is basically whatever the slick salesman tells you it is! with no standards to follow or be forced to adhere to.

My $70,000 dollar FULL ARPA Furuno can track mylar balloons at a mile. And I can get consistant locks on A seagull on a flat day. It does matter how much you pay for it!
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Old 28-09-2012, 11:57   #464
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Re: Freighters vs. sailboats

There is no specific warning for tethering. Just as there is no different signal for a tug working along side. But, this is part of the boaters overall responsibility to study up on these things. Far too many boaters have a wider wallet than they do an expanse of knowledge about the ecosystem they are floating and boating in.

I can't think of a better reason to take a boating course. Can you?
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Old 28-09-2012, 12:12   #465
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Re: Freighters vs. sailboats

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Originally Posted by cappy208 View Post
@Dockhead: You need to do some more research about what 'stabilized' means. I think you will be disappointed in your newfangled RADAR from what it appears you are expecting.

I have never heard of a gyro stabilized RADAR, that removes heading oscillations of the kind that make ARPA and MARPA accurate like you are expecting.

Stabilizing refers to the data input, and the relationship of travel through the water, OR over the bottom. It is NOT about your heading movement.
Now where's that head scratching smilie when you need it?

With respect, it seems to me that you are confused. A gyro stabilized compass (actually it doesn't use a gyroscope, but a sensitive 3-axis accelerometer) is gyro stabilized in order to improve the accuracy of the heading data, not to remove heading oscillations from ARPA calculations (that is what dampening is for -- I think you are confusing the two).

Accurate heading data is really important -- without accurate heading data your radar is only good for range and relative bearing, and ARPA can't do anything. Crudely speaking, without accurate heading data [in modern gear, supplemented with rate-of-turn data -- there are separate PNGs for that in NMEA], ARPA can't know whether it's you yawing around or the target jumping around. ARPA simply can't plot the path of the target. Radar only tells you where the target is relative to your bow. 34 degrees off the port bow. It doesn't tell you that the target is bearing 275 from you. For that, you need to include your exact heading at the moment of the sweep.

ARPA makes its calculations in two layers -- first of all, it wants to know where is the target, bearing and range, on every sweep. It must have accurate heading data to get bearing. Then, it wants to know what the relative motion is between you and the target. It uses GPS data to determine where you are for that layer of the calculation.

If your path through the water oscillates because you're in heavy seas or playing the wind, then it needs to know how coarse or fine to average out the data points -- that's dampening. With increased dampening -- coarser averaging -- the % uncertainty of your projected path increases, but that is inevitable if you are slewing around out there in big seas.

And don't forget that your COG may be very different from your heading -- so COG derived from GPS data is useless to calculate bearing to the target.

So a good gyro stabilized compass makes a world of difference in the usability of yacht radar. An ordinary fluxgate compass only have dynamic accuracy to 5 degrees or 6 degrees or even more RMS. If you can get that down to 2 degrees RMS, then MARPA starts to give more or less usable calculations. It makes a vast difference.

The gyrocompasses on commercial vessels cost $20,000 or more -- that's how important that data is.
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