I STILL can't get it....

Re: AIS

At the moment they are expensive and the integration options are limited but I'm convinced that this will change - they'll integrate well AND drop in price. The only question is how quickly...

I'm certainly not going into the market yet but will watch developments with interest. I remain convinced this is the way things will go.

Ed

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Re: I STILL can\'t get it....

Steve - I don't think the " spinning round " happens - just like your splats on the windscreen.

I was run down in a similar situation many years ago, on a 45' yacht, hit with a glancing blow by a very large tanker in ballast; after being hit we were then pushed off temporarily by the bow wave and then sucked back in to run down the side of the tanker. I thumped the side of the ship in anger ( pretty pathetic really)

I can, to this day, clearly remember every detail, including the sparks ( it was at night ) as the rigging and cross trees scraped along the side of the ship.
There was no pushing off or spinning round effect from the pressure wave ahead of the tankers bow, just a direct hit - like your gnats !!!
The biggest fear, for all of us , when we talked about it afterwards was not sinking but being mashed up by the prop. we counted ourselves lucky to have survived.

Any other experiences out there that might enlighten us?

Stephen

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Re: stephenh

I recall a Sadler 34 suffering the same during a (1990) YM Triangle Race, no bow pressure effect, just a prolonged scrape alongside & dismasting. What we don't know is the angle of incidence. Arguably, an oblique angle of incidence might miss any pressure wave whereas a boat directly ahead might possibly experience the spinning effect, I'd rather someone else did the research though!
For the record, the ship slowed, had a quick look at the yacht and departed, ignoring VHF16 totally - no offer of assistance

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SWMBO\'s comment

It's a long post now so apologies if this is mentioned elsewhere.

When discussing this with Mrs Magic, she sniffed and said "why didn't they try radio contact".

Good point really.

Magic

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Re: SWMBO\'s comment

Radio is almost useless in this situation and not recommended for collision avoidance.

Think about it (hint - how do you know you are talking to the correct vessel?).

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Re: SWMBO\'s comment

Although a securitee announcement on CH16 might be worth it?

<hr width=100% size=1>.. whit way roon should it be again ..
 
Re: SWMBO\'s comment

The problem is always one of identification unless you can do like the Traffic Contol centres do and quote Lat/Long course and speed of the vessel bugging you. The problem is that whatever situation you describe (westbound ship on my stbd side.....) could be repeated several times over within the range of your transmission. The only thing it might do if your voice suddenly comes up loud on 16 is to wake up an inattentive watch officer and get him looking harder at his radar.

Some Yeoman plotters though have a facility to interface with radar to put a moveable 'lollipop' on the screen by moving the Yeoman mouse, this could be used to get the Lat/Long of the target and with enough time get course & speed. Our Yeoman puts a waypoint location lollipop on the radar screen but we cannot do the moveable by mouse one.

Trouble is by the time you feel you want to call you don't have a lot of time to do it. Best is to try and avoid close quarters situations if possible though it doesn't always work like that, especially if there is lots of traffic and dodging one puts you too close to another!

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Re: SWMBO\'s comment

I appreciate the difficulty. But, surely Wakhuna could have identified his own lat/long very accurately from the GPS and, using his radar, have got a pretty accurate position and heading for the P&O.

He could then have radio'd "vessel in position ****, heading **** - I am in position **** and concerned about a collision.

The Captain of the P&O could then have accurately plotted the position of the Wakhuna - this would at the very least have alerted him to the fact that his own radar (ARPA I think they called it) was in error and taken avoiding action.

At the end of the day, he didn't turn to starboard because his ARPA told him he would leave Wakhuna 2 cables to port - had he had a very accrate fix, he would have realised that wasn't the case.

Even if he didn't definitely know it was him the Wakhuna was radioing, then he could have still steered to starboard as a failsafe measure.

I think that's a reasonable arguement (I don't have a radar so am not entirely conversant with it's capability).

Anyway Tome - as you are well aware - best not argue with the Mrs!/forums/images/icons/smile.gif

Magic

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Re: SWMBO\'s comment

In order to establish the ship's heading and his course you would need to do a proper radar plot on paper, which requires plotting his relative bearing and range at least twice with a suitable time span between. What you see on small boat radar is all in relative motion although the Moody had (but didn't know how to use yet) a Mini ARPA function that might have provided a rough idea, most small boat sets do not have this feature yet and it also requires the radar to be linked to compass and GPS. There is again the question of time, from realising there is a potential problem to a possible collision point is measured in minutes when you have a ship at 27kts (about 6 minutes to cover 3 mls).

What you can see on small boat radar is that there is another vessel approaching on a steady (relative) bearing. This can be seen from either the electronic trail feature on most sets or the EBL (electronic bearing line) which you can set on the target echo. If the ship continues on this line one or both of you needs to take action, either by altering course or changing speed (including stopping). I have used the option of slowing almost to a stop and it works, but if you STOP completely you lose steerage and then your radar is effectively useless since the boat (and the radar heading) is pointing all over the place. Radar is not about what you see at one particular moment but what you see changing/evolving hence a steady course is needed and a change in course (from either vessel) takes time to re-evaluate on screen.

IMO, and I know lots will disagree, this is the reason why radar is not best installed at the wheel, rather down below. At the wheel a human helmsman will inevitably be distracted by the presence of a close target and may stray from a steady heading, confusing the radar picture of the evoving situation. Our radar is at the Nav table below, next to the chart plotter, and we have autopilot control from there as well so can alter course as required onto a new but steady heading and watch to see if this solves the problem. The watch on deck is there to keep as good a lookout as they can, probably a token only in 25yd vis, though they can listen for the usually non-existent foghorns!

In the final analysis too it is worth remembering that collisions still occur between ships which have very sophisticated radars and highly trained operators. Us little boat people need to allow larger margins of error!




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Re: SWMBO\'s comment

again - with AIS you would talk to the correct ship, and will in the next software version be able to send/receive 'text' style messages, stating your INTENDED manouevre - the knowledge that a ship WILL turn to port (or whatever) would be a real asset in some circumstances. Having said that - the concept of 2 ca CPA would be scary in full visibility in 50 metres of murk it hardly bears thinking about.

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Re: SWMBO\'s comment

I agree with you on the trail facility, but ..........

We used to have a Furuno radar. Its trail facility could be used to produce either a dotted or a continuous trail, the dotted trail enabling you to judge speed. But the trail stayed on the screen until you cleared it.

Then we changed to a Raytheon radar. The Raytheon trail gives a number of scans at full intensity, then a number of scans at a reduced intensity, then disappears. The result (particularly when using a long range setting) is that the screen trail is so short that its direction is indeterminate.

The Furuno was a very good anti-collision device, the Raytheon nowhere near as good. Yes, I know the trick of putting an EBL onto the echo and waiting to see whether the ship is running down the line. It works well (though you can't get a CPA from it, as you can from a trail). But it's not so good when there are several ships in view; which one do you select for your EBL?

The Raytheon can be adjusted to give short, medium or long wakes (although even the long is nowhere near long enough). It's done by software, of course. If only they could have short, medium, long or permanent wakes then the Raytheon would be a much more useful radar. I know that Wahkuna had radar, but noone has mentioned the make. I just wonder .....

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Radar trails

We too had a Furuno 1830 with a largeish CRT screen on our last boat and it was superb. The 'plot' facility to leave continuous trails on screen was really useful, it only had one EBL but you could leave the crosshairs from the trackball mouse on a 2nd target an imagine (or lay a rule on the screen) the second bearing line.

Our latest boat came with a Raytheon with a small LCD screen and it is not in the same league as the much older Furuno set. Yes you can set 'trails' as short medium or long but as you say even the long one is shortish! Also if the gain is on 'auto' it tends to set it too high and the 'trails' of every little screen speckle quickly obliterate the screen! Newcomers might well have all the adjustments on 'auto' so could find this difficult, we have all the controls now on 'manual' and it is better. The one bit I do like and didn't have set up on the Furuno is the waypoint lollipop on the screen, very helpful when for example the WPT is between 2 buoys say, this helps confirm that the echoes on the screen are the buoys not say a guy in a boat fishing.



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