Radar/Chart Plotter - which way up?

[BlueSkyNick]

[ QUOTE ]
Several (well 2) tut tuts Nick!

1 tut) Why were you messing with the Needles Channel in fog? The North Channel is much easier and indeed at most states of the tide there is a straight route to/from Poole from just NW of Hurst, no need to pass inside of North Head Buoy. The Needles is more like a winding country lane by comparison.

2 tut) Why were you not in Cherbourg with the rest of your Moody clan and several forum folk, some of which did sterling service replacing the main halyard I lost down in the mast?



[/ QUOTE ]

Robin, Your second question is answered by your first really!!

We got out through Hurst in just a bit of drizzle, heading for Bridge. 20 minutes later, it was 0.3nm away on the GPS but we couldn't actually see it! It was still daylight at the time. Hung a left for Cherbourg, and sailed quite nicely for 8 miles. Fog was not patchy - it was one bloody great bank! At 2000 decided to turn back while we still had an hour of 'daylight', and head up the Needles as the shortest route to Yarmouth, and picked up a buoy in the dark. Woke up at 0530 for the forecast, SCG lady at Lee on Solent says viz was less than 100yards so back in my pit. Woke up at 0730 couldn't see Yarmouth harbour wall, when we are swinging on a buoy outide of it - "bolleaux to Cherbourg", said I.

Hence we didn't get to the lunch, or to play with your halyard. Tut tut to you, too. What are you doing trying to replace a halyard in a forein port? Much better to do such things at home, so if it goes wrong there is no rush to fix it, IMVHO.

To the other serious comments, all noted thank you, very much appreciated. I will keep the existing GPS, am getting the laptop sorted for the chart table, and already have a H/H if all else fails (with lots of spare batteries!)

To Jimi and Para, go and hijack somebody elses thread ! /forums/images/graemlins/wink.gif

 

[ParaHandy]

look, peering at all these screens will make you shortsighted /forums/images/graemlins/grin.gif

 

[Robin]

[ QUOTE ]
Hence we didn't get to the lunch, or to play with your halyard. Tut tut to you, too. What are you doing trying to replace a halyard in a forein port? Much better to do such things at home, so if it goes wrong there is no rush to fix it, IMVHO.

[/ QUOTE ]

It's funny but I thought that too and SWMBO actually said it. She said it a several more times after the mouse line broke and the halyard fell back down, along with 'well I'M not going up the b$$$$y mast to sort it out either'. 20/20 hindsight but I have done that job many times before without a problem and in the event probably got more immediate offers of help than I would have found at home! Richard and James from Hana (rb-stretch) were the main helpers with a watchful eye from Becky and a crank on the handle from the Moody 336 guys in the next berth. We then sailed all the way home with just the genoa so didn't try the new Dyneema gold plated job until last Sunday beating back to Poole from Lymington with 2 reefs in, yippee it didn't stretch like the old one did!

Robin

 

[BlueSkyNick]

All's well that end's well /forums/images/graemlins/smile.gif

 

[Oldhand]

<We run our chart plotters on NORTH UP because that is the way charts are used on the nav table in paper format and again because without a gyro compass anything else would be innacurate with a constantly moving boat.>

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Why do you think using North Up gives you greater accuracy on a constantly moving boat? How do you think your display knows where North is? It can only come from an electronic heading input and thus is no more accurate than if you were using Course Up! If you want azimuth accuracy on a constantly moving boat you must provide an accurate high speed heading input for any azimuth stabilised mode! /forums/images/graemlins/confused.gif

 

[pvb]

Errrr....

If you think about it for a moment, the default setting for a chartplotter is north up. No compass is needed. It's like the default setting for a paper chart is north up, unless you turn them around.

 

[Oldhand]

I wouldn't shrug off the hsb2 networking capability of the RL Plus series displays quite so quickly in your deliberations. If, for example you chose a RL70CRC to have outside, you could get a cheap second hand RL70Plus display (off ebay as I did) to have at the chart table. If the RL70CRC is powered up, the "radar only" RL70 becomes a plotter as well as a radar display when connected by hsb2. Having a plotter function at the chart table for voyage planning, plotting and storing waypoints and developing routes is much better than having to do all it outside in an unenclosed cockpit. If you connect the 2 displays by Seatalk as well as hsb2, then when you make a route "active" on one, it becomes the active route on the other automatically, thus everything is singing from the same hymn sheet. This would surely be better than having some third party electronic navigation system at the chart table. I would also suggest that if RL70CRC's are still availble, they can be had for less than £800.

Alternatively, you could get a C Series display, and have 2 mounting positions for it, one at the chart table and one in the cockpit. However, to get radar at both locations you have to build a "Y" split cable, ensuring both ends are a similar length from the split. I know of such an installation and the owner is very happy with it.

I suggest you look at the cartography for each system more closely as this could be the deciding factor. Having installed the RL Series system, I am less than impressed with C-Map NT+ cartography. After examining equvalent Navionics Gold charts on a C120, I believe it to be a considerable improvement on the C-Map.

Hope you find this a serious and helpful response.

 

[ParaHandy]

how about this for eye strain in the wheelhouse of a 10m fishing boat ...

 

[BlueSkyNick]

Very helpful on all counts, thanks OldHand. I will probably make a final decision when I am in the shop with my credit card out !

 

[tcm]

Re: yeah well

It's a bit ambiguous to read that you wouldn't recommend your better half to anyone else. Why?

 

[duncan]

Can anyone spot the compass?

 

[Robin]

[ QUOTE ]
Why do you think using North Up gives you greater accuracy on a constantly moving boat? How do you think your display knows where North is? It can only come from an electronic heading input and thus is no more accurate than if you were using Course Up! If you want azimuth accuracy on a constantly moving boat you must provide an accurate high speed heading input for any azimuth stabilised mode!

[/ QUOTE ]

Actually I have 3 very clever chart plotters all of which know full well that North is at the exact top of their screens, this is irrespective of any compass or GPS input it is indeed the default position. Even the Yeoman paper chart plotter knows that too unless I put the chart on it upside down or sideways! It is correct though in this position to say that the little blinking vessel which depicts current position will move around in the direction it points trying to keep up with the heading information from the electronic compass, though the little extra optional arrow that shows the COG is a mite more stable! /forums/images/graemlins/smile.gif

 

[Aardee]

Hanging from the ceiling, above the distictly domestic-looking computer screen...

 

[pugwash]

Please explain

Radar must be head up, chart must be north up..? I read this two minutes after I'd been speaking to a technician about how I could make my (rther old) radar go north up because I find there's a lot of 'smear' -- that is, a target is not so much a blip as a line because the course is wandering about a fair bit. Although the radar is connected to the Sea Talk and gives a lat and long, when I try to go "north up" it replies: "No data." So this is the problem I was trying to fix (unsuccessfully so far).

My question is, am I barking up the wrong tree? Should I even be trying to make the radar go north up? And if not, if I keep the radar head up, how can I stabilise the picture?

Any thoughts from those wise men TCM and Robin would be appreciated.

 

[fireball]

On A C series you said "However, to get radar at both locations you have to build a "Y" split cable, ensuring both ends are a similar length from the split. " .... we are contemplating a C series (as E is far to expensive and I prefer landscape to portrait) ... but why do the split ends have to be similar length?

Just thinking on the fly here ... I suppose other options would be to have a multiway switch to activate the desired instrument position or a multiway plug & 2 sockets to get the same result...

 

[pvb]

Multiway plugs/sockets...

It might be cheaper to use a multiway plug and 2 sockets, rather than buying a second set of Raymarine cables to get the right connectors. I've fitted a C-series display in my cockpit, but I'd like the facility to occasionally use it at the chart table, so I've been wondering about wiring options. Trouble is, it needs a minimum 22-way connector!

 

[tcm]

Re: Please explain

can't explain the lectronix fix tho i understand the problem.

Thing is i suppose put simply, that one sees targets on radar as if "walking along" : you wouldn't say "i was walking down the street heading 120 degrees when someone attacked me from 270 degrees ..." - someone is "in front" or "behind" or i and many others use "at 3 oclock" or "at 10 o'clock" etc - and this immediately informs people and directs someone where to look for lights and which way to turn. It also, incidentally, indicates how very much better a clock face is at quickly giving info rather than digital but that's a sepret issue..

Chartwise, even moderately experienced people don't usually look at charts/maps orintateed "head-up" - they have them North-up. We are all a bit wary of people who can't read a map except by turning so they look "down the road".

I spose it's an issue of the normally received method of human brain (or learnt methods of) accepting and processing the data - slightly differently for radar and chart. I wd be extremely ary of myself trying to read a radar northup, and the weaving of the boat shouldn't be an issue - the blob will be big and should be avoided by big margin. Lots of things of course are stationary and so will smear a lot as approached rather than plough their own course on radar.

Nothing partic wrong with "overlay function" but i wd have it on a separate (third) screen. First screen radar, and very much second screen is chartplotter - tho inshore (esp enclosed solent and similar) of course the chartplotter is signif more important i spose.

HOWEVER, presuambly depending upon the software, some "overlays" are indeed fab - because they other targets and trails their ACTUAL previous position on trace - so you see where they are headed perfectly. Nonetheless, even with this, i wd always resent people with uncluttered "head up" radar so they will see and scan every target or possible target.

Recently, with loads of night and fog i used the overlay fuction er just once. But that was offshore. Special solent conditions again, i suppose - much easier out at sea and don't much need a chartplotter at all - you heading generally west, say, but will happily turn to port 60 degrees if there's something ahead on collision course. Not so easy if not much searoom.

hope this helps.

 

[Oldhand]

I asked why North-Up gives you greater accuracy on a constantly moving boat and your response gives no answer to that. It is the relationship of the vessel's heading to the chart display that is relevant for accuracy and it doesn't matter which way up your chart is. The only thing that matters is the accuracy of the heading information of the vessel displayed relative to the actual vessel heading. When you start using your display as a radar as well, either in overlay mode or just normal, the accuracy of the vessel's heading provided to the display is critical in relation to target bearings for collision avoidance plots.

 

[Oldhand]

A radar's timing measuerment circuitry has to be set up correctly to give accurate target ranges. Part of the "time path" for the signal transmitted and reflected back from a target is the video cable between the scanner and the display unit. The latter being where the time measurement giving the target dispalcement from the centre of the display is made. The radar can only be "tuned" correctly for one video cable length, thus if one leg of the "Y" was significantly different in length to the other, ranges measured with the dispaly in one location would be different form those measured in the other location.

 

[Oldhand]

Re: Multiway plugs/sockets...

I think you will find the video cable within the scanner to display cable is a co-ax which would give you problems with any standard multi-way connector. The way to do it is to cut the first installed cable from the scanner at a convenient place in the boat, and connect it to a tag strip in a suitable junction box. You then connect the cut-off end with the display connector plus another radar cable cut to the same length in parallel on the tag strip to produce a "Y" feed. The co-ax video cable will be OK if the inner uses one terminal on the tag strip and the outer (sreen) is joined on a neighbouring terminal.