I was awake early after an early night to find a heavy mist, it had not been forecast and I suspected it was fairly local so decided to move off to get at least the first hour or two against a relatively slack tide. At 06:30 I could see both banks of the Loch, 5 minutes after I had got the anchor up everything had disappeared with the visibility perhaps 20 yards.
I was tempted to put the anchor back down but decided not to and gingerly went down the Loch at a walking pace, fortunately my modern doppler radar is particularly good close in with essentially no minimum range and at 100 meters (or less) will show just about everything, even reasonably sized pot markers in smooth water.
There is quite a lot of detail in the next bit as I am thinking of using it as part of a post or page on navigating in fog.
I had two independent DGPS's running and visible, one the 9" plotter with Garmin vector charts derived from the UKHO, the other a 10.5" iPad with raster charts including the very accurate Antares GPS charts of the entrance and the anchorage (the lap top with Admiralty & Antares raster charts and different vector charts was not going to be any use as it is on the chart table). I could also have had a spare iPad and / or phone running vector or raster charts but that would have been a bit over the top!
As a bonus the plotter and iPad has tracks from previous visits (optionally displayed) my track inbound was my preferred one to follow as it was clear of lobster pots the day before and I displayed just that one on the iPad, see below.
 |
Previous tracks are often a help in fog, on this occasion I only
displayed the one of my arrival. Note the scale, and unlike
some Admiralty carts and those derived from them (most) they
are up to date within a few years rather than decades and were
made using GPS and echo sounders rather than manual methods
and a lead line as can be the case with charts. |
Most of Loch Aline was last surveyed by lead line for the UKHO in 1921, and a few parts of the Sound of Mull not since 1904, I have frequently seen much older and current plotters, other than seriously expensive ones for commercial use, don't tell you. Another good reason for having Admiralty raster or paper charts, or both (Imray charts don't tell you either). The Antares survey was in May 2015. |
About 150 yards from where I anchored, nothing visible. The
radar is showing 3 other anchored boats (large blobs), the
small red blob is the pole on Sgeirean nan Ron (a short reef).
Making < 3 knots through the water, 3.6 over the ground with
the ebbing tide. Range rings at 250 metres.
|
In fog the Split screen mode is usually better than radar overlaid on the chart as weak radar returns are not hidden by chart detail, past tracks etc.. Also the radar view can be set for short range targets and the chart view for longer range for situational awareness and more distant AIS targets.
In open waters I would typically have the radar looking out one mile to ID boats without AIS in time to avoid and with a sporting chance of seeing small navigation marks without radar reflectors. The Chart view I would set to 5 - 10 miles or more to see vessels with AIS in plenty of time. On this occasion in confined water the GPS was at greater magnification for ease of viewing. AIS and planned track if set, can be displayed on both.
Both displays are set for North up (from the fluxgate compass, they can be set independently, without the compass most modern systems will estimate using GPS). I find that better for situational awareness and particularly for collision avoidance, others get confused and prefer heading or track (if available) up - I find that confusing! I did a poll once on an aviation forum with a significant number responding, IIRC 60 - 70% of > 100 responses preferred track up, clearly my brain is wired differently to the majority! I would certainly recommend people try head up as radar controlled collisions are less likely, particularly vs heading up and especially if you like "bread crumb" trails set on - I don't, there is more opportunity for confusion and radar usually showing trails for fixed objects! The radar's MARPA if available or AIS will show tracks for selected vessels which is more helpful.
Approaching the loch entrance, the red blob ahead of me is the port lateral buoy, about 150 yards away, I saw it at 50 as the fog lifted. With a good rise of tide I could be sure of not running aground if I stayed within the previous tracks some of which were at low water.
The red line on a similar track is a large motor yacht that was a mile or so ahead of me and was classified as dangerous (to my parameters) by the AIS system and so it's past track is automatically displayed. Range rings at 150 metres.The AIS contact at the top of the radar screen "Lara of Chichester" is, as I write, one berth down from me at Tobermory. She had left her AIS on whilst parked and arrived there in the early evening. |
My inbound (right at the bottom) and outbound
tracks, the channel is about 75 yards wide.
|
 |
The ferry on her berth, about 75 yards away with the fog
lifting further. |
The fog stayed patchy until I was well north of Ruba Aird Scisg and the fish farm north of there, about 5 miles, then it suddenly cleared but was still there behind me. With a freshening wind I was able to sail for about an hour but not making a great deal of progress against the tide.
Whilst still in the fog I was rather disconcerted to find a large ferry coming up behind me making 14 knots over the ground, about 16 through the water. I was perfectly safe as I was using GPS and radar to keep well to the right of the main channel and a couple of hundred yards off shore, was broadcasting my presence on AIS and could see hers. She past me under 250 meters away (by AIS and Radar) and was only just visible. How she would have avoided anything not visible on radar a good way away, I don't know.
 |
| 14 miles in 4 hours. |
As previously forecast some bad weather is coming and it is looking worse every day. I could be here until Tuesday or Wednesday 😞and it is unlikely I will be able to head out via Coll as wind is likely to be making the anchorages untenable for some time. Direct to Barra or via the Small Islands may be an option but the ECMWF and UKMO violently disagree on the weather from Tuesday.
No comments:
Post a Comment