Uh-Oh! More studies of the environmental impact of anchoring...
- Thread starter Fossil
- Start date
Neeves
Well-known member
Well spotted Fossil 
This is the article that forms the basis of the link, which is a summary, provided by Fossil
The footprint of ship anchoring on the seafloor - Scientific Reports
I may have missed it but the article focusses on large commercial vessels, the sizes of which are defined, but there is no mention of anchor actual size, in terms of physical dimension nor weight.
One factor not emphasised, but is more obvious if you interpret the charts - the impact is in confined or tightly focussed specific areas, defined by location (close to a port where items, including passengers, can be easily discharged) and depth. The damage below the seabed surface is surprisingly shallow. One of the pictures, in Fossils link, looks to be of an Anchor Right SARCA, (the picture of the anchor with a roll bar and a swivel? at the shackle end of the shank) hardly an anchor used by a large commercial vessel. The picture hardly shows an anchor damaging seabed at 0.8m depth.
One might conclude that the sturdy clearly underlines, given that large commercial vessels are an essential fact of life that having clearly defined locations for vessel to anchor, outside of which no anchoring by said vessels would be permitted, would solve or restrict any future damage. Additionally installation of large mooring buoys (as used, for example, in Hong Kong harbour) would negate the need for large commercial vessels to use their own ground tackle.
Jonathan
This is the article that forms the basis of the link, which is a summary, provided by Fossil
The footprint of ship anchoring on the seafloor - Scientific Reports
I may have missed it but the article focusses on large commercial vessels, the sizes of which are defined, but there is no mention of anchor actual size, in terms of physical dimension nor weight.
One factor not emphasised, but is more obvious if you interpret the charts - the impact is in confined or tightly focussed specific areas, defined by location (close to a port where items, including passengers, can be easily discharged) and depth. The damage below the seabed surface is surprisingly shallow. One of the pictures, in Fossils link, looks to be of an Anchor Right SARCA, (the picture of the anchor with a roll bar and a swivel? at the shackle end of the shank) hardly an anchor used by a large commercial vessel. The picture hardly shows an anchor damaging seabed at 0.8m depth.
One might conclude that the sturdy clearly underlines, given that large commercial vessels are an essential fact of life that having clearly defined locations for vessel to anchor, outside of which no anchoring by said vessels would be permitted, would solve or restrict any future damage. Additionally installation of large mooring buoys (as used, for example, in Hong Kong harbour) would negate the need for large commercial vessels to use their own ground tackle.
Jonathan
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Stemar
Well-known member
It'd be a heck of a buoy to hold a big container ship in a typhoon, or would they send'm to sea if winds over XXkts are forecast? I could imagine big ships being safer at sea than on a buoy or even alongside. Is that actually the case?
onesea
Well-known member
Anything is possible, allot I guess will depend on the shelter available. Ships still get lost to typhoons even large ish container ships.
'I'm a goner': El Faro’s last hours as ship sails into storm
newtothis
Well-known member
Back when there were still huge numbers of ships anchored off LA/Long Beach, masters were advised to head to sea on a couple occasions to avoid weather. But I think that was more to do with the crowded nature of the anchorage and what would happen if any lost grip.
Not sure I'd prefer to be at sea in a typhooon over being alongside. Alongside it is just a bit windy. At sea it is breezy, with added catastrophic waves.
Bilgediver
Well-known member
Many ports already have defined anchorage locations which would minimise this damage. However with the level of port congestion seen recently in some areas there might have been a lot of anchoring going on recently.
I suspect the locals in some areas might be more concerned by the amount of fishing the crews have been enjoying while sunbathing at some of these locations.
I suspect the locals in some areas might be more concerned by the amount of fishing the crews have been enjoying while sunbathing at some of these locations.
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Neeves
Well-known member
The coal and iron ore ships off Newcastle (Oz) are ordered off the anchorage, which is simply a bit of the Tasman Sea off Newcastle, where forecast winds are to be 25 knots or stronger. This was implemented after the Pasha Bulker went ashore. They are expected to motor up and down until winds ease - we don't have Typhoons off Newcastle but seas can be 11m (off Sydney - a few NM south). With seas that large cruise ships have been denied entry to Sydney Harbour (possibly because the sea would be beam on when the ships come through the heads). The last 11m event I recall only a few years go - damage to cruise ships was quite large - balcony windows 'failing'. I do know of a cruise ship that altered its itinerary and anchored off Esperance, transmitting Melbourne to Perth, when 11m seas were forecast at Cape Leeuwin (they set up a 'box' anchored, ran engines in forward, dragged with the wind, when they reached the end of the box lifted the anchor, motored forward, dropped anchor - on a regular basis (full crew and passengers).
I'm just an idle spectator to all of this Kukri is our man.
But the article is the damage potentially caused under 'everyday' condtions - not under the extremes. I imagine that a failure under unusual conditions would allow damage under everyday conditions to pale into significance - which was the issue with the Pasha Bulker on a 'tourist' and local beach (and worse a bulk oil carrier that breaks its back).
To me - large, or very large, commercial vessels are still an essential (even cruise ships) - we cannot get rid of them - thus we must accomodate them. However to equate the damage cause by these vessels anchoring with damage possibly caused by 'us' anchoring is a very big step and the inclusion of a SARCA Excel is too large a step for me - and is a worry. The power of the research is denigrated by the suggestion that we should be included in any condemnation.
Jonathan
I'm just an idle spectator to all of this Kukri is our man.
But the article is the damage potentially caused under 'everyday' condtions - not under the extremes. I imagine that a failure under unusual conditions would allow damage under everyday conditions to pale into significance - which was the issue with the Pasha Bulker on a 'tourist' and local beach (and worse a bulk oil carrier that breaks its back).
To me - large, or very large, commercial vessels are still an essential (even cruise ships) - we cannot get rid of them - thus we must accomodate them. However to equate the damage cause by these vessels anchoring with damage possibly caused by 'us' anchoring is a very big step and the inclusion of a SARCA Excel is too large a step for me - and is a worry. The power of the research is denigrated by the suggestion that we should be included in any condemnation.
Jonathan
Bilgediver
Well-known member
The ships in Hong Kong harbour used to be removed from the buoys and sent to a typhoon anchorage. It could get exciting there in 100 MPH winds and big ships drifting down the anchorage out of control. We were running our engine at 1/2 speed for a few hours while the deck crew monitored the anchor tension from the fo'csle head.
The only way up the foredeck was on ands and knees .
Neeves
Well-known member
We lived on Lantau Island and during a typhoon the ferries would be closed down - we thus never saw the harbour under 'lockdown' and only saw the big mooring buoys being used when the weather was good. In anticipation of a complete lock down the typhoon shelters would fill up completely with local boats, maybe unto about 60' and it was quite possible to walk from one side to the other of the shelter simply by climbing from boat to boat - everything was packed tight.
I'm interested - how did you measure rode tension and what sort of tensions would you achieve vs size of vessel. In the article they are mentioning seabed disturbance of 0.8m which to me seems small and suggests that the flukes might have been 'just buried' with the shank sitting on the seabed - offering a very small area for hold. However they also seem to be saying that the chain itself was buried (but maybe I misinterpreted) which suggest the shank was buried.
Their measurements would be of vessels anchored under fairly benign conditions - or as you suggest - if the weather was nasty - they would have been ordered to a 'storm' anchorage.
The SARCA picture they show has the anchor simply scraping the top surface of the seabed - to me a well set leisure anchor is one you cannot see at all.
Jonathan
Bilgediver
Well-known member
I worked on ships from 10,000 to 25,000 tons. Small fry by modern standards and back in days when tension meters were not installed though we did have them on the oil rigs I was involved with. The tension was measured by a load cell incorporated in the structure of the windlass.
Hong Kong used to operate a storm warning number system from 1 to 10 . at each level certain actions were taken ashore and afloat and things started to get serious at about 5 when small craft stopped operating . We were sitting on a buoy near the runway with the harbour police ordering us to the anchorage. Not really possible due to the lack of skipper, chief engineer and others. A police boat delivered then at about storm warning 6
When in storm conditions such as the typhoon there was an anchor watch on the foredeck. Unlike yachts with their wee 10 mm chain the chain on ships nearly always develops a catenary providing the water is not too shallow. Under typhoon conditions the chain will be taking severe loads and just eyeballing it from the bow you get a good idea of what is happening from the angle it is leaving the hawse pipe. What has to be avoided is a loss of the catenary effect. In the case of the typhoon we started the main engine as wind speeds increase and for some were running at various speeds to reduce the chain load.
Conditions were not good with very little visibilty due to heavy horizontal rain. and CH 16 was interesting. One coastal ship was trying to climb onto Kai Tak runway and another was being blown onto the sea water intakes of the main power station for HK. In the anchorage things became interesting when a Glen Line ship broke free and was blown back right through the anchorage. Luck was with them and they regained control at the back of the anchorage steaming back to their allocated location at the head. anchorage.
I was surprised to see when crawling back after a windlass inspection that the rain had taken most of the paint from the front of the bridge. An interesting few hours.
Regarding anchoring in general different anchors perform in different ways and even their behavior varies according to the seabed conditions. The Sarca picture you refer to suggests hard sand and not a particularly deep location, Combine this with a standard Byers type anchor and only enough chain to satisfy water depth requirements then you have a recipe for exactly what you see. The harbour authority could possibly avoid this by giving advice about seabed conditions and possibly advising more chain be paid out. In these conditions you are going to get severe abrasion of the seabed as the ship wanders around the location at the whim of the tides and wind. The only way to avoid this is to use pile anchored buoys. This then involves the rigmarole of breaking an anchor of its chain prior to arrival so the ship can shackle to the buoy as in HK.
Oil rigs use high holding power anchors and these are designed to dive into the seabed and do in ideal conditions . The catanery effect is still important and in deep water they do not use anchors but employ azimuth thrusters for dynamic positioning which can achieve amazing accuracy with a high fuel consumption.
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Neeves
Well-known member
Thanks Bilgediver for taking the time - interesting and educational.
Jonathan
Jonathan
oldharry
Well-known member
A group of eco-dogooders tried to muscle in on the Studland debate claiming that anchored boats 'destroy and area several times the size of a football pitch' They had picked up an account of a large container ship at anchor and transposed it to the Studland anchorage.
They sank without trace when I shot that one down...
They sank without trace when I shot that one down...
