PowerPoint Slideshow about 'Universal Nets Global Aquaculture' - unet1
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Socially Acceptable; Products and Technologies must help to mitigate social issues frequently associated with marine aquaculture operations.
Examples of social mitigation would be that of possible noise control and that of improved worker safety
Cost Effective; Products and Technology must be cost effective in terms of economic feasibility, covering such issues as ease of deployments, decreased maintenance efforts and be readily integrated with existing operations and stock density ratios
Eco-Friendly; Products and Technologies must help to reduce the Environmental impact associated with the operational footprint, benthic nutrient loading, and escape interactions with wild fish stocks, among other environmental issues
Professionally Managed and Engineered Solutions; Products and Technology needs to be professionally proven and Due Diligence site specific engineering engaged to protect the client. An appropriate Quality Assurance Regime needs to be in place
A well mapped implementation plan “Roadmap” managed jointly and cohesively between Industry and the designated Regulatory and Government bodies. This will ensure a positive prospectus to potential stake holders and Investors Financial Institutions and Sustainability
Robust for Survival and Adaptable; Products and Technologies must allow for expansion into “High Energy Sites” Fish welfare is therefore a priority consideration of Technology and Product as well as planning
There are three main types of anchors in use today
The Deadweight or Clump weight,
The Pile or Pin
The Drag Embedment Anchor.
The Dead weight is probably the oldest style of anchor in existence. The holding power is generated by the mass of the material used and partly by the friction between the mass and the seabed. Common materials in use today include iron, steel and concrete. They have a very low efficiency.
The Pile is typically a hollow steel pipe, though pins from solid round bar can also
be used in smaller applications. These are generally installed by means of
hammers or drills. The holding power is generated by the friction of the soil along
the pile and lateral soil resistance. The pile normally has to be installed at a great
depth below the seabed to obtain the required holding capacity,
they can resist both horizontal and vertical loads.
Pile solutions are very expensive and the cost of installation usually exceeds the cost of the pile.
Drag Embedment Anchor
Drag Embedment Anchors are the most popular type of anchoring device available today.
The drag embedment anchor has been designed to penetrate into the
seabed, either partly or fully. The holding capacity of the drag embedment anchor
is generated by the resistance of the soil in front of the anchor.
The drag embedment anchor is very well suited for resisting large horizontal loads, but not for large vertical loads although there is some drag embedment anchors available today on the market that can accommodate some degree of vertical load.
The History of Drag Embedment Anchors
No one can be exactly sure when anchors were first used, though it is known that
anchors were used in ancient China as far back as 2000BC.
Typically they were large stones or baskets of stones connected to lines of vegetable fiber.
The weight of the stones and the degree of friction obtained on the seabed were what kept the vessel on station.
The introduction of iron into anchor manufacture saw new developments such as
teeth or flukes being built into the anchors, this allowed penetration into the seabed thereby offering improved stability and holding power. These anchors were primitive by any standards and as such often broke under the pressure of the loads.
Around 1813 curved “arms” were introduced to add further stability and
from 1852 onwards the “Admiralty Anchor” was introduced to service the ships of
Further refinements continued throughout the 19th century including the elimination of the stock, this improved handling and stowing ability of
the anchors, qualities still valued highly today.
Many anchor types have been developed through the years, some have
prospered, others have fallen by the wayside.
The most recent designs are based on the vast amount of experience gained from the use of anchors through the ages as well as extensive testing programs designed to make the new generation of anchors much more efficient then those of past times.
The following brief overview of the types of anchors in use today is presented to
give users a wider understanding of how anchors have evolved and the relative
efficiencies of each.
Based on certain characteristics of anchors such as fluke area, shank design and
stability it is possible to classify the various types of anchors. To enable a
comparison of anchor types an indication of anchor efficiency is provided.
Efficiency, is based on the holding capacity divided by the weight of the anchor
and is expressed as a ratio, e.g. 33:1 = 33 x anchor weight.
The anchors are classed from A, best performing to G worst performing.
These are slender highly engineered anchors with ultra penetration in which the
holding power extends to the third power of penetration. Efficiency above 50:1,
examples include the Stingray F and Stingray HD anchors. Stingray anchors can
exhibit efficiencies up to 200:1. These types of anchors may also allow uplift angles at the mud-line, for example Stingray anchors can accommodate loads at up to 20 degrees above the horizontal.
Anchors with elbowed shank allowing penetration into the seabed. These anchors have an efficiency of between 17 and 25:1 and include the Bruce SS, Bruce TS and AC-12 Bruce SS
Anchors with open crown hinge near the centre of gravity and relatively short
shanks with stabilizers. Typical efficiency of 14-25:1 and include Stevin, Stevfix
and Flipper Delta. Stevin Mk3 Flipper Delta
These are anchors with hinge and stabilizers at the rear and relatively long shanks and stabilizers. Efficiency range 8-15:1 and include the Danforth, LWT, Moorfast- Stato-Offdrill and Boss anchors.
This class is for anchors with extremely short, thick stabilizers, hinge at the rear
and short basically square shaped shank. Typical efficiency 8-11:1 and includes
anchor types AC-14, Stokes and Snugstow.
Anchors with a square shank where the stabilizers are built into the fluke design.
These anchors have typical efficiencies of 4-6:1 and include Halls Stockless, US
Navy Stockless, Byers and Spek models.
These include anchors with a stock and small fluke area with the stabilizers at the front of the shank. Efficiencies are typically less than 6:1 and the anchor types include Single Fluke Stock, Dredger and Stock types.
It is sometimes useful to compare anchor types based on the applications for which they were designed to see which specific anchor best suits a particular application.
The AC-14 or Admiralty Class 14 anchor for instance was developed to provide a
high holding power boats/ships anchor that would perform well in certain bottom
conditions but not necessarily give the absolute best performance in a permanent
mooring application. These anchors have proven themselves to be reliable for
ship’s applications, they are relatively efficient, easy to use and offer a reduced
weight over traditional boat style anchors.
During testing carried out by the British Admiralty the AC-14 was proven to be a
high holding power anchor when it demonstrated holding power efficiencies of
between 6:1 for soft bottoms to a maximum efficiency of 12:1 for the best holding
The Stingray anchor developed in Australia primarily for Pearling Long-line
applications and permanent mooring systems performs exceptionally well in all
bottom conditions except rock. This anchor exhibits considerably higher holding
power than the Bruce as it is designed for permanent mooring applications where
the primary consideration is the anchor holding capacity, not the ability to be used as a boat anchor.
Typically this anchor has holding powers as high as 200:1 in small sizes and around 100-150:1 for anchor sizes used in long-lines and most small to medium work-boat moorings. These holding powers were proven in field tests conducted in 1998 as well as tests witnessed by the Classification Society Det Noske Veritas (DNV) in 2002 when a five (5) kg Stingray was shown to develop over twice the holding power of a 28kg Danforth.
Other advantages of the Stingray include an ability to be stacked flat for pallet
loading thereby reducing transport and handling costs. They are of steel plate
fabrication and so are not prone to suffer from casting imperfections that can
reduce the structural integrity of any cast anchor.
The comparison then shows us that the AC -14 would be the preferred choice for a vessel anchoring application, but that a Stingray would be more effective for a long term mooring application. To complete the comparison then we should also look at the size of anchor required to perform a specific task. In this instance we will concentrate on a long term mooring application rather than a short anchoring of a boat.
To do this we must first ascertain what size of anchor is relevant to the application, the first thing we must do then is to compare the anchor efficiencies.
When we do this we see that the Stingray has an efficiency at least eight and up to 12 times higher than that recorded for the AC-14, therefore, for any specific
mooring application the AC-14 should be at least 8-12 times the mass of the
To put that into operational terms, if it was determined a Stingray anchor of 50kgs was required then a 400kg to 600kg AC -14 would be required to generate the same level of holding power. This is not to say that a AC-14 anchor is not a good anchor, just that there are other types that are better suited to these long term applications.
If on the other hand we were looking for a boat anchor then the AC-14 would
probably outperform the Stingray in areas such as stowage and the ability to self right.
Typically these are not highly valued qualities for a permanent mooring
anchor as they tend to be “installed” to a pre-determined pattern or position and
are not simply thrown over the side and allowed to drag until they eventually hold.
Some other advantages of Stingray permanent mooring anchors are their lack of
damage to the sea floor, whereas other anchor types tend to drag for rather long
distances and as such they carve great troughs into the seabed which is not good for the environment in that proximity. Stingray anchors have been approved by various Government departments and agencies as being friendly to the
environment and are being used in marine parks such as Ningaloo Reef, The
Rowley Shoals and Ashmore Reef for this reason.
Stingray anchors can accommodate far greater vertical loads than the AC-14 or
any conventional anchor. In field tests carried out the Stingray anchors has
demonstrated an ability to handle loads up to 30 degrees from the horizontal,
though the manufacturer claims no more than 20 degrees.
Stingray anchors are patented so you are getting the supply from the source, not
someone copying another anchor and selling it on price alone which inevitably
leads to reductions in the quality of the build as reductions in cost are investigated.
In recent comparisons performed for a major contractor Stingray anchors were determined to have a cost of holding power of around half that of the other major anchor types. It is this cost that users should concentrate on, not the actual cost of the anchor.
It has been demonstrated above that the weight of an anchor is not necessarily the best way to select the anchor required, it really is the holding power of the anchor that is important.
It can clearly be seen that there are a number of different issues that need to be addressed when selecting an anchor for a specific application.
It is important to understand the difference between anchoring and mooring as a first principle, then to establish the needs of the application. Once this has been determined then the anchor selection process can begin.