Session #4 underwater field school 2011, Spencer's presentation
Spencer Williams <br />Session 4<br />Advancement in Anchors <br />
Anchors <br /><ul><li> Anchors are a device used to connect a sea faring vessel to the bottom of a body of water to prevent the vessel from drifting due to wind or current.
The earliest anchors were made with stone while more modern anchors have been constructed using wood, iron, lead, and recently steal.</li></ul>Photo:<br />Spencer Williams<br />Port de saNitja<br />19/07/11<br />
Early anchors were made using stone.<br />“A heavy stone tied to a crude rope was prehistoric man's first ‘anchor’. To tie the stone more securely, grooves were cut around the oblong shapes but they relied on weight alone for holding rather than hooking or burying as did later anchors.” <br />Early Anchors <br />Photo:<br />http://anchors.synthasite.com<br />Prehistoric Anchor <br />22/07/11<br />
<ul><li>Another early version of stone anchors involved cutting holes into slabs of stone and tying a rope through the holes.
The stone slabs were in many different shapes including circles, triangles, and squares.</li></ul>Early Anchors <br />Photo: Stone Anchors <br />http://www.underwaterarchaeology.gr<br />22/07/11<br />
The Roman Anchor was the first anchor to include teeth or “flukes” that allowed it to fasten themselves to the sea bottom. <br />Roman anchors were generally made of wood with iron brackets that provided stability. <br />Roman anchors resemble modern anchors having a fluke, shank and stock. <br />Roman Anchors <br />Photo: Roman Anchors<br />http://nautarch.tamu.edu<br />22/07/11 <br />
Modern anchors have many different styles depending on the size and purpose of the vessel that utilizes it. <br />Types include Stockless and Mushroom anchors with the most common being Admiralty pattern anchors and Danforth anchors. <br />Modern Anchors (1400-present)<br />Photo: Mushroom Anchor <br />Photo: Danforth Anchor<br />Photo: Admiralty Anchor <br />Photo: Stockless Anchor <br />
Danforth Anchors <br /><ul><li>Danforth anchors also known as fluke anchors use a stock at the crown to which two large flat triangular flukes are attached. The stock is hinged so the flukes can orient toward the bottom and burry its self in the sea bed.
Danforth anchors are commonly used for smaller vessels such as row boats, small fishing boats, and rib boats. </li></ul>Photo: Danforth Anchor<br />http://www.photographers1.com<br />22/07/11<br />
The Admiralty Anchor is the most iconic anchor today. <br />The concept of the Admiralty anchor has existed for since the roman period with its major change being the size of them and a use of iron rather than wood. <br />Admiralty anchors are most commonly used by large fishing vessels. <br />It is considered by many mariners to have the greatest holding power, weight for weight, for all types of bottoms.<br />Admiralty Anchors <br />Photo: Admiralty Anchor<br />http://www.hansanchor.com<br />22/07/11<br />
Stockless anchors were developed in the nineteenth century, representing the first major change in anchor design in hundreds of years.<br />Stockless anchors have a significantly lower holding power to weight ratio then the Admiralty anchor.<br />They are praised for their easy storing ability because they are simply raised until the shank is in side the hawsepipes and the flukes are resting on the hull. <br />They consist of large heavy flukes and a shank with a shackle connecting to a chain . <br />Stockless Anchor <br />Photo: Stockless Anchor<br />http://www.photographers1.com<br />22/07/11<br />
Are known as permanent anchors because they keep a vessel in place for extended periods of time (for example marker bouys). <br />These anchors are only suitable for a silt or mud bottom, since they rely upon suction and cohesion of the bottom material, which rocky or coarse sand bottoms lack.<br />The holding power of this anchor can be from twice as much as it weighs to as much as ten times its weight when fully buried. <br />Mushroom Anchor <br />Photo: Oil tanker with mushroom anchor<br />http://upload.wikimedia.org<br />22/07/11<br />