MTC
Anchor Handling Course
The way to break the anchor loose of the bottom is therefore:
Slowly to increase power in a direction away from the rig (pull the anchor out backwards) until the above mentioned “breaking loose force” and then holding this power to let the under pressure or “suction force” be reduced / equalised so as to ease the break out.
If the anchor is not loosened after 30 to 40 minutes (a mater of estimate), then slowly increase 10% and so on.
An example from the North See:
The anchor was buried 60 meter. Maximum allowed tension on the system, 130 T.
The AH-vessel used 18 hours to break loose the anchor – but it came, without breaking anything.
Changing the heading of the vessel might also help to break the anchor loose, but before this is performed it has to be verified with the rig, as going off line with the vessel gives a high risk of bending the shank of the anchor.
The forces on the wire might be considerably increased if there is significant swell as the boat heaves up and down.
It is very important during the “Breaking loose operation” to keep the actual tension on every piece of equipment in use, i.e. wires, swivel, connecting links and winch, below allowed maximum working load.
Below is a bad example of a written procedure about how to retrieve the anchor:
“When the boat has the chaser at the anchor, it will increase power and maintain app. 50% bollard pull for 15 minutes. If no appreciable forward movement is recognised, the boat will reduce bollard pull to 30% and
shorten work wire length to water depth plus 30 meters!
The boat will break the anchor off-bottom by increasing power until the anchor is free from the seabed but will exercise caution not to exceed 200 metric tons work wire tension unless approved by the rig’s OIM and or barge master.”
As mentioned in the Vryhof Anchor Manual:
“Anchors in very soft clay can be buried very deep. Have patience, take your time and be gentle with the equipment; the anchor will come.”
M:\ANCHOR HANDLING\Course Material\Training Manual New\Chapter 11\Breaking the anchor off the bottom.doc
Chapter 11 |
Page 3 |
Anchor deployment, example of
DANMARK |
Polaris |
1 |
|
JK MultiMedie |
+45 6474 1995 |
Anchor deployment, example of
• The Maersk Trainer will back up to rig.
• Rig passes over PCP to deck of the Maersk
Trainer using rig crane.
AHTS backs up to rig to recieve PCP on deck
POLARIS |
DANMARK |
|
POLARIS |
AHTS
PCP MAERSK TRAINER
15 mt (w/ chaser) Stewpris anchor
2
JK MultiMedie +45 6474 1995
15 mt
3" dia. work wire
(~1638 m outboard) 3 
Anchor deployment, example of
POLARIS |
DANMARK |
9
JK MultiMedie +45 6474 1995
vryhof
anchor manual 2000
1
ACCREDITED BY
THE DUTCH COUNCIL
FOR CERTIFICATION
Reg. No 24
ISO-9001CERTIFICATED FIRM
DET NORSKE VERITAS INDUSTRY B.V., THE NETHERLANDS
Copyright
© Vryhof anchors b.v., krimpen a/d yssel, the netherlands 1999.
No part of this book may be reproduced in any form, by print, copy or in any other way without written permission of vryhof.
Vryhof, Stevin Mk3, Stevpris, Stevshark and Stevmanta are registered trade marks.
Vryhof reserves all intellectual and industrial property rights such as any and all of their patent, trademark, design, manufacturing, reproduction, use and sales rights thereto and to any article disclosed therein.
All information in this manual is subject to change without prior notice. Vryhof anchors is not liable and/or responsible in any way for the information provided in this manual.
First edition published 1984. Print run 7,500 copies.
Second edition published 1990. Print run 7,500 copies.
Reprint second edition print run 5,000 copies.
Third edition published 2000. Print run 2,500 copies.