Monday, March 9, 2015

Magnetic DP Ship Thrusters
American Admiralty Books Safety & Privacy Policies   
 Image: U.S.Minerals Management Service The Illustration above is of a Mobile Offshore Drilling Unit or MODU on your left and a drill ship on your right. You'll note that the MODU is held in position by multiple mooring lines leading to anchors on the sea floor. This is not always the case with MODUs but it illustrates a point in our discussion. The Drill ship on your right by contrast has no mooring system. The scale is too small to illustrate the thrusters but the ship is Dynamically Positioned (DP) using thrusters. Generally the thrusters would consist of four rotatable propellers mounted on each corner of the hull. An electronic position indicator on the well head tracks the relative position of the hull above the well head and feeds that information to an on board computer that controls the thrusters. Thus the hull, though having no mooring lines attaching it to the seafloor, none the less maintains a constant position over the well head on the sea floor. DP technology has been around more than twenty years and appeared in advance of the move off shore into waters so deep that the multiple physical moorings of shallower water weren't practical. DP
technology makes the hunt for oil in "Deep Water"viable.


American Admiralty Books Safety & Privacy Policies   
Retractable DP thrusters by Thrustmaster, 

 Since the advent of the DP system there have been a variety of improvements. Some have been to the thrusters themselves and others have been in the electronic positioning and control systems. Pictured above is a subsurface view of a drill ship depicting the thruster elements. The illustration above is from Thrustmaster a company that provides an innovative retractable thruster. Rotatable thrusters allowed fewer to be used, Retractable thrusters like Thrustmaster's allow the thrusters to be retracted inside the hull creating a more hydrodynamic hull form and allowing for safer and faster transits between drill sites in a business where time literally is money.

 The general trend towards miniaturization manifesting itself in so many areas today had an effect on the DP system market as well. Smaller sized units could be utilized on the small offshore service craft that bring crews and supplies to the drilling vessels and rigs. These boats must "live boat" , that is maintain station adjacent to the rig plumb under the cargo crane's cargo whip. Being highly maneuverable twin engine craft skilled captains were able to perform this task with differential throttling and rudder movements in a reasonable range of sea states. But few captains could produce the results now available from small scale DP systems.

File:Toisa Perseus&Discoverer Enterprise.jpg
Photo: PD Offshore Service Vessel of the Type that can now use DP systems, Drill ship in background

American Admiralty Books Safety & Privacy Policies   
 Today we bring our offshore oil industry professionals news of yet another refinement in the available DP system options. OCEANHUB  recently released the story of magnetic thrusters. The magnetic thruster is a new technology related to the thruster propeller drive and transmission system. As we understand it, the overall thruster size below the water line remains dictated by the propeller design which is related to the amount of thrust needed. The size reduction is in the hull space needed for the drive and transmission systems since the magnetic thruster is almost self contained within the the Thruster's propeller cowling. We'll let  OCEANHUB explain the system since their article which is very informative is also copyrighted. We just wanted to draw the attention of our OSV professionals to the post at and introduce our more casual readers to the concept  not only of DP technology but also of "Industrial vessels", vessels manned by our Merchant Mariners that do not primarily earn revenue by hauling cargo or passengers, the usual layman's image of the "American Merchant Marine." These increasingly complex ships small and large perform work in the marine environment. Often the work is related to the extraction of mineral resources but "work" also includes building submerged pipelines, supporting aquaculture, salvage, marine construction like building platforms and wind farms,supporting oceanographic research and simply maintaining ocean infrastructure.

 The concept of "ocean infrastructure" is hardly thought of by laymen. As recently as 1948 once a ship was off the beach and out of sight of land it was out of sight of any human activity or habitation. In the same decades that brought us the international space station American Merchant Mariners and Petroleum engineers have literally colonized a offshore area the size of Africa, America's Exclusive Economic Zone and Outer Continental Shelf waters. Twenty four hours a day, seven days a week not only are humans now constantly present in space aboard the space station, but thousands are at work, living and sleeping aboard platforms, artificial islands and industrial vessels at sea. American success on the Outer Continental shelf has fueled success elsewhere such as Europe.  Off of Africa and in the China Seas progress is slowed by politics. The Politics of the Exclusive Economic Zones was immaterial before technological progress led mostly by Texas and Louisiana based innovators made the literal colonization of the continental margins possible. This is a success generated by private enterprise, at a profit, from private investment but it has improved the government treasuries of the adjacent coastal states because these newly colonized areas are in the commons, so extractive industries must obtain licenses from the adjacent coastal states. The American media is fast to be critical of the industry when accidents happen. But the popular media has never simply brought the public the story of this stupendous feat of mankind, The colonization of the ocean. Manned space flight, largely a government endeavor and moving very slowly gets attention and adulation from the media, Manned ocean industries bring benefits to mankind every day and were an even more strenuous endeavor in mechanical and electrical engineering,electronics, computer science , naval architecture, and hydrodynamics. We're hardly NBC but maybe at least our few tens of thousands of readers will become more aware of story of ocean progress and more cautious  of government plans to control things.   

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