Prismatic Coefficient

What Hull Shape Is Best?

Back at the dawn of maritime history, a coastal dweller first took a log and ventured out on the water. Over time his craft evolved from a rough log to one that had shape at the ends and was hollowed out. These changes to the basic log shape were the first example of modifying a hull form to increase carrying capacity, improve ride comfort, and to reduce resistance. Since then, shipbuilders, naval architects, and ship owners have experimented with hull shapes and the number of hulls to find the "best" design. Let's look at some of those variations to understand the challenges of choosing a hull shape. Monohull Design The basic monohull can be defined by six key numbers: length, beam, depth of hull at midships, design draft, prismatic coefficient, and displacement. Length, beam, and draft are familiar to everyone. Depth of hull at midships gives an idea of the freeboard as well as an indication of the hull strength in bending. The prismatic coefficient is a measure of how much shape there is in the ends of a hull. A high prismatic coefficient means that the ends are full such as a tanker bow. A low prismatic means that the ends are fine, with little volume, such as a tugboat stern. The choice of what dimensions to use depends on the intended use of the vessel. For a passenger vessel, there are considerations of carrying capacity, operating environment, and type of operation

Safety: Slip and Fall Accidents in the Marine Environment

Because the exposure to the marine environment and motions of a vessel, slips and falls are a significant source of personal injuries in floating equipment, probably substantially greater than most industry groups. Although there are a good number of publications, books and articles written regarding the subject of slip and falls, there are almost none addressing the conditions found in a marine environment, which influence slips and falls. Consensus

RoPax Propulsion Concept Proves Efficient

Wärtsilä, in conjunction with the Finnish research project SEATECH 2000+, has been developing some new machinery solutions for RoPax vessels. A promising concept is a semi-diesel electric machinery, where mechanical propulsion is combined with a diesel electric power plant. This new RoPax concept was presented for the first time at the Europort 2001 exhibition. The RoPax vessel has a semi-diesel electric machinery featuring a diesel mechanical part driving a conventional CP propeller and a

MHI LNG-FPSO Approval for Two Tank Types

Mitsubishi Heavy Industries, Ltd. (MHI) completed development related to floating production, storage and offloading units for liquefied natural gas (LNG-FPSO), and has obtained two kinds of approval in principle (AIP) from major international ship classification societies. In tandem with intensified activity in medium- and small-scale offshore gas field development, demand for LNG-FPSOs, a new method of gas production offering movable capability, has been increasing globally

DSME's New LNG Tank Technology Approved by LR

ACTIB ((Aluminium Cargo Tank Independent Type B) tanks - prismatic, large, independent cargo tanks -  reduce sloshing, suitable for LNG containment The ACTIB tanks, constructed of insulated aluminium 5083, will have the world’s largest storage capacity in an independent, insulated LNG tank system. The volume capacity in the initial design will be nearly three times larger than comparable types currently in operation.

DSME Technology Approved by LR

ACTIB tanks, prismatic, large, independent cargo tanks, will reduce sloshing and are suitable for widespread use for LNG containment.   Lloyd’s Register has approved new prismatic IMO Type B independent cargo tanks, so called ACTIB (Aluminium Cargo Tank Independent Type B). The initial approval is for use in a DSME-developed 210,000 m3  STD LNG-RV design in accordance with LR’s Guidance notes for liquefied gas carriers and floating offshore installations adopting IMO

Teekay Builds on its LNG Service Offering

Teekay has purchased two unique liquefied natural gas (LNG) carriers that, in future, may help its customers develop smaller gas fields and open up markets that were previously inaccessible. Teekay acquired two specialized LNG carriers. The Polar Eagle pictured here has been renamed the Polar Spirit. He says the SPB (Self Supporting Prismatic shape IMO Type “B”) cargo tank is a robust design which has been likened to “an egg in a carton

Gas Ship Facts: LNG Fast Facts

LNG (liquefied natural gas) is natural gas, primarily methane, which has been cooled to its liquid state at -260°F (162.2°C). Liquefying natural gas reduces the volume it occupies by more than 600 times, making it a practical size for storage and transportation. LNG (the liquid itself) is not flammable or explosive How is LNG shipped? • Specially designed ships are used to transport LNG to U.S. import terminals

Lloyd’s Register and GTT Reveal LNG Study Results

Lloyd's Register and Gaz Transport & Technigaz (GTT) have jointly commissioned MARINTEK to carry out a series of model tests to investigate the effects of sloshing in partially filled prismatic LNG tanks. A typical four-tank ship design with a capacity of 140,500 cu m has been used for the purposes of the study. For the moment, the results show that: for the filling levels below 10% of tank length and over 70% of tank height the tests showed good results

Steerprop CRP Model Tests Confirm Efficiency

Steerprop is now taking one step further, improving the efficiency still by introducing the dual-end CRP propulsor. As a part of the ongoing research and development process of the Steerprop propulsor technology, Steerprop Ltd. recently conducted a series of model tests at Krylov Shipbuilding Research Institute in St. Petersburg, Russia. The Steerprop dual-end contra-rotating propulsor configuration was tested in both the towing tank (open water tests) and in the cavitation tank.