Propulsive Efficiency , trawlers & ligth tugs (recopilation, shipyard workshop)

Here I publish everything that must be known in propulsive terms to design a trawl and/or light tug, according to the parameters expressed in the chart (data source)
This is the summary of my experience in 20 years of work
I hope it will be useful to young naval architects

Ruder Stock Repair

RUDER STOCKS REPAIR (IACS RECOMENDATION #55 BASED)

Repair of rudder stocks/pintles by weld cladding Rudder stocks and/or pintles may be repaired by welding replacing wasted material by similar weld material. After removal of the wasted area (corrosion, scratches, etc.) by machining and/or grinding the build-up welding has to be carried out by an automatic spiral welding according to an approved welding procedure. The welding has to be extended over the area of large bending moments (rudder stocks). In special cases post weld heat treatment has to be carried out according to the requirements of the Classification Society. After final machining, a sufficient number of layers of welding material have to remain on the rudder stock/pintle. A summary of the most important steps and conditions of this repair is shown in the Figure (Lower). In the case of rudder stocks with bending loads, fatigue fractures in way of the transition radius between the rudder stock and the horizontal coupling plate cannot be repaired by local welding. A new rudder stock with a modified transition geometry has to be manufactured, as a rule (See Example 1). In exceptional cases a welding repair can be carried out based on an approved welding procedure. Measures have to be taken to avoid a coincidence of the metallurgical notch of the heat affected zone with the stress concentration in the radius’ area. Additional surveys of the repair (including non-destructive fracture examination) have to be carried out at reduced intervals.

IACS document solution (help&guide)

Need assistance in new building inspection or existing repair ships ?
Take a look at this nice guide

http://www.iacs.org.uk/document/public/Publications/Guidelines_and_recommendations/PDF/REC_47_pdf193.pdf

or

http://www.iacs.org.uk/document/public/Publications/Guidelines_and_recommendations/PDF/REC_55_pdf695.pdf

Advanced Technology of Propeller Shaft Stern Tube Seal (Yamajo & Matsuoka-SNAME)

The paper outlines the details concerning historical perspective and recent developments to meet a requirement that lube oil and seawater leakage must be prevented under any circumstances. Using a compressed air chamber, the lube oil in the stern tube is completely separated from seawater by providing a controlled “buffer zone” between lip type sealing rings. A constant quantity of compressed air supplied from within the ship, passes through the air chamber and is spouted into the sea. An air control unit automatically detects any change of draft level and adjusts the pressures to maintain the optimum pressure on each sealing ring. The key mechanism to detect the draft change correctly and to adjust the pressure balance is explained. Specific design and project applications for the stern tube air seal on ocean going and other marine vessels using line shaft propulsion and pod propulsion are explained.

Folow at:
http://www.kemel.com/product/pdf/SNAMEAirSealFinal07_30_03.pdf

Efficient propeller Designs based on Full scale CFD simulations

(By N.W.H. Bulten, P.W. Stoltenkamp, J.J.A Van Hooijdonk // Wärtsilä Propulsion, R&D-Hydrodynamics, Lipsstraat 52, 5151 RP Drunen, The Netherlands )

In order to be able to further enhance the performance of ship propellers, the possibilities of full scale numerical flow simulations have been investigated. The aim is to get a full understanding of the occurring flow phenomena on the actual ship. With this knowledge the optimum propeller design can be made. During the validation process a critical review of the model scale measurements methods has been made. The validity of some of the commonly used procedures has been evaluated. The use of full scale CFD simulations provide direct full scale data on the hull wake field and the propeller performance. It has been shown that the commonly used extrapolation methods predict different answers. Decomposition of the forces acting on the hull, the propeller and the rudder is being used to get a proper insight in the flow field at full scale. In the end the design features which contribute to efficiency increase, and thus fuel consumption reduction, can be isolated, based on the results from detailed flow simulations.

Follow this interesting paper at :
http://cdn.wartsila.com/docs/default-source/product-files/gears-propulsors/propellers/white-paper-o-p-2014-efficient-propeller2287854a7f0f601bb10cff00002d2314.pdf?sfvrsn=4