Ship construction has rapidly evolved in the past decade owing to the advancement in science and technology. In the past, ships were designed by experts with years of experience in the industry. Beginning in the early 19th century, the science of hydro-kinetics and hydrostatics has taken over the industry, and the knowledge of materials and structures used in shipbuilding largely determines ship construction. This article provides step-by-step guidelines for the installation of marine machinery on ships and the machinery needed.
Marine Equipment and Machinery
The main equipment includes a main or propulsion engine, air conditioning, fire extinguishers, deck machinery, cargo handling equipment, stabilizers, refrigerators, electrical generation systems, control, and safety equipment, and other auxiliary machinery. The auxiliary machinery required for marine installation includes steering gear, deck cranes, heat exchangers, shafting compressed air, propellers ballast water arrangements, and sewage systems. The propulsion devices required for marine installation include propellers, podded and azimuthing propulsors, contra-rotating propellers, overlapping propellers, tandem propellers, controllable pitch propellers, and cycloidal propellers. You can use a Garmin marine radar that provides high-resolution radar images to your plotter. Advanced Garmin radars that provide sharp images with clear target separation have become a necessity today.
Here is the step by step guideline that explains different stages of marine machinery installation on ships.
1. Selection of Propulsion Engine
You should consider the key factors that influence the performance while selecting an engine. These include cost, maintenance workload, the efficiency of propulsion, size, and weight of propulsive machinery, and suitability for unattended operation. Another important factor that you must check before selecting an engine is the capability of an engine to burn poor quality heavy fuel without detrimental impact on engine components known as spare costs. The rating figure is indicated as bhp or kW per cylinder at a given rev/min that is an important indicator of a marine diesel engine.
Machinery installation is more than tightening the bolts and nuts or lifting and mounting onto the foundation.
2. Equipment Lifting
Before installing marine machinery on the ship, you should check that all the required machinery is available. The lifting equipment includes cranes, shackles, spreader beams, pad eyes with a capacity of 1.25 times heavier than the weight of equipment lifting. Here’s what you need to do before starting to set up the marine machinery installation process. To be on the safe side, you need to conduct a risk assessment on your machinery, before lifting, to avoid any accidents. Prepare a clear and concise lifting plan and share it with all your team members and make sure they understand the process fully. You should consider explaining each step with details by using diagrams and sketches for an explanation. While lifting rotating equipment without thrust bearing, you must restrict the axial movement of the rotor.
3. Positioning Of Equipment To The Foundation
You should place the machinery and driving unit on the same foundation. Analyze the rotating equipment dynamically while checking for vibration and ensure that vibrations are within the limit. To avoid resonance, you should consider selecting a foundation of relatively higher mass. There should be a sufficient number of anchoring points for your machinery.
Before the installation, you should shrink the fit bolts using liquid nitrogen or dry ice and then hammer it to the foundation bolt hole. The clearance between the bolt holes and foundation should be kept between 2-3 mm. Make sure that you tighten the bolts to the recommended torque value mentioned in the installation manual. For the steam system, all the bolts should be retorqued to avoid the effects of thermal expansion.
Two forces are known as tension force and clamping force come into action during bolt clamping. Tension force develops when the clamped component resists any further movement of the nut. The reaction force that compresses the component to be clamped is known as the clamping force. To calculate the pre-load, use the following expression
T = K X Db X Fp
K is the Nut factor
Db- bolt diameter and
Effect of lubrication on torquing
The torque- preload relationship shows that torque is affected by the nut factor which is related to bolt lubricant. You should not use any lubricant in the fasteners since we had calculated the torque for non-lubricated fasteners.
What is shimming?
You can use a stainless steel shim to fill the gap between equipment and foundation that is under 12 mm. for larger gaps, you can weld a double plate to level the foundation with the base plate.
What is chock fast?
Epoxy material is used for casting or in simple words to fill the gap between foundation and equipment. There are two types of chock fasts; orange should be used for precise alignment like in marine engines while grey is used for non-precise alignment, for example, heat exchangers.
4. Shaft alignment
The process of making a collinear axis for power transmitting elements is called shaft alignment. The vertical and horizontal distance between two shafts’ rotating axis is called offset while the angle between two rotating shafts measured as the slope is called angularity. You can also find relevant information about marine driveshafts on www.drivelinesnw.com.
5. Pipe installation
The next step in the installation of marine machinery is pipe installation. For pipe welding, do not use oxy-acetylene when the thickness of the pipe is greater than 12 mm. For copper or nickel pipes, use GTAW and GMAW. According to the guidelines API, 686, pipe and equipment holes should not be more than 1.5 mm offset. Place reducers in the suction line of the pump in an eccentric position that resists air pockets in suction. Use a long radius elbow in the suction line and a spectacle blind to isolate the inlet and outlet of the system.
Pipe hydro test: PH = 1.5 X P
PH = test pressure
P – design pressure
For working temperature above 300 degree Celsius,
PH = 1.5 X (s 100 / s) x p
s100=permissible stress at 100 degree Celsius.
s = permissible stress at design temperature.
The final step in marine machinery installation is commissioning. You should make sure that there are no foreign particles and all the pipelines are properly flushed and cleaned before commissioning. And lastly, don’t forget a quality assurance function test before commissioning and the system is ready. If you want to read more about marine electronics and installation, visit Marine Tech for all your queries.