Page 120 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

108 CHAPTER 5 Vehicle Design and Stability
deployment resources/platform, and operational requirements. This chapter will address the design and stability of an ROV. Chapter 8 will address the principles of tether design, integration, and management since they can help create (or destroy) the perfect ROV.
5.1 Vehicle design
The overall mechanical design of the ROV is driven by the job it has to accomplish and the condi- tions it is expected to work within. It is essentially a “truck” to transport a payload to a location. This could be any number of items including a camera, sensor, manipulator, and/or tool to the worksite and be stable enough once on-site to perform the assigned task. The various payloads and onboard equipment that the ROV may use are discussed elsewhere in the manual. Needless to say, the payload must be designed to be integrated with the vehicle or attached to it (such as using a tool skid mounted below the vehicle). With that in mind, the designer’s goal is to “connect the dots” between payload, thrusters, pressure vessels, tether, etc., and create a stable, maneuverable platform. The dots are connected with the vehicle’s frame. Buoyancy is then added to float the hardware and stabilize the system. The tether is then integrated with the vehicle, its effect often overwhelming many of the carefully designed aspects of the vehicle (see Chapter 3). These key areas will be discussed in the following sections.
5.1.1 Frame
The frame of the ROV provides a firm platform for mounting (or attaching) the necessary mechani- cal, electrical, and propulsion components. This includes special tooling/instruments such as sonar, cameras, lighting, manipulator(s), vehicle/payload sensors, and sampling equipment. ROV frames have been made of materials ranging from plastic composites to aluminum tubing. In general, the materials used are chosen to give the maximum strength with the minimum weight. Since weight has to be offset with buoyancy, this is critical.
The ROV frame must also comply with regulations concerning load and lift path strength. The frame can range in size from 6 in.36 in. (15 cm315 cm) to 20 ft320 ft (6 m36 m). The size of the frame is dependent upon the following criteria:
• Weight of the complete ROV unit in air
• Volume of the onboard equipment
• Volume of the sensors and tooling
• Volume of the buoyancy
• Load-bearing criteria of the frame, in many cases requiring shock resistance
The benefit to today’s engineer is that computer-aided design software makes the job of design- ing the frame much easier. However, ignoring critical design details can cause problems in the long run. Additional things to consider include:
• Requirement for cathodic protection systems
• Attachment points for ancillary tools or tool skid
• Effect of manipulator and/or tool movement on stability