Final Design

The BAI can be broken down into two distinct parts: the sensor unit, and the base station. The sensor unit is a mechanical system attached to a keel block. It interfaces with the ship’s keel during the drydocking in order to perceive the location of the ship. The base station is the human-facing part of the BAI. The data gathered by the sensor unit is displayed to the operator by the base station in an easily understandable manner. Each part is broken down into more detail in the following sections.

BAI Sensor Unit

Breakdown of BAI Sensor Unit

CAD of Arm Coupler

Arm Coupler

The arm coupler is a key mechanical component designed to enable rotational movement and house critical sensing equipment. It connects to an HDPE plate via a stationary stainless steel shoulder screw, allowing it to rotate freely around the screw. The coupler houses an inclinometer that measures tilt angles for misalignment calculations. A carbon fiber tube, secured with 3D-printed plugs, uses a 90° twist-locking mechanism to ensure a secure fit during operation. The coupler is designed with a 40° tilted mounting surface to adjust the inclinometer’s orientation, allowing for an upward range of motion of up to 85°.

TSDA Inclinometer Sensor

Inclinometer Sensor

A sensor that measures the angle of tilt or slope relative to gravity. The most common types of inclinometers use accelerometers to detect changes in gravitational acceleration along different axes and calculate the tilt angle accordingly.

CAD of Carbon Fiber Rod with Plugs

Carbon Fiber Rod 6Ft

The arm coupler contains a carbon fiber tube with 3D-printed plugs at both ends. These plugs enable a 90° twist-locking lug mechanism when inserted into the arm coupler, ensuring that the assembly remains securely attached during operation.

CAD of Release Mechanism

Release Mechanism Functionality

Located at the center of the frame is the centering / activation feature. The activation feature locks the arms horizontally and allows the operator to manually release them. It uses a pulley system to compress a spring and unlock a hook. During the drydocking operation, a cable is pulled by the operator, allowing the buoyant force of the carbon fiber rods to push up against the crossbar and activate the entire system. The whole process is shown in Figure 2.2. This is a one-and-done feature. Once the arms are released, there is no way to pull them back to their starting positions without having a diver manually do it.

CAD of Mounting Brackets

Mounting Bracket

Lateral and vertical traverse adjustable mounting brackets.

CAD of BAI System on Keel Block

BAI Sensor Unit Installed on Keel Block

The BAI sensor unit is attached to a keel block through the mounting brackets.. Two screws are all that is needed to firmly adhere the device to the block. The attachment points are slots to allow for adjustability during the attachment process. A bubble level ensures that the device is level when affixed to the block–this is critically important to the functionality of the device. If the device were to be installed askew, the calculated ship position may become inaccurate.

BAI Base Station

BAI Station Set Up

The operator can read the data on the base station or from the handheld receiver.

BAI Base Station

There are four main electrical components: the power supply, the uninterruptible power supply (UPS), the battery backup, and the data processing unit. The power supply accepts an input voltage of 120-240V AC through the plug / breaker installed in the case and outputs 24V DC. The output goes to the UPS, which is connected to both the data processing unit and the battery backup. If the power to the power supply were to be interrupted, the UPS seamlessly switches to the battery backup to ensure the data processing unit is always on. The data processing unit is connected to the data cable from the BAI sensor unit through the installed ethernet port in the case.

BAI Base Station Electrical Assembly

The battery backup is two 12V lead-acid batteries wired in series. This ensures the UPS receives the required 24V. The battery backup has enough energy to power the base station for up to 52 hours if required, more than long enough to complete a drydocking. Figure 2.6 illustrates how each component is wired together. The input breaker routes 120V AC into the Power supply. The Power supply converts that into the 24V and gets routed into the UPS Module. The UPS Module is a switchover device with integrated battery charging, meaning it charges the batteries with 24V, and outputs 24V from the battery or the power supply depending on if the power supply is on or not. The 24V from the UPS is routed into the LILYGO® T-Connect Compute unit. The LILYGO® sends and receives CAN signal from the sensors, and sends 24V to the sensors over the modified ethernet cable.

Handheld Receiver

LILYGO Receiver

The base station is able to broadcast the misalignment data to a handheld device, allowing the operator to be mobile if required. The screen will display the transmitted misalignment measurement data in inches, along with arrows indicating whether to move the vessels to the left or right. When the vessels are centered in the BAI system, the transceiver will display the word "Aligned."

System Performance Summary

The project successfully addressed the critical need for an automated, real-time alignment indicator system to improve the precision and efficiency of drydocking operations. The team developed the Block Alignment Indicator (BAI) system, featuring a rotating contact beam sensing device that directly mounts to dry dock blocks. This system utilizes two waterproof inclinometers to measure angular deflection from ship contact, sends information via CAN signal to a water resistant base station with an integrated microcontroller to compute lateral offset, and transmits offset information wirelessly to handheld devices with LoRa. The system is fully waterproof and was successfully tested in an underwater environment, confirming its reliability in real-world marine conditions. More detailed testing and explanations can be found in the Final Report.

Ultimately, the developed prototype meets the project's primary objective of accurately detecting vessel misalignment within a ±0.5-inch margin, enabling precise centering during drydocking. The BAI system offers a viable, data-driven enhancement for current drydocking procedures, with the potential to significantly improve precision, reduce dependence on divers, and decrease overall alignment time.

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