Final Design

Major Components:

Buoy

The buoy, when released, floats to the surface of the water and it contains a spool of cable that unwinds as the buoy rises to the ocean surface. The cable is attached to the passive sediment sampler on one end and attached to the buoy on the other. When the buoy is located by the user on the surface of the water, the entire passive sediment sampler is hoisted up by the user via the cable.

Figure 1: Buoy

Pressure Housing

The final PVC pressure housing consisted of a PVC plug, a PVC O-ring union, a PVC pipe section, and a PVC cap. A PVC O-ring union was selected to ensure a watertight seal because of its robust, watertight performance during pressure tests and its ease of dis-assembly and re-assembly, which allows easy access to the internal components of the pressure housing. All other PVC sections of the pressure housing were joined together using PVC primer and PVC cement glue to ensure a watertight seal at all the regions of connection between PVC parts. In order to waterproof the opening in the pressure housing where the threaded rod protrudes from, an Ikelite gland was utilized, which contains an X-ring seal around the threaded rod and an O-ring seal against the pressure housing. All O-ring and X-ring seals in the pressure housing were lubricated with a silicone dielectric compound to ensure watertight operation.

Figure 2: Pressure Housing

Release Mechanism

The release mechanism consists of a motor and threaded rod. The threaded rod is initially engaged into internal threads in the buoy to hold the buoy in place during deployment of the passive sediment sampler. When initiated to release the buoy for retrieval, the motor will turn the threaded rod and unwind the threads engaged between the buoy and the threaded rod. This action displaces the buoy vertically upward and subsequently releases the buoy from the pressure housing to float to the ocean surface.

Figure 3: Release Mechanism

Cable Spool

Technora 250 was chosen to be utilized as the tether line between buoy and frame due to its ideal breaking strength, diameter, and cost. The strength of the line had to be sufficient to withstand the tensile load associated with hoisting the entire passive sediment sampler.The length of line required for a deployment depth of 15.25m (50ft) was determined to be approximately 46m (150ft) for the buoy to reach the water surface. A removable cable spool is used to wind the cable by hand or by using a rotary mechanism before attaching it to the buoy for deployment.

Figure 4: Cable Spool before being inserted into the Buoy

Electronics

The electronic components inside the pressure housing consist of a real-time clock, a microprocessor, motor driver, and battery. The real-time clock measures the time during the deployment of the passive sediment sampler. The microprocessor uses the measurement of the real-time clock to determine the moment when the buoy needs to be released. The duration of the deployment is programmed into the micro-controller before the passive sediment sampler is deployed into the seafloor. When the micro-controller detects that the time has been reached to release the buoy, the micro-controller will initiate the turning of the motor, via the motor driver board, to turn the threaded rod and release the buoy. A battery is present to power the micro-controller, real-time clock, motor driver, and motor.

Figure 5: Electronic components before being inserted into the Pressure Housing