When ships’ hulls are exposed to seawater for a long period of time, barnacles and algae begin to grow rapidly on the ships’ hull. This can harm the performance of the boat and cause long term damage. The accumulation of these unwanted organisms is called fouling. In order to prevent the growth of the fouling, scientists developed anti-fouling coatings to be painted onto the hulls. These coatings emit small trace metals, making it an unfriendly living environment for barnacles.
Our sponsor, Patrick Earley, works at the Environmental Science Division at SPAWAR. He and his team are in charge of investigating more environmentally safe paints as well as monitor current anti-fouling paints being used in the Navy. To test whether or not the coatings emit the correct amount of trace metals to hinder the growth of unwanted organisms, the leach rate is measured. This is the measurement of the concentration of metals released per volume of water per time. The procedure to measure the leach rate is slightly complex and will be discussed further in the report, but one of the necessary steps is to gather water samples while the hull is submerged underwater. The system our sponsor currently uses to gather these samples is called the In Situ Anti-Fouling Testing System. This system consists of three main components: a dome which is fixed to the testing surface, a peristaltic pump and 50 ft. Teflon tubing connecting the peristaltic pump to the dome
This system, however, has two primary faults. One being is the system requires manual operation throughout the whole procedure to gather the water samples and document the pressure changes in the system. The second fault is the dome structure, which was poorly designed. The 20+ pieces that make up the dome are prone to fractures which cause water leaks and result in contaminated samples. Therefore, the primary objectives of our project include automating the sampling process so that minimal user interaction is required, and to ruggedize the dome structure so that it is less prone to failure.
After fifteen weeks of planning, fabricating prototypes and testing, the student engineering team has designed the 2nd generation In Situ Anti-Fouling Testing System. The team has introduced the “Five +1 Sample Collection Manifold”, which is used to automatically collect up to five samples over a period of one hour. The new design utilizes six solenoid valves attached to a polycarbonate manifold to control water flow and collect the samples. A microcontroller was implemented to operate the solenoid valves and to eliminate manual labor. The controller and circuit board are placed into a control box, which is operated by the user via a OLED display and four buttons.
To address the problems of the dome, a simpler, three piece design was constructed. This was constructed from three 14” diameter acrylic rods. It was fabricated using a CNC machine, since alignment of all three pieces prior to gluing them together was necessary.
In terms of cost, the team had an internal budget of $1,000 and a $1,500 usage fee to the machine shop. During the first few weeks of researching design solutions, it was quickly learned that the cost of equipment for the new design was going to be way over the given budget, therefore an external budget of $3,000 was provided by the Environmental Sciences Division. The final design and prototype used all $5,500 of the budget. A brief analysis was made to determine the savings in labor costs of the new system and it was found that within 3 months of implementation, it would pay for itself[1].
[1] Patrick J. Earley. Patrick.earley@navy.mil. Wrap-up of Project. June 8, 2012.