Design Notes

The design for the initial prototype is tentative only. It is part of an ongoing, iterative process. Any images should be considered working sketches only.

Initial Concept

The basic skimmer concept as first envisioned resembled an inverted cow-catcher. Instead of directing cows away from the front of a locomotive, it would be straining the waters and directing the catch toward the pocket like a cross between a giant litter scoop and a catcher's mitt. From there it could be lifted out for further processing.

Key Considerations

Propulsion

Wind power is the natural choice for propulsion on this project. It's a choice with a relatively small environmental footprint that is both familiar and accessible to people around the world. The cost of fuel is, for the most part, limited to the cost of sails and rig maintenance.

Drag

Drag is the primary limiting factor for the design. Any surface area in contact with the water will create additional drag. Even towing a typical dinghy can result in a modest drop in speed when under sail. The total drag from the system will need to be limited and controlled so that it doesn't overload the available wind power and bring operations to a halt.

Overall drag will be limited by minimizing drag from each component as much as possible. Fine entry points and narrow, thoughtfully-spaced components will limit the need to bulldoze through high-pressure entry waves. Foil shapes will further help by minimizing turbulance. Removing the catch from the water at the earliest opportunity will limit its drag effects as well.

The remaining drag from the system will need to be controlled to make operations manageable. The simplest way would be to make the skimmer retractable. This makes the depth of the skimmer and its resulting drag adjustable. Just as importantly, it could be lifted out of the water altogether as needed. This should allow for a variety of operating techniques to improve overall efficiency.

Biocatch

In the pursuit of a plastic catch, it's important to guard against a biological one. Ideally, we would be able to remove plastics while leaving plant and animal life unharmed. Slow speed operations as expected under sail should give fish the opportunity to swim free while retaining the plastics.

Plant life may prove a little more difficult to avoid. One potential approach involves the use of a leader comb to try pushing plant matter far enough under the surface for the skimmer to pass over. The skimmer itself would then be set back far enough aft to give plastics time to rebound into the catch zone (assuming the plastics would return to the surface faster than plants). A leader comb would introduce more drag, but if effective might be worth the extra effort. Only testing will tell.

    Key Terms
  • "secured" - purchased, registered, insured, required safety equipment, reasonably confident it won't sink.
  • "minimally functional" - safely sailable, working auxiliary power, functioning head and galley.
  • "initial prototype" - a prototype towable skimmer.
  • "minimal projected budget" - it might take more, but I don't think I can do it for less.