Simple early game kelp farm with minimal cost.
The schematic does not include the glass walls shown in the screenshot, an extraction method for the contraption or a way to turn the contraption.

This schematic is intended to be placed at the bottom of an ocean or similar deep expansive water source. The saws will harvest the entire kelp stalk.

An extraction method would be as simple as adding a portable storage interface, a hopper beneath it and a chest under it. Or you could move the kelp to your base some other method like a bubble elevator.

A way to generate rotational force should be placed below the bearing like an encased fan facing into a heat source. This was not included in the bearing as it would add a lot of dirt to the blueprint and people may decide to plant the kelp on a different material like gravel or rich soil.

Walls not included as they are not needed on the bottom of the ocean.