The Plank was still an unfinished item, and will stay so since development has ceased. It had the same function as the Gem stone of Mani.
The <plank of Carneades> (a plank of when unidentified, seems to be a translation error of a sort) is a shield found in the Elona+ mod of Elona. It has a unique sprite. It may be found in the inventories of Theif guild member and Fisherman (a 1/200 chance).
|It weighs 0.5s.|
|It is made of wood.|
|It is precious.|
|It modifies DV by 1 and PV by 1.|
|It makes you better swimmer. [###] (+10)|
|It increases your Constitution by 9.|
|It sometimes nullifies the damage you take. [#####+] (400)|
|Note: attributes may vary depending on luck.|
|A slab of wood that was used for a ship.
A piece of the Queen Sedona, which was sunk due to the Ether Winds. It can be used as a shield, but doesn't provide reliable defense. It floats, but can only support a single person.
～Irva Fantasy Encyclopedia～
The sprite for the plank is located at row 21, column 9, at position 702.
- The item is apparently referencing a philosophic term explained here. Typos in the swimming description are how it looks in the game.