Above: For a proper wharrl- hunt you also need nhorrmal wharrls. This here is a blue wharrl (on the left the top side, on the right seen from below).
A blue wharrl is about as big as a norrmal cheap umbrella with sawn- off stick and screwed- tight slider that somebody has glued cloth and foam- spikes on, then painted it with acrylics...
Never use only one colour- the “blue” upper side for example is not blue at all but shaded blue/ black.
The 2- part-bottom is designed to host a cheap bathing ring to keep the thing on the surface after being thown overboard. The plastic- strips hang out from the middle for a jellyfishlike touch.
*= 500- year- old german expression for “Good fishing!”