Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.
At first I thought it was an emergency flag, but judging by the split in the right side and the size, I'd guess it's a boom tent. The rear stay would go in the split, it would be draped over the boom, and the sides would be tied down to the stanchions or life lines to give you some shade or rain protection while at anchor.
Nice finding useful items, especially when you can figure out what they're used for! I had Defender make me a boom tent that I mainly use at anchor if it starts to rain, but I've also used it in the blazing sun.
I found one of those in my boat as well....canvas and pretty yucky, but I laundered it up and it came out really clean and nice. Mine also has a loop in the middle for the main halyard to hoist it up, and the long sides have a hem that a pole inserts into. (explains the 2 small aluminum poles with my whisker pole)
Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.