Tattoo's first night on the water was in a cove protected from waves but somewhat exposed to the wind. She "sailed around her anchor" all night long. It seemed that she would make a wide arc of almost 180 degrees from one side of the anchor to the other. I tried changing the scope of the rode, CB down / up, tiller lashed and/or let go. Nothing seemed to stop it.
So, I'm going to try a "staysail" that isn't actually on a "stay" but held up by the peak halyard (to its head) and a line (from its clew) through the fairlead at the end of the boom (which when sailing anchors the outhaul) with its bitter end belayed to the transom. A line from its tack goes forward over the top of the gaff and is belayed to the mast. The luff is stiffened with a 1/4" x 1.25" wood batten. It won't take up much space when not in use. Hope she works. I'll report after Tattoo's next time at anchor. If any of you have experience with stabilizing sails (while at anchor) let me know if you consider 4.5 sqft sufficient for a boat like PocketShip. I haven't made the sail yet, so I could still make it larger or smaller.
Note that Tattoo's gaff was made longer by about 8 to 10 inches than the design length. With the extra length the gaff extends just beyond the gallows. There is a short "crutch" that straddles the boom and raises the gaff by about 6". That holds the gaff on the certerline and provides enough space under the gaff to furl the sail [to it] and also provide a little more head room under the tent that I spread over the gaff. So -- I have a "gaff" tent rather than a "boom" tent. The crutch is stowed in one of the coaming "side pockets."