For the slip ring anchor, slowly lower the anchor into the water, so the ring stays at the top. I used to have one of those, and a couple of times when I "chucked" it in the water, the ring stuck at the bottom of the anchor and it just drug.
Agree with the others, bit of chain, proper scope and set the anchor.
That 11# anchor should be sufficient for your 18.5' boat. I have a 9# Danforth on my 18'er and like it.
I buy the tow chains from harbour fright 14ft. cut in half and have two anchor chain setups
I did the same, but used one of their 5/16" 20' chains and lopped 7' off one end for the stern anchor, then 13' for bow anchor.
If fishing deep, 100+-', I'll drop all 20' of chain out the bow. Just breezy, I don't have to run any scope on the anchor line, just enough out so I can feel the chain end bouncing, with the anchor line vertical. When the wind picks up, let out anchor line ...