My recommendation doesn't hit all of your points, specifically the Gaff rig element.
I had a trailer sailor for some time and my biggest obstacle to getting out sailing- by far, wasn't launching it, or trailering it or weather
. It was stepping the mast
, especially if you will be alone.
Based on that, I would suggest something fairly small with a lightweight aluminum
rig. The smallest Hunter
, the 15' seems to meet most of your criteria, I'm not sure any Gaff rigger would be very easy to rig for an afternoon sail.
A 15 should be big enough to keep you dry, carry a couple of freinds, even carry some camping equipment
and an outboard
if you desire.
Just writing this response is making me want to load a dinghy
up with camping gear
and go sailing in the desert.
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