I worked with the last app that I wanted to try on the iPad last night. It's really designed more for design illustration/rendering than really "drawing" (think home interior sketches that you see when building a house). It did okay for some things, but I got a little derailed and the result wasn't all that good:
Recognizable, but not what I wanted. Total non-boating "doodle" here, but the app I did the sketch of the Silverine in is a pretty capable app:
And that painting of the eye is about 30" x 30" in a printable resolution (technically, so is the drawing of the Silverline).
These two aren't off the iPad. Someone mentioned Old Thompsons and Lymans earlier, and this is a sketch I did years ago (real pencil and paper):
And just 'cuz it's boats, one more of the City of Detroit III - an excursion boat that ran the Detroit River and my Grandfather remembered both being in the salon of (all mahogany) and getting in trouble for swimming under her keel while was at the pier:
So, kinda' a dumpy iPad drawing but I tried to make up for it with a couple of pieces from way back when.