Yachtie Pottie.
Or... Yachtie Pottie Pumper
Or... Yachtie Pottie Pumper Doo
Or... Stinkpot
Or... Baby Ruth (Reference to Caddy Shack) Nobody will get it which is actually a good thing.
Name on the transom... This Really Sucks...Seriously
More realistic and descriptive... Potty Pumper
I would put a big windsock or
windvane on it with an arrow pointing upwind that says... <-- Pass this side.