You go backwards toward a "hole" in the front of the building.
You can see this "hole" as you walk up to the Maelstrom building.
From the boat, it doesn't really look like a "drop" but that's kind of the idea.
The fact is, if you don't look over your shoulder while you are moving backwards, you won't see ANYTHING behind you that even looks like a drop (or the "hole" for that matter).
Your backwards motion just comes to a stop near the "hole", the boat's position is "shifted" slightly and, in a few seconds, the boat moves forward and rolls down the "hill" into the "North Seas" storm scene (you pass through that scene in maybe, 10-20 seconds.)
imo it's a "baby" hill but my friend who is afraid of hills literally panicked and tried to climb out of the boat when we got to it ,i had truthfully forgotten it was even there or i would have warned her.( she kindly forgave me but we really had to grab her and pull her back down into the seat) so of course when we go now i get her something from Norway to remember the"fun times"
the backup part is more like a pause, you don' t see anything scary( maybe the back row does, don't know if i ever sat there)
so if you are like my friend and really really afraid of any drops skip it. however it's a fun ride so if you are just kind of afraid of big drops don't worry.
This is about right. Think of it as a "Y". You go forward from the base of the Y and turn a slight right, putting you on the "right" part of the Y shape. There is an opening to a waterfall (the same waterfall that is visible on the outside of the Norway pavilion) and the ride briefly makes you think you're going to go down it, but then you turn backwards (to the other side of the Y) by going down a drop no longer than the length of the 4-row boat.
In my opinion, the drop at POTC is much more significant than the one in the Maelstrom. And another thing to consider is that the POTC at DL is much scarier than the POTC at WDW, and the one in CA has 2 drops instead of one.