Assuming that your game will not be scaled down more than 50% you might try to speed up the anim to at least 2 pixels per step. Maybe the effect is "less ugly" then
This method work perfectly with horizontal of vertical scene scrolling.
When I use this script :
There's a very strong aliasing effect.
But when I write:
No more aliasing. The scrolling looks good!
So I've tried the same method with the boat as you suggested.
But it doesn't work.
The aliasing is still there.
After watching closely to the scene, I've noticed the aliasing effect is visible even before the boat start to move.
Here is a detail of the boat at the original resolution:
And here is the same detail down-scaled (pixel perfect):
I have the feeling that all the oblique lines have that kind of distorsion when down-scaled (pixel-perfect).
I've added two simple squares to the scene so the effect is more obvious.
At the original resolution:
Down-scaled (pixel perfect):
Fortunately, this effect is almost unnoticeable when the objects are motionless because the lines are hand-drawn and irregular in my game.
It only becomes obvious when the boat starts to move.