When you are in a boat at full speed, you can not change the direction... just going straight.
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Comments 56

In 1.5.1 they can.
Can't be steered with "backwards" key either.
Most annoying thing ever. I'm afraid to play any of the snapshots on my survival game because of all the anoying bugs.
Confirmed

@Vaporizer: If I remember correct, that's been like this before the change in 1.6.
You are correct, I never noticed that it changed in 1.6. But I guess this is still a bug since it was possible to move a boat with just the A or D keys in 1.5. It currently seems broken, or at least very counterintuitive (or am I the only one to think this?) to require holding W or S while moving sideways. W should be forward, A left and both at the same time should be in between.
Like Vaporizer, I think boat controls should work at any time, not only when I pressing Forward or Back. I played since old 1.7.3 beta, and there it was perfect. But now in 1.6 it's been changed, for what?

... but making boats turnable only when having speed is more realistic ...
This has nothing to do with speed or realism just the controls that are needed to steer. Holding A should have the same effect as holding both W and A currently does in 1.7.1.
That's because boats cannot be steered by using the left and right keys.