In order to hold the interpretation I have suggested in verse 12, verse 13 must be read that they didn't know the correct places to steer the ship. It is much more likely that they made an attempt to at least hold the course rather than sitting back in amazement that they didn't know where to go. This also gives a little more meaning to the "insomuch that there arose a great storm." The phrase appears almost causative, yet it is hard to see how indecision could cause a storm. It is very likely, however, that not knowing how to steer to avoid the storm would allow them to be caught in the thrall of it.
It should be remembered that it is likely that the Lehites set sail during a monsoon season, when it is certainly not unusual for such a storm as is described.