R’ Tuvia Singer states that as an experienced diver, he dived in the Red Sea as well as throughout most of the world (save for the Muslim countries). He points that the Red Sea has a flat drop wall dive (a boon for divers so they don’t have to walk too far in) of between 8,000 – 10,000 feet, being one of the deepest points in the world to dive. In other words, if the Jews crossed in those spaces, assuming that the sea was cleared, there would be a cliff which the height would have been the equivalent of some skyscrapers today. You would need a helicopter to pass through!
This holds true for every part of the Red Sea save for one spot: the Gulf of Aqaba where Nuweiba Beach is located. That spot is only 60-70 meters deep. He also mentions that when a ferry passes by there’s a huge surge due to the turbulence caused by water current banging on the relatively high wall, such that you would need to tie everything down to prepare for it as the ship will violently shake as it passes. As a result, passengers can get very sick from it.
The wheels and axles encrusted in coral also help.