Then he went into the tank-room and instantly saw what was the matter.
It gave him a shock.
The outer lining of the tank had become perforated, and water had flooded the forward compartment.
This was of sufficient weight to hold the boat in suspension.
It could be sunk by letting water into the tank as usual.
But though the tank was emptied as readily as usual, it was not sufficient in buoyancy to carry the boat to the surface.
In other words, the extra water in the forward compartment overcame this needed buoyancy and held the Dart in suspension.
It was most unfortunate that the water had invaded this part of the boat.
Frank was bathed in a cold perspiration. He knew that it was impossible to expel this water by any ordinary means.
It would be necessary for the Dart to reach the surface in order to do this.