stick a picture up of the damage or you can email me one over to email@example.com
As phil says, surftechs don't have stringers, what you can see is probably the hight density foam skin.(divinycell)
Simple way to tell if it's watertight is to stick your mouth over the damage and see if you can suck air through the cracks.
If you don't fancy doing that then stick the board outside in the cold for an hour then put the board in a warm room for an hour.
Smear some soapy water over the damage and if it's not water tight it will blow bubbles as the air warm up and expands inside the board forcing it's way out of the cracks.
If you ever think you may have got water inside the board then put some cling film over the damage and tape round the edges so it is air tight.
Stick the board in a warm room for a few hours and if when you come back to it the cling film has misted up on the inside then there be water in the board.
For getting water out of the board stick the board in a warm room with the damage facing down, as the air inside the board warms up and expands it will push the water out.
After a few hours the air inside the board will reach room temperature and stop expanding and the drips will stop.
With the damage facing down at all times put the board out in the cold again to shrink the air insdide the board and repeat the process for as long as it takes to get nothing out. Could be days or weeks.