No, light does not have mass because a photon does not way anything.
You could use clay, sticks, rocks, Legos,
What is missing is the density of salt water. Let's denote it ρ.
<span>The pressure at depth d then is: </span>
<span>p = p0 + ρ g d </span>
<span>, where p0 is the atmospheric pressure at the surface of the sea. We assume it is equal to the 1 atm inside the sub. </span>
<span>Hence the pressure difference between inside and outside of the window is: </span>
<span>Δp = ρ g d </span>
<span>The force on the window is this pressure difference, multiplied by the area of the circular window of diameter D. The latter equals </span>
<span>A = ¼ π D². </span>
<span>So </span>
<span>F = p A = ¼ π D ²ρ g d. </span>
<span>This should be less than Fmax. </span>
<span>Hence d < Fmax / (¼ π D ²ρ g ). </span>