Re: Viewports gobbed on with silicon

[protek@shreve.net]

    Something to think about if you are talking about a 1 atm sub rather
than a wet sub: 
    
    Suppose the viewports can withstand hundreds of pounds of differential
pressure where the pressure is greatest on the outside.  Suppose the
windows can't stand very high pressures, where the pressure is greater on
the inside.  Now, lets dive this sub to say 100 feet.  You are down
enjoying the view but unknown to you there is an air leak in a pneumatic
line inside the hull.  Slowly the inside pressure creaps up till it reaches
what is equal to say 20 feet of depth.  The windows are still firmly
planted against the seats.  You have 80 feet of water pressure as a
differential.  Now lets take the sub to 10 feet.  At this depth you have a
10 foot of water pressure differential from the inside.  Suddenly you have
a 6 inch viewport pop out.  Air blows out then water rushes in.  You go
negative.  The sub begins to go down.  The deeper it goes the more water
rushes in and on and on.
    Subs have gone down due to the same thing happening with the hatch.  A
slow leak builds pressure until when the sub gets near the surface the
hatch retaining mechanism breaks and the hatch blows open under water.  Air
rushes out in volumes and water rushes in in the same volumes.  I have had
a pressure buildup due to a slow leak through a pneumatic cylinder's seal.
When I open the hatch it burps expelling air.  Most hatches are not made to
withstand this kind of pressure.  Neither are viewports, BUT at least there
should be a retainer other than just silicone seal to hold a window in.
This is inviting trouble.

Gary Boucher