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Demonstrates an air bubble in a flooding ballast tank with an air vent below the tank top. The pressure in the air is 1.0 atm when the water in the tank is at or below the vent. As the water rises further the pressure increases which keeps the water from rising to the outside level. The increase in air pressure is inversely proportional to the decrease in air volume.
    proj bubble
    
    `Make a simple hull with tanks:
    enter pm
    create hull
    ends 0 100
    out 10
    top 10
    bot 0
    /
    create tank5.s
    ends 40 60
    in 5
    out 50
    fit hull
    /
    create tank5.p
    opposite tank5.s
    /
    write bubble.gf
    quit pm
    
    depth 7
    vcg 5
    solve weight, lcg
    
    macro prt`macro to print 1 page of status
     subtitle \%1\
     page
     solve
     status
     di(*) status plan, profile, body @50
    /
    
    macro pp`macro to print preview and end
     print prev
     report off
     end
    /
    
    report
    tank * `selects all tanks
    tanks
    refpt bottom
    \refpt bottom\
    tanks
    type flood
    .prt "Tanks Flooded"
    type intact /hbl
    .prt "Tanks Intact with load of flooded
    
    type bubble
    .prt "Tanks Bubble"
    macro press
     `%1 = new bubble pressure
     load * /pressure: %1
     .prt "Tanks Bubble - Pressure: %1 - Load unchanged"
    /
    .press 1.05
    .press 1.1
    .press 1.15
    macro heel
     `%1 = new heel angle
     heel %1
     solve dr trim tcg
     .prt "Tanks Bubble - Pressure Unchanged - Heel %1"
     heel 0
     solve dr trim tcg
    /
    .heel (3,5) 5
    .pp
    
    
    
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