Pressure Hull – the structure that provides the occupants of an underwater submersible with a dry, pressure resistant habitat.
The pressure hull consists of spherical or cylindrical shapes in various combinations. Table 1 illustrates the advantages and disadvantages of various pressure hull shapes.
Shape |
Advantages |
Disadvantages |
Sphere |
1. Most favorable weight to displacement ratio 2. Thru-hull penetrations easily made 3. Stress analyses more accurate and less complex |
1. Difficult and inefficient interior arrangements 2. Large hydrodynamic drag |
Ellipse |
1. Moderate weight to displacement ratio 2. More efficient interior arrangements than in Sphere 3. Thru-hull penetrations easily incorporated |
1. Expensive to construct 2. Difficult to perform accurate structural analysis |
Cylinder |
1. Inexpensive to construct 2. More efficient interior arrangements than in Ellipse 3. Low hydrodynamic drag |
1. Least efficient weight to displacement ratio 2. Interior frames required to increase strength |
The selection of an appropriate pressure hull material is based on the following criteria:
Submarine pressure hull are usually made of steel, aluminum, titanium, acrylic plastic and glass. However, the most widely used material is steel, because of a high degree of knowledge available to designers and manufacturers as well as of its outstanding performance in the ocean.
There are several problems with Aluminum and Titanium:
Solution: Aluminum pressure hulls can be bolted together instead of welding; it can be anodized to resist stress-corrosion cracking.
Solution: Titanium graphite alloys do not exhibit this problem.
Glass: Despite of its weaknesses, such as its brittleness, high sensitivity to surface abrasion and considerable strength degradation at joints, glass and glass-reinforced plastic have a low weight/displacement ratio. Figure 1 clearly shows that titanium, glass and glass-reinforced plastics are the top three pressure hull materials.