Spherical Shell Sector Acrylic Plastic Windows with 12,000 ft Operational Depth for Submersible Alvin

It has been found that the 90-deg plane conical frustum windows with t/D_i = 0.7 ratio in ALVIN submersible can be replaced with 90-deg t/D_i = 1 spherical shell sector windows without any modification of window seat flanges. The 90-deg spherical shell sector windows with t/D_i = 1.0 possess not only a higher short term critical pressure but also develop more uniform stress distribution during a typical dive to 12,000 ft than the t/D_i = 0.7 acrylic conical frustum windows that they replace. The 90-deg t/D_i = 1.0 spherical shell sector windows (1) withstood, without catastrophic failure, 100 hr sustained loading to 20,000 psi, (2) 33 pressure cycles of 7-hr duration to 13,500 ft depth without any signs of fatigue, and (3) experienced less than 15,000 μin. strain during a simulated typical prooftest dive to 13,500 ft depth. The 90-deg t/D_i = 1 spherical shell sector window presents a 50 percent larger view in water than a 90-deg t/D_i = 0.7 conical frustum window that it replaces. This permits the observer inside the submersible to cover visually more ocean bottom during a single pass along the bottom and thus decreases the cost of a typical bottom search mission for a submersible.