Underwater Window Technical Specifications

Ready-to-Install Underwater Windows (System Hydrosight)

1. System Description

Hydrosight underwater windows are factory-prefabricated, monolithic glazing elements designed for use in swimming pools, aquariums, and specialized water-retaining structures. The system consists of a stainless steel frame, the structurally calculated PMMA glazing, and a certified sealing and casting system.

The component serves as a load-bearing interface that safely transfers the resulting forces from water pressure and self-weight into the building structure. Manufacturing takes place under controlled conditions (Factory Production Control FPC). Delivery is carried out as a ready-to-install complete component, including leak testing.

2. Components and Materials

2.1 Frame Construction
The frame functions as a mechanical adapter to the building structure and decouples the glazing from structural movements and constraints.

  • Material: Stainless steel V4A (Grade 1.4571 / AISI 316Ti).
  • Execution: TIG-welded, fully pickled, and passivated.
  • Variants & Connection Types:
    • Adhesive flange: For tiled and concrete pools.
    • Loose/Fixed flange construction: For liner pools and plastic pools (PVC/PP).
    • Welding flange: For stainless steel pools.
    • Water stop plate: For exposed concrete pools (cast-in/grouting installation).
    • Special constructions: On request.

2.2 Glazing
Monolithic cast blocks made of Polymethyl methacrylate (Acrylic glass).

  • Material: PMMA cast (GS).
  • Standards Compliance: Corresponds to DIN EN ISO 7823-1.
  • Quality Assurance: ISO 9001 certified production of raw blocks; annealed to relieve stress.

2.3 Sealing and Chemical Bonding

  • Standards: The sealing system meets EOTA ETAG 002 (Structural Glazing), EN 13022, and ASTM C1184.
  • Material Properties: Hardness Shore A approx. 45, Elongation at break approx. 300 %.
  • Quality Proof: 100 % factory pressure and leak testing before delivery (documented by inspection seal on the component).

3. Mechanical Properties and Dimensioning

3.1 Viscoelastic Behavior & Long-Term Loads
Unlike mineral glass, structural acrylic (PMMA) is a viscoelastic material. Under permanent hydrostatic load, the material exhibits time-dependent deformation (creep).
Consequently, standard linear-elastic calculations are insufficient for underwater glazing. The structural analysis utilizes the Apparent Long-Term Modulus of Elasticity to predict material behavior over the service life.

3.2 Design Stress Limits (Permissible Stress)
Thickness dimensioning is governed by specific Permissible Stress limits to ensure the material operates within its elastic range.

  • Water Side (Wet): Maximum permissible tensile stress 3 MPa.
  • Note: The reduced limit accounts for water absorption and plasticization effects on the polymer surface.
  • Dry Side (Air): Maximum permissible tensile stress 5 MPa.

3.3 Deflection Limits (Design Target)
To minimize optical distortion and ensure the integrity of the sealing flange, the panel thickness is calculated with the aim of limiting deflection.

  • Target Deflection: f <= L/300 (where L is the shortest span of the window).
  • Note: This value represents a design objective to reduce the optical "lens effect". Actual deflection may vary depending on installation tolerances and specific boundary conditions.

3.4 Calculation Protocol
Panel thickness is determined individually for each project based on the following parameters:

  • Water Column Height: Exact pressure load.
  • Support Configuration: 4-sided support (standard window) vs. 3-sided support (infinity edge/overflow).
  • Operating Temperature: Calculations are adjusted for temperature-dependent modulus changes (e.g., heated hydrotherapy pools vs. ambient tanks).
  • Engineering Note: General thickness tables do not account for specific load cases. Final manufacturing thickness is determined exclusively via project-specific structural calculation.

3.5 Material Properties PMMA (Guideline values at 23 °C)

Property Value Standard
Density 1.19 g/cm³ ISO 1183
Modulus of Elasticity (Tensile) 3300 MPa ISO 527-2/1B/1
Tensile Strength ≥ 70 MPa ISO 527-2/1B/5
Coeff. of Linear Thermal Expansion 70 x 10^-6 /K ISO 11359

The dimensioning of the panel thickness (30 mm to 200 mm) is carried out on a project-specific basis based on water depth (hydrostatic pressure) and the clear opening dimensions.

3.1 Load Limits

  • Maximum Water Column: Standard design up to 20 m (higher pressures on request).
  • Fracture Behavior: PMMA behaves in a ductile manner (viscoelastic). There is no risk of spontaneous brittle fracture (cf. tempered/laminated safety glass).
  • Serviceability: Dimensioning ensures that deflection remains within the optically and structurally permissible range.

3.2 Material Properties PMMA (Guideline values at 23 °C)

Property Value Standard
Density 1.19 g/cm³ ISO 1183
Modulus of Elasticity (Tensile) 3300 MPa ISO 527-2/1B/1
Tensile Strength ≥ 70 MPa ISO 527-2/1B/5
Coeff. of Linear Thermal Expansion 70 x 10^-6 /K ISO 11359

4. Optical Properties

Hydrosight glazings offer a light transmission of approx. 92 % with complete UV absorption.

Optical Quality (Distortion-Free)

  • Test Criterion: Legibility of standard text through the material block.
  • Test Setup: Distance 50 cm behind the panel.
  • Reference: Font Courier New 12pt (approx. 16 characters/inch).
  • Permissible Tolerances: Free from waviness, burrs, and perceptible depressions.
  • Exclusion Criteria: No visible voids, scratches, or foreign body inclusions.

5. Thermal Properties and Fire Behavior

  • Thermal Conductivity: 0.19 W/(m·K). The material offers high thermal insulation and minimizes condensation.
  • Operating Temperature Range:
    • Standard: +5 °C to +30 °C.
    • Extended (optional): -40 °C to +45 °C.
  • Temperature Differences: A Delta T > 15 K between the water and air side (e.g., due to direct sunlight on an empty pool) must be taken into account in the structural design of the joint.
  • Fire Behavior:
    • Glazing: Building material class B2 (normally flammable) according to DIN 4102 / Class E according to EN 13501. Burns almost smoke-free, no flaming droplets.
    • Frame: Non-combustible (Class A1).

6. Chemical Resistance

The overall system (Frame 1.4571, PMMA, and sealants) is resistant to the following media:

6.1 Swimming Pool Water

  • Free Chlorine: Continuous load up to 0.6 mg/l (Standard according to DIN 19643).
  • Shock Chlorination: Short-term exposure (high chlorination / chlorine shock) permissible in case of microbiological indication.
    • Limit Value: Concentrations up to 100 mg/l.
    • Exposure Duration: Max. 2.5 hours (150 min).
  • pH Value: 7.0 to 7.4 (neutral range).

6.2 Other Media

  • Ozone: Resistant to ozone-enriched water up to 200 pphm and use in skimmers at approx. 0.5 - 1.0 mg Ozone/h.
  • Saltwater / Brine:
    • Standard execution: Seawater resistant (Salinity approx. 3.5 %).
    • Special execution: Brine resistant > 3.5 % (High brine) on request.
  • Potable Water: Execution compliant with the KTW guideline of the German Federal Environment Agency (UBA) optionally available.

6.3 Cleaning Warning

  • Prohibited Substances: Contact with organic solvents (acetone, alcohol > 5 %), thinners, strong acids, or abrasive cleaners must be strictly avoided.
  • Reference: Further information and detailed care instructions can be found in the Hydrosight Operation and Maintenance Manual for Underwater Windows.

7. Installation and Assembly

The window is delivered as a ready-to-assemble unit. The on-site connection to the primary sealing layer (water-impermeable concrete, sealing slurry, liner, etc.) is made via the integrated stainless steel frame. Detailed installation instructions can be found in the project-specific installation manual.

Status: February 2026 | Subject to technical changes. | Manufacturer: Hydrosight GmbH, Emmerich am Rhein, Germany

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