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Technical Data

This page contains all product data of Hydrosight Underwater Windows. It describes all technical aspects of the product.

1. Operation Environment

Hydrosight Underwater Windows are permitted for constant use in:

  • Chlorinated water with less or equal to 0.04 PPM Chlor concentration. Swimming pool water, that is safe for human access is permitted for Hydrosight Underwater Windows.
  • Ozone enriched water; Test passed for a ozone concentration of 200 pphm, test report May 2018
  • Skimmers using concentrations of Ozone of 0.5-1mg/h are safe for Hydrosight glazing
  • Drinking water, according to KTW-Leitlinie, comparable to WRAS drinking water approval. Drinking water approval comes optional.
  • Sea water. That is water with equal or less salt concentration than sea water. Salt concentration in sea water is 3-5%. That equals to 3-5kg on 100l of water. Higher concentration of salt leads to corrosion of the steel frame. Only windows for tiled pools are suitable for higher salinity.

Hydrosight uses without exception Marine Graded Stainless Steel 316L ("Inox", EN-Norm 1.4404) or 1.4571 (EN-Norm 1.4571). Bolts and Nuts in A4 or 316 (EN-Norm1.4401). Lower grade 304 are available on request with reduced price.

Cleaning the Glass Chemisches Verhalten Plexiglas.pdf(1.96 MB)

2. Depth Rating

Hydrosight Underwater Windows are rated for a maximum water depth. Windows installed on this water depth can permanently withstand the given water pressure. Even a higher water level than officially accepted does not lead to any short term failure of the window. However it is not recommended to install windows exceeding their depth rating. There is a risk of long term failure (creep).

Short term failture due to fracture of the glazing is only possible in artificial test environments with a pressure of several atmospheres (ATM). The physical limit of Hydrosight Underwater Windows is approx. 20m below water.

The letter h stands for the water height over window bottom. Each individual Hydrosight Underwater Window is rated with a maximum h - often called h_max. The maximum water level is individually calculated for each desired window.

The water level determines the level of stress in the underwater window. The following levels of stress should not be exceeded:

Safety Stress Permissible water side = 3 MPa
Safety Stress Permissible air side = 5 MPa *1
Safety Stress Bonded and Tempered = 2.5MPa
Tensile Strength at 23°C = 80 MPa

*1 : Max. safety stress (up to 40°C) Plexiglas GS 5...10 MPa published by Deguassa, Ref No. 211-1 April 2004. Compare to 5.5MPa = 800PSI in "Crazing and Degradation of Flexure Strenght in Acrylic Plates..." published in United States Ocean Systems Center, 1989

Acrylic Panel Thickness Standard Sizes

3. Temperature

Minimum Temperature Range: 5°C to 25°C 1
Maximum Operation Range: -40°C to +80°C 2

1 - default, for all windows delivered.
2 - These are the absolute extremes permitted by the materials used. Special purpose windows, details on request.

Emptying the Tank Thermal Conductivity

3-1. Flammability

  • Classification E, according to the “EURO-Norm” (DIN EN SO 11925:2:2002-07)
  • B2, with no burning droplets, according to DIN 4102 (Germany)
  • M4 (no droplets) according to NF 92500+ (France).
  • The Results of tests for fire propagation when tested to BS 476 Part 7 confirm that acrylic glazing achieves a Class 3 classification (U.K.). This material can thus be classified Category TP(b) according to BS 2782, Method 508 A for thermoplastics material as defined by the building regulations.

Its standard glow wire resistance is IIIa or BH3 to DIN VDE 0304, Part 3, and the UL flammability is UL 94 HB.

Fire Rating of Acrylic fire rating for plexiglas.pdf(2.14 MB) plexiglas non smoker.pdf(2.48 MB)

3-2. Thermal Conductivity / Insulation

Thermal Conductivity: 0.19 W/m2

The dew point is normally inside the window block -> no condensation.
The sides (steel frame) might need additional insulation.

Insulation of Pool Wall Send me the new 2018 Hydrosight catalogue

4. Sealing

  • Shore A hardness: ~45 (CQP 023-1/ISO 868)
  • Elongation at Break: ~300% (CQP 036-1 ISO 3/)
  • These norms are fulfilled: EOTA ETAG 002, EN 13022 and ASTM C1184
  • The Hydrosight guarantee does not cover sealing ("maintenance joint"). Seals covered are by DIN EN 52460 instead.

5. Optical Properties

Colors, Surface Structure

  • natural (untreated) for all not visible steel frame parts.
  • visible steel surfaces can be brushed k240 or k400 (not standard)
  • color of the sealant: black


  • Material: Acrylic PMMA, Monolithic Cast
  • Optical Transmittance: approx. 92%
  • UV Transmission: No
  • Ultraviolet Light: UV light, eg. sunlight is allowed.
  • Glazing Thickness t: between 30mm and 200mm, depending on window and its environment

Clarity Test

The minimum optical requirements of any underwater window can be verified easily without the need of special equipment. On the dry side the client should refer to performance demands of any other window, like store front windows or windows for residences.

On the wet side the underwater window should allow the reading of typewritten text located 50 cm behind the panel. The text size should be 8pt font size using the font Courier New.

To achieve this performance, the surfaces is allowed to be polished. It should not have any obvious surface irregularities in the form of waviness, ridges, pits, dimples, bumps, scratches or scruffs.

The official standard for this is called ASTM D4802 (replacing old standard ASTM D 702)

Cleaning the Glass Tolleranzen Send me the new 2018 Hydrosight catalogue