Comparison
Aluminium versus acrylic subsea enclosures
The two dominant pressure vessel materials for small underwater vehicles differ on far more than depth rating. Here is the head-to-head, and the cases where each is clearly right.
Depth rating: not a like-for-like number
An anodised aluminium tube has the same depth rating at every size, typically 1,000 m, because its wall is thick enough that diameter does not limit it at the depths these vehicles work at.
Cast acrylic does not behave that way. Its rating falls as diameter and length increase, roughly from 250 m at small diameters down toward 20 m for the largest, longest tubes. This catches people out when they scale a design up: moving from a 4-inch to a 6-inch acrylic housing for a bigger payload can halve the vehicle's depth rating.
The practical consequence is that acrylic is a shallow-water material that happens to be transparent, and aluminium is a general-purpose material that happens to be opaque. If the operating envelope is deeper than a couple of hundred metres, the comparison is over before it starts.
Optical access is the one thing acrylic does that aluminium cannot
Full optical clarity through the tube wall is the entire case for acrylic, and where a payload needs it, nothing else will do. A camera that looks sideways through the housing, a light sensor or an optical communications head all need acrylic.
But check whether the payload needs to see through the wall or only through the end. A forward-looking camera only needs a window, and you can fit one as an end cap on an aluminium housing: flat acrylic for shallow work, a moulded polycarbonate dome for wide angle and less drag, or a borosilicate glass flange cap where good optics and frequent servicing both matter.
The dome is worth understanding. A flat viewport refracts at the water-to-window interface, narrowing the effective field of view and introducing distortion at the edges; a dome port with the lens at its centre of curvature largely avoids both. For wide-angle inspection work that difference is significant.
Thermal behaviour matters more than teams expect
Aluminium conducts heat; acrylic effectively does not. On a housing containing a passive data logger this is irrelevant. On one containing a Jetson-class compute module, a power converter or a motor controller, it decides whether the electronics survive.
A sealed acrylic tube is a thermos. The heat has nowhere to go but into the trapped air, and the internal temperature climbs until the electronics throttle or fail. An aluminium tube passes that heat into what is, for practical purposes, an endless supply of cold water. The usual approach is to bond the hot component to the tube wall with a thermal pad or a machined bracket, which turns the whole housing into a heatsink.
If the payload dissipates more than a handful of watts continuously, that alone can decide the material.
Servicing, handling and the things that go wrong
Acrylic is brittle and notch-sensitive. It crazes when exposed to solvents, including some cleaners used to remove marine growth, and it scratches. Tightening again and again against an acrylic sealing face can dent or crack it, so acrylic end caps suit housings that are seldom opened. Clamping an acrylic tube straight to a rigid rail concentrates stress on a thin wall, which is why purpose-made clamp sets exist.
Aluminium tolerates handling, tolerates solvents, tolerates being clamped to a frame, and can be serviced repeatedly without the sealing faces degrading. Anodising protects it, but aluminium in seawater that touches a different metal will corrode galvanically, so you have to choose fastener and fitting materials with care. Acrylic does not have this problem.
One genuine advantage of acrylic beyond optics: you can see inside. Spotting condensation, a displaced connector or the first sign of ingress through the wall is a real diagnostic benefit on a test platform.
How to choose
Choose acrylic when the payload must see out through the tube wall, the depth is comfortably within the rating for that diameter, the internal heat load is small, and the housing will not be opened often.
Choose aluminium when the depth is more than a couple of hundred metres, when the payload gives off real heat, when the housing is opened every deployment, or when the vehicle takes knocks. That covers most working vehicles.
A common and sensible outcome is both: an aluminium main housing for compute, power and heat, and a small acrylic or domed-cap housing for the optical payload. There is no rule that a vehicle has one housing material.
Sources & basis
What this is based on.
- Depth ratings, materials, diameters and weights for the Blu-Sub acrylic and aluminium pressure vessel ranges as listed in the Vebix Automation shop.
- Optical throughput figure of approximately 95% for the borosilicate glass flange end cap, as listed in the same shop pages.
Published 16 August 2026. Last revised 16 August 2026. Corrections to sales@
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