An awkward-shaped bilge or a wasted corner of hull space is exactly the kind of problem a custom-built tank solves. Rather than fitting a standard metal tank and losing capacity to whatever space is left over, you can build a tank from fibreglass cloth and epoxy shaped precisely to fit, saving weight and sidestepping the corrosion that eventually catches up with metal tanks.
Choosing the Right Kit for the Job
This only works with the correct epoxy for the liquid the tank will hold, and the two aren't interchangeable. Our Fresh Water Tank Build & Repair Epoxy is formulated to be safe for drinking water, while our Fuel Tank Build & Repair Epoxy is formulated to hold up against diesel or petrol. Both are designed specifically for building a new tank with cloth reinforcement, not for coating an existing metal or plastic tank — if that's your situation, you're looking at a different product entirely, so check with us before you start if you're unsure.
Building the Tank
The basic method is the same for either kit: build up a shell from fibreglass cloth wet out with the epoxy, laminating enough layers to give the finished tank the strength it needs to hold its shape and cope with the movement of liquid inside it as the boat moves. We stock glass biaxial stitched cloth for exactly this kind of job — it wets out cleanly, goes fully transparent once saturated, and drapes into complex shapes without a fight, which matters when you're working into an awkward tank void rather than a flat panel.
Lay the cloth in dry and let the resin wick through from underneath rather than trying to force it through from on top; a simple spread followed by a light roller pass is usually all it takes. Build up your layers with a good overlap between each piece, and don't rush the schedule — if you can still mark a layer with a thumbnail, you're fine to keep building on top of it, but once it's fully cured you'll need to abrade the surface with 100-grit paper before continuing.
Fittings, Baffles and Access
Plan your fittings — fill point, breather, outlet, level sender — before you start laminating, not after. It's far easier to build a boss or a reinforced pad into the shell at the right stage than to cut and patch a finished tank. If the tank is of any real size, consider a baffle plate to control how the liquid surges as the boat heels or pitches; it's a simple addition to the build sequence and makes a real difference to handling once the tank's fitted.
Testing Before You Fit It
Once cured, pressure or fill-test the tank before it goes anywhere near its final position. A leak is a five-minute fix on a bench and a miserable job once the tank is boxed in under a sole or behind a bulkhead. It's a small step that's easy to skip when you're keen to get the boat back together, and one you'll regret skipping if you do.
If you're planning a build like this and want to talk through the right kit or lay-up schedule for your specific tank, our contact page is the quickest way to reach the workshop team.
