Building Lightweight Composite Shelves for a Catamaran Interior
On a boat, every millimetre of storage space is worth fighting for, and every kilogram you add to get it is worth thinking twice about. In this stage of Paikea’s interior refit, we tackled both problems at once: building a set of composite shelves into a bunk-end cupboard, designed to hold books and drink bottles without adding weight we’d rather not carry.
Designing to the Eye, Not the Tape Measure
The tricky part of this build wasn’t cutting the panels — it was working out exactly where the shelf should sit. A boat interior is full of competing angles. The cockpit sole slopes one way to drain water off to one side. The helm station sits at its own angle again. Settees, decks, and bulkheads all lean in slightly different directions depending on what they’re built to do.
That means a shelf that’s technically level, measured square to the boat’s centreline, can still look wrong sitting in a cabin full of other angles. Line it up “correctly” on paper and it can read as though it’s sloping or sitting crooked, simply because everything around it is angled differently. The fix isn’t more precise measuring — it’s standing back and eyeballing it until it looks right, even if that means deviating slightly from the technical line. It’s a step worth taking seriously on any boat interior build, and one that’s easy to skip if you’re working purely off a tape measure.
Cutting Composite Panels: Choosing the Right Blade
The shelf panels here are composite with a PVC core, and cutting them cleanly comes down to picking the right blade. A jigsaw is a good tool for the job — it doesn’t burn the resin or the outer skin the way some other cutting methods can, and it keeps heat away from the PVC core so it doesn’t melt as you cut.
Blade choice matters more than the tool itself. For solid, monolithic material like solid carbon or glass laminate, a diamond-coated blade gives the cleanest cut. For composite panels with a core, a serrated blade — sometimes just called a “toothy” blade — is purpose-built for the job, and has the added benefit of cutting through wood as well if you need it to. That versatility comes at a cost, though: wood is harder on these blades than composite is, and will blunt them faster, so it’s not worth reaching for a composite-rated blade on wood unless you actually need to.
Dry-Fitting and Filling the Gaps
The first dry fit rarely comes back perfect, and this one was no exception — a visible gap turned up where the panel met the boat’s structure. That’s one of the genuine advantages of building in composite: gaps like this aren’t a problem to solve by remaking the part, they’re a problem to solve with foam and glass tape. Pack the gap with foam, then glass tape over it, and the result is a strong, monolithic joint rather than a visible seam.
Building It on the Bench, Not in the Boat
The real time-saver on this build was doing as much of the finishing work as possible before the shelf ever went into the boat. The panels were glued together on the bench first, creating one stable unit. From there, most of the interior surfaces — the parts that would be nearly impossible to reach once the unit was installed inside a tight cupboard — were primed and painted while still sitting out in the open. Only the bare edges, the ones that still needed fibreglass taping in place, were left unfinished.
Finished and primed, the whole unit weighed just 1.55kg — light enough that the weight cost of the extra storage barely registers.
Working this way means the awkward part of the job — sanding and painting in a cramped, low-visibility corner of a cupboard — mostly disappears. Anything that can be done on a bench, with proper light and easy access, is worth doing there first.
Installing and Taping
With the unit pre-finished, installation was straightforward: glue it into position, then tape the joints to the boat’s structure. Peel ply went over the wet fibreglass tape on installation, which is worth doing on any tape-in job like this — it leaves a smooth, prepared surface that only needs a light sand before painting, instead of the lumpy, uneven finish tape can leave without it.
The Result
Painted white to match the rest of the cabin, the finished shelf disappears into the space — it reads as though it was always meant to be there, rather than an add-on. It’s not designed as a structural element, but being glued and taped directly into the boat’s interior gives it some incidental rigidity on top of the storage it provides.
For anyone tackling a similar interior weight-reduction project: trust what looks right over what measures right in a boat’s angled interior, get a blade suited to the material you’re actually cutting, and finish as much as you can on the bench before the part goes anywhere near a cramped corner of the boat.
In the Members Library, you’ll find more detail on selecting jigsaw blades for different composite builds, along with technique guides for the finishing work covered here. Explore the Boat Building & Composites Hub for more on working with composite panels throughout Paikea’s refit.