If you’ve ever stood inside an empty fibreglass hull, you’ll know it doesn’t look much like a boat yet. It looks like a very large, very green bathtub.
That changes the moment the bulkheads go in.
This week in the shed, Darren completed the bulkhead installation on our V930 Series 2 Grand Sport – currently under construction at Pacific Point Marina, Steiglitz. I asked him to walk me through it, we filmed it, and I learned more in forty minutes than I expected to.
Here’s what I took away.
What is a bulkhead?
A bulkhead is a vertical structural panel that runs across the width of the hull – think of it as the internal skeleton that divides the boat into sections and holds its shape under load.
In a fibreglass catamaran, the hull comes out of the mould as a single piece. Strong, yes – but without internal structure, it would flex under the stresses of offshore use. Bulkheads are what stop that from happening. They’re glassed directly into the hull, becoming part of the structure permanently.
Every bulkhead has a job. Some define cabin spaces. Some carry the load from deck fittings above. Some manage the structural forces generated by twin outboard engines at speed. None of them are there by accident.
Why does placement matter so much?
This is the part where I said to myself. “Of course!” Darren doesn’t just drop bulkheads in at regular intervals. Each one is positioned based on what it needs to carry, where the loads are coming from, and how the spaces above and below deck need to work. Get it wrong at this stage and you’re either fixing it later, expensively, or living with a boat that doesn’t perform the way it should.
The V930 hull is hand laminated using vinyl and isophthalic resins, solid fibreglass to the waterline, built to survey standard. The bulkheads are cut and fitted by hand to match the exact contours of each hull, because no two hulls come out of the mould in precisely identical shape. That’s what hand building means in practice. We make ours of Armacell as standard now, but they used to be wood.
What are bulkheads made of?
Older builds used timber for bulkheads. Wood is workable, familiar, and was the standard for decades. The problem is that wood and water are a long-term combination with a predictable outcome. Even in a well-built fibreglass hull, moisture finds its way into timber bulkheads over time, and when it does, you can get rot, delamination, and structural panels that are no longer doing the job they were built to do.
Voyager now uses Armacell PET foam throughout. It won’t rot. It doesn’t absorb water. It bonds cleanly to the fibreglass laminate and provides genuine structural strength – not just filler between skins. It’s also lighter than timber, which matters on an offshore vessel where weight is always a consideration.
It’s one of those material upgrades that doesn’t announce itself visually but makes a real difference to the long-term integrity of the boat. The kind of decision that gets made quietly by builders who’ve seen what happens when it goes the other way.
What happens next?
With the bulkheads in, anything that sits below deck is added – fuel tanks are an example from our builds.
After that the next major milestone is joining the hull and deck. Once that happens, the major structural work is complete and fitout begins.
Fitout is where a Voyager build becomes yours – engines, layout, cabinetry, electronics, finish. The decisions that turn a production hull into a vessel built around how you actually use the water.
If you’ve been watching this build and wondering whether there’s still time to get involved – there is. The fitout on this V930 hasn’t started yet.
Find out more about this build →
Watch the walkthrough
Darren walks me through the bulkhead installation in this short video – filmed in the shed, sound isn’t perfect, but it’s genuine. This is what building a Voyager actually looks and sounds like.
Watch the bulkhead walkthrough on YouTube →
Have a question about the build? Get in touch at info@voyagercatamaransaus.com or head to our Connect page.
More From The Build Journal
This is one story from a wider series on choosing, building and owning a Voyager – from picking your layout to the survey paperwork to the questions only an owner thinks to ask.
Got a question this post didn’t answer? Email us at info@voyagercatamaransaus.com and we’ll get back to you – good questions sometimes become the next post!