Diagnosing and Repairing Hull Delamination: A Real Structural Repair, Not a Cosmetic One
Pulling up an old floor panel to find “a little bit of delamination” turned into a full structural repair once the actual extent of the damage became visible.
Finding the crack, and following it further than expected
A suspected crack in the bulkhead started this repair, matching similar damage already dealt with on the boat’s other side. What began as a plan to remove roughly 100mm of material either side of the crack grew significantly once grinding actually exposed what was underneath — the crack ran considerably further than the surface damage suggested, and pulling back the top skin revealed a genuinely large area of delamination, with the core visibly flexible and separated from the skin above it. What looked like a contained, minor repair on the surface turned out to be a much larger structural problem once properly investigated.
Where this kind of damage actually comes from
The root cause traced back to a block of wood at some point pressed hard enough against the hull to shear the inner skin away from the core underneath — not a clean puncture through to the outside, but enough force to break the bond between skin and core locally. That distinction matters structurally: a sandwich panel’s core exists specifically to carry shear load between the two outer skins, transferring force from one face to the other. Break that bond, and the panel loses its ability to carry shear load in that section entirely, regardless of how intact either skin looks individually.
Repairing shear damage properly: slurry, not straight resin
Fixing a broken core-to-skin bond isn’t a matter of squirting straight resin into the gap. Pure resin on its own is genuinely weak in isolation — it lacks the reinforcement to resist cracking, and cracks that do form propagate easily through unfilled resin. The fix is a slurry: resin thickened with filler, which resists crack propagation far better than resin alone and restores genuine structural bonding between the core and the skin above it, not just a cosmetic fill.
Where the top skin needed removing to access buried delamination, the process is straightforward: grind back the damaged skin until sound material is reached in every direction, work slurry into the exposed core to re-bond it fully, then laminate new skin material back over the top once the core repair is solid — full reconstruction of the sandwich structure, not a surface patch over a still-broken core underneath.
Laminating without waiting for a full cure
One detail worth knowing if you’re tackling a similar repair: freshly ground and filled bog doesn’t need to fully cure before laminating over the top of it. New glass can go directly over uncured filler, provided the surface is properly prepared first — though any area filled with slurry or bog still needs sanding smooth before lamination, since a rough, uneven filled surface won’t give the new laminate a clean, consistent surface to bond to.
Building in a structural bulkhead that actually gets taped
Alongside the skin repair, a new half-bulkhead went in at this location — properly laminated and taped into the surrounding structure, unlike the original, which had simply been sitting loose rather than genuinely bonded in. That distinction is exactly why this section had cracked and delaminated in the first place: an unsecured bulkhead doesn’t share load with the surrounding structure the way a properly taped one does, leaving the panel around it to absorb stress on its own.
The new bulkhead includes a return flange along its top edge — a detail that solves a genuinely awkward access problem. Once a floor panel is fitted on top of a bulkhead, there’s no way to get underneath it into the bilge to tape the joint from below. Building the return flange in before the floor goes on means that taping work is effectively already done — the floor panel simply sits down onto the flange, with the structural connection already complete rather than needing to be finished in a space nobody could physically reach afterward.
Fitting the new floor
With the repair and new bulkhead complete, the replacement floor panel — built by infusion, and needing its own small repair after cold weather kept the infusion resin from fully reaching one corner — went into place using polyester resin, matching the boat’s original construction throughout. Bog quantities varied panel to panel depending on how much gap-filling and coving each particular floor needed — not every floor cavity is identical, and matching bog volume to the actual gap rather than a fixed formula avoids both wasted material and an under-filled joint.
The unglamorous parts, done by the crew who actually did the work
This repair, like much of this refit, involved the whole family working through real, sometimes tedious tasks — grinding back delaminated skin, chasing a crack until it was genuinely gone rather than just cosmetically hidden, sanding cured bog smooth before laminating over it. Not every finished floor comes out perfectly even — some sections show it more than others, an honest reflection of a real, hands-on build rather than a polished, idealized version of the process.