(Things that go “Tunk” in the night)
“Tack. Tack. Tack. Tunk…”
“Tunk” is a sound no boat owner wants to hear – at least no fiberglass boat owner. It’s a sound which invokes images of unknown weakness, possibly extensive and expensive repair work, and just generally bad things. Maybe. In any case, it’s a sound that rates right up there with “Plunk”in our book, which is the sound made by a dropped, expensive tool as it takes a dive for the freedom of the deep.
Good, solid fiberglass laminate (the alternating and intermingled layers of fiberglass cloth and plastic resin that make up a boat hull) makes a very clear, sharp “tack” sound when you gently tap on it with a light hammer or the handle of a screwdriver. It’s what you hope to hear when you’re inspecting the condition of a boat, whether you already own it, or are thinking of buying it.
But fiberglass has a serious weakness, which is that it’s not really waterproof. It’s very water resistant, yes, and if properly maintained will act waterproof, but if water does find its way into the laminate, it begins to migrate… The result can be a release of the bond between the layers of glass, or the wood core used between major layers. That break in adhesion creates a hollow, and that hollow results in the “Tunk” sound that brings despair to the boat owner.
…And joy to the boat repair shop. Delamination repair is labor-intensive (and therefore expensive), though it’s not particularly difficult.
Because boats have fittings and hardware and holes throughout, it’s a constant battle to keep the water out; both the water she’s sitting in, and the water that falls from the sky. Fittings on deck and through the hull must be regularly inspected, and not infrequently those on deck must be removed and re-bedded in sealant to assure that leaks don’t start, or don’t progress beyond the initial stage of “nuisance drip.”
When we were buying Sionna last year, we had a pre-purchase survey done by a very thorough fellow, and received a recommendation that we remove and inspect a couple of the chain-plates (which are original 1963 equipment), as well as repair a mild crack in the surface on each side of the deck near the aft end of the cockpit.
Starboard forward chain plate removed, which pulled up the surface of the deck.
Area just outboard of the cockpit’s aft edge, starboard side, after grinding
partway down, showing cracked surface and dark moisture staining of wood core.
These were both “You might want to look at these areas someday” recommendations from the surveyors point of view, but because the boat is insured, the insurance company gets to decide what THEY think is important – and those items got flagged.
So (being a staunch DIY kind of guy) I pulled the two forward chain-plates at the main mast for inspection. Both bronze castings passed inspection with flying colors, naturally, but not so the deck through which they had been pulled! A significant bit of the upper deck pulled away during the removal, revealing discoloration – a sure sign of water intrusion. I was about to have my first lesson in deck laminate repair.
On Sionna the decks throughout are a sandwich of ½” marine plywood, with a 1/8”-3/16” layer of fiberglass on each side. This is a common construction technique, though frequently balsa wood is used for the core, and in modern boats it’s now often a plastic honeycomb material instead of wood. In our case, because the damaged area was quite small, the answer was to grind out the fiberglass around the area to a shallow slope, and then use epoxy and glass cloth layers to fill in the resulting void, sand it out fair with the old deck, and then repaint it. With luck you’ll hardly know there was ever an issue, but more importantly, it won’t leak!
After grinding, the required number of layers of glass cloth are laid out, largest first, providing about 1” of under-lap all around where feasible.
The epoxy is then applied to each layer so everything is well saturated, and allowed to harden, with the chain plate in place.
Once the first layer is set, a form is created around the rough shape desired,
and filled with thickened epoxy to create the shelf around the chainplate.
The shelf is then filed and sanded to it’s final shape and smoothness.
And finally, paint is applied to protect the epoxy repair.
Once the repair and painting is complete, the final step is to bed the mating surfaces with a sealant, so that when there’s standing or flowing water on the deck, there’s no where for it to flow but AWAY. This I generally accomplish with a 3M company product known as “3M 4000” This is a very tenacious sealant and adhesive, so you want to be very sure it goes only where it belongs AND that you’re unlikely to need to take things apart any time soon. At least, unlike its sister product – “3M 5200” – it CAN be removed, though with difficulty. 5200 is permanent. (I’ve heard rumors of a solvent for it now, but I’ve never tried it.)
The chainplate cover, installed with 3M 4000 sealant, and four screws.
Strong, and waterproof!
And that’s really all there is to it. A rather dirty job, what with the grinding, but not hard, and once accomplished, it should be better than new for many years to come – which in my book is a perfect boat project!