Wet deck core: how surveyors find it, grade it and what recoring costs

Most yacht decks are a sandwich: two skins of fibreglass with balsa, foam or plywood between them. The core is light and stiff while it's dry. Water gets in where fittings are bolted through the deck and the sealant has failed, spreads through the core, and over the years the balsa or plywood rots and the skins part. The deck goes soft, and fittings bolted into it lose their hold.

How a surveyor finds it

Walking the deck finds the worst of it: soft or springy patches under foot, usually by stanchions, chainplates, the windlass and the mast. Then the hammer and the meter map it.

Sounding with a phenolic hammer gives a sharp note over sound core and a dull one where the skins have parted or the core has rotted. The moisture meter shows where the water is, but only as a comparison. Practical Sailor's tests make the limits clear: a meter reads about a quarter of an inch deep, gives no true moisture percentage in fibreglass, and a lot of water deep down can read the same as a little near the surface. Readings need a dry, uncoated surface and can't be trusted below freezing. Non-skid paint and a wet morning both make a dry deck look wet.

Last, the fittings. A chainplate or stanchion base that moves when loaded by hand means the core round it has gone.

What decides the grade

What the wet core is holding. Soft core round a chainplate, the mast step or a pulpit base is an A: the fitting can tear out under load. Wet core over an area that is still firm is a B, worth fixing before it softens and spreads. Slightly raised readings close round a stanchion base, with sound deck beyond, is a C: rebed the fitting and stop the water.

What recoring costs

Labour is most of the bill: cutting the skin, digging out the core, new core, glass and fairing, and matching the non-skid. Recoring from below avoids refinishing the deck but means taking the headlining down.

Photos to take

The area with its boundary marked in tape or chalk, the meter on the deck with the reading visible, the fitting it centres on, and the deckhead below if there's staining. With Axsail, say the readings as you go and they go into the finding with the photos.

Writing it up

Name the fitting it centres on, give the size of the wet area, the readings against a dry reference, how it sounds and whether it's soft under foot. Then say whether anything bolted through it moves. That last point is what turns a B into an A, and what a buyer's yard will ask first.