Excerpted from Don Casey’s Inspecting the Aging Sailboat
DELAMINATION
Delamination in fiberglass is the functional equivalent of rot in a wooden boat. Well-constructed solid-fiberglass hulls (meaning not cored) almost never delaminate unless they have suffered impact damage or unless water has penetrated the gelcoat. This is because proper hull-construction technique – adding each layer before the previous one has cured – results in the resin linking chemically into a solid mass. Occasionally a manufacturer defeats this by leaving an uncompleted hull in the mold over a weekend; but most know – and do – better.
Introduce core into the formula and the likelihood of delamination increases dramatically. A core divides the hull in three distinct layers – the outer skin, the core, and the inner skin – with the bond between them strictly mechanical. Polyester resin adheres chemically to itself with amazing tenacity, but it has never been very good at adhering to other materials. At the slightest provocation it will release its grip on the core material, regardless of what it is.
PERCUSSION TESTING
Tapping a fiberglass hull is akin to spiking a wooden one. Use a plastic mallet or the handle of a screwdriver to give the hull a light rap. If the laminate is healthy, you will get a sharp report. If it is delaminated, the sound will be a dull thud. Your hull is sure to play more than two notes, but map all suspect returns; then check inside the hull to see if a bulkhead, tank, or bag of sails is responsible. If not, it is the laminate.
It is essential to do a thorough evaluation of a cored hull because core delamination is unfortunately common and robs the hull of much of its designed strength. Tap every 2 or 3 inches over the entire surface of the hull. Be especially suspicious of the area around through-hull fittings and near signs of skin damage or repair. Percussion testing can also reveal filler patches.
Don Casey’s book, Inspecting the Aging Sailboat will show you, step by step, how to evaluate the condition of an older fiberglass sailboat – the one you own or the one you’d like to purchase. Buy a copy of your own from Practical Sailor’s online bookstore.
