Tap testing, also called sounding or percussion testing, is a testing method that can be used to detect anomalies in composite materials like fiberglass. We found it extremely useful in detecting underlying issues while our Leopard 45 catamaran underwent warranty repairs in Trinidad so wanted to share what we learned.
How yachts are tap tested
To tap test a hull all you need is a small hammer and an idea of the interior structure of the vessel. The hammer used on our hull was a small metal hammer with a wooden handle. The people who tap tested the yacht also put blue tape on the end of the hammer to help protect the gel coat from marks.
To tap test the yacht they went up and down the fiberglass, lightly tapping it in sections. There was less than 1cm between each tap and they would go back and forth in a search pattern to make sure nothing was missed. As they went, they were listening to changes in the sound the tap made.
You can watch our hull and another Leopard 45 being tapped in this video. Listen carefully to the sounds the hulls makes as the hammer taps it.
What tap testing can detect in a hull
By listening to changes in the sound the hull makes as the hammer taps it, it's possible to detect a few different things.
Bulkheads (useful for hauling out)
Delamination in the fiberglass caused by things like osmosis or the layers next to the core separating
Separation between the gel coat and fiberglass
Dry fiberglass (no resin)
Sections where the bulkhead tabbing hasn't bonded or has separated
Voids
Who can tap test a hull
Usually owners or prospective owners would employ a marine surveyor to tap the hull. Our hull was tapped by the owner of a marine services and repair company with decades of experience repairing fiberglass hulls. If you're undergoing repairs in a shipyard some of the contractors may have experience sounding hulls, just make sure they actually know what they're doing.
Is tap testing non-destructive?
If done correctly tap testing should be relatively non-destructive. There may be marks on the gel coat if the end of the hammer isn't taped or a bit of bottom paint could flake off. Also, if the area is already compromised it could crack, for example a blister or void near the surface.
Tap testing during handover
After our experience we would not talk an owner out of tap testing their hull during handover. Regardless of whether it's a new boat or new to you if you want to have it tap tested for your own peace of mind, do it. If you do have someone tap the hull I would advise you to watch, listen and learn what type of sounds to expect from your hull.
This video builds on the previous one, showcasing a few places on our hull where tap testing indicated there was an issue and further investigation proved that to be correct.
Σχόλια