Some Like It Hot
To many surveyors and their clients, the moisture meter is the ne plus ultra of laminate-testing tools, a technical leap and a half beyond whacking the boat with a soft-faced hammer. But not for long: Moisture meters are so 20th century. Today cutting-edge surveyors are using expensive infrared cameras along with traditional surveyors' tools. Colorful IR, or thermographic, images provide trained interpreters more detailed, more accurate information than a meter can and in a graphic format that paints an at-a-glance picture of the laminate's condition. And while anybody with a few hundred bucks can buy a moisture meter and call himself a surveyor, IR equipment is expensive (they start at around $6,700) and requires extensive training to use, so only serious, experienced pros are likely to make the investment. One who has is Mark Ashton of Independent Marine Systems, a surveyor specializing in composite construction.
Using his Raytheon Pro 400 Digital IR camera (it looks like a camcorder with a PDA mounted on top and can shoot both video and stills), Ashton observes and records a hull thermographically, one section at a time. Voids, moisture, delaminations, and other anomalies heat and cool at different rates than laminate in perfect condition and therefore show up differently over time on the infrared images; wet areas cool more slowly than dry areas, for example, and voids appear hotter. Thermography gives Ashton a kind of "X-ray vision" so he can analyze the state of a laminate more accurately and with more confidence than if he used only traditional tools. (Ashton also carries a moisture meter and the surveyor's standby, a hammer for sounding the hull.) Thermography is the most accurate nondestructive method of inspecting laminates, at least with today's technology, he explains.
How does it work? Any object produces infrared energy relative to its temperature—the hotter the object, the more IR it produces. But like X-rays, microwaves, and radiowaves, IR is invisible to the human eye, so we need a little help: Thermographic infrared cameras are engineered to interpret infrared energy and produce an image using temperature, not light, as a scale. A conventional camera, whether film or digital, reads visible light. Yes, film cameras can use infrared film, but it records a combination of visible light and some reflected IR as well; it's not the same as thermography. "Night vision" goggles or cameras amplify small amounts of visible light, but that's not thermography, either.
This article originally appeared in the September 2006 issue of Power & Motoryacht magazine.