By Barry Tranter
The very first boat survey I ever witnessed involved an amateur surveyor stabbing the blade of his pocket knife into the planking of an old ketch. Unfortunately, the owner of the old ketch was also watching. He didn’t watch for long; his face went purple and the amateur surveyor was given the boot – almost literally if it hadn’t been for him being a bit useful on his feet.
A brief lifetime later, Sydney boatbuilder/surveyor, David Holmes is showing me on his computer screen two photographs of a modern fibreglass yacht hull on a slip. One photograph, a conventional digital shot, shows a perfectly normal-looking hull. But the shot taken by the thermal camera shows a purple hull with dark-coloured stripes, which run athwartships (the colours aren’t relevant; it’s the contrast that matters). The dark colour indicates that the foam core of the hull’s internal framing grid is holding water. This also tells David that the hull has flexed and separated the grid from the skin, admitting moisture to the foam core. What is not recorded is what the yacht owner said when given this information. Or what colour his face went.
David is, as far as he knows, the only surveyor offering thermal analysis as part of a survey. The device he uses is a cross between a camera and a gun; it has a lens and it has a trigger, which records the image. The operator aims the gun where he wants, clicks the trigger and the image is stored. Later, it is downloaded onto a computer and the dedicated software helps analyse what the gun has ‘seen’. I ask David about osmosis and how the imaging system sees it.
“Osmosis traps water, which shows up as a different colour,” he says. “Osmosis blisters show up as cooler. The camera can show them up in a number of different colours, but dark seems to have the best effect. But osmosis blisters can be seen with the naked eye.
“What thermal imaging shows up are dark or cooler areas, which have not yet reached the blister stage. This is what the naked eye cannot see.” How about dry rot in timber yachts, the osmosis of an earlier time?
“Dry rot is warmer, as the moisture in the wood is heated by the air temperature and the heat is retained. Similar to compost,” he says. David also uses thermal imaging to inspect engineering systems. We look at another image on the computer screen; a diesel auxiliary mounted in a cruiser.
“You run an engine up to temperature and check water flow through the whole system,” says David. “You can see if there is a blockage because when the water runs slowly, it heats differently.”
Waving the magic camera over the injectors gave a different story. “Injectors should all be within a few degrees of each other, but if one injector shows irregular temperatures, there is a problem.”
The image we are looking at shows the colour of one injector to be less intense than the others. An engineer was called in and he was able to go straight to the defective injector, instead of having to pull them all down.
“This boat has two engines and we found that one exhaust was running 40 degrees hotter than the other. The engineer tracked this back and found one sea strainer was restricting water flow. In big engines, you can make massive savings.” The camera helps analyse electrical systems, too.
“On every survey, I switch on all the electrics and pull the main panel down. It takes only five minutes to check a system. If all the fuses are drawing properly, they are all the same colour. If there is a bad joint, it will show up. It is just a matter of looking at it – you don’t have to use meters and gauges.”
A cursory scan of a 24-volt system showed that one diode was running at 50°C and one at 40. One was working harder than the other. An electrician investigated and found a problem.
“The thermal gun finds the fault,” says David. “It doesn’t have to analyse it or fix it. I leave that to the specialists.”
David uses his system on new boats, too. It can detect a problem with a composite lay-up, where an outer skin is laid up over foam. The gases in the foam can expand, causing partial delamination of the skin.
New rudders and rudder stocks, made from vacuum-bagged carbon fibre, can cause trouble if there is a void in the lay-up. The thermal camera can find voids at the time of manufacture, minimising the chance of the rudder failing at sea.
David brings up one last image; the hull of an old ketch he has inspected with his thermal imaging camera. The image on the screen shows water trapped in a large area on the hull side, indicating that the caulking in that area is stuffed. Every fastening is shown; every joint. No need to pull out the pocket knife.
For more information, call David Holmes, tel: 0412 918 289.