01-27-2009, 10:41 AM
[center][left]One of the items that marine surveyors check under the heading of basic hull components are thru-hull fittings. These are simple pieces of hardware that are often ignored, but a failure can be catastrophic, causing a sizeable yacht to sink in short order. So what do we look for?
![[Image: thru-hull_1.jpg]](http://www.boattest.com/images-gallery/News/thru-hull_1.jpg)
[/url]Take a close look at this thru-hull. Notice the gap in the bedding compound. Water could be seeping through.
First, from the outside, I want to see that the bedding compound is still present. On older boats this is particularly important. Some of the bedding compounds and sealants introduced as “the magical cure” in the past didn’t prove to be so magical. They’ve deteriorated over time, for a variety of reasons, and the integrity of the seal between the outside the hull and the inside of the hull may now be in question.
The material from which these fittings are made is also critical. Like sealant compounds, we’ve learned a lot about materials in the last twenty or thirty years. Some of the plastics which were thought to be indestructible have proven to be less than ideal. In fact, plastic thru-hull failures may account for more sinkings than any other single cause. The older nylon, when exposed to the elements for a period of time, can literally crumble away.
![[Image: thru-hull_2.jpg]](http://www.boattest.com/images-gallery/News/thru-hull_2.jpg)
[/url]On this thru-hull fitting the bedding compound has disappeared completely from around the flange.
Fortunately, the newer ones are substantially better than the old, thanks to the addition of inhibitors in the molded material. In addition to material failure from deterioration, it’s not a real stretch to see how these fittings can structurally fail from the inside. A plastic thru-hull can easily shear off if someone were to, say, use the fitting as a place to brace his foot when working in the engine room. Worse yet, the failure may not happen at that point, but add some vibration underway, and you may be broadcasting a “MAYDAY” before too long. Although the newer plastic thru-hull fittings have been greatly improved over the older ones, metal thru-hulls are far superior to their plastic counterparts.
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[/url]Take a close look at this thru-hull. Notice the gap in the bedding compound. Water could be seeping through. First, from the outside, I want to see that the bedding compound is still present. On older boats this is particularly important. Some of the bedding compounds and sealants introduced as “the magical cure” in the past didn’t prove to be so magical. They’ve deteriorated over time, for a variety of reasons, and the integrity of the seal between the outside the hull and the inside of the hull may now be in question.
The material from which these fittings are made is also critical. Like sealant compounds, we’ve learned a lot about materials in the last twenty or thirty years. Some of the plastics which were thought to be indestructible have proven to be less than ideal. In fact, plastic thru-hull failures may account for more sinkings than any other single cause. The older nylon, when exposed to the elements for a period of time, can literally crumble away.
[/url]On this thru-hull fitting the bedding compound has disappeared completely from around the flange.Fortunately, the newer ones are substantially better than the old, thanks to the addition of inhibitors in the molded material. In addition to material failure from deterioration, it’s not a real stretch to see how these fittings can structurally fail from the inside. A plastic thru-hull can easily shear off if someone were to, say, use the fitting as a place to brace his foot when working in the engine room. Worse yet, the failure may not happen at that point, but add some vibration underway, and you may be broadcasting a “MAYDAY” before too long. Although the newer plastic thru-hull fittings have been greatly improved over the older ones, metal thru-hulls are far superior to their plastic counterparts.
[/left][/center]
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