FASTENER FAILURES IMPROPER FASTENER SELECTION SINKS YACHT
In a recent case, a large, unattended sail boat sank while at its mooring, due to a leak through its hull. It was identified that the water, which initially entered through the hull, did so through a ¼ inch hole at the stern of the boat. Further analysis identified that the hole was created for a steel fastener, used to mount a stainless steel swimming ladder to a stern of the boat. During salvage of the boat, the fastener for the hole could not be found. However, other steel fasteners used in the installation of the stainless steel swimming ladder were examined and found extensively corroded.
Our analysis indicated that improper material selection for the fasteners was the root cause of the loss of the steel fastener. A steel fastener should not be used to secure a stainless steel component in an aggressive environment such as the marine environment. Steel corrodes quickly when in contact with stainless steel in an aggressive environment due to what is known as galvanic corrosion. During galvanic corrosion, the steel fastener corrodes whereas the stainless steel component does not. In fact, the steel fastener protects the stainless steel component. As a result, the steel fastener corroded quickly, and to a point that the bolt actually fell out of the hole, leaving the opening through the hull for water to pass.
This common mistake was made by the ladder installer. A shiny new steel fastener looks like a stainless steel fastener.
Why are inadequate fasteners selected? There are at least three common reasons why amateurs mistakenly select inadequate fasteners. They are as follows:
Lack of knowledge the installer does not realize that he or she is making a serious mistake.
Cost since higher quality fasteners and high performance alloys are generally more expensive, installers are often economically motivated to use cheaper grades of fasteners.
Availability the fastener may not be readily available so the installer uses whatever is at hand. This is often the case for cottagers and for repairs made when away from fastener supplies.
Although lack of knowledge, cost, and availability are often motivators to use substandard fasteners, there are means for the consumer to avoid falling into the trap. The following list can help to prevent the use of inadequate fasteners.
When replacing manufacturer installed fasteners, use only identical or specified replacement fasteners.
When installing components, use supplied fasteners or contact the manufacturer for a suggested fastener system.
Purchase replacement fasteners from reputable suppliers such as manufacturers authorized repair serviceman.
Learn fastener basics.
If in doubt, have the fastener replaced by a competent mechanic or authorized repair serviceman.
Keep a supply of replacement fasteners available.
After an emergency repair, replace an inadequate fastener installed for temporary use as soon as possible.
Dont be fooled. There are volumes of fasteners and teams of sales representatives available to industry.
Manufacturers expend considerable energy in searching for the best fastener for each application. Therefore, instead of our guessing the experts, use fasteners recommended by the manufacturer and avoid the costly mistakes which may sink your dreams.
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Walters Forensic Engineering | 277 Wellington
Street West, Suite 800 | Toronto, ON M5V 3H2