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The picture on the left is what not to do if starting from scratch and installing new seacocks. If your thru-hulls and valves, on your boat, are installed & look similar to this configuration you're not alone. This photo was taken on a brand new 2011 production sailboat.
Unfortunately, for many owners of production boats, the factories cut many corners to save money, proper flanged seacocks being one of them. This is understandable as the cost savings is huge to the manufacturer, and they can be relatively safe, though no where near as strong as a flanged seacock.
A proper seacock installation involves more than just a thru-hull or mushroom-head, as some refer to them, and a valve. The problem becomes more complicated when you learn why this is not necessarily the safest way to install a seacock.
The vast majority of all available thru-hulls or, mushroom-heads, have what's referred to as a straight thread or NPS (National Pipe Straight Thread), and the vast majority of all ball valves are a tapered thread or NPT (National Pipe Tapered Thread). NPS thread and NPT thread are NOT intended to be used together! Many unknowing boaters though know nothing about NPT or NPS threads and as such many times use the two together quite incorrectly.
In short, a proper seacock must have a female NPS flange that is through bolted to the hull to which the NPS straight thread thru-hull or mushroom head is then threaded into.
Another major problem with this installation is the mismatching of metals below the waterline. That hose barb is yellow brass and not bronze! This particular builder "claims" to build to ABYC specs but the ABYC P-06 standard / UL 1121 standards specifically states that all metals must be galvanically compatible. Yellow brass and marine bronze bronze are not galvanically compatible and never have been.
Please remember this is a 2011 vessel. The picture below of the broken thru-hull comes from this same builder..