It is important to be able to shut off the flow of water into a boat if one of the hoses fail. This is commonly done with a ball valve screwed onto the thru-hull fitting or with a real seacock as shown on this page. As thru-hull fittings are made from cast metal it is possible for them to have hidden flaws. They are not overly strong anyway. If a heavy object is dropped on them they can and do break. If a ball valve is used as the means of shutting off the flow, your only recourse is to try to plug the hole. If the thru-hull is equipped with a properly installed seacock, it is very unlikely to break as the seacock protects it. Even if the thru-hull fitting corroded completely away, a properly installed seacock would continue to function. The Groco IBVF ball valve flange gives you the strength of a seacock but with the ease of changing a ball valve.