Same as the rigging- 10 years and replacement. I do not remember the source but the reason of the keel refitting every 10 years is that factory sealant ( glue ) is shrink or life time expire etc ...
Like many of these suggestions, this is another "cod" surveyor recommendations, although in this case its origins are more from the insurance companies rather than from any technical source. Rig failure almost always occurs in extreme circumstances such as on highly stressed racing rigs or on boats that are extensively sailed in stronger wind conditions such as long distance ocean sailing. The latter in particular invariably happens to boats older than 10 years so it is not surprising insurers ask for rig inspection and possible replacement before insuring boats for this kind of use. There was then a process of "mission creep" and surveyors covering their backs started to report in surveys on rigs older than 10 years and of course insurers started to require replacement before insuring. This is despite no scientific evidence that rigging wire or fittings decay with age - or even usage, nor does it take into account how the rig is designed, or particularly how the boat is used. A boat such as most of those owned by most people here that maybe sails a few hundred miles a year and rarely in winds over force 5 and is stationary almost all its life is treated the same as an offshore racer or cruiser. Unfortunately there is little systematic collection of data on rig failures (even less than for keel failures) mainly because it is so relatively rare and the claims are spread over large number of insurers so it is difficult to challenge the received wisdom.
There is a little more support for regular keel bolt inspection (and indeed removing keels and replacing bolts) - but this derives as I said earlier from wooden boats where the wood backbone had iron ballast attached often with mild steel or wrought iron bolts. Two things happen. The boat flexes and the seal between the iron and the wood fails and corrosion occurs in the middle of the keel bolts, known as waisting. Second, there can be a chemical reaction between the bolts and the surrounding wood, particularly oak and to a lesser extent some mahoganies causing decay of the wood. As I mentioned earlier I owned a wooden boat for nearly 40 years and I changed the bolts twice and removed the keel once. When I sold it last, it really could have done with the keel removing again as the seal had failed around 2 bolts. I still have three of the original bolts which clearly show waisting and in fact one of them came out in two pieces. I had quite a bit of interest in the keel bolt corrosion as a colleague of mine at the university did his PhD in the subject and used my bolts as examples in his classes.
When GRP first came in there was a move to bolted on fin keels and particularly twin keels so that boats could take the ground. Many of these were poorly designed, particularly the attachment and internal support. This was so bad on one model from a major builder had warranty claims that forced the company into receivership. Many fin keels of that era were poorly designed with inadequate fastenings and hulls that had insufficient internal reinforcement such that the keel would flex just under sailing loads, breaking the seal, and indeed on some boats breaking the (poor) casting at the fine ends.
However, none of this is remotely relevant to the boats we own and sail now - but the myths continue because they serve the interests of the people who benefit from the work they create.
