Whatever the reason - those or the bottom ripping out or the bolts snapping off or whatever - it should be uncommon to the point of freakishness.
I work as a mechanical engineer though not on highly loaded structures but my feeling is that all these software simulation programs every engineer uses these days are partially to blame.Prior to Drum it rarely to never happened (I can't recall a single incident) and fin keels had been the norm for 15-20 years at that point.
Except that a grounding or collision seldom if ever results in the keel falling off (which is what we are talking about here). The damage from such a collision is more usually a puncture of the hull near the trailing edge of the keel, or destruction/delamination of the keel grid.I agree in principle, but in reality hardly anyone is willing to incur the weight, performance, and financial penalties of specing a keel that will withstand a collision at speed with a semi-submerged shipping container. Maybe you could get away with it in a heavily built full-keel boat, but hardly anyone reading this site sails those.
Well hopefully you justify and defend your loading assumptions.I work as a mechanical engineer though not on highly loaded structures but my feeling is that all these software simulation programs every engineer uses these days are partially to blame.
Almost nobody does hand calcs anymore. You ball park the design based on your experience and run it through FEA, tweak a few things to hit your design target and send it. This leads to a false sense of security because you trust the software but don’t do as much agonizing over your assumptions of the max loading conditions.
When we were not as good at designing things to the limit before all the fancy software existed, a lot higher factor of safety was baked into the design that helped with lack of perfection in construction or installation.
how come small boats don't lose their keels ?I don't agree.
"The facts: surely everybody remembers the keel that some years ago fell off a Bavaria Match 42 and recently all know that an almost new 90ft Oyster lost the keel. Some know about two First 40.7 but less know about a Bavaria 390, a Jeanneau 37, a Vand den Stadt 45, a Sweden yacht 42, a Fast 42 a Maxi 110, a Max Fun 35 or more recently a Comet 45 and some days ago a Davidson 50.
Nor many know that since the mid 80’s more than 75 boats have lost the keel with the loss of 28 lives.
Probably the numbers of keels lost or boats abandoned offshore with problems on the keel are way bigger and much bigger the number of boats that were found with keel problems before actually a disaster would occur. These are only the numbers regarding the cases that were found by a work group formed by World Sailing to study the problem and most of them were high profile cases.
Some of the keels were lost due to the contact with the ground or submerged objects, some due to poor design or poor building like the cases of the Match Bavaria 42, the modified Oyster 825 or the Max Fun 35. Others due to the weakening of the structure as a result of bad maintenance, groundings whose damage passed unnoticed or were improperly repaired while others, like the recent case with the Comet 45, remain a mystery."