Kankama said..
Energy going somewhere is a good point - it is what car designers have to do. back in the bad old days, car makers didn;t want to know about adding safety features like crumple zones, safety cells, soft interior furnishings and air bags. In the end, the US government got around the industry's reluctance and the big car companies head in the sand mentality by stipulating that all government cars would have to have air bags. With such a big contract on offer, one of the big companies blinked and now we all have air bags.
Getting energy somewhere is pretty easy IF someone thinks about it. First, put a small crumple zone on the bottom and front of the keel, a crash box. Cats and tris have been doing something similar for decades. Newick even designed a crash box into his dagger cases. In my case the entire tip of the board is cut off and reglued back on. It broke off when I hit a rock at 7-8 knots - zero damage to the case. How much hassle to implement? Almost none. Weight, performance, build issues? None. Upside - I still have a boat, instead of a waterlogged cat with a case ripped through its bum. Tens of thousands maybe vs me in the shed with some cedar and glass.
A good fast cruiser could easily have a small foam/glass section at the front and bottom front of the keel - with a layup sufficient to slip it fine but with enough foam to cushion any 11.5 knot impact. All you need is to increase the time - doubling the time of stopping halves the force. It could be small and do a huge difference. As time of impact is directly proportional to distance - if the Oyster's keel deflected 1cm in the above example (lead deforming) and you put on a small 10cm crash edge, you would increase the distance by 10 times and reduce the force by something similar. At virtually no cost or hassle during the build. So the guys would still have a boat.
Also make that root long and add one extra tight but weaker than normal keel bolt at the front on the centreline. This one would take the initial load and break. Rock climbers have tight stitching that lets go on safety devices to reduce impact loads when falling. Its a oncer but it saves the boat.
I needed to make a new tip and glue it on my cat when I hit the rock at 7 knots or so. If my 500mm chord, 1.6m deep board, into a cedar and 600gm glass hull show absolutely no damage after hitting a rock when I was stupid, then a boat built like a brick dunny can also do it. You just have to do what I did when I built it. Think just a bit about what could happen and work a fix up.
Sparau - As for Leopards - no they are just dumb. To not dry out is awful in a cat and it causes issues when lifted. A yard near me doesn't lift some Lagoons because they put one on its kesl and it crunched and caused a court case. Considering it is really easy to build them properly, I can't understand it. Again there is no reason that an engineer couldn't do this - the builder just cant be bothered. As for Seawinds - you must have got bad one. Most sail pretty well and almost no Schionning has had a racey window designed in about 15 years - those days are gone thankfully.
I do shake my head at dumb design because, having built and designed boats, I know that you can make the boat better with a bit of forethought. It aint hard but it does require you to acknowledge the problem. The fact that any cruising keel falls off is a problem that can be fixed. It is just engineering and building, it aint hard.
Designing a bolt-on keel structure that can withstand a high-speed impact is extremely challenging. Because the impact point is 2m or more below the hull attachment point, the impact force is multiplied exponentially resulting in massive dynamic bending. I think it if it weren't such a hard problem, it would have been solved by now.
Of course, there is a solution, and it's an encapsulated keel that is structurally part of the hull. Or a multihull :-)
