See, it's not all the "old/nothing new here" kind of thread. Many do not exactly know about these things and only few have the courage to ask.
1. No amount of wind can capsize a monohull. The monohull will heel further and further until the righting force of the design equals the force of the wind in the sail. The further the boat heels, the less force the wind can transfer to the boat. Also, mono's righten back up from heel angles far beyond 90 degrees, think 120 degrees.
2. It is waves that capsize monohulls, unlike cats that can be flipped by the wind and are much less likely to capsize due to waves. When a cat lifts a hull
up from the water
... the further it lifts it up, the more surface area of the hull
is facing the wind until it is maximized at 90 degrees heel. This counters the diminishing surface are of the sails
and makes it possible to flip by wind force alone.
Here's what helps a mono from not capsizing from waves: more length, more freeboard, more beam, more surface area of superstructure to complement the freeboard. Weight in the keel
doesn't help much. What provokes capsize is wing keels that work like a drag when heeled around 90 degrees and prevent skidding. There's the whole skidding off waves factor which by itself is often at the center of debate.
The shear beam of a cat is what prevents it from capsizing by waves. Only massive high breakers have a chance.
3. Most monohulls that sink, do so because they have either sprung a leak or caught fire. The leak is most often a problem with plumbing
. Cats also can sink, their cored hulls are no match for the weight of engines, mast
and all other stuff aboard (and they burn as easy as monohulls). However, they don't sink that often because cats are mostly modern designs with features like watertight bulkheads. Also, their low weight without keel/ballast means they can be tossed around a lot (more than mono's) before that leads to constructional damage.
4. Both designs have inherent weaknesses. For cats, it's the rigging
and the superior stability when upside down. The rigging is the more serious one while the flipping thing gets all the attention. When a cat flips it's mostly because of real big mistakes
from it's crew, but sometimes nature can throw so much at a boat in an instant, that the crew gets overwhelmed and doesn't get time to reef or even let go of sheets
etc. You can't compare with racing
cats that need to lift
a hull from the water
to be competitive, knowingly increasing the risk of capsize by a huge factor.
For any long time sailor it's obvious that there are areas where cats make more sense and areas where mono's make more sense. Buyers know that too so you can determine this from the ratio of cats vs mono's in the marina's. When there is 1 cat for every 10 monohulls it's sure that a cat is a better fit imo.