Stability : what is the weakest link?

Question: Flipping over is the only thing about Catamarans that bothers me. Would not a weaker rigging make more sense? I would rather my rigging blow away than flip the boat over.

Answer: Your question is one that occurs to everyone at various times in the design process, ‘What is the weakest link, and can I plan for it to save the day?’ It only seems to work for electrical systems, in the form of fuses. Tangible things tend to store up a lot of energy in the process of reaching the overloaded state, releasing a lot of backlash when failure occurs, and broken stuff on board is usually broken for good.

Designing something to fail at a particular threshold flies against another pillar of engineering practice; the margin of safety. Most engineered items on the boat are 2 to 3 times as strong as the theoretical calculations suggest that they need to be. This is contrary to race design practice; ‘If it doesn’t break, it’s over engineered.’ Working equipment, including cruising gear, has to be built with forgiveness of;

  • miscalculation or incorrect identification of the true loads,
  • equipment degradation over time,
  • inadvertent extraordinary loads,
  • misuse or accident.

The possible dropping of a tall and heavy mast and rig with consequent structural damage and encumbrance of the vessel’s seaworthiness as it bashes away alongside or underneath represents a real threat. This likely scenario would not balance well against the unlikely capsize scenario. (Once again, what margin of error should be applied to deciding a breakaway strength?)

There have been attempts to invent sheet release mechanisms that I believe you may find discussed at the Amateur Yacht Research Society (AYRS). The absence of such gear from the gadget loving market (which is not entirely stupid) indicates the level of success/acceptance achieved. This type of gear always has consequences that may be as bad or worse than the one targeted and I believe that is the fundamental impediment. You can burden any function with sufficient devices to ensure its ultimate safety, it doesn’t work anymore and just becomes part of the landscape.

With the exception of monohull sailboats with external ballast keels, virtually every other thing that has ever been identified as a boat or ship has been subject to capsize without any expectation of recovery. For some reason catamaran cruising boats take particular criticism that would be equally applicable to fully rigged clipper ships, or even cruise ships. (Best stay on shore I expect.)

The primary reason (among many) to adopt a stable cruising catamaran design is the absence of several tons of essential lead ballast that tries, from the day the sailing monohull is launched, to drag it to the bottom. Sailing monohulls spend most of their time in a semi-capsized condition; they persist in cruising application primarily due to love of tradition and entrenched misconceptions. The threat to personal wellbeing in every regard that this vessel configuration engenders would not be endured in any other application. Capsized monohull sailboats are inevitably dismasted in any case by the exercise with consequent structural damage and loss of integrity. Perhaps they should be equipped with breakaway keels so the wreckage might float, and you can have something to hang on to? Bobbing around safely and indestructibly appears to be an attribute exclusive to the ducks.

Please do not equate the marginal stability of the sport catamaran (of any size) with an appropriate cruising design. The misapplication of race design rationale, though attractive to marketing, is counterproductive and possibly dangerous to cruising. I believe that is the real underlying issue in regard to ultimate survivability for vessel and crew. At the other end of the scale, having worked on self-righting rescue lifeboat design, I know that giving top priority to survivability in ultimately bad conditions will result in a bizarre vessel that is otherwise a burden to own and operate, and still there are no guarantees.

To go back to your question, one would like to see the shrouds and all running rigging miraculously and safely part, just as the weather hull cleared the water, leaving the spars etc. free to make a clean exit to leeward, but in practical terms this is impossible. The loss of the spar would be a very dangerous and messy event with ongoing ramifications.

Despite the action photography we strive for that captures our cruising cat cutting through the waves at just the right moment, the impression of ‘flying a hull’ is just that, an impression. You are very unlikely to get a cruising weight catamaran hull to lift like a beach cat. If it does, you are pressing the envelope rather severely, but hey, take a picture for us!

We believe that the vessel should do its best to take care of its crew, regardless of their level of experience and are confident that the vessel we offer demonstrates the best effort and rationale to achieve that.

Good question though, wouldn’t it be nice? How about explosive chainplate bolts? No wait I didn’t mean it!

TC

Advertisements