CT 249 wrote :
"Sports that suffer such deaths due to significant increases in the power and speed of the equipment have normally reduced the power and speed of the equipment as a result. Sporting bodies have introduced major performance-restricting rules as diverse as the ban on turboes in F1 to the change in rules in javelin design, the end of F1 offshore multis and design restrictions on Tour de France bicycles so why not the AC?"
I don't think the above can be used as an argument for what we're discussing here. Yes, the AC72's are dangerous, mostly only if they capsize.
Yes. And due to their extreme design such is not only likely to but almost certain to happen
Since you can't totally ensure a catamaran that is designed for performance will never capsize, the efforts in making the boats safer must be in ensuring structural integrity of the platform while capsized, and developing quick methods of retrieving crew trapped under the overturned platform. Concentrating on total capsize prevention is not really the correct direction to follow, unless you limit the design so much that it is impossible to capsize. I don't think we want to see slow boats on the course again after seeing what can be achieved.
Just remember, when one of these capsizes, it is doing so at or near highway speeds. Add to that the extreme light construction, which makes these high speeds possible, and you have a recipe for almost certain injury or death. Like a hydroplane, these boats are likely to break up as they capsize, throwing the crew into broken chunks of boat, which may even have sharp, jagged edges. Hydroplanes have protective capsules for their drivers, for this reason. Also, hydroplanes were meant, as a class, to be raced in only smooth inland waters. Not so with the more traditional America's Cup. To reduce it to those conditions is, IMHO, dumbing it down for the sake of mere high performance.
Your comparison to F1 and Tour de France is not convincing me - F1 is going back to turbo engines next year. Their focus on safety has been in providing the driver with a safer protective shell in the event of an accident, not limiting performance to the point where an accident can't happen. If they did that we would see 35mph limits on their top speed.
The speeds that the cyclists do on the Tour through the mountain passes is enough to kill someone who falls off a motorcycle with full protective gear at those speeds, a bicycle helmet and lycra shorts offers far less protection. The limit on what bicycles can be used has little to do with safety.
It isn't the javelin that makes the sport unsafe, it's the ridiculous practice of having folks with tape measures standing in the field where the javelin is being thrown.
The AC72 class could be much safer if they had 6 crew per side of the boat, that remain in their stations at all times, and don't cross the boat in tacks. Perhaps even with seatbelts on. 2 helmsmen, one for each tack. In the event of a pitchpole or capsize, they are in a safe position and have quick release systems to eject from their station when their hull lands in the water. With 10minutes of bottled air as they already have, it should be relatively easy to get out of the boat. The danger is mostly being pinned under a 50ft x 50ft trampoline, which could be eliminated as the boat won't need to have one. Safety problem solved, now we can see if we can make these boats faster for the next Cup.
Now this is an intelligent suggestion. Elimination of the trampoline would also help prevent kiting, which is a huge hazard for these boats.
Sharpii wrote :
"To give a slight idea of how extreme they are, I will scale them down to the size of a Hobie 16.
For a Hobie 16 to have the same D/L as an AC72 it would have to weigh only about 120 lbs. Maybe about 140 lbs, after the crew was added."
I don't believe that you can scale these ratios as you have, as it brings about some weird comparisons. Quite correct, the crew would weigh 20lbs if you work it your way, but another conversion method (11 crew at 85kg each = 935kg, 16/72 x 935 = 207kg, more realistic if not overweight ?
Nope. I didn't know exactly how many crew these boats had when I made that post. I guessed at 10. So, my reasoning went as follows: 10 * 91 kg = 910 kg = 0.91 mt. That is added to the high end weight of 5.9mt to get 6.81 mt, which gives you a D/L of 18.27.
A Hobie 16, to have the same D/L would have to weigh 136 lbs total. including crew. Even though I was wrong about the number of crew, I was not too far off on the D/L.
Your math doesn't work because it over estimates, by a huge factor, the proportion of crew to boat weights. In order to get it to work, you need the following formula: ((16/72)^3) * 935. This is because you are shrinking the crew in three dimensions, not just one (same with the boat).
Also, the AC72 at their top speed is doing one boatlength per second, so by your comparison, the 120lb Hobie 16 with 20lb crew and 200square foot wingsail will have a top speed of 9,5knots.
Nope again. Planing speeds and foiling speeds do not scale up and down the same way displacement speeds do. Displacement speeds are limited by wave making. For this reason they scale up and down more exactly. Your wave making drag increases geometrically with speed. If the Hobie 16 and the AC72 were both non planing monos, the boat lengths per second would be a fairer comparison. Since, in both these cases (of the AC72 and the Hobie 16), the limiting factor is power/friction, your comparison is all but useless and therefor misleading.
Oh yes, and if the wind limit set for racing is scaled the same way, they would be doing all that in a maximum wind strength of 4,4knots.
That right there, is pretty safe !
Nope again. 16/72*38=8.44kts top wind speed. (Per your scaling formula)
