OK - I am going to have my say now.
Firstly - There has been a lot of rubbish written above - I wish some people would check their physics books before describing facts.

As we have a spinner, we want to use it and use it in a safe way that is reasonably competitive. Therefore I endorse the concept of trying to arrive at a workable ruling - but have seen little to encourage me yet. Let me explain.

1)Simple estimations of MOI dont work in many cases. Forget mass and guessing where most of it is - just use a rotating pendulum and measure the thing directly. I have had several communications with Paul Hill about his site - some of his equations are wrong (still) but he insists in trying to derive them from first principles. OK thats fine for him, but if he gets it wrong.....

2)Measuring rotational speed - this is easy - yes you can use a tacho - but I for one will not stand next to 13B at full disk speed - it needs to be remote - either a laser or on a very long stick with remote read out. This we have done before. Question - since it takes several minutes to achieve maximum speed (which you never do in the arena) just when will you take the reading? After 1 sec, 10 sec, 30 sec, 60 sec? All will give different readings.

3)Blade design - This is a fun one. Imagine an infinitely smooth drum as a weapon. OK you might not want to put your hand on it at high speed, but it is hardly a threat to an arena. Compare that with a triangular section hardened steel point for maximum crack inducement - as we have on 13B - a little more dangerous perhaps even if the disk has the same energy.

4)What is acceptable? I saw Kevins fancy curve plots on Sat - but how on earth has that any relation to Jonnos arena? Or anyone elses?

The crucial question in my mind is :
How much energy will this disk impart to this arena wall in a likely (or a worst case) impact, and can the arena withstand this impact without any ejection of material outside the arena?

Disk speed, MOI, blade shape, blade material, blade stiffness, arena shape, arena stiffness and arena material, potential angles of attack etc ALL NEED TO BE TAKEN INTO ACCOUNT.

Some empirical data can be obtained by testing. I strongly suggest we do this so that we all can learn real numbers and make sensible decisions.

Rant over!

Richard
13 Black