Situation
The sailing instructions specify an arbitration procedure for breaches of rules of part 2 and rule 31 which is voluntary for the parties, but when the procedure is agreed, no witnesses are permitted, and the decision of the arbitrator is stated to be final.

Question 1
Is this valid?

Answer
The basis of arbitration under Appendix T is that that the parties are given an opinion which they may either accept, or reject and proceed to a hearing.
The procedure described is in effect a hearing, therefore Section B of Part 5, Hearings and Decisions, applies. The sailing instructions may change rules 63.6 and 66, so that witnesses are not allowed at a hearing, and a reopening of a hearing cannot be requested. However, the right to appeal may be denied only under rule 70.5.