With just a day to go until the start of the 34th AC is once again in doubt, what’s the matter this time?

You can be sure that the America’s Cup is about to begin when the arguments over obscure details in the rules start. From past accusations of ‘cheating’ plastic boats in the 12metre era to the ‘Hula’ of 2003 there’s always something to characterise any given Cup episode. This time around, for the 34th America’s Cup, it would seem that the topic is rudders, or rather the T-foils that are attached to them.

The issue is a complex one involving the question of whether a specific rules change to allow larger T-foils is a performance or safety driven feature. The Kiwis and Italians see the proposed changes as set out in one of the 37 safety recommendations produced following regatta director Iain Murray’s post Artemis crash investigation, as being unacceptable given how close to the event they now are. But with the start of the Louis Vuitton Cup just hours away, the pressure could not be greater and a game of brinksmanship has begun. The two key Challengers have issued protests against the race organisers while the regatta director has responded by saying he is happy to see the event cancelled if his recommendations are not accepted in full.

Welcome to the 34th America’s Cup.

Last week I was in San Francisco talking to teams and organisers as the countdown to the Cup moved into the last few days. It was clear then that tensions were running high and that the conspiracy theory factory was working overtime. Now the pressure looks set to boil over as both sides wait to hear what the jury has to say following protests from the Challengers.

There are two issues at stake, both relate to the T-foils that are fitted to the bottom of the rudders on the boats. These foils act like the tail plane of an aircraft, maintaining fore and aft trim as the aircraft balances on its main wing. The T-foils balance the cats on their main foils when the cats are flying. But the T-foils also help to stop the bows going down during a bear away by providing a down force at the stern like a car’s rear spoiler as the boat pitches nose first. It is this aspect that provides a degree of safety, helping to prevent the boat from pitchpoling. The trouble is that the area of the foil on the boats isn’t really big enough to do the job properly.

At the beginning of the year Team New Zealand skipper Dean Barker raised this issue with regatta director Iain Murray in an email, suggesting that the area of the horizontal T-foil be increased. Others have apparently expressed concern that the foils lacked sufficient bite to hold the stern down. In addition to this Murray told me that there had been several incidents in which teams had come close to losing control as the rudders lifted from the water during a manoeuvre and had caused concern for the teams.

Following the Artemis tragedy Iain Murray’s review panel recommended a greater area for the T-foil, a move that his team felt would at least help to reduce the chances of a serious nose dive. When the draft rules were shown to the teams there were no issues raised and yet now the Kiwis and the Italians appear to have taken issue with the recommended change to the rules.

“I made these recommendations to the teams on May 22, over six weeks before the first race of the Louis Vuitton Cup,” said Murray. “At that meeting, all of the teams agreed to all 37 of the safety recommendations. Grant Dalton (managing director of Emirates Team New Zealand) walked to the front of the room, shook my hand, and told me, ‘Good job. You won’t get any push back from us.'”

But on June 28, Emirates Team New Zealand filed a protest with the International Jury over the changes. A few days ago, Luna Rossa Challenge did the same.

But the problem goes further.

There is another rule that limits the amount that any part of the boat, the T-foil when the rudder is rotated in this case, can overhang the stern. The position of the rudder stocks is therefore crucial. The further forward they are, the more inside span on the T-foil can be included when the rudder is rotated.

It is believed that the Kiwis and the Italians have enough space with their rudder stocks fairly well forward to fit a decent amount of extra foil span. Oracle and Artemis are understood to have their rudder stocks further aft and would find it harder to add additional span without moving the rudders forward. But it now sounds like the Kiwis and Italians feel that their T-foils have enough grip and no longer need or want to increase them. It would appear to me that preventing the rule changes from taking place could stop their opponents from making such modifications and therefore hamper their performance.

This approach is easier to understand if you believe the current dock talk in San Francisco that says that in making their boats robust and better behaved when foiling, the Kiwis and Italians have sacrificed some performance. Oracle has lower drag foils that are more difficult to sail on, giving their boats a more skittish appearance under sail, but as the Defenders learn to balance the boat on the skinnier foils, they are starting to look significantly quicker than the Kiwis and Italians.

There are other details too that are adding to the pre-event stress such as when the adjustable T-foils have to be locked off, but in essence, as we get closer to the first race, the dispute appears to be far more about seizing every possible opportunity to exploit a potential advantage.

Welcome to the America’s Cup, which should start with the first race of the opening round robin of the Louis Vuitton Challenger series on Sunday.

But then again it might not.

If the jury agrees with New Zealand and Luna Rossa, Murray said he’ll go back to the Coast Guard, which issued a racing permit this week, and say he doesn’t think the racing would be safe.

In that case, the Coast Guard would almost certainly withdraw its permit. “Without a permit to race on San Francisco Bay, there will be no regatta,” Murray said.

Either way Sunday will be a big story.