This can be incredibly frustrating and an issue I have only ever seen the race committee do anything about once in decades of racing in numerous places.
I can see the administrative difficulty of advising a boat that has no radio comms, that they are in another fleet's start, and to leave or be DSQ'd, but in keelboat classes that often have a VHF, there's no excuse for not broadcasting a reminder before each start, and penalizing the offenders.
Perhaps we need a new rule 30.5 that requires the RC to display sail numbers of offenders and once displayed, that offender is given the equivalent of a DNC; I can think of many acronyms for this behaviour but let's keep it clean and  call it DNKO "did not keep out". !!

First, I'd regulate this issue in the Sailing Instructions as a DP rule. Boats not starting have to stay clear of the starting line. Maybe mentioning this in the course diagram helps. Second, I'd send a rib.

Eric, I think the big boat is neither creating "a hindrance or obstacle" for the centerboarders, nor hindering / impeding them, as they have no need to take avoiding action. She's interfering with the RC, but there's no RRS rule against that. Unfortunately, absent an SI that prevents boats from being in the starting area when not racing, I don't see any rule you can hang your hat on to penalize them.

- John

 RRS 23.1 If reasonably possible, a boat not racing shall not interfere with a boat that is racing 

Protest her, DSQ in the nearest race, she'll learn for the next time

For the sake of discussion, I’ll take the “breaks 23.1” position and argue that ….

PS:  I think the RC might have considered postponing the start and starting the sequence over.  

This is all something of a non-argument. Any Club running mixed fleets and/or multiple starts will have included the wording found at 12.4 in the WS Sailing Instructions Guide, or something like it: 12.4  Boats whose warning signal has not been made shall avoid the starting area during the starting sequence for other races. It can be a DP or if the RC so desires.

A Club running these events without using this wording has no basis to penalise a boat that is 'in the way' but has not broken any rules.

Angelo, I wholeheartedly agree that a postponement, general recall, or abandonment and restart of this race might have been a good move, but with due respect, I must take issue with a couple of your assertions about the common understanding of "interfere";
     a) If you're trying to tune in a radio station and failing for the reasons you state, you're not getting interference from the building, the radio station is. You're just in a place with no radio signal.
     b) I think you're just mistaken about whether an American football defender would be penalized for pass interference as a result of blocking the view of a receiver without touching him. I've certainly never seen such a penalty, and I've seen many a defender who blocked the view of a pass receiver. I'm by no means a football expert, but I'm unaware of any rule that protects a receiver's view of the ball.

I agree with Nick Hutton that it was a mistake to omit language in the SI that keeps boats not racing away from the starting area, but since it appears they did in this case, I think his last sentence can be shortened: "A Club...has no basis to penalize a boat that...has not broken any rules."

John … you are correct about the NFL … my mistake there.  It’s a High School Football rule.  It’s a type of pass interference called “face guarding”. 

Like I said. I’m taking my best stab at making the case “for the sake of discussion”. 

What about my points #1-#3?

Before one can determine if Boat A  interferes with Boat B .. shouldn’t one consider what Boat B is doing or attempting to do?

Are they rounding a mark?, attempting to tack? sail to windward? Start?

As I expected, a wide variety of opinions!  I have already proposed adding the appropriate language to the SI.

The question remains:  Is a boat not racing but blocking the view of the starting mark "interfering" with boats attempting to start?

I like Tim's new "letter" score.  Since we now have NSC (Not Sailed Course) we might add NKO (Not Keep Out).

If I had been the race officer I hope I would have postponed.

 .....If I had been the race officer I hope I would have postponed. 

Correct.

a n d .... i definively add....

....   If I had been the race officer  I would have protested her under 23.1 

Looks you are quite timid at time of protesting and DSQing. Boats that do not behave are annoying other boats, so if you let them, you are not making a favour to the fleet.

Aldo - Not sure why you are calling me "quite timid".  I was not involved in the incident, nor on the RC.  Other well-certified commenters on this thread are not nearly as certain as you that a rule was broken.  "Annoying" is not a rule breach.  My reason for the original post was to explore the definition of "interfere" as used in RRS 23.1.

Eric re: " "Annoying" is not a rule breach"

One can dream can't they? :-)

Eric, I was not referring to anyone. From all the replies, I felt a sort of hesitation, like the fear to make a tort to a boat,  if protested.
And  about the "annoying",  also to clarify my point (Angelo) :  interfering IS breaking a rule. Boat breaking rules are annoying. 
OK, the protest should first come from the boats, rather than the RC, but sometime RC or PC have to take the initiative. 
Well, in the case of a boat that makes me repeat a starting sequence, I definively will.

Thanks, Aldo.  No offense taken.
This incident did occur last Thursday.  There was more to it than the hypothetical I posted above, as a centerboard did need to take avoiding action.  Protest filed, big boat took a Post-Race Penalty, incident resolved, and hopefully lesson learned.  Now waiting for the blessing of our Chief Judge for the proposed amendment to the SI, which includes that the RC "may" impose a 30% penalty on a boat they observe to be "interfering".

There are many different workaround solutions for this problem, but as this is a forum called the Racing Rules of Sailing we should really limit ourselves to rules-based solutions. I would not consider a 'naming and shaming' regime as applying the RRS. Simply write it in your SIs that boats whose warning signal has not been made shall keep clear of boats that are racing or similar (Appendix L provides some nice words), and protest boats that fail to keep clear. Applying a rules-based solution lessens the likelihood of accusations of bias and should not unnecessarily embarrass anyone. It is even possible that the competitors will read the SIs and actually keep clear! Ok, call me a dreamer.