In team racing we have the redflag, in match racing the y.
A redflag generally means a protest, if seen as it should be you can take a penalty.
I like the flag, as a protest committeeit is easyif you gave flown it. 
To me optimists and other small singlehanded boats had developed simple ways of displaying flags.
I agree the size distinction is not justifiable.
All boats should display flags if it was my call.

Just a question on boats like Optimist or ILCA where do you display a red flag all the race long until you finish? 
Secund thing, imagine a TP52 race with a lot of noise onboard due to the fact of carbone structure, do you really think you could hear «  protest » ! 

The answer is definitive if you are a keeper of records. The flag used to be required by all boats until 3 or 4 or 5 ... rule books ago, when the Racing Rules Committee made the change. Their reasoning should be in their minutes, or the memories of the older IJs.

As to Didier's question: kodak film cannisters, under the boom. But we don't use film anymore ...

  Using a red flag remains important in youth sailing. It helps reduce unnecessary back-and-forth on the water and clarifies when a competitor is actually making a protest. Out on the course we often hear things like “circles” or “do your doughnuts,” while the word “protest” is rarely used. Hoisting a red flag and stating “protest” serves two key purposes:

Verbal exchanges can easily be missed in the heat of competition or amid the noise and conditions of an incident—especially when contact occurs, such as masts touching or boats colliding. The red flag reduces ambiguity and ensures the process is understood by everyone involved.

Well, I'll play devils advocate.

1. A boat should know if she has broken a rule.
2. A boat that has broken a rule is required to take a penalty even if there is no hail or flag.
3. It therefore follows that to only take a penalty if and after the protest notification requirements have been met is at the least verging on unsportsmanlike conduct.
4. Given a really strict and literal interpretation of 44.2 it could be held that the time interval for hearing a hail and seeing a flag exceeds the delay permissable for starting to get clear of other boats, and therefore makes the alternate penalty invalid.

My own view is less extreme. I find it unacceptable that a failure to follow procedure precisely on the part of the injured party should constitute a get-out-of-gaol-free for the guilty, but it could justify a PC imposing a lesser penalty than disqualification.

The requirement for boats under 6 meters to display a red flag was removed in The Racing Rule of Sailing 2001-2004. Prior to 2001, the beginning of the digital photography era marked the end of film canisters, and consequently, the need for boats less than 6 meters to display red flags. Previously, film canisters were attached to our booms, with red flags stuffed inside. When a protest was necessary, one would hail "protest" and pull the flag out of the film canister. No more film canisters, no more red flags for small boats. Probably not but sounds plausible!

The Racing Rule of Sailing 1997-2000
61.1
A boat intending to protest because of an incident occurring in the racing area that she is aware of shall hail 'Protest' and conspicuously display a red flag at the first reasonable opportunity for each.

The Racing Rule of Sailing 2001-2004
61.1 Informing the Protestee

(a) A boat intending to protest shall always inform the other boat at the first reasonable opportunity. When her protest concerns an incident in the racing area that she is involved in or sees, she shall hail ‘Protest’ and conspicuously display a red flag at the first reasonable opportunity for each. However, boats of hull length less than 6 metres need not display the flag, and if the other boat is beyond hailing distance the protesting boat need not hail but shall inform the other boat at the first reasonable opportunity. A boat required to display a flag shall do so until she is no longer racing.

Perhaps Angelo's question could have been better posed as 'Why is there a lesser requirement for boats under 6m?'

Here's some history

Red Flag

Prior to 1961(?) the purpose of the red flag was to inform other boats that a boat was 'sailing under protest'.  The red flag was the primary means of signifying this information, and was required, at least since 1947, to be displayed at the first reasonable opportunity.

Up to 1985, the requirement to inform the protestee orally was ancilliary and was not time limited:  Rule 68 merely  provided A protesting yacht shall try to inform the yacht she intends to protest that a protest will be lodged.

My personal recall is that in the late 1960s/early 1970s, at least by convention, for Lasers, a white handkerchief was acceptable in lieu of he red flag.

I'm not sure when the under size dispensation for dinghies was introduced, but I recall that it was originally 20 feet, which was exactly the loa of a Flying Dutchman.

The argument for introducing the dispensation was that for trapeze or solo boats it was impractical to display the flag without delay after an incident in manuy cases
 
Hail

The requirement for an immediate hail was introduced in 1985 in support of taking on-water penalties, which were introduced at that time as 'alternative penalties'.
 
The 1985 rules added the requirement for an immediate hail:  A protesting yacht shall try to inform the yacht she intends to protest that a protest will be lodged.  When an alternative penalty is prescribed in the sailing instructions, she shall hail the other yacht immediately.

The requirement that the hail include the word 'Protest' was introduced in the 1995 rewrite.

The hail thus became the primary means of informing the protestee, or perhaps better said the means of informing the protestee became the hail and flag together [at the first reasonable opportunity for each].

The requirement that the hail include the word 'Protest' was introduced in the 1995 rewrite.

Considering the background it is clear that the ONLY purpose of the hail of 'protest' is to facilitate the taking of a penalty.

Practicalities

In a small solo or trapeze boat it is often impractical to display a red flag without delay and continue to sail the boat to advantage.  Incidents will usually take place at fairly low relative speeds between boats so that it will be usual for a hail to be readily heard.

For larger boats, it is usually quite possible to display a red flag immediately after an incident without affecting the performance of the boat.  Larger boats may have greater speeds of separation after an incident so that it may be impractical to repeat an indistinct hail, and confirmation by the display of the red flag us useful.  A protestee may be unsure that they have heard a hail of protest, but the red flag may assist them to make the decision to take an on-water penalty.

Doc Sullivan

said Today 01:14 ID: 19698

So the OA was asking Judges/Umpires to give them refereed racing.  Were you OK with that?

So what?  If you were satisfied that they took an on-water penalty you could withdraw the committee protest, or if not immediately satisfied, go ahead with a hearing and maybe conclude that they had taken an applicable penalty and not penalise them further.

Only if the NOR/SI have switched off RRS D2.1(b) which always requires a red flag.

Don't your team racers have red flags sewed into the cuffs of their sailing shirts?