A few weeks ago, in one of my very first sailboat races, I was the boat astern and I had to take avoiding action.  But I hit the boat ahead about 3 seconds (2 boat lengths?)  after she had completed her tack. A better sailor likely would not have hit her. I could find no answer to the question of how much time she needed to give me to avoid contact. Does it matter that I am a beginner sailor and it took my brain 3 seconds (not one second) to process what was going on?  Is the answer objective or does the tacking boat "take me as she finds me" as the lawyers say?  This must be an incredibly common situation.  I think it boils down to:  "How close s too close?"

Hi David
When the Port tack boat is tacking she is obliged by RRS 13 to keep clear of the Starboard boat.
When she has completed her tack and is on a close hauled course she is clear ahead and the original starboard boat is required by RRS 12 to keep clear. If she can keep clear while  manouvering in a prompt and seamanlike way then the boat that tacked has given her room as required by RRS 15.
Once a boat becomes the give way boat she needs to take immediate action provided she can do so promptly in a seamanlike way.
Paddy

Sorry my last sentence was confusing let me try to clarify
When you become the give way boat you must take immediate action to keep clear. If you can’t keep clear while maneuvering in a prompt and seamanlike way the boat that became the ROW boat has not given you the room to keep clear. 

Answer to Bob: being begginner or experienced sailor does not make a difference to any rule. 

To the question: I think it is always safe for the port boat to 1. avoid hitting the boat that tacked in front, 2. silently cursing the other captain, and 3. hail a protest (and let the judge decide if it was too close or not).

It seems that the answer to my question is that if a seaman-like sailor would not have hit the ROW boat, then I was at fault. Which I figured was the answer. 
I think, though, that the nub of David's question is whether there is a "rule of thumb" that helps us decide the question.  That's what I kept asking folks at the club. Isn't there a rule of thumb?

From the case book (103) we get that “The phrase “seamanlike way” in the definition Room refers to boat-handling that can reasonably be expected from a competent, but not expert, crew of the appropriate number for the boat.” So being a beginner doesn’t give you more room.. 

15 requires you to give the keep clear boat initially room to keep clear. How long that is, obviously depends on the wind, waves, boat type and such. But normally I’d say that after the tack is done, the keep clear boat needs to immediately start doing things. 3 sec is too slow in basically every situation. If the non-tacking boat needs to start reacting before the tack is done, then it’s a penalty on the tacking boat for 13. 

Also it’s important to remember case 50, which talks about “a genuine and reasonable apprehension of collision”. So if the stb boat feels that he needs to luff early, and there is a genuine and reasonable apprehension of collision, then the penalty again goes to the tacking boat.

But if the question is about a generic rule of thumb, then the answer is no.. it always depends on the boats and conditions 

Thanks.
It is difficult for me to get my head around some of this.  But, perhaps, one thing that is a big question for me is whether the non-tacking boat (whether expert or beginner) has a duty under the rules to anticipate the actions of the tacking boat, and how that affects ultimate liability. See, 1 second is much shorter or much longer depending upon whether one has seen what comes before. Or something like that. :)
I will stop talking now.  Thanks.

You do need to keep a lookout all the time, also as the ROW boat. So you should see the boat on port coming and tacking. And  if you need to react before the tack is done to avoid contact, then you should do that. And it’s a good idea to protest. if you see the boat coming, you keep your course, you see the tack done and then react and keep clear, it’s all good. So no need to anticipate, but for sure a need to keep a lookout and do all you can to avoid contact (breaking 14. Anyways, there’s nothing wrong with avoiding a bit early, if you feel you need to, and protest. that’s what the protest committees are there for :) 

David Dalli

said Created: Today 13:51

If there was no contact then there was room to keep clear unless contact was only avoided by an unseamanlike act or a miracle.

If it was not possible for the give way boat to avoid, acting promptly but no sooner than the other boat actually gained right of way (in this case, reached her close hauled course), and in a seamanlike way, then the right of way has not given room to keep clear.

Relevant Cases are

Case 21

 

Definitions, Mark-RoomDefinitions, Room

When a right-of-way boat is obligated to give mark-room to a boat overlapped inside her, there is no maximum or minimum amount of space that she must give. The amount of space that she must give depends significantly on the existing conditions including wind and sea conditions, the speed of the inside boat, the sails she has set and her design characteristics.

Case 103

 

Definitions, Room

The phrase “seamanlike way” in the definition Room refers to boat-handling that can reasonably be expected from a competent, but not expert, crew of the appropriate number for the boat.

2- Does 'room to keep clear' in this situation imply that immediate  avoiding action need not be taken by the give way boat.

The rules do not expressly oblige a boat to act immediately on becoming a give way boat.

Case case 88 is not particularly relevant to your scenario.  Case 88 is a scenario where the right of way boat is NOT required to give room to keep clear.

A better explanation of 'keep clear' is in Case 50

Case 50

 

Definitions, Keep ClearRule 10, On Opposite TacksRule 14, Avoiding Contact

When a protest committee finds that in a port-starboard incident S did not change course and that there was not a genuine and reasonable apprehension of collision on the part of S, it should dismiss her protest. When the committee finds that S did change course and that there was reasonable doubt that P could have crossed ahead of S if S had not changed course, then P should be disqualified.

So imagine the scenario of the second post where the starboard boat is coming in fast enough to hit the port tacker but is unable to luff up due to a boat above her? It seems that the test would not see a way for a competent captain and crew to avoid contact so sufficient room was not given? I have often ducked so as not to put someone in this spot when coming into a freight train of starboard boats fetching the windward mark.

Hi Dan
Would there be any reason why the starboard boat speeding in could not bear away in a prompt seaman like way to avoid contact. If it’s possible and a luff is not, she must bear away to avoid contact
Paddy