I was racing on Sunday and had the following situation.
I was next to and slightly behind a cat, both heading towards some moored boats. I was matching it's speed. Well almost
See really bad drawing below.
We were both close hauled on port tack.
I wanted to sail in as far as possible to get a better line to the next mark.
I was not sure who had right of way here so I kept going till something was said.
I constantly kept looking around my #1 to keep an eye on them as the #1 was blocking my view.
The crew on the cat eventually signaled they were tacking. So I tacked, and didn't make the mark.
I am pretty sure it is this rule that applies.

12. On the same tack not overlapped.
When boats are on the same tack are not overlapped, a boat clear astern shall keep clear of a boat clear ahead.

Was I in the wrong by waiting for them to say they were tacking?
It was a long race and I didn't get a chance to get back to the clubhouse to ask anyone.

I believe the vessel that is up-wind (you) have to give way if both travelling at the same speed.
If overtaking you must give way.

Without going into rule specifics, depends on a couple of factors.
If he is able to complete his tack onto starboard without hitting you, then you must give way to him (Port / Starboard) when he completes his tack, and he is letting you know before hand that you will have a problem in a moment.
If he would not be able to complete his tack without hitting you, he should call for 'room to tack' (old call was for 'water') to avoid an obstruction. You can tack (as you did, or hail back that he can tack and you will avoid him (by ducking and going a little bit further above his line)

Sounds like the second scenario and both of you have done it correctly.

Well said EC that about sums it up perfectly

The description's a bit vague, but if they tacked because they were about to sail into the moorings then yes you had to tack to give them water. If they wanted to tack because they were laying the mark then there are two other scenarios.

Scenario one is they could tack and complete their tack before they got to you, then you would have to tack to avoid a starboard tacker.

Scenario two is they could not complete their tack before you had to avoid them. In this case they have infringed you. You can only very rarely force another boat to tack when surrounded by navigable water and "on the same tack".

My guess is that if you were looking around the #1 to see where they were then they would probably completed their tack in time but they are a catamaran so not necessarily so.

This is only a very basic explanation and I'm sure many will get into it deeper...


Edit: Opps, EC got in while I was typing

We were about 20m apart and no room for him to tack.
We were approaching to moored boats fairly quickly. And yes, hadn't thought about the cat needing way more room to tack.
So I am thinking he was needing to tack to avoid the moored boats, whereas I wanted to go closer.
Thanks everyone for clearing this up for me.