Ras Katy is short hop south of main Sharm El Sheikh on a headland called Ras Umm Sid. The site can be quite overrun and does have "submarine" boats (glass bottom boats) visiting it. The are a bit of nuisance and liveaboard dive operators tend to use the site as a check dive site now, which is a shame as it has stunning wild life.
The boats tend to tie up either on the north erg or near a collection of underground mounts a bit further south. Diving is easy, jump in and explore. Towards the coast the depth is only about 5 metres and typically you will not go much beyond 16 metres (unless you go further out) - just beware the current can pick up as you move away from the reef. Generally, the current is very gentle and depending on the tide will be either north-south or in opposite direction.
The site is extremely popular with snorkellers and you can have a number of day boats tied up with anything of up to 100 snorkellers above you (especially if you are close to the north erg or shore) - it is even worthwhile to have look up, you might be able to see of Italian or Russian fish swimming above you.