View attachment 2407 (Photo Property of Paul Lee. Link: http://www.paullee.com/titanic/NMM_Pics/
For the ship that is blocked by the sail of the boat this one has some key identifying features that will help in identifying her. If you look at the fore mast and main mast she appears to only have a birdbath style platform on the forward mast. She does not appear to have any form of platform on the rear mast. The forward mast just like the HMS Powerful is situated just aft of the superstructure. You have a verified 3 stack arrangement as well. I decided to look up just a three stack ship of the time and found a convincing hit for a Gem class cruiser. Mainly the HMS Topaze
Gem Class Cruisers
You can see in the link above the lower left HMS Topaze photo shows she has a platform on forward mast that looks similar to what we see in the photo above. I will be digging a little deeper to see if I cant find a more proper fitting ship but so far this is the only suspect I have as of now.