Reliable fellow's powerful tugboat? (5,2,8)
I believe the answer is:
tower of strength
This might be a double definition.
'reliable fellow's' is the first definition.
(tower of strength means a very dependable person)
'powerful tugboat?' is the second definition.
'tower of strength' can be an answer for 'tugboat?' (I've seen this before). I'm not sure about the 'powerful' bit.
(Other definitions for tower of strength that I've seen before include "one you can depend on" , "powerful tug?" , "Person giving support" , "One very reliable" , "person to be relied upon" .)