Travelling in secret by boat, Washington twice replaced regiment in plot
I believe the answer is:
stowaway
'boat washington twice replaced regiment in plot' is the definition.
I can't judge whether this definition defines the answer.
'travelling in secret by' is the wordplay.
'travelling in secret' becomes 'stow' (I can't justify this - if you can you should believe this answer much more).
'by' becomes 'away' ('away' can be a synonym of 'by').
'stow'+'away'='STOWAWAY'
Can you help me to learn more?
(Other definitions for stowaway that I've seen before include "Non-fare paying traveller at sea" , "Travel secretly" , "Ship's non-fare-paying passenger" , "Unauthorised passenger" , "Shirley Temple film" .)