Boat sure to be wrecked — by this person? (8)
I believe the answer is:
saboteur
'this person?' is the definition.
(saboteur is a kind of person)
'boat sure to be wrecked' is the wordplay.
'to be wrecked' indicates anagramming the letters.
'boat'+'sure'='boatsure'
'boatsure' anagrammed gives 'SABOTEUR'.
'by' is the link.
(Other definitions for saboteur that I've seen before include "Deliberate wrecker" , "One who deliberately subverts" , "One who wrecks" , "He destroys in order to subvert" , "Rue boast about one who inflicts deliberate damage" .)