The deliberate fire was started on a vessel on the canal towpath in Oxford.
A man in his 70s and a woman in her 60s were the victims of an arson attack on their vessel, moored on Canal Street in Oxford, on Saturday morning.
A passerby spied the fire and alerted the elderly couple and, with the help of others, they extinguished the flames.
At around 2:20am, the fire service called the police to a fire at a shed 1.5miles along the same towpath.
Police believe that the boat was targeted between 12:30am and 2am.
No one was hurt in the attacks.
A shed near Godstow Road bridge in Wolvercote was also burnt down.
Read about how to tackle on-board fires, including the five types of fire extinguisher that should be carried in your vessel.
Flash fire at Deganwy Quay marina guts yacht
Three fire engines attended to the blaze on the Sandpiper of Hamble 14 foot craft.
Boats gutted by fire at Hythe Quay in Essex
Two vessels on the banks of the River Colne were destroyed by fire earlier this week
Classic wooden powerboat saved from fire on Lymington River
RNLI crews from Yarmouth and Lymington were able to get the blaze under control before it caused too much damaged