cheers for any help
It only looks bad and does not affect performance. but can be fixed pretty easily too.
This is called "oil canning" and used to be common on whitewater boats. with yours being near the end I'm wondering if it has been sitting on something for awhile as it usually happens under the seat. when I see this, it's usually been on a rack for awhile or tied down to tight transporting it. I use a heatgun and heat up the plastic, then when it is hot enough I push down and put weight on it til it cools. if this boat has a rear hatch, I would simply heat it up, flip it over and fill it up with water. You might want to put some weight directly on it if you can? then fill it up with water. Never hold the heatgun in one spot, you want to circle around the depression more than heat the deep spot. it's better to not get it hot enough and have to start over than to burn a hole in it. Most of the time the plastic will start to get "shiny" thats when I back off or quit and try pressing down using a chunk of foam cause its hot. this plastic is good about memory retention and will go back, i usually have to do it 2 or 3 times slowly massaging it each time before it stays. it may take longer this way but I have never ruined a boat either. I just fixed a dent in a Dagger Axis yesterday, worked 1st try. And now I have a 2012 Axis for $350 just because it had some dents. I hope this helps and once you fixed it get a 3 or 4 inch thick piece of bulkhead foam, cut it to fit in that area and it will keep it from happening again.