The first plastic kayak was made in 1984.
you melt it
weld it with nylon rod using iron plastic welder.
JB Weld
A Kayak made out of clear plastic so you can see through it into the water.
Kayaks are remolded by taking tiny plastic beads and putting them into a big kayak mold. The mold is then heated up and rotated around until the plastic beads conform to the kayak mold. The mold is then cooled, and the kayak is removed, cleaned up, then the seat, hatches, and deck rigging are installed.
You aim the hot air at the plastic edges and it melts as you put them together.
Not recommended.
A Kayak made out of clear plastic so you can see through it into the water.
I had 2" crack on top of the radiator. I tried JB Weld and other similar putty but they did not work on plastic. I bought Permatex PermaPoxy™ 5 Minute Plastic Weld from Advanced Auto Parts for $7. It took 10 minutes to finish the job and it worked.
Jb weld expoxy mix
I doubt very much it will hold.