PVC releases all kinds of nasty chemicals when it burns. At 482 degrees, PVC begins releasing HCl (Hydrochloric Acid) which, when inhaled, sears the lungs. And may begin to break down rubber hoses and fiberglass, which undetected could result in a sinking boat.
Secondly, burning PVC releases Dioxin, a really toxic chemical. Dioxin is a serious cancer hazard and causes severe reproductive and developmental problems along with damaging the immune system and a lowered testosterone production. Dioxin was one of the bi-product ingredients in Agent Orange, the chemical the US sprayed over Vietnam to kill the thick vegetation. Since then there have been countless lawsuits from Vets with all kinds of health problems. Try doing a quick google search.
Uncooled exhaust temperatures are in excess of 700-800 degrees.
Normally I’m all for DIY stuff. Though, on this one, I wouldn’t mess with PVC.