Depends on how much you want to spend. The engine room on my trawler
has about 500 sq ft of ceiling and outside walls so I'm going with two layers of 1.5 inch foil backed foam covered with 1/2 inch plywood
, total cost of materials of about $1 / ft. It's not fireproof, but than neither is the 3000 gls of fuel
. Other than the air vents, there's only one hatch
so I'm going to rely on an inert gas fire suppression system with backup extinguishers. My engine is a 8/71 Detroit Diesel
that screams and it works pretty good.