Vetus Louvred Air Suction Vents. Between model of 20 and 60 are anodized aluminium, Between model of 70 and 150 are AISI 316 stainless steel. A marine diesel engine needs sufficient air in order to function correctly. The model numbers given in the table relate to the engine horsepower for which they are suitable. For example: A boat with an engine of 80 HP will require for the combustion and ventilation air, 2 louvred air suction vents type 80 (1 x starboard + 1 x port). All standard air suction vents can be supplied with a synthetic dorade box as an option.