Sailboat ventilation chest for low profile cowl vent

This low-profile cowl vent box is designed to prevent water ingress into the interior of a boat using a simple labyrinth water trap. The box is extremely low-profile and facilitates cheap rubber cowl vents available on the market. As an additional feature, I included a closing cover for rough weather, which can be operated via a crank lever from the interior.

I have used this system for two seasons now, and it has proven to be a great alternative to poor-performing solar vents. My previous solar vents collected a lot of water inside and provided weak airflow. With this new design, I keep the cowl vent always facing forward, and even when a bucket of water is thrown at it, not a single drop enters the interior.

Assembly Requirements:

Cowl vent with a 116mm hole diameter (e.g., Sea-Dog Line or any similar vent available on the market)

Stainless steel threaded rod: M6

M6 nuts: 4x (stainless steel or brass)

Bolts to fix the cover and chimney to the deck: Long and slim; at least 12 pieces of 3x70mm. Print and test before final selection.

UV-resistant sealant for hole protection

Some grease

CA glue

Assembly Instructions:

Find the best mounting spot.

Cut a hole in the deck (minimum 110mm; I made mine 116mm).

Insert the chimney into the hole and seal it on the walls and mounting flange.

Insert M6 nuts into the chimney slots at the bottom and top cutouts in the center.

Install M6 nuts in the hand crank and chimney cover, securing them with CA glue.

Screw the M6 rod into the chimney so that it goes all the way through.

Attach the chimney cover from the top so that the rod does not protrude above it (glue it with CA so it rotates with the rod).

Apply a small amount of grease to the cover from the bottom.

Install the top cover:

First, screw in the part that covers the chimney (this will push the chimney and top cover together).

Then, mount the cowl vent's mounting flange and secure it with the top cover to the deck.

Attach the cowl vent to the flange.

Adjust the interior knob:

Screw in the knob and lock it with an additional nut.

Test the opening and closing function by rotating the knob.

Adjust the best travel distance (fully open should touch the chimney nut in the center).

Cut off any excess M6 rod.

Secure the knob with CA glue to prevent it from rotating out.

Important Notes:

Always use sealant on any hole in the deck to prevent water ingress to fiberglas.

Wind flow is significantly better than a solar vent of the same size.

If mounted correctly, the vent can withstand being stepped on.

I printed the parts in PETG, and it is strong enough to endure mechanical stress.

Always mount the vent higher than the chimney. The chimney has drainage holes on its side that allow any water ingress to drain out of the box.