Cowl Vents and Dorade Boxes: How Can I Add A a Shut Off?

[Tom_F]

I need more/better interior ventilation in the living spaces on my boat. I have two solar-powered mushroom vents I want to add, but I'm also thinking about adding a couple of screw-in cowl vents on the cabin top. Something like this: https://www.defender.com/product.jsp...800&id=7607907 with a traditional teak dorade box. However, living in a colder climate there are times I am going to want to close these off. I know I can remove the cowl vent and screw in a deck plate, but is there a way to add a shut off that can be opened and closed whenever the need arises, preferably from inside the boat?

I know Vetus and others make round dorade boxes that the vent mounts directly on top of that have screens and shut offs (like https://www.defender.com/product.jsp...800&id=7421967) but I'm not crazy about the look and I'm concerned about whether they function well, especially with wind-driven rain when the boat is on its mooring with no one there to close the vent. I also know they make mushroom vents (like https://www.defender.com/product3.js...143&id=1648744) that have shut offs, but that seems to be overly restrictive.

Any good suggestions?

Thanks.

Tom

[Manateeman]

If you have a traditional dorade box all you need is to stuff a towel up the deck pipe. You could add a slide closure but towels work for us. A good dorade box ought to have a short baffle on the inside of the top so water and rain do not go down the deck pipe to the interior. This helps stop drips. There are all sorts of drawings for the perfect dorade box on wood boat web pages. The length of the pipe going through the deck from below can make a big difference. Too close to the top of the box and you cut flow in light winds...too low and you get drips. A drip baffle inside the box between the cowl and the cabin pipe is often missing in some of the teak boxes but easy to add.
I’m not a fan of the Vetus round box as I think it’s a bit complex and might restrict air flow...but they do make nice cowls. I don’t think the solar fan vent things do much. One good cowl moves a lot more air if there is any wind.
If you had my manatee crew, you need a lot more ventilation.
Happy trails to you
Captain Mark

[Tayana42]

You could mount a deck plate under the vent inside the cabin top. Then you could screw in or remove the cap as desired.

[Bill O]

Once again, Capt. Mark is on the money about dorade vents. Instead of a towel to close off the incoming pipe, we use packing peanuts in a sealed plastic food bag. Either would work fine.

Many years ago we made our traditional wood dorade boxes w/4" vents and have attached a link to an article we wrote up. In our unbaffled smaller aft cabin boxes we used mushroom vents to close off the air flow into the cabin. This works ok, but can allow water to come in if the mushroom vents left open in the rain. The correctly built traditional baffled boxes are much better in keeping water out of the cabin and still have good air flow.

If you want dorade vents on the fore deck, then you will want to have a dorade guard of some sort so you don't rip your vents or hang up the sheets on every tack. We had custom ones made that were relatively inexpensive.

Originally we made the dorade boxes out of wood, but recently replaced the boxes made out of high density urethane (HDU) and painted white. While the box design remained the same, the new boxes where lighter (weight), less maintenance and reduced the box heat than from the darker wood. Similarly, one could make mold and make boxes out of fiberglass.

[Chotu]

Manateeman for the win. Shove wherever rag/towel up the hole and it’s closed. That’s what I’ve always done.

[Tom_F]

Rags, towels and a bag full of packing peanuts? Great ideas all! Thanks to all for your wisdom. Clearly I was overthinking this.

@Mark, thanks for the reminder about the baffle. I’ve decided to buy rather than build (unless I can get some appropriate size Azek or other synthetic lumber, in which case I may change my mind) but I will check for an appropriate size baffle. I’ll also make sure the drain holes are adequately sized.

@Tayana42, good idea on the deck plate.

@Bill, thanks for the link to the article. My preference is to have them behind the mast so I do not need guards. Fingers crossed.

@Chotu, thanks for taking time away from your project to add your thoughts.

Tom

[Don C L]

This came up some years back, and at the time as I recall there was a dorade box with a screw-on cap for the vent on the inside discussed. But a bag of peanuts is cheaper I guess...

[Bill O]

Over the years I've seen other ways to partially/fully close off the inside vent. A round w/a single point axis can be rotated in place or some have made hatch type sliders to move the mini hatch over the vent hole.

With our teak trim ring in place, neither looked that great so we went w/the bag of packing peanuts. Only need to shut them down when using a heater.

The bags of packing peanuts are also used in the fridge/freezer for air displacement when not as full. Haven't done any actual testing to see if it really makes much difference, but seems to help.

The only other suggestion is to go with the largest cowl vent possible for better air flow. A 4" provides significantly more air flow than a 3" w/a properly designed box. Many commercial boxes are designed for 3", so be certain to do the calculations to make certain the box is not the bottle neck if you go w/a 4".

[brianc]

Get some 4” thick memory foam (yoga block on Amazon is the cheapest way to go), and cut a plug. You can probably drill through the center to “through bolt” a handle of some kind. It would look better than a towel. I use a towel fwiw.

[Boatyarddog]

Originally Posted by Tom_F

I need more/better interior ventilation in the living spaces on my boat. I have two solar-powered mushroom vents I want to add, but I'm also thinking about adding a couple of screw-in cowl vents on the cabin top. Something like this: https://www.defender.com/product.jsp...800&id=7607907 with a traditional teak dorade box. However, living in a colder climate there are times I am going to want to close these off. I know I can remove the cowl vent and screw in a deck plate, but is there a way to add a shut off that can be opened and closed whenever the need arises, preferably from inside the boat?

I know Vetus and others make round dorade boxes that the vent mounts directly on top of that have screens and shut offs (like https://www.defender.com/product.jsp...800&id=7421967) but I'm not crazy about the look and I'm concerned about whether they function well, especially with wind-driven rain when the boat is on its mooring with no one there to close the vent. I also know they make mushroom vents (like https://www.defender.com/product3.js...143&id=1648744) that have shut offs, but that seems to be overly restrictive.

Any good suggestions?

Thanks.

Tom

Shove a tennis, baseball, socks, ect in the opening to the boat.
No need for a complicated answer here.
Be sure to allow for water to splash into those vents, and exit thru dorade box, limber holes.
Remember to offset the cowl vents from the, air to the cabin holes, and elevate the openings at least 2" to keep water out of your cabin.
Boatyarddog

[mnh]

We use the orange foam cones available from West Marine. They are used to plug holes in the boat. i guess the dorade opening is a hole? Anyway, they fit exactly into the 4" dorade hole when placed upside down. Not sure if they come in different sizes. We've used them for 20+ years now, and they thoroughly plug the wind
mnh

[Boatyarddog]

Originally Posted by Tom_F

I need more/better interior ventilation in the living spaces on my boat. I have two solar-powered mushroom vents I want to add, but I'm also thinking about adding a couple of screw-in cowl vents on the cabin top. Something like this: https://www.defender.com/product.jsp...800&id=7607907 with a traditional teak dorade box. However, living in a colder climate there are times I am going to want to close these off. I know I can remove the cowl vent and screw in a deck plate, but is there a way to add a shut off that can be opened and closed whenever the need arises, preferably from inside the boat?

I know Vetus and others make round dorade boxes that the vent mounts directly on top of that have screens and shut offs (like https://www.defender.com/product.jsp...800&id=7421967) but I'm not crazy about the look and I'm concerned about whether they function well, especially with wind-driven rain when the boat is on its mooring with no one there to close the vent. I also know they make mushroom vents (like https://www.defender.com/product3.js...143&id=1648744) that have shut offs, but that seems to be overly restrictive.

Any good suggestions?

Thanks.

Tom

Remember these vents are exposed to a lot of sun, heat, on deck.
Plastic will get brittle and degrade in hot sun.
Make some nice custom boxes, mount them and add cowling to them.
Don't forget the baffle as mentioned.
Boatyarddog

[SVTatia]

Originally Posted by Tom_F

I need more/better interior ventilation in the living spaces on my boat. I have two solar-powered mushroom vents I want to add, but I'm also thinking about adding a couple of screw-in cowl vents on the cabin top. Something like this: https://www.defender.com/product.jsp...800&id=7607907 with a traditional teak dorade box. However, living in a colder climate there are times I am going to want to close these off. I know I can remove the cowl vent and screw in a deck plate, but is there a way to add a shut off that can be opened and closed whenever the need arises, preferably from inside the boat?

I know Vetus and others make round dorade boxes that the vent mounts directly on top of that have screens and shut offs (like https://www.defender.com/product.jsp...800&id=7421967) but I'm not crazy about the look and I'm concerned about whether they function well, especially with wind-driven rain when the boat is on its mooring with no one there to close the vent. I also know they make mushroom vents (like https://www.defender.com/product3.js...143&id=1648744) that have shut offs, but that seems to be overly restrictive.

Any good suggestions?

Thanks.

Tom

One of these over the cabin opening.

https://www.seascrew.com/browse.cfm?...-&p=0000001754

[Catboat Willy]

Could always tape a Styrofoam plate over the vent hole from inside the boat. Worked for me.

[Cadence]

Originally Posted by Tom_F

I need more/better interior ventilation in the living spaces on my boat. I have two solar-powered mushroom vents I want to add, but I'm also thinking about adding a couple of screw-in cowl vents on the cabin top. Something like this: https://www.defender.com/product.jsp...800&id=7607907 with a traditional teak dorade box. However, living in a colder climate there are times I am going to want to close these off. I know I can remove the cowl vent and screw in a deck plate, but is there a way to add a shut off that can be opened and closed whenever the need arises, preferably from inside the boat?

I know Vetus and others make round dorade boxes that the vent mounts directly on top of that have screens and shut offs (like https://www.defender.com/product.jsp...800&id=7421967) but I'm not crazy about the look and I'm concerned about whether they function well, especially with wind-driven rain when the boat is on its mooring with no one there to close the vent. I also know they make mushroom vents (like https://www.defender.com/product3.js...143&id=1648744) that have shut offs, but that seems to be overly restrictive.

Any good suggestions?

Thanks.

Tom

Use the same type deck plate flange the cowl would use and mount it on your overhead so you can screw the plate in from below. Or use a towel.