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Old 01-08-2015, 02:04   #1
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Need ventilation in compartment

Forward port and star compartments used for sails and such - I need some ventilation there to keep the moisture out.

Each compartment has a hatch and my plan is to mount ventilation in these hatches. Looking at either a solar powered option, or passive ventilation, I need to be absolutely sure these vents don't allow water inside, whether from rain or spray.

Take the Marinco AirVent 500. It says

"Center damper shuts vent off from below"



Does that mean no water can enter? Or is it built into the design itself?

I would presume that any ventilation mounted deckside would naturally be waterproof - but I want to be sure.

-

I can add on that this is a 55' sailing cat. I have now run air con (summer) and dehumidifier (winter) 24/7, as external units. These provide over pressure to most of the hull, except for those compartments (and a few other isolated ones). It's really nice, as the boat is DRY everywhere, including the heads, bilges and such. Except for these remote compartments, not connected to the cabin.

There is a small pathway for conditioned air to flow into the compartment already - all I need is for the air to vent out at the other end - hence those vents. Even a very low flow of sufficiently dry air will do, I just need to keep the dew point below ambient temperature.

Thank you for your help.
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Old 01-08-2015, 04:25   #2
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Re: Need ventilation in compartment

"Center damper shuts vent off from below"

The damper is manually operated, and does not allow ventilation, when closed to prevent water entry.
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Old 01-08-2015, 06:49   #3
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Re: Need ventilation in compartment

Can these compartments be accessed from the interior cabins by cutting holes? If they can, use some fans to circulate the cabin air.

For lining the floor of my bow compartments, I got some mesh material made for installing under roofing and it helps air movement up there.

I'm guessing you are interested in ventilation mainly at the dock. If so, I don't think you would have much problem with rain entering the vents you are looking at. We had one in the main cabin of our previous boat, left open all the time, and water never came in. Crashing seas on the bows would be different.

Curious about your external heat pump. So that brings outside air in?

Quote:
Originally Posted by DITB View Post
Forward port and star compartments used for sails and such - I need some ventilation there to keep the moisture out.

Each compartment has a hatch and my plan is to mount ventilation in these hatches. Looking at either a solar powered option, or passive ventilation, I need to be absolutely sure these vents don't allow water inside, whether from rain or spray.

Take the Marinco AirVent 500. It says

"Center damper shuts vent off from below"



Does that mean no water can enter? Or is it built into the design itself?

I would presume that any ventilation mounted deckside would naturally be waterproof - but I want to be sure.

-

I can add on that this is a 55' sailing cat. I have now run air con (summer) and dehumidifier (winter) 24/7, as external units. These provide over pressure to most of the hull, except for those compartments (and a few other isolated ones). It's really nice, as the boat is DRY everywhere, including the heads, bilges and such. Except for these remote compartments, not connected to the cabin.

There is a small pathway for conditioned air to flow into the compartment already - all I need is for the air to vent out at the other end - hence those vents. Even a very low flow of sufficiently dry air will do, I just need to keep the dew point below ambient temperature.

Thank you for your help.
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Old 28-08-2015, 21:31   #4
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Re: Need ventilation in compartment

Quote:
Originally Posted by GordMay View Post
"Center damper shuts vent off from below"

The damper is manually operated, and does not allow ventilation, when closed to prevent water entry.
Thanks GordMay.

So in very foul weather one would have to remember to close all these?

I am considering hard rain (good sized thunderstorms here in the summer), and then waves. We have a lot of separate compartments, it would take a lot of bad luck to sink us - yet I won't use that as an excuse for allowing chance to cause misfortune.
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Old 28-08-2015, 21:53   #5
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Re: Need ventilation in compartment

Quote:
Originally Posted by ggray View Post
Can these compartments be accessed from the interior cabins by cutting holes? If they can, use some fans to circulate the cabin air.

For lining the floor of my bow compartments, I got some mesh material made for installing under roofing and it helps air movement up there.

I'm guessing you are interested in ventilation mainly at the dock. If so, I don't think you would have much problem with rain entering the vents you are looking at. We had one in the main cabin of our previous boat, left open all the time, and water never came in. Crashing seas on the bows would be different.

Curious about your external heat pump. So that brings outside air in?
Thank you, ggray.

Ventilation at the dock, but generally, I would like it to be whether docked or sailing. Water (and moisture) is what gives us all life, but also death (and things in between, like mould, fungi, insects and all kinds of other baddies). I don't mind mould and other growths, as long as they are not in or on my boat.

I found that cockroaches can live for months without food, but only about two weeks without water. Since we applied the "always dry" concept, we have seen one (1) cockroach in 2 years, so I added new traps again. When we bought the boat, one hatch was marked as "has a moisture issue". Not any more now. Apart from those remote compartments, we are seldom over 65% RH inside. Added benefit: In the summer, even with an awning, it takes a lot of A/C to keep the boat comfortable inside. We often run close to 85 F inside but found that as long as it's rather dry, it's fine. We don't need 65F / 40% RH! Outside is hovering around 100 F in the summer, and 85-95% RH, coming inside to 85F / 50% RH feels plenty cool.

To keep us dry, I got an "R2D2 shaped" air-air A/C, put it in the cockpit at the helm and then let the cold exhaust enter the main saloon. Foam boards for ducting, looks like cr** but works wonders. Obviously removed for sailing, or we would need an endless extension cord!

This A/C uses the condensed water to further cool itself down, while the model we had before had a drain pipe for that. The new one works even better than the old one, and we only use the Webasto 12,000 BTU on board when it's really hot.

Because the "R2D2" is pumping air in, it makes a positive overpressure. Had we put it inside and connected it as designed, it would expel the hot air but in turn, draw in false air everywhere else on the boat. This is a great mistake in the use of simple A/C setups - people don't realise that when you pump something out, something else must come in. Smell from heads, moisture everywhere.

This over pressure air finds its ways all throughout the boat, and exits at any leak, hatch, LPG drain, heads and so on. As for the heads, it's brilliant - it makes sure no odours enter the main cabins. And after shower, it dries up quickly (again - I just hate things staying moist for too long). Despite quite moderate air flow for the boat, it is sufficient: As long as the dry air comes in and moist air goes out - boat stays dry. Everywhere the air can find its way.

Finally - front compartments: Yes, we have made small holes (some were there already from existing installations like wiring) to vent some of the air. In fact, because of our R2D2, we don't even need extra fans, as there is already an overpressure from the cabin. All we need is ventilation from those compartments to the outside. Letting air inside isn't enough, it needs to be able to further escape, or no air will enter. I don't like water to be able to enter, though - hence my original question in post #1.

So I still need to find something that will allow air to escape, but not rain/waves to enter. Is it clear as milk tea now ?
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Old 07-09-2015, 14:01   #6
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Re: Need ventilation in compartment

Just thinking out loud, but if you are worried about the water integrity of whatever deck vent you might consider at the location of these lockers, you could in addition to sufficient vent holes cut into the bulkheads, run a small duct from said compartment to a place aft in the boat where the vent would be less vulnerable. Pressurized air would flow to the locker, and exit aft through the small duct to wherever it can "pop out" safely. IF there is a good place to run the duct.
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Old 07-09-2015, 14:31   #7
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Re: Need ventilation in compartment

Quote:
Originally Posted by DITB View Post
Thanks GordMay.

So in very foul weather one would have to remember to close all these?

I am considering hard rain (good sized thunderstorms here in the summer), and then waves. We have a lot of separate compartments, it would take a lot of bad luck to sink us - yet I won't use that as an excuse for allowing chance to cause misfortune.
They don't leak in a heavy rainstorm, (from experience) but I imagine they would leak some in a situation with green water over the boat.
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Old 07-09-2015, 14:53   #8
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Re: Need ventilation in compartment

Our solar vents (by Nicro) fit into deck rings mounted in the deck or a hatch. They were watertight in Texas rainstorms. When going offshore, you removed the mushroom vent and replaced it with a plastic blank deck plate. If properly installed, these deck plates are green water tight.

Cheers!

Steve
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