MacGregorSailors.com

Pretty much anything stiff enough to support a body sleeping on top of it is going to need to be dense (= not very breathable) or very resilient so it can spring back to breathable state when the body removes. The air conditioner filter material might be resilient enough - don't know.

The Dri-Dek would definitely work as it will not crush nor become unbreathable.

Unless AstroTurf has a much more breathable backing than normal indoor-outdoor carpet it will just get condensation between it and the boat instead of the cushions getting it.

No vested interest but, I don't see how anything would work better than the Dri-Dek - which also had a non-mildew ingredient in its plastic.

Before you mount a fan or vent in the forward hatch consider whether you ever want to lay it all the way back onto the deck.

My hatch adjuster allows unscrewing and I sometimes lay the hatch all the way back to get it out of the way. I can step on it that way if I step in the middle so the deck under it supports it. Couldn't do that with a vent mounted in it.

There's some synthetic fabric stuff I've seen advertised to help condensation problems, I just remember thinking it was kind of pricy. Kind of rough like Moe was talking about. Reminded me of those scrubbie sheets you wash dishes with. I think Dry Deck would work great, Home Depot has similar stuff that's cheaper (in black and white only). I'm experimenting with now on the cabin sole. Maybe I'll use some in the berth. Still think a real dehumidifier aboard during storage would help, if there's a temperature difference between cabin & outside you're gonna get condensation somewhere, unless you're sailing a thermos.

Even if you don't get actual condensation, the humidity is high enough to support mildew growth.

Gary,
I found that stuff for bunks I'd read about but couldn't remember where. It's called "Ventair" and it's made to allow circulation under boat & RV bunks. There's a writeup in PS (Mar '04) & they gave it a thumbs up. It's a mat you cut to fit, made out of a sandwich of polyester fabric with plastic wire in the middle. Costs about $55 for 39" x 78".

Ventair Website

The cross-section drawing sure does look like the packing material I was thinking of. Too bad there's no info on their website. Are you gonna give them a call?

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Moe

Dry Bunk also work extremely well. For years it has been the liveaboards choice when dealing with humidity under beds. It's relatively thin, durable, and lightweight. It normally comes in a 26X120 inch sheet and cuts with normal scissors. Last time I bought some it was like 18USD

Another alternative is HyperVent - Moe, perhaps this is what you were remembering?

That also looks like it, Kevin, but what I'm remembering was denser.
Wow! $7.35 per linear foot, 39" wide. But at $3.35 per square foot, Dri-Dek is $10.99 for the same amount. I'll be it didn't cost near that much when it was being used for packing material.

I think any of these products should work, as long as they don't compress.

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Moe

We just prop up the low cusions so the vinyl isnt on the fiberglass when we leave the boat and it is dry when we return.