Ajax

A/C ducting

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This is a little ghetto but bear with me...

I've decided that the portable Cruise-Air is too feeble to cool my boat and too awkward and space consuming to store. It also doesn't fit well on my cabin top hatch. I don't want to install a permanent A/C system because we really only need it a few days per year. We really try to do without A/C but sometimes when you've been sailing for 8 hours in 93F degrees and 95% humidity and the predicted low is only 80F with high humidity, with no evening breeze, you really could use a break from the elements.

We have a compact, "window shaker" unit that cools the boat really well. It's lighter and stows well when I need to bring it. It's smaller than typical residential window units. I want to set it on the cabin top to blow down into the hatch just aft of the mast.

To make this work effectively, I'll need to fabricate a small duct assembly to fit on the front of the unit that will channel the cold air down into the hatch while allowing the unit to draw hot, cabin air into its intake/return, keeping the two air flows sort of separate. I'm searching for a material that is thin, flexible, water proof and epoxy's well.  I'd prefer some sort of plastic vs. making something out of thin aluminum sheeting but I'll use metal and rivets if I have to.

I've attached a (very) crude drawing of what I'm attempting to do. The sides of the duct will be covered so try to imagine flat pieces on each side.  Cool air blasts out of the top vents and warm cabin air is drawn up into the lower return (rather than hot air from outside of the cabin).  I'll make up a little sunbrella cover to encapsulate the front half of the unit, the duct and the hatch just as the Cruise-Air uses, to nominally seal things up.

Thoughts?

ACduct.jpg

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I'd sew that sucker up out of Sunbrella or equivalent.

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But how to give it some rigidity?

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2 hours ago, Ajax said:

But how to give it some rigidity?

A couple short wood or fiberglass rods from the bottom edge of the unit to the inside edge of the intake side. The outgo side will self-inflate.

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I might first mock it up with cardboard and duct tape to see how it works on the boat one nice warm and sultry evening.  If good, then I might just make it out of 1/4 ply.  You could make two ~ 45 degree angles for the  turns, vice the nice curve you show.  You could then get fancy and cover the exterior of the ply with some lightweight glass, and paint with brightsides or similar to match the deck color...A couple small eye-straps screwed into the sides would allow you to use shock cord to hold it against the face of the AC unit...a lip along the edge that mates to the AC unit would allow you to put a piece of foam or weatherstripping on it to cut down on any leaking of cold air...

I also think the Sunbrella approach would also work.  A large "U" shape metal rod, sewn into the sleeve at the correct angle (as described by IStream) would hold the intake side out...You might lose some efficiency due to heat transfer through the cloth compared to a more rigid/thicker duct, but not sure it'll make too much of a difference...

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Lots of good ideas. I was really hoping to find a sheet of "something" and just bend a nice curve in it but cutting pieces of ply into the desired shape can be done.

This'll end up being a minor winter project along side the toilet and water heater replacement.

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1/8 inch FRP panel from Home depot or if that is too stiff, some plexiglass and a heat gun and bend it to the correct radius.

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We built a cabin top box for our boat for the summer.  Used plywood and 1" pink foam from home depot.  There are alot of little boxes or setups like you have shown on boats in the marina.  They are really inefficient, you end up loosing all of your cooling capacity out the transition.  You need the hood portion to have about the same volume as the size of the AC unit, the hood panels should be well insulated and ideally come back over the ac unit to the condenser vents about 3/4 of the way.  The divider is not necessary if the hood is well insulated, you could make a collapsible one out of sunbrella or something like it double walled pockets for the foam to go in.  The whole thing should collapse to a store-able size.  In 90 F 90 % humidity we are keeping the boat very comfortable with the unit in eco mode shutting off at night.  

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How about coroplast? Light strong and with the double wall it may even offer some insulation.

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On 8/20/2018 at 3:24 PM, steele said:

How about coroplast? Light strong and with the double wall it may even offer some insulation.

Ah, this is the stuff that front lawn campaign signs are typically made of? I hadn't thought of that.  It has limited flexibility but could be pieced together.

I agree with Sass that this hood should be insulated to reduce inefficiency. Sunbrella would be easy to make but unless I stuff it with foam panels, the cold air will absorb too much exterior heat on its way down into the cabin.

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On 8/16/2018 at 11:09 AM, Ajax said:

But how to give it some rigidity?

Why?  When I was deployed overseas and living in tents, the A/C ducting was a cloth sleeve, and it worked adequately to get the air circulating inside the tent.  Plus. you get the addiotional benefit of easy stowage. 

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13 hours ago, Max Rockatansky said:

Wonder if REFLECTIX would work for you. Just use their foil tape to fab it up. 

Ding. This might be the winner. It's rigid yet flexible so I might be able to make something the collapses and stows flat. It's insulated (at least more than plain sunbrella) which will preserve the cold air as it travels into the cabin. Cheap, readily available.

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Posted (edited)

I saw a picture on a brokerage site a few weeks ago, that had a lewmar hatch deck hatch on the vertical wall of the cabin house beside the companionway... with a window unit about the right size for it.  Can't say I would of thought of it, but they had it mostly in the cabin with just a bit of the condenser hanging out the back.  Would solve a lot of struggle, without a whole lot of work and store the thing when not needed.  

Googling, I think it might have been a Lewmar 30 rectangular hatch and a LG 6000 btu A/C just judging by dimensions. 

Edited by Zach
more info

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