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Fitting a ventilated window in companionway washboard


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Stepping Out is getting a bit of mould from a lack of ventilation.  With the heater now fitted, I want to be able to close the companionway but still get some ventilation through it.

I'm proposing to cut a window into the upper washboard, fit it with 4.5mm acrylic sheet rebated into the ply on the inner and outer surface (so, two sheets of 4.5mm with an airgap between them).  The outer sheet will have ventilation holes (about 25mm diameter) across the bottom of the sheet, the inner will have vents at the top.  There is approx 6mm airgap between the sheets.

All corners radiused to reduce chance of cracking.  If they are fitted with MS35 or similar, would they need to be bolted through?

Yes, the companionway can be opened from the inside!

Have at it folks - what have I missed or mis-engineered?

 

IMG_20210729_124329_1.jpg

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Not saying you’ve missed anything but I’ve noticed on May race boats that a series of holes are often drilled on an angle sloping downwards to the outside, to allow ventilation but stop rain

Also see on cruising boats solar powered hatch vents

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Hi s this for when you’re on the boat, or away from it?

Will the lower holes be at the very bottom edge to stop water accumulating between the sheets?

Depending how much you want, not sure that setup will allow much airflow, especially if there is no other opening into the cabin. 

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9 hours ago, mattm said:

Hi s this for when you’re on the boat, or away from it?

Both

9 hours ago, mattm said:

Will the lower holes be at the very bottom edge to stop water accumulating between the sheets?

I think so.  I may put a couple of 6mm drain holes in each bottom corner of the outer sheet if it looks to be a problem.

9 hours ago, mattm said:

Depending how much you want, not sure that setup will allow much airflow, especially if there is no other opening into the cabin. 

There are two dorade boxes at the front of the cabin and a third in the head, as well as a hatch at the front with a ventilation latch that just cracks it open, but there's nothing at the back , so no real air flow.  This design gives a vented area of about 30cm2 in the washboard, so I'm hoping enough for some air movement when the yacht is head to wind, not necessarily an obvious breeze.

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1 hour ago, Deep Purple said:

Isn't that round the wrong way? :-)

Yep, holes should be low on outside high on inside or they will allow water ingress..

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Take out your washboards, take them to Acrylic Creations, and tell them to copy the washboards in tinted acrylic. They will put in a vent as well if you ask...

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2 hours ago, Deep Purple said:

Isn't that round the wrong way? :-)

Yes of course - it’s French - everything is done the opposite way around. When it rains it rinses the dust off the companionway steps.

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2 hours ago, Island Time said:

Take out your washboards, take them to Acrylic Creations, and tell them to copy the washboards in tinted acrylic. They will put in a vent as well if you ask...

Yeah, sorry, forgot to add the budget constraint...  My budget for acrylic on this is about $50.  The rest all happens in my workshop.

 

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1 hour ago, Fogg said:

Yes of course - it’s French - everything is done the opposite way around. When it rains it rinses the dust off the companionway steps.

Its a northern hemisphere thing.  Everything is upside down.

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21 minutes ago, aardvarkash10 said:

Yeah, sorry, forgot to add the budget constraint...  My budget for acrylic on this is about $50.  The rest all happens in my workshop.

 

Hmm, thats a problem. A sheet of 8 or 10 mm Arylic is more than that...

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1 hour ago, Island Time said:

Hmm, thats a problem. A sheet of 8 or 10 mm Arylic is more than that...

Yup.  This way I only need 2 pieces of 4.5mm at 400 x 600.

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Redesign.  Single sheet, angled smaller drillings like described and shown above, rebate half depth of the washboard, window sheet on the outside, chamfer the edge so its flush at the junction between ply and acrylic.  Still fix it using MS35.

Meesaged you.  Cheers

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I like the "double glazed" idea, and agree with comments about the slope for keep the water out. 

That aside and going back to your original drawing, if the air inside is warmer than that outside how much airflow through the holes? It would go through if there is air coming forward to force it. 

What if the low holes were on the inside and high on the outside? as the warmer air goes in and rises it goes out the top, creating (a very small) thermal draft.

Or I could be way over thinking it....

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Thanks for the comment Grant.  Overthinking is good.  Its easier to back away from overthinking than to fix underthinking.

I'm working on the theory that most of the time you are anchored and pointing into the wind.  Ergo, the rear of the cabin is at the lower pressure end of the boat and so air will naturally circulate coming in the dorade boxes, through the cabin, and exiting out the ventilated washboard.  Under way things are obviously different, but so unpredictable its not worth designing for except to keep water out.

Looks like I'm going with Lateral's offer, so the design changes to single 10mm sheet.  That allows for angled drilling, probably 6mm diameter and angled at 45 degrees

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