Mushroom Vents leaking

[SLC]

We have taken our boat out for the first time and parked up last night. The thunderstorms were very heavy. Water started to come through one vent grill into the cabin but we also noticed that it came through the ceiling at the side of the boat. I unscrewed the grill covering the vent and found a length of plastic tube which lined the ventilation hole but which imho was too short. It did not cover the gap between the roof and the insulation between the wooden ceiling. Top of this tube was wet, it was not sealed and water came down vent and rather than continue downwards, flowed across insulation form and presumably hit the side of cabin.

Boat has been recently been repainted, there are no leaks and water must have bounced off the roof into the cabin. I am not sure if the brass cap was fully screwed down although I think it was. I note the cap can only go so far down by design.

So, questions. Should cap be screwed down as far as possible or up to prevent this recurring?

Is there a simple solution to prevent this happening?

Also, I am thinking of getting some 4 inch diameter plastic pipe, cutting it 25mm longer than existing liner, inserting it into the shaft and then sealing the top of pipe so that at least water comes into the cabin and not into the ceiling void. Not ideal as you ideally do not want any water coming in.

The other 5 mushroom vents do  not appear to have leaked but I cannot be sure.

Comments and suggestions appreciated.

 

 

[mrsmelly]

In very heavy rain, on some boats, the water bounces of the roof and up under the domed bit of the vent and hits it and enters the boat. If not this then remove vents, seal (there are many methods ) and screw them back down. Ensure correct size screws and seal the thread also.

[SLC]

I am certain that the rain bounced off the ceiling. There is no other way to get in as all seals good, boat just repainted.

Rain was very, very heavy. Sides of vent on the outside very wet right up to the brass cap.

Mind you we were not as wet as the person who fell in this morning pushing their bow off to move off. But I digress.

[Jen-in-Wellies]

25 minutes ago, mrsmelly said:

In very heavy rain, on some boats, the water bounces of the roof and up under the domed bit of the vent and hits it and enters the boat.

Yes, heavy rain does that. Hail stones too.

[David Mack]

36 minutes ago, SLC said:

Also, I am thinking of getting some 4 inch diameter plastic pipe, cutting it 25mm longer than existing liner, inserting it into the shaft and then sealing the top of pipe so that at least water comes into the cabin and not into the ceiling void.

Yes. At least you will then know where the water is rather than having it running behind the lining and doing goodness-knows-what damage.

If it is a regular problem you could always hang a bowl under the vent to catch the water.

[ditchcrawler]

You can buy liners to bridge between the ceiling and the brass mushroom

[David Mack]

30 minutes ago, ditchcrawler said:

You can buy liners to bridge between the ceiling and the brass mushroom

But those liners just tidy the appearance seen from the inside. They don't seal against the cabin roof plate or mushroom vent tube. The design of some ensures that any water running down the side of the mushroom vent tube enters the roof void rather than falling into the main cabin space.

Edited June 12, 2023 by David Mack

[BEngo]

The vents don't go fully down so that the ventilation  cannot be closed off. 

 

 It matters not much whether you screw the mushroom down or not.  If the rain is heavy enough it bounces off the roof and into the vent.  Any breeze inducing a slant into the direction of fall makes things worse.

 

If you know it's going to P down stuffing a foam bung in can be a good idea, but remember about the ventilation.

 

N

[Bee]

stick a bucket with a brick on top over the thing

[SLC]

The liners are 4 inches too short. The gap between the ceiling and the roof which is filled with foam is quite deep. Any liner has to be long enough to bridge the gap and sealed at the top to prevent water leaking on the outside of the liner into the roof space.

Mrs C has suggested a doughnut shaped sponge with a slot in to wrap around the vent.

Sadly, the design of these vents leave a little to be desired.

[pearley]

For ours I cut 50mm wide strips of Karndean flooring left over from laying the floor. It easily bends into a 4 inch circle. Cut to length and pushed up the inside of the wooden liner and into the underside of the foam.

 

 

[ditchcrawler]

1 hour ago, David Mack said:

But those liners just tidy the appearance seen from the inside. They don't seal against the cabin roof plate or mushroom vent tube. The design of some ensures that any water running down the side of the mushroom vent tube enters the roof void rather than falling into the main cabin space.

They do if you put sealant round them

[Jak]

2 hours ago, David Mack said:

Yes. At least you will then know where the water is rather than having it running behind the lining and doing goodness-knows-what damage.

If it is a regular problem you could always hang a bowl under the vent to catch the water.

^^^^^^ this, exactly what I did to prevent an occasional damp bed!

[Kiwidad]

Terracotta pots just large enough to fit over the mushrooms. The air can still vent correctly but no water ingress

[Tracy D'arth]

Perhaps its because they are badly in need of polishing?       🤩

[David Mack]

1 hour ago, ditchcrawler said:

They do if you put sealant round them

The brass spun liners I removed from Belfast were tapered down to about 3" diameter at the top which sat inside the 4" diameter shaft of the mushroom vent. The 1/2" gap all round would have been hard to seal, and would really need the mushroom top to be removed so you could see what you were doing when placing the sealant. As it was any water coming down the gap would end up in the roof void.

[nine9feet]

6 hours ago, Jen-in-Wellies said:

7 hours ago, mrsmelly said:

In very heavy rain, on some boats, the water bounces of the roof and up under the domed bit of the vent and hits it and enters the boat.

Yes, heavy rain does that. Hail stones too.

Yep! Hail stones :

[robtheplod]

My mushroom vents let a few spats of water in from the very heavy rain over the weekend... not much you can do really... quite refreshing!

[blackrose]

You could use those square sponge washing up cloths. Cut a hole in each cloth approx the size of the mushroom upstand and stretch it over the dome onto the roof (or take the dome off and put the hole in the cloth over the upstand). When it rains heavily the energy of the water droplets around the vent will be absorbed and they won't bounce. You wouldn't want to leave the cloths there all the time as eventually they'll lift the paint underneath (and they look a bit naff too!)

 

Edited June 12, 2023 by blackrose

[SLC]

Thank you everyone who went to the trouble to reply. We went back to the boat yesterday and again found water on the floor that had entered from the mushroom vents following heavy thunderstorms. Mushroom vents are quite impractical if you cannot screw them right down, which I understand of course they are designed to prevent this from happening.

To stop the leak into the roof space I have fitted a 100mm diameter plastic pipe into the void about the length of the ventilation shaft. Used sealant to seal the top and bottom and hope that now I can prevent the heavy flow into the roof space, accepting that it will flow into the cabin and onto the floor. However, this was not easy as the mushroom vent diameter was 100mm but the hole in the steel roof of the boat was around 90mm and that wasn't going to be enlarged! Also, access from the top is not easy as there is a strip of metal across the aperture which raises the mushroom cap 20mm or so above the top of the vent.

It is one vent that appears to cause the problem - the other three appear to be OK so for the time being I am leaving well alone until I have time to examine them further.

Again thanks and we have the sponges to hand.

[blackrose]

I had some water come in through one of my mushroom vents on Monday during an epic torrential downpour. I've screwed the dome down a bit.

[cuthound]

Despite water pouring out of the rear handrail drains in similar volumes to a tap (it normally dribbles out of the drains but was coming out with sufficient force to overshoot the gunwhales) during the recent heavy thunderstorms, the water didn't overwhelm the mushroom upstands. 

 

Perhaps the OP's drains are undersized?

[Derek R.]

7 hours ago, SLC said:

We went back to the boat yesterday and again found water on the floor that had entered from the mushroom vents following heavy thunderstorms. Mushroom vents are quite impractical if you cannot screw them right down, which I understand of course they are designed to prevent this from happening.

(snipped)

 Kiwidad's suggestion of a terracotta pot sounds ideal. With some silicone daubed around the rim contacting the cabin rood, no damage will be caused to roof paint, and the hole in the bottom of the pot (now above the mushroom dome) will still allow necessary venting to take place, while preventing any rain bounce and splash-up. Give the man a cigar!

[Jak]

Great minds… 👍

though the BSS inspector did tut at me and I took it off for him!

 

Edited June 22, 2023 by Jak

[Ray T]

This is how a onetime CWDF member cured the problem a long while ago now. However, I would NOT recommend this approach.

 

I am unaware if this was altered after any BSC examination.

 

Not my photo, copied from this forum.

Edited June 23, 2023 by Ray T