Fixing a hole in the roof

[Top cat]

When I take out the now redundant balance flue outlet that used to feed my Alde boiler I will be left with a hole a bit over 5" dia in the roof.

I want to remove the flue because it sticks up a lot and will be conducting heat out of the boat.

The roof is 4mm steel with 1" polystyrene insulation below then another 1"or so air gap before the roof lining which has a slightly larger somewhat irregular hole.

 

I've considered having either a patch or bung welded in/on but am worried about setting fire to the insulation beneath.

 

Other ideas have included fitting a mushroom or flying saucer vent but getting one big enough seems to be difficult.

 

Has anyone any better ideas?

 

Is it possible to avoid the fire risk if welding?

 

Anyone know where I can get vents that suit a 5" plus hole

 

Thanks

 

Top Cat

[MtB]

When I take out the now redundant balance flue outlet that used to feed my Alde boiler I will be left with a hole a bit over 5" dia in the roof.

I want to remove the flue because it sticks up a lot and will be conducting heat out of the boat.

The roof is 4mm steel with 1" polystyrene insulation below then another 1"or so air gap before the roof lining which has a slightly larger somewhat irregular hole.

 

I've considered having either a patch or bung welded in/on but am worried about setting fire to the insulation beneath.

 

Other ideas have included fitting a mushroom or flying saucer vent but getting one big enough seems to be difficult.

 

Has anyone any better ideas?

 

Is it possible to avoid the fire risk if welding?

 

Anyone know where I can get vents that suit a 5" plus hole

 

Thanks

 

Top Cat

 

 

Welding isn't the only way to securely fix a panel of steel in place over it.

 

4mm steel is plenty thick enough to cut a screw thread. If it were my boat I'd cut/obtain a piece of say 16 gauge steel about 8" square and drill holes around its perimeter about 40mm apart, then drill and tap the roof and bolt the panel in place.

 

Put some insulation in the hole bebore bolting it in place, obviously.

[ChimneyChain]

Chemical metal a piece of steel to the under side then apply filler to the outside, sand and paint. 3hrs max work load.

 

Darren

[alan_fincher]

Not sure if all Polystyrene is the same, but based on what I have found so far on Flamingo, heat caused by welding seems to melt it and cause it to become thinner and more solid at the welded points, but no evidence of anything having caught fire.

 

As MTB says bolting a patch on with tapped holes is very feasible. I have done this on Flamingo where a Kabola has been removed. Also for a cat flap!

[OldPeculier]

Having moved my stove from one end of the saloon to the other, I too am faced with a hole in the roof. My plan is to fix a piece of aluminium to the inside with CT1 and self tappers then fill the depression with P38. The way things are going tho, it might not be until next year so the upturned plant pot will have to do till then.

[MtB]

Having moved my stove from one end of the saloon to the other, I too am faced with a hole in the roof. My plan is to fix a piece of aluminium to the inside with CT1 and self tappers then fill the depression with P38. The way things are going tho, it might not be until next year so the upturned plant pot will have to do till then.

 

 

That's a good point. Another perfectly durable repair which will last many years is a saucepan place over the hole...

[Nightwatch]

Not sure if all Polystyrene is the same, but based on what I have found so far on Flamingo, heat caused by welding seems to melt it and cause it to become thinner and more solid at the welded points, but no evidence of anything having caught fire.

 

As MTB says bolting a patch on with tapped holes is very feasible. I have done this on Flamingo where a Kabola has been removed. Also for a cat flap!

Alan, can your cat use a screwdriver then?

[John V]

I changed my flue position about 8 or 9 years ago and as a temporary measure I used Sikaflex to stick a disc of 3mm steel over the hole. Now with several layers of paint over and showing no sign of leaking etc ............one day I might want to change the flue back and then I'll have a ready cut hole

[MtB]

Not sure if all Polystyrene is the same,

 

 

There are two types. The original polystyrene which first became popular catches fire and burns shockingly freely and easily. It generates massive quantities of CO and airborne flecks of soot. Impressive to see and very scary.

 

A number of fatalities resulted in 'flame retardant" polystyrene being developed. This will burn weakly if you make it hot enough but is a big improvement. There was a helluvalot of original highly combustible polystyrene sold though. The only way to tell is to break a piece off and in a safe place try to light it. If it catches and burns freely then yours is not flame retardant.

[Boat&Bikes]

There are mushroom vents on eBay that would suit. Ian

[bizzard]

A nice WW2 retractable periscope would fit just right, to peer over hedges and things, about the same shape as the Aldi comfort boiler.

[gazza]

There are mushroom vents on eBay that would suit. Ian

Exactly what I was thinking, just stick an additional vent in its place.

[Chewbacka]

But if the op was concerned about heat loss, then another vent will make the boat colder. Just bolt and bond a plate. Anybody object to fire rated foam to insulate the back of the plate?

[gazza]

But if the op was concerned about heat loss, then another vent will make the boat colder. Just bolt and bond a plate. Anybody object to fire rated foam to insulate the back of the plate?

 

Heat loss from one extra vent would be tiny.

 

its not the same as 5" flue doing nowt.

Besides, Heat loss from the windows is far greater than anything a vent will cause.

Take your pick

 

http://www.asap-supplies.com/marine/mushroom-air-vents

[Top cat]

Thanks guys

 

There is already a ring of tapped holes where a flange was that held the flue in place I will use that for the patch

 

Top Cat

[DHutch]

If you are happy with a patch secured on top, with a PU sealant I would suggest, there is no harm in that at all.

 

However equally I am sure you could weld a patch in without much issue, cut the insulation back to maybe two inchs from the weld location, get some wet cotton rag down there, switch welld it in short spells as you would to reduce destorion anyway. As said by Alan Fincher most PS used on boat is the 'fire retardant' type, which while it can burn, and feels very wrong, seems not to catch fire even if you weld basical against it it, as happens on our boat changing the anodes.

 

You would then be able to fill/fair it to become basically invisible.

 

 

 

Daniel

[blackrose]

I would just stick the patch on with marineflex or sikaflex too. No need for all those tapped holes and screws, they just mean extra potential for leaks.

[koukouvagia]

I would just stick the patch on with marineflex or sikaflex too. No need for all those tapped holes and screws, they just mean extra potential for leaks.

Couldn't agree more. I've got a brass surround to a roof light stuck on with Sikaflex because I didn't want to drill holes into the roof. I works perfectly.