Accounting for slight roof angle with chimney collar

[Poppin]

As it turns out, I need to raise one side of the roof collar 5-10mm to properly account for the roof angle. 

 

What is the best practice? I know lots of people make up hardwood spacers. What about using metal spacers and tilling the gap with CT1 and body filler?  Somone else suggersted just taking off 5mm the other side using flappy disc on the grinder. Personally I'm not sure I can do this straight. 

 

Any suggestions seriously welcome!!

[David Mack]

You can get roof collars with angled flanges for just this situation.

[Puffling]

I need to reset my collar next year. 

I considered the hardwood option. A lot easier if you have a mitre saw, but still masses of fine work to get it looking trim.

 

So I'm going to try a casting with epoxy mortar and see how that stands up to heat.

[Sea Dog]

I've just redone my roof collar on a similarly angled roof. I looked at it this way and that way and, finally, the way I got over it was - I just got over it and kept the jaunty chimney!  It had, in truth, never really been an issue. 

[Poppin]

12 minutes ago, David Mack said:

You can get roof collars with angled flanges for just this situation.

I have one, its not quite enough of an angle 

[Poppin]

12 minutes ago, Puffling said:

I need to reset my collar next year. 

I considered the hardwood option. A lot easier if you have a mitre saw, but still masses of fine work to get it looking trim.

 

So I'm going to try a casting with epoxy mortar and see how that stands up to heat.

interesting. how would you do this? place to collar on a bed of the stuff, prop it up and thats it? Or just some kind of sheet to stop it sticking?

2 minutes ago, Sea Dog said:

I've just redone my roof collar on a similarly angled roof. I looked at it this way and that way and, finally, the way I got over it was - I just got over it and kept the jaunty chimney!  It had, in truth, never really been an issue. 

my concern is a straight flue inside the boat

[magnetman]

There should be a bit of room as the flue itself is not a tight fit inside the collar. I'd plonk the angled collar in place and see if you can drop the flue from above to come onto the fire in a straight line. Then cut the flue orf just above the top of the collar and seal it up. 

 

There is usually a little bit of leeway. 

 

[Jen-in-Wellies]

6 minutes ago, Poppin said:

my concern is a straight flue inside the boat

There needs to be a gap between the flue and collar. This is filled with fibreglass rope and high temp silicone sealant. In addition to reducing heat transfer to the collar and roof, its main purpose is to reduce expansion stresses on the stove as the flue heats and cools. This gap can also take up any mismatch in angle between the collar and flue. It does on my stove, which has a centrally mounted stove, with a vertical flue that goes through an angled collar. I keep meaning to replace the collar with a zero angle one, but meh.

Edit: @magnetman beat me to it by a couple of seconds!

[magnetman]

 

Is this a liverpool boat? They do have very curved cabin tops. 

1 minute ago, Jen-in-Wellies said:

. I keep meaning to replace the collar with a zero angle one, but meh.

 

When I went to Uxbridge Boat Centre a number of yars ago they only had angled collars and said they were no longer supplying the plain flat ones. 

 

 

[Jen-in-Wellies]

4 minutes ago, magnetman said:

 

Is this a liverpool boat? They do have very curved cabin tops. 

When I went to Uxbridge Boat Centre a number of yars ago they only had angled collars and said they were no longer supplying the plain flat ones. 

 

 

Nope. Not Liverpool. Piper. Quite a shallow curve and the flue exits in the middle. A zero angle collar would be ideal. Midland Swindlers still sell them, but not worth changing, as unless you know, you can't see the angle.

[magnetman]

I meant the OP boat. They are presumably putting the fire to one side with a boat which has a significantly curved cabin top. 

[Jen-in-Wellies]

6 minutes ago, magnetman said:

I meant the OP boat. They are presumably putting the fire to one side with a boat which has a significantly curved cabin top. 

Makes more sense!

[magnetman]

Yes the bit where I quoted you was a separate post which automatically attached itself to the previous post. 

[Poppin]

17 minutes ago, magnetman said:

I meant the OP boat. They are presumably putting the fire to one side with a boat which has a significantly curved cabin top. 

Colcraft widebeam, stove is to the side. 

[Puffling]

1 hour ago, Poppin said:

interesting. how would you do this? place to collar on a bed of the stuff, prop it up and thats it? Or just some kind of sheet to stop it sticking?

my concern is a straight flue inside the boat

Not really thought it fully through yet, but I was planning on making a mould, once I knew the angle I needed to add to the existing angle of the collar. Like yours, my collar doesn't compensate enough for the roof curvature, and I prefer a straight flue run.

 

Scrounging through builders' skips is bound to turn up a plastic tub of the right diameter. This can be cut down to include the top angle, so the epoxy mortar comes out like a chunky, wedge-like pancake. Finishing with an angle grinder should be trivial.

 

I did have a company which produced bespoke metal wedges for this exact requirement in my bookmarks ages ago, but all I can remember is the price was the same as a new collar, and then some...

Edited October 15, 2023 by Puffling

[magnetman]

Another approach is to get a welded-in collar. 

 

There are advantages and disadvantages but it is worth considering in this circumstance. 

 

Needs doing properly. 

 

And you may need a made to measure external terminal rather than an off the shelf job. 

 

Both of my boats have welded in collars but neither of them are on angle parts of the cabin top and they are both one-off boats with rather unusual features. 

 

Welded in is nice as you can't get any leaks through the collar/cabin top interface because there isn't one. 

 

 

 

 

 

Edited October 15, 2023 by magnetman

[Machpoint005]

2 hours ago, Jen-in-Wellies said:

Nope. Not Liverpool. Piper. Quite a shallow curve and the flue exits in the middle. A zero angle collar would be ideal. Midland Swindlers still sell them, but not worth changing, as unless you know, you can't see the angle.

 

Even if you do know, why worry? The smoke will still go upwards.

 

 

 

 

[blackrose]

5 hours ago, Poppin said:

I have one, its not quite enough of an angle 

 

So get a hardwood spacer too.

Edited October 16, 2023 by blackrose

[Poppin]

7 hours ago, blackrose said:

 

So get a hardwood spacer too.

 where from? do i have to make one?

[Jen-in-Wellies]

Just now, Poppin said:

 where from? do i have to make one?

Almost certainly yes. Either you, a friend, or pay some one. It will be custom for your boat. Too small a market and too many variables for anything off the shelf.

[David Mack]

13 hours ago, Puffling said:

 

I considered the hardwood option. A lot easier if you have a mitre saw, but still masses of fine work to get it looking trim.

No mitre saw needed. Just a plane (or a flap disk in an angle grinder) to shape the taper, and a jigsaw to cut the rounded ends and the hole in the middle. Both tools which the average DIY woodworker is likely to have.

[jonathanA]

Agree with comments above the angled collars don't have much of an angle ! 

 

Make a template out of a piece of softwood (e.g pine or plywood)  once you have that right then you need to find some hardwood. you might need to start with a fairly thick piece 200x50 say (end of a joist or something similar). Or you can take the template and see if someone will do it in hardwood for you. 

 

I was lucky and had a bit of hardwood left from an old school laboratory worktop than i'd saved out of a skip.   You still want a decent thickness at the thin side.  

 

Making a 6 inch hole for the collar was the hardest bit.  jigsaw, patience and lot of filing with a rasp.  

[magnetman]

 

 

I've cut several 7 inch holes in 48mm thick mahogany before with a holesaw and a good 14.4v Makita drill. 

 

It will go through. I used a bosch holesaw. 

 

 

However a bit of teak, opepe or iroko would be nicer for outdoors. 

 

 

[David Mack]

3 hours ago, jonathanA said:

Making a 6 inch hole for the collar was the hardest bit.  jigsaw, patience and lot of filing with a rasp. 

?? Since the hole in the middle will be unseen once the collar is fitted, it doesn't need to be a quality finish or a good fit. So a jigsaw alone should do the job once you have drilled a small hole to start the cut. 

And you don't need a 6" holesaw, something most DIYers won't possess.

[jonathanA]

11 minutes ago, David Mack said:

?? Since the hole in the middle will be unseen once the collar is fitted, it doesn't need to be a quality finish or a good fit. So a jigsaw alone should do the job once you have drilled a small hole to start the cut. 

And you don't need a 6" holesaw, something most DIYers won't possess.

I'm speaking from experience not theory...  it ain't easy cutting a round hole in 1 inch+ thick hard wood with a jigsaw - even a good one and then the edges need rounding as most collars are cast and don't have nice sharp corners.    then add in the slope of the fillet piece your making and the angle of the collar itself so unless  you made a hole with a big clearance then you will need to do some 'fine tuning' to get everything to sit nicely.  Of course you can't make your clearance too large or you will hit the securing bolt holes or the collar 'flange' won't cover it and you will have a big hole for the rain to get into... 

 

and as I'm sure you know its easy to take a bit more off/out but very hard to stick a bit back... 

 

My largest hole cutter was only 127mm and whilst I love buying tools I really couldn't justify the expense of a 6 or 7 inch jobbie, which I suspect would be a bit big for anything less than a 24 or 54v battery drill.