Sagging steel roof

[Peteonthelee]

Hello 

 

I have recently have my steel roof sag to the extent it has caused a drop of the wooden slatted ceiling inside the boat. I intend to take the inner ceiling down and inspect it from underneath. Does anyone have experience with what might cause this and how to rectify it?

 

Thanks

Pete 

 

[MtB]

Is the sag visible from outside on top? Can you post a photo perhaps?

 

 

Presumably this is a steel narrowboat, perhaps you could confirm. Who was the sheel builder and how old is it?

 

 

[jim mitchell]

10 minutes ago, MtB said:

 

Presumably this is a steel narrowboat, perhaps you could confirm. Who was the sheel builder and how old is it?

would add a note of caution - before you remove the inside, have something (Tarps or? ) to hand if the steel is rotton removing the cladding may suddenly give you a very big hole for rain to enter - then a storm like Lily could end up sinking you in short order😭

[MtB]

18 minutes ago, jim mitchell said:

before you remove the inside, have something (Tarps or? ) to hand if the steel is rotton

 

This is what I was wondering when I asked the age of the boat.

 

Liveaboards with just Rockwool insulation suffer extensive corrosion from condensation on the inside face of the steelwork. If a cheap builder used 3mm roof steel and the boat is 40 yesrs old it could easily have rusted through from the inside. 

 

 

Edited August 26, 2024 by MtB
spelling

[blackrose]

Before you start taking the wooden lining off is there any way you can even get a limited view of what's going on? Any mushroom vents in the sagging area? If so perhaps you could remove the trim on the inside and shine a torch in to see if it's heavily corroded. Also please tell us what sort of insulation you have there.

 

I'm thinking it's more likely to be thermal expansion contraction of a thin steel roof (assuming it's steel) that's causing the issue, with perhaps inadequate roof bearers.

Edited August 27, 2024 by blackrose

[Peteonthelee]

Hello. Thanks for your thoughts. The boat is 36 years old and yes, insulation is rockwool. There is a vent there and yes I know there is some rusting on the underside as I have had to re seal that vent before. The dippping actually stems (I think) from the mushroom vent. I will re check the extent of rusting as well I can from the inside. I was thinking I might try to 'jack up' the dips so they can pop out (not sure how well that will work). Also worried that removing the slatted ceiling will create a lot of work - but this may be unavoidable.

Pete

[dmr]

If the roof has failed from severe rust then this should be obvious from the outside. Have a good look and do a bit of tapping with a hammer.

Can you see the sag from the outside and post us a photo please?

 

Did the roof sag suddenly? were you standing on it at the time etc etc? How much of a curve does the roof have? A very few are flat, Liverpool boats have a huge curvature, most are in between.

[MtB]

I'm beginning to wonder if the term 'sag' is misleading us here. Might 'dent' be a better term? 

 

I once had a narrowboat with a thin steel roof and when walking on the roof, sometimes it would do what my dad used to call "tin-lidding'. I.e when you put you weight on a bit with no brace underneath it would flex in by about an inch then pop back out when you took your weight off again.

 

I'm wondering it this has happened but the roof failed to pop pack out and stayed dented. In which case some judicious pushing up on the inside might make it pop back out again. 

 

 

 

[jim mitchell]

2 hours ago, dmr said:

Can you see the sag from the outside and post us a photo please?

 

Definitely i think required

 

3 hours ago, Peteonthelee said:

I know there is some rusting on the underside as I have had to re seal that vent before. The dippping actually stems (I think) from the mushroom vent. I will re check the extent of rusting as well I can from the inside. I was thinking I might try to 'jack up' the dips so they can pop out

If you have more than 0ne dip/ dent then  taken with the Rockwool lining and already found rusting / leak then i would urge extreme caution with any investigation/ recovery fix  - ie proceed on the assumption that the roof is on its last legs structurally 😰 sad i relealise but a case of better slow and safe than S*** what happened !!!

[David Mack]

2 hours ago, MtB said:

sometimes it would do what my dad used to call "tin-lidding'. 

My father called it "oil canning".

[Peteonthelee]

Here are the pictures. The sag, dent or dip happened suddenly but initially there was no affect on the inner ceiling. then months later I think it sagged more and then the inner ceiling dipped. There has been a very slight dip on the other side of the mushroom vent, which has been there since I bought the boat, which you may be able to just make out on the first picture  looking toward the bow of the boat. And yes I know the roof needs a good paint job -I do plan to take back to the metal and repaint (soon!).

[David Mack]

The cabin roof steel may have thinned, but it doesn't look to have perforated, so this should be recoverable. But that dent didn't appear on its own. Have you been storing something heavy up there? Or did someone leap down onto the roof from a lockside?

In any event I thing you will need to add some additional ribs inside to support the roof sheet and hold it in position. That will mean stripping out the ceiling lining and insulation, then getting a boatbuilder/welder to install the extra ribs.

[Bod]

@Peteonthelee

Do you know who built the hull?

 

Bod

[MtB]

Has this boat been stretched? There is a distinct change of direction of the starboard handrail in your photo!

 

I wonder if this has any bearing on the weakness of the roof. 

 

Interesting sculpture at the front, too.... 

[agg221]

5 hours ago, David Mack said:

In any event I thing you will need to add some additional ribs inside to support the roof sheet and hold it in position. That will mean stripping out the ceiling lining and insulation, then getting a boatbuilder/welder to install the extra ribs.

I agree that this would be the usual, and tried/tested, solution. However, I have been trying something else for various reasons on Oates, with considerable success.

 

One of the difficulties we have is that a slow-revving engine hits various resonant frequencies within the steel roof and cabin sides, which have been built lightweight to add stability to the round bottomed hull. You could actually watch the roof bouncing and it caused the bullseye to leak.

 

I noticed on a trip out with a friend on FMC The King that it was much quieter and this seemed to relate to no resonance, which I thought was likely to be due to the wooden cabin. It suited the layout and the look of Oates to have some wooden frames, so I have made and installed a wooden cabin frame at the point of worst resonance. I used 2" width x 3" depth oak (for stiffness) and whilst it is properly jointed to itself, it is held in place with structural adhesive to the cabin side and top, after a good cleaning of the steel and painting with a surface tolerant epoxy primer. The adhesive and the paint should prevent interaction between the steel and the oak, which would be highly undesirable.

 

So far, it has not dis-bonded, being wooden it has good insulation and it has had an excellent effect on damping the resonance, which has also made it much quieter. I am only one frame in, but I intend to fit another three down the boat which I think will have a significant effect if the first one is anything to go by.

 

Just a thought.

Alec

Edited September 2, 2024 by agg221

[jonathanA]

9 minutes ago, MtB said:

Interesting sculpture at the front, too.... 

Sculpture ? I thought it was ianDs fancy rudder ... 🤣

[Peteonthelee]

The dent actually did 'appear' to happen on its own. There was nothing stored the roof here at all. I do keep a kayak on top but that's much further down the boat.

 

Should also say the boat has not been stretched. ( I think that's all the questions answered). I still haven't investigated from underneath - building up the confidence.

[David Mack]

17 hours ago, agg221 said:

so I have made and installed a wooden cabin frame at the point of worst resonance. I used 2" width x 3" depth oak (for stiffness) and whilst it is properly jointed to itself, it is held in place with structural adhesive to the cabin side and top, after a good cleaning of the steel and painting with a surface tolerant epoxy primer. The adhesive and the paint should prevent interaction between the steel and the oak, which would be highly undesirable.

Not a bad idea, and perhaps more within the capabilities of a DIYer than welded steel ribs. But still requires the lining and insulation to be stripped out.

[Cheshire cat]

It needs someone to have a go at it with a seasearcher magnet. Might Save dismembering the interior

[dmr]

23 minutes ago, Cheshire cat said:

It needs someone to have a go at it with a seasearcher magnet. Might Save dismembering the interior

 

I've just purchased a good fishing magnet to make it easy to lift the hatch in the back deck above the weedhatch. Its most impressive and much too strong, unless I use a bit of card under it I am unable to pull it off the deck without making a lever from a mooring pin and a block of wood.

[truckcab79]

No point asking people who are just guessing. You need to take a section of ceiling down to investigate.  Very unlikely to be rust. Much more likely to be a dent.  Chances are if you push / jack it back out then as soon as it’s walked on it’ll just pop back down.  Steel does that.  You need to get someone to get some heat into it or as a bodge pop it back up and bond some timber forms under it to reinforce it when walked on.  
 

 

Edited September 8, 2024 by truckcab79

[Peteonthelee]

Hello all - well I plucked up the courage and voila......

So I have 3 ribs coming away from the roof and where the dip is most pronounced is the photo of where the rib has dropped completely (no surprise there). I still have the problem of needing to push the roof out in the dipped area - any ideas for this?  I thought using a jack with something to push it out slowly if I can find something of suitable length and strength to sit on top of jack. Then, I am thinking to re weld the ribs. 

 

[NB Esk]

To make the job that bit easier, grind/sand the areas to be welded before you push them back into place.

 

 

[PeterF]

Acrow Props may well work, you can probably hire them easily enough. See link to see examples.

 

https://www.scaffolding-direct.co.uk/acrow-props-prop-mates/

[jonathanA]

I would have thought a couple of bottle Jack's and some suitable timbers would do it. Welding would be best, but some machine screws and nuts might hold it in place until it can be welded.