Sticking on a new superstructure to a NB

[W+T]

Ok i need to plan this project. I will be welding on a new superstructure to a 47 foot steel hulled NB  I will be using 3mm steel fro side and top, some will say use thicker plate, 3mm is good enough. Now i want to do this properly can anybody link me to any decent place to look up on doing this.  I have seen some right contraptions on my travels.  I have a good idea how i would do it an dit would work but then there is the proper ( professional )  way.

 

Captain Faffer  

 

 

[OldGoat]

1 hour ago, W+T said:

Ok i need to plan this project. I will be welding on a new superstructure to a 47 foot steel hulled NB  I will be using 3mm steel fro side and top, some will say use thicker plate, 3mm is good enough. Now i want to do this properly can anybody link me to any decent place to look up on doing this.  I have seen some right contraptions on my travels.  I have a good idea how i would do it an dit would work but then there is the proper ( professional )  way.

 

Captain Faffer  

 

 

Made I larff -

Some will say use thicker that 3mm but I AM going to ignre that, ...... however it appears that be wants to do it properly (disregarding the common practice) can we (by inference) direct him  to somewhere he can find information on how to do 'it' improperly??

 

Good Lord, preseve us.....

 

(Let's see how many posts can be generated from the requirement......

[Alan de Enfield]

1 hour ago, W+T said:

I have a good idea how i would do it an dit would work but then there is the proper ( professional )  way.

I'm not sure that I'm right, but logic would suggest that :

Step 1) Strip out the inside.

Step 2) Remove the old cabin

Step 3) Weld on new cabin

Step 4) Refit insides.

[dave moore]

3mm will distort as you weld, giving you what I call “ North Atlantic “ cabin sides...if that’s of no consequence, carry on. Our old boat, Resolute, carried 5mm and showed no blemishes, stitch marks or waves, just pure straight beauty where it mattered....

[Tracy D'arth]

3mm roof will distort and change shape when walked on, usually permanently. Or put curved formers at closer centers, say 15"-18"

Mig all the top hamper, less heat. Move round every foot or so welded.

Weld up the handrail and its inside grip part first then weld to the side.

Consider gluing the cabin side bracing rather than welding, just welding top and bottom.

Edited August 13, 2020 by Tracy D'arth

[Steve56]

17 minutes ago, dave moore said:

3mm will distort as you weld, giving you what I call “ North Atlantic “ cabin sides...if that’s of no consequence, carry on. Our old boat, Resolute, carried 5mm and showed no blemishes, stitch marks or waves, just pure straight beauty where it mattered....

Would agree with this. I have seen 3mm used and it looks bad. Also get all the frames in place before even thinking about the sheet steel

[dmr]

Most cars and vans use steel of 0.9mm or less, I think the 2CV was about 0.7 in places (but it was tricky to weld), so I reckon 1.5mm would be fine for a boat superstructure. It looks like an old Harborough boat so much of the hull is probably less than 1mm thick anyway.

 

................Dave     (?)

[Steve56]

6 minutes ago, dmr said:

Most cars and vans use steel of 0.9mm or less, I think the 2CV was about 0.7 in places (but it was tricky to weld), so I reckon 1.5mm would be fine for a boat superstructure. It looks like an old Harborough boat so much of the hull is probably less than 1mm thick anyway.

 

................Dave     (?)

Yes but most cars are made of pressed steel panels which are spot welded together

[W+T]

Thanks i will look into using thicker steel , just what most other folk have said that i spoke to who built a few boats say 3mm will be ok. 

 

still any link please. 

38 minutes ago, OldGoat said:

Made I larff -

Some will say use thicker that 3mm but I AM going to ignre that, ...... however it appears that be wants to do it properly (disregarding the common practice) can we (by inference) direct him  to somewhere he can find information on how to do 'it' improperly??

 

Good Lord, preseve us.....

 

(Let's see how many posts can be generated from the requirement......

why you talking shit, 

did i say `i am going to ignore that`.....no

[dmr]

I'm a very amateur welder and if I welded flat plate it would go wobbly. However looking at boats on the cut a lot of professional boat builders have the same problem so why make life harder for yourself?. If you get rust problems in ten years time, like behind a window frame, the pitting of 1.5mm or so is not uncommon so using thicker steel will also almost double your "safety margin to a hole right through".

 

Some builders claim that using 5mm means you can use no or much reduced framing but I dunno if this is true.

 

I like the shape of them olde boats, especially the extra bit of tumblehome, so it would please me if your retain the cabin shape and character ?.

 

I assume you will do any hull overplating whilst out of the water.

 

................Dave

[Murflynn]

40 years ago I fabricated a narrowboat using 3mm plate for the cabin.

 

Using sheets about 3m x 2m (3m in cross section view and 2m lengthwise) and with the help of a local sheet metal fabricator I arranged for the top corners of the cabin to be folded in their press to an angle of about 80degrees.  The 2m cabin segments were welded together with the aid of a backing strip.  After assembly, steel angle stiffeners about 40x40x3 that had been radiused by another steel fabricator were fitted to the ceiling to form a perfectly curved roof.  Longitudinals of the same material were fitted from end to end of the cabin, level with the top and bottom of the window openings.

 

It all came together with minimal heat distortion.  Windows were cut out with an angle grinder and cutting discs, using a flame only for the curved corners.

[W+T]

5 minutes ago, Murflynn said:

40 years ago I fabricated a narrowboat using 3mm plate for the cabin.

 

Using sheets about 3m x 2m (3m in cross section view and 2m lengthwise) and with the help of a local sheet metal fabricator I arranged for the top corners of the cabin to be folded in their press to an angle of about 80degrees.  The 2m cabin segments were welded together with the aid of a backing strip.  After assembly, steel angle stiffeners about 40x40x3 that had been radiused by another steel fabricator were fitted to the ceiling to form a perfectly curved roof.  Longitudinals of the same material were fitted from end to end of the cabin, level with the top and bottom of the window openings.

 

It all came together with minimal heat distortion.  Windows were cut out with an angle grinder and cutting discs, using a flame only for the curved corners.

Took long enough for a good reply, and not meaning to use 3mm sheet but sensible to the question asked. 

 

Still need a link to look into it though as first question.  

[David Schweizer]

12 hours ago, dmr said:

I'm a very amateur welder and if I welded flat plate it would go wobbly. However looking at boats on the cut a lot of professional boat builders have the same problem so why make life harder for yourself?. If you get rust problems in ten years time, like behind a window frame, the pitting of 1.5mm or so is not uncommon so using thicker steel will also almost double your "safety margin to a hole right through".

 

Some builders claim that using 5mm means you can use no or much reduced framing but I dunno if this is true.

 

I like the shape of them olde boats, especially the extra bit of tumblehome, so it would please me if your retain the cabin shape and character ?.

 

I assume you will do any hull overplating whilst out of the water.

 

................Dave

Our old boat had 5mm sides and roof with no apparent framing, just lugs onto which hardwood battens were bolted. The sides and roof showed no distortion.

[dmr]

29 minutes ago, David Schweizer said:

Our old boat had 5mm sides and roof with no apparent framing, just lugs onto which hardwood battens were bolted. The sides and roof showed no distortion.

I think one company (Big Fish?) claimed that they requested their shell supplier to make the cabin sides from a single sheet (roll) of 5mm steel so that there were no visible welds on the cabin side. I am trying to visualise handling a roll of 5mm thick steel and getting it flat, I bet it was hard work.

 

................Dave

[Murflynn]

33 minutes ago, dmr said:

I think one company (Big Fish?) claimed that they requested their shell supplier to make the cabin sides from a single sheet (roll) of 5mm steel so that there were no visible welds on the cabin side. I am trying to visualise handling a roll of 5mm thick steel and getting it flat, I bet it was hard work.

 

................Dave

can be delivered flat on a 40ft truck bed, will fit many cabins just fine.

[Tracy D'arth]

There was a Bridgewater builder who had long sheets delivered with the ends where the stockholder had cut the roll marked so that he could join them up again as they were rolled to avoid any distortion. Now that is pedantic but sounds like a caring guy.

 

The other way to avoid cabin side ripples is to weld them on the gunnels  slightly too upright then pull them together at the roof imparting a vertical bow in the sheet, that will prevent longitudinal ripples forming. A lot of tacking up before continuous seam welding helps too. And changing section very frequently when welding to prevent getting one area hot.

 

Avoid flame cutting of apertures at all costs.

 

TD'

Edited August 14, 2020 by Tracy D'arth

[dmr]

4 minutes ago, Murflynn said:

can be delivered flat on a 40ft truck bed, will fit many cabins just fine.

Yes, I had assumed it came flat and the "roll" was some sort of marketing speak, but I do like the image of a giant roll of 5mm steel with a bloke on each end trying to unroll it. Some boatbuilders and boat fitters have always tried to turn little features into major advantages to set them above their competitors.

We use a single piece of steel for the baseplate,   we weld the baseplate both sides, we build Birmingham square to give you extra space, just look at what we do under the gunnel to appreciate our quality of workmanship etc.  etc  These things then get cast as essential in the buyers mind so everybody else has to fall in line (or make a counter argument). 

 

.................Dave

[dmr]

8 minutes ago, Tracy D'arth said:

There was a Bridgewater builder who had long sheets delivered with the ends where the stockholder had cut the roll marked so that he could join them up again as they were rolled to avoid any distortion. Now that is pedantic but sounds like a caring guy.

 

The other way to avoid cabin side ripples is to weld them on the gunnels  slightly too upright then pull them together at the roof imparting a vertical bow in the sheet, that will prevent longitudinal ripples forming. A lot of tacking up before continuous seam welding helps too. And changing section very frequently when welding to prevent getting one area hot.

 

Avoid flame cutting of apertures at all costs.

 

TD'

 

Had never really thought about that, it makes a lot of sense. During lockdown I took most of my portholes out to derust behind them and did note a very slight curve on the cabin side. It was also interesting to note how flexible 4mm steel is round the porthole "hole", there was very obvious movement as I tightened up the porthole bolts.

 

................Dave