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BARGES: All about barges and barging - building, buying, maintaining, equipment, handling on the water, etc.
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TOPIC: Iron hull replacement

Iron hull replacement 03 Mar 2020 04:39 #114097

Hi Balliol
Thanks for the link, what a project, in such a short period, fantastic. The planning must have been incredible, investment in plant and equipment etc.

Obviously I have never seen flame shaping on this scale (who has?), But yes it's exactly what I was talking about, and this on some pretty thick plate.
On thin plate I've seen cold water applied with a sponge, or hose / spray. It all depends on the curvature required.
Unfortunately I have not got access to oxy acetylene these days, as I would love to spend a day experimenting with some play off cuts.

As you and Tam say, cold forming small section, or thin plate mild steel is quite easy, just look at how little force from a shopping trolley is required to modify the shape of a car door.

Wrought iron is even more maluable than low carbon mild steel, so is ideal for metal bashing.

All interesting stuff.

Paul Hayes

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Iron hull replacement 01 Mar 2020 19:43 #114094

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Here you go Paul. The last ten minutes covers quenching/ line heating.

m.youtube.com/watch?feature=emb_title&v=t1998s__sUY&time_continue=51

Balliol.

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Iron hull replacement 01 Mar 2020 19:25 #114093

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Tam Murrell wrote: When we converted ex-working Friesland we put the necessary curve in the tee section roof frames by holding them at one end, resting on a bed of sand, and "hitting it with a hammer" until they matched the curved drawn on the ground. No heat involved. It is possible to achieve convex shapes in a similar fashion.

Tam


Yes, we used to do the same if we needed just a few beams, rather than take them to be rolled.

For plates, I think a lot of Dutch bows (and sterns) were formed to an extent by hammer since you can sometimes still see the hammer marks if you look carefully on the inside. Presumably formed either in a sand pit or over universal formers. I also recall being told that the compound curves in a Josher bow ( a particular type of old narrow boat) were formed by beating the plates out hot over concrete formers or moulds, but this would presume a bit of “tooling” investment in the moulds for a production run.

These forming dents are even more obvious on the gloss painted round corners of many original stern cabins.

I guess these plates may have been formed by steam or pneumatic hammers though. The same would be just as possible with a trusty sledge hammer, but I would not want to be the one swinging it.

Paul suggests quenching. I was once given a long lecture on this by a supposed expert, but I never really got to try it. I suspect you could waste a lot of plate practicing, but it would be interesting to experiment. Not sure you would find evening classes on the subject though!

I suspect that if the strakes on the subject tjalk are removed carefully and laid on the ground they will prove to be an interesting shape “opened out flat,” but that they will not actually have that much compound curvature , which is the difficult thing in steel, just as in 2” oak (and the talk was of course originally a planked wooden barge). A bit of pulling and twisting on a long strake, aided by chain hoists, wedges and cramps, may be all that is needed. I recall when we built our replica luxemotors the developed shape of the reverse strake on the fantail stern was very interesting, but basically just cut from a piece of flat plate that we then just pulled round to shape with chain hoists etc. The difficult bit was developing the shape (and this was in the days before CAD), but if you have the old strakes as templates then that is the difficult bit covered.

I know that LVBHB members in Holland are partial to a bit of total restoration, so a few phone calls and a trip to the Netherlands could prove very educational. They might have a member doing just this job at the moment.

Balliol.

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Iron hull replacement 01 Mar 2020 17:28 #114090

When we converted ex-working Friesland we put the necessary curve in the tee section roof frames by holding them at one end, resting on a bed of sand, and "hitting it with a hammer" until they matched the curved drawn on the ground. No heat involved. It is possible to achieve convex shapes in a similar fashion.

Tam

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Iron hull replacement 01 Mar 2020 15:34 #114088

Much great advice, so will only add one thing.
Shaping bulbous shapes in plate can be (with a deal of practice), be nicely formed using a oxy acetylene cutting gun and cold water.

Even on 6mm plate a controlled switish cross of a plate with the other side cooled with a wet sponge will induce a bend, a cross again in 90 degrees to form a "plus" sign will induce a perpendicular bend.

This can be used as the start of forming a "bulb" shape.
The amount of bend, depends on 1. Heat applied andd 2. Amount of cooling.

A few hours practice will be enough to get the skills to build on, I've seen some really impressive shapes formed like this, even compound curves, eventually reversing like an S shaped spoon.

One advantage is that the stress in the plate is "natural, and not trying to pull back to flat.

I hope this helps

Paul Hayes
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Iron hull replacement 01 Mar 2020 12:06 #114085

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"how do you blow out a rivet" ?
Using oxy acetylene to cut metal requires you preheat the metal red before introducing a jet of oxygen to "cut" the metal. Geneally speaking it's only possible to continue that cut on the one piece. Any other metal no matter how close won't be cut as it's not hot enough. With a bit of skill you'd heat and cut out the rivet to leave a clean hole with the adjacent metal (in this case the frame and plating) untouched. The rivet is reduced to slag.
You can get rivet cutting nozzles which are used to take the head off. You still have to punch out the rivet as you would with an angle grinder.
The oxy acetylene method is at least twice as fast. A nick raised in the rivet head with a chisel reduces the time to preheat the rivet to a few seconds.
No punching being required.
Not had success with plasma as it will quite happily cut whatever is in it's way without preheating.

Derek
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Iron hull replacement 29 Feb 2020 20:30 #114081

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[quote="Jakob Schröter" post=114080

How do you 'blow out a rivet'? I just cut off the heads with an angle grinder.[/quote]

Flame cut (oxy-propane or oxy-acetylene) or I guess plasma might do it. Yes, an angle grinder is good if working from the inside, and probably quicker on a clear run of rivets, but not in tight corners and you still usually have to drift the rivet shank out. With the gas axe you can blow the whole river shank out in one operation. Horses for courses!

Balliol.

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Iron hull replacement 29 Feb 2020 19:02 #114080

Cutting to shape was a pain indeed. I tried to make sure I have a right angle and two straight edges in my cut-outs, then pushed the new plate in place, with a small overlap at the third edge (fourth edge would usually be where the next new plate joins), then cut that overlap off from the inside using an angle grinder. Gives a nice 1mm gap that's perfect to weld.

How do you 'blow out a rivet'? I just cut off the heads with an angle grinder.

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Iron hull replacement 29 Feb 2020 14:15 #114078

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Jakob Schröter wrote: Yes, I welded to the old riveted steel along the chines and at the forward end of my replaced section. I cut and then welded directly behind one rivet to keep away as far as possible from the next one. I did not have any leaks, but wouldn't notice yet as there are now 6 or 7 layers of 2k epoxy on the outside and a few more on the inside.

I did not overlap my plates but butt-welded them.


A few weeping rivets will soon rust up!

One advantage of lapping the plates (as per original) is that you have a bit more leeway in terms of accuracy of cut.

More usefully however if the long seams are lapped then, given that you will be pulling the plates around a bit, the lap will tend to produce a fairer seam. Also, if you tack the laps, then pull the plates round under a bit of tension;, then weld inside and out then the heat from that can allow the plates to relax a tiny bit and help take the curve, sort of a bit like a joggled seam.

Balliol.

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Iron hull replacement 29 Feb 2020 14:03 #114077

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Craig Andrews wrote: Hi there. I would assume that the curved sections at the bow , chine and stern are formed as the original profile if the planks naturally follows the intended curve and profile as a two dimensional plate/plank/ strake follows the elliptical shape of the hull frames, into a 3 dimensional shape, which includes the bow profile.
Did you need the new steel to the existing iron? And if so, did the adjacent rivets cope well, i.e no weeping rivets afterwards due to localised heat from the welding ?



I think if I were doing the full bottom job I would want to take the ship back to bare frames (sequentially of course, as said, no area too big). I would not want to be welding to the iron plating if possible. Sometimes it can be laminated and there can be real doubt as to how much penetration you are getting. Below waterline you are better to lose all the rivets. Weld the plating to the frames.

Above the water (the bits you see) it can be nice to keep the frame rivets, and sometimes you can crop out between frames and let plates in if the plating actually on the frame remains good. I would not really want to be welding up to lines of rivets along lap seams though. You could always weld false rivets on! That will make purist restorers wince, but if that is the case then they should rivet the whole thing (which some do of course!)

Jakob’s advice is good but certainly on the narrower strakes at the ends I would try and do a bit more than 1.5 metres at a time. The longer strips might be easier to twist to a fair curve and you will have less butt seams to keep fair.

Balliol.

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Iron hull replacement 29 Feb 2020 14:02 #114076

Yes, I welded to the old riveted steel along the chines and at the forward end of my replaced section. I cut and then welded directly behind one rivet to keep away as far as possible from the next one. I did not have any leaks, but wouldn't notice yet as there are now 6 or 7 layers of 2k epoxy on the outside and a few more on the inside.

I did not overlap my plates but butt-welded them.

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Iron hull replacement 29 Feb 2020 13:43 #114075

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Craig Andrews wrote: Well that's great, and actually answers many of my uncertainties. Yes a big job, but and opportunity to make this good. Do you think that the one steel steel strake could replace a double strake profile, just to reduce joints, welding etc? And the bolts are suggested for what purpose? Temporary clamping? Or to fasten the strakes to the frames?
Does epoxy replace all the other types of blacking/primer/protection often suggested?


Most hulls of this type were built with wider strakes where the going was flattish, becoming two strakes at the ends so that a bit more twist could be coaxed into the plates. I would stick to the strake plan as built. Blow the rivets to drop each strake outa day you should have a good template.

The bolts are for temporary clamping, to pull plates up to the frames. Remove afterwards and weld up the holes. There are various plating tricks available, wedges and strong backs, modified G cramps, acro props, toe jacks etc, the use of which will depend upon working conditions, such as do you have a dry dock wall to shove against.

So far as plate forming is concerned you will have to do some fighting to pull the plates into place, but try and minimise this by preforming the plates as much as possible. We never ran to plate rollers, press brakes or portal presses, but used the facilities in a friend’s fabrication shop where necessary. Bilge plates for example (on the parallel hull section, if you have any!) can be rolled to a template, but always under roll slightly and fight the last bit. A portal press could be made quite easily to tweak some of the more complex curves into the plating, but we tended to use the rear jack legs on our JCB (although sometimes the machine had to be chained down!) so perhaps get the bilge plates rolled, and resort to good old ingenuity for the more awkward areas, but if you keep to narrow strakes life will be a lot easier even though there is more welding.

Epoxy? Yes, grit blast and epoxy. I would not waste time and money on any modern single pack paints.

Balliol.

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Iron hull replacement 29 Feb 2020 13:30 #114074

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Sorry a few typos
Original profiles "of" the planks
And
Did you "weld" the new steel to the existing iron

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Iron hull replacement 29 Feb 2020 13:26 #114073

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Hi there. I would assume that the curved sections at the bow , chine and stern are formed as the original profile if the planks naturally follows the intended curve and profile as a two dimensional plate/plank/ strake follows the elliptical shape of the hull frames, into a 3 dimensional shape, which includes the bow profile.
Did you need the new steel to the existing iron? And if so, did the adjacent rivets cope well, i.e no weeping rivets afterwards due to localised heat from the welding ?

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Iron hull replacement 29 Feb 2020 12:51 #114072

I'm in no way an expert on this topic, but can report of a successful replating of about a quarter of my praam's bottom. About half of the entire hull's length has been replated by her previous owners before, and I just continued in the same fashion. I cut out sections of about 1.5 sqm at a time using a plasma cutter and welded a new plate in before continuing with the next section. I first tacked the plate to the frame with ~10 cm welds (about 3 to 4 per meter) before welding the edges inside and outside.

I did only 1.5sqm at a time because that's about the size of plate I could handle by myself (about 50kg per new plate) with the limited tools available (a pallet jack and 4 ancient lifting/rack and pinion jacks) . Replacing more sqm at a time will certainly speed things up, but I was also cautious not to weaken the overall structure too much.

I welded plates of 5mm in because I was told by the surveyor that the already-replated section was 5mm thick. When I cut her open I measured those newer plates manually and they turned out to be 6mm. I would have used 6mm for my new plates had I known this before. In any case, I'm quite happy with the outcome (and will in fact continue this summer). Meanwhile she is happily afloat.

So far I have only replaced flat sections. I have a follow-up question to the wider audience here: How would I go about replacing rounded sections at the chine? Are they usually pre-shapeed, or forced into shape in place? I could perhaps do the latter with 3mm plate if simply overplating, but not with 5mm. How do professionals do this?

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Iron hull replacement 29 Feb 2020 12:38 #114071

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Well that's great, and actually answers many of my uncertainties. Yes a big job, but and opportunity to make this good. Do you think that the one steel steel strake could replace a double strake profile, just to reduce joints, welding etc? And the bolts are suggested for what purpose? Temporary clamping? Or to fasten the strakes to the frames?
Does epoxy replace all the other types of blacking/primer/protection often suggested?

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Iron hull replacement 29 Feb 2020 12:26 #114070

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Presuming that a significant proportion of the shell plating has been condemned then complete replating is the pragmatic way, particularly since the old iron may be a b. to weld. I would start at the keel strake and build up new plating following the existing strake lines and lap seams. Don’t cut out too much at a time. The old plates should serve as templates for the new ones. Overlap as before, fully welded inside and out. Leave each strake sagging slightly away from the frames as you build up the strakes so that you can get an internal weld behind each frame, then push the strokes home to the frames. A bag of bolts might come in useful.

There is a temptation to suggest thicker plating on the flatter areas, perhaps 8mm, but with modern epoxy paints etc. 6 mm is probably plenty and the boat might not take the extra weight.

I don’t know what you know, so perhaps best for you to just ask any questions rather than me write a thesis which might be teaching you to suck eggs!

Best of luck. Big job!

Balliol.

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Iron hull replacement 29 Feb 2020 08:36 #114066

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Hi balloil. Yes, that is the planned route. Unless advised otherwise. I'm in your hands, and I'm inspired by many of your other opinions on other posts you've commented on. 👍. Thanks for responding so far. I'm told the boat is well worth saving. So I am prepared to put in the extra effort required.

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Iron hull replacement 29 Feb 2020 08:14 #114065

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Just to clarify, you are intending to cut out all the existing underwater riveted plating and then fit new welded mild still plating to the existing frames?

Balliol.

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Iron hull replacement 29 Feb 2020 07:27 #114064

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I am looking at replacing the below water line section of this 1908 riveted 6mm iron hulled tjalk, with welded steel of similar thickness. I have trawled this forum and internet, and as much as there is a large volume of information about hull welding, any description, guidance, process and recommendations from previous successful build routes of this nature appear to be limited. Can any members guide me, or point me in the right direction to acquire any further details on this project. I am an engineer and have coded welders and a fabrication shop to hand, so not completely naive around this subject, just not completely experienced with boats!! Thanks in advance.
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