amp- thickness

[KemppiFrog]

Bit late in here, but I have been around boats since I was walking. Not so many steel ones, mostly plastic and wood. But Gwil not only has done it, but gives the best advice. Boats are very lightly stressed in general, except for point loads like rigging and rudders on sailing boats, as said, canal boats like yours are lightly stressed tin boxes and unlikely to suffer from weld failures . Can't think of a problem that wasn't caused by corrosion and usually internal. Since you are overplating, there are probably loads of examples right in front of you.
I was recently working on the systems of a Dutch built steel canal barge. The owner has spent the last couple of years scrupulously de-rusting the inside and époxy coating, cos he knows where the problem is. Boat is 70ft x 20ft and hull is 6 & 4 mm plate. 3mm would be fine on a canal boat, but the demon rust would find a way, hence replating with 25mm on the bottom etc.
A few yards from the barge, some guys were cutting out and replating a 35ft sailing boat. 4mm hull and rotted from the inside. They had an inverter 125amp welder and were using 2.5s with some tacks followed by a single pass.
Good luck with the boat.

Seems I am duty cook, so gotta go...
KF

 

[Gwil]

Just remembered that one of the last jobs I did before hanging up my ultrasound gear was a very nice steel 40 foot cutter. Plating was fine, all in 4 and 5mm plate, except for serious pitting along the waterline.

'Where' I asked, politely, 'cos after all I was being paid, 'are the anodes?'.

'There aren't any' said the owner. 'When I had the hull built they said that this design doesn't need anodes'.

Duh? I never got to the bottom of this. The hull plating was very competently executed, but somewhere was a guy making hulls who believed that the shape of the hull affected its susceptibility to corrosion.

If only life was that simple, you could have made Lancias a slightly different shape and they'd all still be with us....

 

[abnormalsheep]

Finally back at the boat..! Been away for a few weeks for a much needed break. Rewdy to get cracking!

Very reassured to read about the guy who meticulously treated the corrosion inside the boat! I've been trying everything, not quite content to just plaster it with a rust converter... I ended up using potato juice, after grinding and sanding the flakey stuff off, even using a chipping hammer. The potato juice was very effective anyway - vinegar just dribbled off, the starch in the juice sorta stuck to it and dried and appeared to fully treat the rust. Then I used Zinc Phosphate (which I think is the 2pac primer?) as it also is suitable to coat the old bitumen that was on the hull inside. After a few coats of that I'll be using Micaceous Iron Oxide that was donated to the project. No rust gonna be popping through that! When I first got the boat there were 2-3cm of flakey stuff.

Some of the people who knew of my intentions mocked me and said it was unnecessary. But it feels really good to do the job as best as possible, and to know someone else has done it... even better, so thanks for sharing that little tale Kemmpi.

25mm on the base sounds a bit excessive but it would certainly stand the test of time I suppose..! I'm still quite concerned with what might be happening between the plates, as the original hull wasnt treated, and there is a fair gap between the hull and the base plate, as the welder didn't attach them soon enough. Not only that, but its been attached from inside the boat. Not much I can do about that now.

I suppose the biggest stress on the hull would be if it gets bumped around in locks, or catches stuff on the bottom of the canal... but surely it wouldnt be such a big knock that it pops the attaching welds... (holes cut in original hull to weld to the new base plate).

Anyway, as soon as I get my hands on a welder and PPE i'll share some pictures of my welding attempts.... see what you all reckon..!

Thanks again and again for all the advice and support! So much appreciated!

 

[BarrieJ]

I suppose the biggest stress on the hull would be if it gets bumped around in locks, or catches stuff on the bottom of the canal... but surely it wouldnt be such a big knock that it pops the attaching welds... (holes cut in original hull to weld to the new base plate).

If the repair patches/sections and the hull are properly prepared prior to welding and the welds have full penetration there shouldn't be a risk of 'popping' anything. Best of luck with it!