Welding fittings onto steel hull

[Someofthegear]

It's not difficult to rent the gear and do blasting yourself and much less expensive though it still costs a lot. I started blasting a few years ago to complete a steel boat project but there was a demand for it in the yard and I have done a fair bit since, mostly on trawlers.
Thanks for the info on the Tercoo. I watched some of the promotional videos for it and wasn't much impressed but it does look as though it could be useful for stripping back soft or gummy coatings which are slow to blast because they absorb grit.


Yes, the range of movement is small so the tacks don't usually crack when pushing on the lever but on the other hand when you're done you can easily twist it free by hand. If the tacks to the lever do crack then maybe try them with 7018 rods which is more crack resistant. Obviously, you'll have to grind all the tacks off after so you want them to be as small as possible.

When you perimeter weld after, keep down the length of continuous weld and keep the welds as small as you can consistent with doing the job. The long edge welds will cumulatively contract which has an effect similar to pulling a thread in a loose weave fabric causing the fabric to ruffle either side of the thread. You can see lots of chine steel hulls with a wave in the chines that is caused by weld shrinkage. I'm guessing that there probably won't be much framing on the inside of your hull to keep the plates fair.


Good luck with that...it's depressing; I well know! If you are careful though you should be able to recycle most of the material when putting it back.

Post some photos of progress..

Thanks. I was planning to back step weld or just jump around all over to keep the heat down. I'm pretty slow so it'll have plenty of time to cool

I was going to cut two slots in the middle of each plate to weld to the original. Any size and shape recommended?

I will take pics of the better welds!

 

[Someofthegear]

One more question- I'm guessing I can't use dye penetrant as I can't access the back of the weld. Is there any other means to check watertightness?

 

[Nick.K]

Is there any other means to check watertightness?

Looking at your welds should be enough.

Look carefully at the transition between the weld and plates and the weld overlaps, it should be smooth but if the weld turns in on itself you probably don't have fusion. Clean up any messy welds with the grinder, don't assume they will be alright underneath because they often won't. Grind out and redo any areas with blow holes or porosity.
If you radius the end corners of the patches they will be easier to weld around
At the end though if it is cleaned and epoxied that will seal up the welds well enough even if there is a bit of porosity.

I was going to cut two slots in the middle of each plate to weld to the original. Any size and shape recommended?

I don't know if there is a standard/ recommended way of doing that but if I was doing it I would cut the holes in the hull not in the new plate and weld them from the inside once the plate was fitted. I would probably use say a 45mm hole cutter (cut the holes before fitting the plate). Getting fusion in the bottom of a slot can be difficult, not least because you can't see the weld very well.

 

[Someofthegear]

I might struggle to get the angle to weld the top of the hole from the inside, at least without taking out more of the floor. As it's under the waterline, would it look awful if I cut the holes in the new plate?

Heating system, loo and kitchen all removed , trying not to find screws in the lining now. On the plus side, actually quite spacious inside now

 

[Nick.K]

On the plus side, actually quite spacious inside now

Something good anyhow!
How do other people do this? At only 2ft wide your new plates may not need pocket welds, they are only there to add corrosion life to the hull and the strength isn't an issue; if they would be difficult to get to from inside why not put them on and see how they look without cutting more holes?

May be doing a day trip on the Grand Union (Northampton) in the next few days