more replating questions

[Dave Patterson]

Thanks for all the advice. I've decided to rent a plasma cutter to aid in removing the old plate. Should I remove all the bad plate before installing new or should I only do a section at a time. Also, there seems to be several schools of thought on how to install the new steel. Start with the largest plate, usually midship, or start with the the most difficult which in my case is the stem. The rest of the hull should be relatively easy. I am replacing the plating approx. 3' on either side of the keel stem to stern.

Thanks.

Dave Patterson

[MikeJohns]

Dave
Cut out the full extent of the wasted plating (all of it) . Then re-plate.

A plasma cutter is a great tool and they are cheap. Remember to make your patches around 1 foot on the shortest dimension and generously radius the corners of the hole (and of course the insert). This can be hard to do using cutting disks.
If any of the framing is wasted you might want to weld a temporary bar along the frame before chopping bits out as then you'll keep the shape.

[welder/fitter]

Dave,
I read your other thread, then this one. to add to what Mike Johns said; don't end your cuts on the frames, take them 1.5" to 2" beyond. Do you know what a dog is? Saddle? If not, say so & I'll draw some quick, basic pictures & put them on this thread. Plasma is great, if you're comfortable with it, but can make a mess quickly, if not. An Oxy-fuel torch will do the job, but you don't want to concentrate heat in one area. As mentioned, either will give you radiused corners - imperative - though you could use zip-cuts for the long runs & plasma or oxy-fuel torch for the ends. How thick is the plate? Crud, supper's ready, I'll load a few photos & drawings to show you what I'm saying, after I've eaten. lol
Mike

[welder/fitter]

Dave,
O.K., if I haven't messed this up, there will be two attachments. Before we go any further, make sure that you cut the old area out with good radii of corners, cuts not ending on existing welds and clean up the area within 2" of the edges, down to metal(better to do before cutting out) and grind your edges. In the first one, the fitter is in the process of dogging in the plate, that is, making it flush with the existing plating. You will note two "dogs" to the right of the fitter. the dogs are tacked to the existing hull plate - tack dogs on one side only so you can knock them off - you place the new insert and drive a wedge between dog & new plate to hold it in place. you can make angular dogs which would be tacked to keel sides to hold base/bottom of plate. When you make your template, then cut your insert to match template, you can use your plasma or oxy/fuel torch to trim insert - better a touch too large than too small. Another way is to dog & wedge the plate over the area that it will eventually cover and cut from the inside, following the edge of the existing plate, this is called scribing in the plate. remember that you'll want a slight gap in the seam between the insert & existing plate. Once you have your insert shaped, start at one top corner, using dog & wedge to make insert flush with existing plate, tack at dog, then gradually work your way out of corner, alternating tacks in each direction(across & down). tacks need only be large enough not to break. Don't tack other corners until you arrive at them & with curvature it is better to do the top longitudinal seam first. If thinner plate(I didn't see thickness mentioned) try to tack dogs to plate where it is supported by frames & stringers, wherever possible. you can find your frames/stringers locations from the outside of the hull plate by running a piece of soapstone across the plate.
I hope this helps & that I haven't missed anything. Best of luck!
Mike

Edit: Almost forgot, if you're new to welding, I recommend tacking & welding with stick(SMAW). To be honest, I'd actually recommend doing everything but the final welds, then having someone with welding experience finish it off, as we are talking about welds below the waterline. After welding inside first, grind root from outside & weld. if inside hull is not, or not fully, accessible, you can use a backing ring to single-side weld the final seam.