Hull plate weld sequence on repair job?

[Steelboat]

I am doing some hull plate and stringer replacement under the anchor locker due to some water pooling up and causing corrosion.

Looking for any feedback on my proposed repair sequence below. It is based on my reading of comments on an old thread by MR Wynand. My skills are pretty basic compared to a professional steel boat builder, so may have to adjust.

1- Cut out corroded plate and damaged stringer (leave chine bar in place)
2- Fit new longitudinal stringer, light tack weld to the transverse frames
3- Fit and tack weld new hull plate
4- Inspect plate for fairness, adjust as required

5- Adjust stringers to the plate as needed
6- Tack weld stringer to hull plate
7- Weld the stringer to the frames
Butt weld the new stringer to the existing sections
8- Weld the stringer to the plating (small interval welds)
9- Weld out the inside of plate
10- Gouge back from outside to remove slag at weld root
11- Weld the outside of plate
12- Carefully sand outside weld smooth (80 grit flap wheel)

 

[TANSL]

There may be more observations but I have focused on two that are important:
- the welding of the reinforcements must not coincide with that of the plates.
- Butt welds between adjoining plates must be separated by at least 50 mm from the adjacent reinforcements, throughout the perimeter of the new patch.

 

[Steelboat]

Thanks Tansl. I will integrate that rule into the plan.
Is there a common source for these rules to pay attention to?
All I could find was "Guide for Steel Hull Welding" ANSI/AWS D3.5-93R. Good info but mostly big ship related.

 

[TANSL]

The best there is, in my opinion, are the regulations of the Classification Societies. Although they are made for boats of more than 24 m in length, their recommendations, in the sense of what we are talking about, are valid for boats of any size.

 

[Ad Hoc]

You basically need to ensure that after you tack weld everything in place, you do the transverse butt welds first, then the long.t seam welds.
Once the insert plate is welded to the existing plating, - fully welded - then you can begin to weld the traverse frame. Once that is done... finally weld the long.t.

Make sure the chine joint is clean and fully edge prepared to ensure a good pen weld. Most likley a good root and 1 or 2 caps...depending upon the thickness.

 

[Steelboat]

Thanks Ad Hoc.
It seems I was using a weld sequence more suited for new construction vs this repair job.

Does this look right?

1- Cut out corroded metal- plate, longs and transverse frame sections
* maintain >50mm distance between plate welds and support structure
2- Tack up new plate and support structure
3- Fully weld inside of insert plate
4- Grind root and fully weld outside of plate
5- Weld in new frame section
6- Adjust longs as needed for contact with plating
7- Weld out longs to hull and frames
Done!

Question- could the tacked-in longs could be left out to make welding out the insert plate easier? Install them after the plate work is done, as they are just in the way?

 

[Barry]

Thanks Ad Hoc.
It seems I was using a weld sequence more suited for new construction vs this repair job.

Does this look right?

1- Cut out corroded metal- plate, longs and transverse frame sections
* maintain >50mm distance between plate welds and support structure
2- Tack up new plate and support structure
3- Fully weld inside of insert plate
4- Grind root and fully weld outside of plate
5- Weld in new frame section
6- Adjust longs as needed for contact with plating
7- Weld out longs to hull and frames
Done!

Question- could the tacked-in longs could be left out to make welding out the insert plate easier? Install them after the plate work is done, as they are just in the way?

What is your plate thickness?
And what is the half round stiffener shown in the drawing? Quite a poor profile to stiffen the plate

 

[Steelboat]

What is your plate thickness?
And what is the half round stiffener shown in the drawing? Quite a poor profile to stiffen the plate

Hi Barry, the 3/4" diameter solid bar is a "chine bar". Poorly drawn by me, it separates the first and second chines of the hull plating. I think it's main purpose is to make a smoother transition between hull flat plates. Perhaps it is also a stronger join, and serves to add some stiffness. In profile it looks like the drawing below, courtesy of Lloyd's and RxComposites.

 

[Steelboat]

What is your plate thickness?

Hull plating is 5mm A36. Longitudinals are 1-1/4 * 3/8 flat bar (32*10mm)