I am building a large aluminum boat. I have one very serious problem I could use some help with.
There is a seam in the hull plate on the side of the boat between two frames that needs to be welded in. The frames are 20 inches apart, and there is a 4 inch gap in the hull plate between two frames that needs to be filled. The frames are fixed in relationship to each other. So it's a 4 inch piece of metal butt welded on each side to the hull plate. Look at it as two plates with a 4" gap that needs to be filled, and the plates are fixed with respect to each other.
The hull plate is 3/16ths 5052. The filler is 3/32 5356. I am using TIG w/ Argon. I am using as little heat as possible (145 amps or so), and going as quickly as possible.
I have used strongbacks, and 1/16 inch gapping and did tack welding first. I skip welded the back and front sides - finally running a full weld on the front (welding with an intermittent pattern).
All looked good, until I removed the strongbacks. Now the seam bows outward (it expanded), though it does not look as though gaps on the butt weld increased after the weld was completed.
It's absolutely amazing. I understand aluminum has issues with weld distortion, but I cannot seem to get around it. I am not sure what really happened either.. would like to know the physics of what is really going on.
What technique would be suggested? I can think of (time consuming) methods to try...including:
1. lap weld a backplate, and then fit in the 4" seam piece.
2. use permanent strongbacks
Re-doing it is very time consuming. Please help.
--- joel
We recently had a finicky stainless job that required minimal distortion on the finished product. The techniques we used are described below.
It's unclear from the description, but is there any way to weld this joint from both sides? Double bevel the joint and weld it that way. The distortion should be minimized. As best as you can, try to keep the parameters the same for the welds on each side. Try to deposit as much metal as you can each pass, reducing the heat cycles.
Charles.
Thanks.
Welding can be done from both sides. It has to be a continuous weld on one side (the outer side of the hull). I am considering just integrating strongbacks into the structure as a permanent solution. The problem is that when temporary strongbacks are removed, a considerable amount of distortion appears. Leaving strongbacks in place implies built up stress that has to weaken the weld.
Why not cut the sides back to coincide with the frames and put in a 20 inch wide section instead of 4 inches. The amount of welding would have been the same and the frame would act as the strongback to prevent distortion. It may be worth redoing it to make it right.
Cutting the sides out far enough to meet at the frames is a smart idea... I had not thought of that. May give that a try. Hate to cut all that metal away.
Have you done any research on vibratory stress relief? There are some companies that claim to reduce distortion with vibration.
http://www.meta-lax.com/
http://www.stressreliefengr.com
http://www.eng-tips.com/viewthread.cfm?qid=80399&page=1
Try these for starters.
Also some companies will rent the equipment so you don't have to purchase it.
It might be worth the effort instead of cutting it all apart and inducing more heat to an already distorted component??
hi joel, I'm building a 25 ft aluminum boat,and i had the same problem.
I dont have a fix for it yet. i may just fair it with putty and paint. but i thought of just using a hammer and a shaped bucker up to take the hickey out.(its worse in some areas than others.)Its not so bad in areas where i welded the transverse seams first.i missed a couple of places and had to go back and weld them after the longtitudinal welds were done.this is where the pucker is the worst.
Here's what I have read from various sources on Hull weld out sequence:
1)longtitudinal stringers should be only tacked to the frames.
2)hull plates fitted and tacked to themselves and to stringers
3)transverse seams next(skip weld and no welds longer than 6")
4) next weld the chine, keel and sheer( spead out the joy here too)
from what i can gather, all the combined welding stresses add up and the hull pulls toward the keel( i also read that there isnt a welded metal boat around that doesn't have its bow and transom a little lower than intended)
Here's a couple things to note, I read somewhere, that there are few yards in the world that can weld out the perfectly fair hull( even the one who say they do, have been caught using quite a bit of fairing compound.)
also, I'm using spoolgun ,so the travel speed is much faster and the heat is less.( but i still got a buckle)
All in all i am quite pleased with my hull( its my first) . she is a very sharp looking boat if i do say so myself.
You may already know all this but,there seems to be a small fountain of wisdom when it comes to aluminum boats,so why keep it to my self?
best of luck and feel free to contact me at (phegan@nycap.rr.com)
regards, Padraic
Ps- i think permanent strongbacks is the way to go,
Hi Padraic,
Thanks for the advice. I will not be painting my hull and I really do not want to use any sort of filler. Yesterday I did permanent strong backs, and I still have the same situation. The strongbacks bent!!!!
I am going to give it one more try with permanent strongbacks that over-compensate for the distortion that I think is going to happen.
The real solution is to create hull plate end to end (bow to stern) and then attach to the frames. Butt welding two pieces of immovable aluminum is nearly impossible.
"Boatbuilding With Aluminum" by Stephen F. Pollard ISBN 0-07-050426-1. McGraw/Hill 1993
I have used the basic procedures in this book with some success. Not too many references on this subject, it seems. Good luck, Scott.
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