welding on a steel yacht hull

Discussion in 'Metal Boat Building' started by Andyman, Sep 21, 2010.

  1. wardd
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    wardd Senior Member

    can you cut back to full plate thickness?
     
  2. Andyman
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    Andyman Junior Member

    it looks like it so far
     
  3. Brent Swain
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    Brent Swain Member

    You could drastically improve downwind control on a boat like that, by installing a rudder on a skeg at the aft end of the waterline , at the back end of the boat, where it belongs, instead of too close to the centre, where it doesn't belong. Such an extreme angle to the rudder drastically reduces it's efficiency as well. Vertical would be a huge improvement.I've done that on my first boat, which was a huge improvement.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Typical 'best practice' plate thickness v gap attached for ref:

    weld size-thickness plate.jpg weld size-thickness plate IACS.jpg

    These should help..
     
  5. pdwiley
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    pdwiley Senior Member

    I don't know that copper as a backing strip is not approved, I don't know that it is. I do know that it has worked for me however. I just use a piece of flat copper plate about 150mm x 50mm x 3mm. Thicker would be better. I corral it with magnets around the edges, wedges off of something else, bits of allthread tacked to the hull, whatever works. Mostly I don't use it, but if I need to, I do.

    BTW allthread tacked to the hull is very useful for pulling edges into close alignment and keeping them there. A few blocks, some angle iron with holes drilled, you can pull plate very precisely into alignment.

    3/16" == 5mm plate, pretty easy to weld. I've been doing a lot of butt welds on 4mm plate using a single V prep and a root gap about 1.6mm. I can get 100% penetration using 2.5mm E4311 rods but you have to have your technique spot-on and do only short runs to prevent overheating the plate. I generally only do this in areas that are going to be a ******* to get to from the other side, like right up in the pointy end from the stem bar back maybe 100mm, or crossing a frame where I've been too slack & lazy to cut a rat-hole for rear access. Most of my butt welds on 4mm plate I use a double V prep and weld from both sides, grinding the outer weld down flush but just knocking the top off the inner side weld. I do a light grind before doing the backing run to get any slag deposits out but with E4311 rods there basically isn't any slag inclusions anyway, it's just dirty black burnt paper in effect. I've cut transverse sections across a number of trial pieces to confirm that I'm getting the root fusion that I want.

    To recap, there are 2 big risks in not getting at the back of the plate.

    Risk 1, you might not get a full penetration weld and you certainly won't be able to get paint on the HAZ.

    Risk 2, you might start a fire and totally destroy the vessel.

    It's the owner's choice as to take these risks or not but it's your professional judgment as to whether you want to share in them. Personally I would not.

    PDW
     
  6. welder/fitter
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    welder/fitter Senior Member

    Andy,
    It'd be beneficial if you could tell us how the damage occured.

    First, you're going to need to get down to bare metal to see exactly how much metal you're going to have to replace. "wardd" has made the point for this, you may have compromised metal further than the tears/holes. The easiest way is to sandblast the hull, at least in the areas that need repair, though the entire hull would be better so you could check the rest of it(those cracks are concerning). If no blasting equipment available, a grinder will do the job, but you've got to grind back at least a couple of inches from the hole/crack edges, I'd recommend 3 inches. all of those doubler plates(patches) will have to come off & the hull surface examined where the patch welds were. You're also going to need a die grinder for the smaller holes/cracks.

    For the smaller holes you can use a small piece, short a welding rod onto it, & hold it in the hole while you tack it in. The benefit of wire or stick over GTAW is that you have a hand free for holding stuff, so i'd recommend that you have a stinger there with some 6011(3/32").

    For the larger holes, if you are using a backing ring, you clamp the ring to the hull, then put small tacks all around, remove the clamps, grind back tack faces(now is a good time to spray or brush some zinc oxide primer around the inside & ring edges), lay in your insert, use dogs(tacked to hull) & wedges to hold insert in place, flush with hull surface. stich it in, moving around a lot & letting welds cool.

    For cracks that only need to be welded up, grind edges back, further than ends of cracks, with radius at ends(no sharp ends). then weld ends, use dogs & wedges to align edges, tack along length, then back-step weld it.

    I can't see any photos where ceramics could be used to advantage.

    Sorry, late night, I meant 3/16" to 1/4". While "Ad hoc's" point is well-taken, if you are using a backing ring, you are dealing with two issues at the same time; keeping weld size to a minimum and ensuring joint is fully welded. In order to get into both root joints, a bit more room is needed than when welding without a backing ring. Perhaps, I should revise my suggestion to
    1/8" to 3/16", but I really think that you'll need 3/16" space. Maybe cut the insert to what would fit with the standards Ad hoc posted, which would be 3/32", then grind off more on the insert if needed. I'll be surprised if you don't end up taking the gap out to 3/16".

    As I said at the beginning of this response, it'd be interesting to know how the damage happened, on more than one occasion it seems, unless this was the casualty of a hurricane or spent significant time on a rocky shore. Regardless, this is a major undertaking. Imho the boat has nice lines & is worth repairing, if other systems & fixtures are in decent operational condition. Those patches, however, should help the owner to realize that half-assed repairs are only cheap when they happen, but, in the end, have to be re-done. Then again, they may have been an emergency repair.

    Mike
     
  7. welder/fitter
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    welder/fitter Senior Member

    All of which, of course, has nothing to do with the thread.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Excellent advice.

    You should never repair a crack without first ascertaining where/how or why the crack occurred in the first place. Without identifying the mechanism, it could/will occur again. Regardless of the repair done and the quality of the repair.

    Again, excellent advice. However, if cracks are present I would strongly recommend you dye-pen test the affected region first before you do anything. So, grind off to expose the metal, as Mike suggests, then dye-pen the whole region.
     
  9. welder/fitter
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    welder/fitter Senior Member

    Andy,
    Some things I forget to mention, because they seem second nature, but I shouldn't assume it's the same for others.

    -You'll need to know the location of every combustible tank, the route of each supply, return & vent line, conduit routes, etc.

    - Make sure that you use fire blanket to protect the interior when installing any backing ring & make sure the fire blanket is wet. Also, have a fire extinguisher within easy reach.
     
  10. tugboat

    tugboat Previous Member

    Ad Hoc--this post is especially appreciated from me as well...cheers!
    where did you find that?
     
  11. tugboat

    tugboat Previous Member

    one method for welds by T Colvin suggests using kerosene or something like mineral spirits or alcohol to test porosity. he states dab a little on the weld and if any bleeds through grind off the weld and redo it...its not an exact quote but you get the idea...
    my rule of thumb is -if the metal breaks or fatigues before the weld--the welds is strong enough.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    I've spent the past 20 years + working in shipyards around the world. As such all boats "we" have built must comply with minimum standards, whichever ones are used. Thus these images are taken from what "we" call common knowledge publications and each welder/plater/fabricator must know when fabricating boats/ships. Since these, and more, are part of their professional training to demonstrate that said person is not a "cow boy" and can weld properly but more importantly, consistently, and pass x-rays day in day out. It ensures that the designs we create are built with a minimum quality standard.

    The first image, is from TWI (The Welding Institute http://www.twi.co.uk/). The yards i have wokred for all used the TWI as their source of information in the early days when "things" went wrong. The TWI has a vast database of reserach and advises many companies around the world.

    The second image, is from IACS (International Association of Classification Socities http://www.iacs.org.uk/) IACS sets the either minimums standards that all Classification socities around the world must comply with, or provides minimum requirements to be complied with. Their data is from companies like TWI, IWW as well as their own research and private institutions.

    Trust this helps.
     
  13. tugboat

    tugboat Previous Member

    Yes this is great!--i have a couple books on welding but they are geared for land and not marine applications...I think if one is professional and your payng someone to build you a boat --i hope they should be able to do near perfect welds day in day out...

    ill look for more of those publications--i already stole what you posted to make sure i do things correctly-- i am an experienced welder -but it is mostly flux core, and im not a pro but capable.

    i am doing a lot of practice on smaw for my project...not that i would because i dont trust it...but i did wonder if its possible to use a small flux core(90 amp mig type) to weld up a large boat using mutliple passes for larger pieces--the one i had could easily do 10.2# plate in one pass...great penetration! i never liked mig for boats. other than for cosmetic reasons and i believe that flux core might even penetrate better than arc??? But for a boat I think arc is the only way to go for steel thicker than 10 guage.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    I think Welder/Fitter (Mike) would be able to give you a much better summary of this than i could.

    But i would say that you are limited with the 90amp set. For example, here's a useful 'rule of thumb' for determining the approximate welding current:

    welding current (amps) = electrode diameter (mm) x 35

    So, for a 3.2mm electrode, the approximate welding current is 3.2 x 35 = 112 amps. Which is too much for your 90amp set.

    Thus for thicker steels, you would be doing lots of runs, as your amps limits your max electrode. This means much more labour and more chances of introducing errors, flaws etc, espeically if you're not professionally trained. Again, Mike can chip in more here than me, he's the pro.

    Trying to maintain the arc length and correct angle with rod to the joint in tight cramped conditions also does not lend itself to MMA (that's what we call SMAW in the UK) too. Bearing in mind the welds, and hence every boat, is fully surveyed and x-rayed, so quality and consistent quality is the driver.
     

  15. tugboat

    tugboat Previous Member

    Thanks ad hoc--ill try to find Mike- im pretty sure ,ost boats would be welded up with smaw....this is what was used in the 40's to do the 45 ft st tugs...im guessing they would have used d c to get nice clean welds but ac welder are powerful and get good penetration too..
    if you happen top catch Mike around the forum ..maybe you can have him look me up on here??
    cheers!
     
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