25' Double Eagle aluminum build (placing stringers)

Discussion in 'Metal Boat Building' started by Northeaster, Mar 10, 2014.

  1. yofish

    yofish Previous Member

    Am I seeing this right? Do I understand that you are attempting to do some shaft alignment geometry without having the hull geometry defined? I see what looks like in this picture, a skin that has no secure relationship with the framing? I'm not familiar with this style of free floating construction, I'll admit. Now, I'm just a pram/canoe builder but IMO, I think you better start nailing scantlings to skin before this puppy turns into a potato chip. Where to start and how to sequence I would not even begin to recommend because I'm not there with eyeballs on.

    FWIW, when welding out, I start in the middle and work out from the centerline, hopping fore and aft with the longs being chain welded and damn little on the transverse frames. Don't even think of that as being good advice in your case.
     

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  2. Northeaster
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    Northeaster Senior Member

    Adhoc - Sorry, I did go to the proboat site, but would have had to pay to read the backissues. Likely not much, but as I had Pollard's book which explains sequencing, and the sequencing notes that came with my plans, I figured I would be OK.
    I have not noticed any significant distortion in the keel or chine areas which are now completey welded on the inside of boat.


    Yofish - I understand your points and I am not trying any fancy aligning before all welding is done. All that I have done is to poke a small hole through the keel seam (which still has to be welded on the outside anyway) and tacked a couple of flatbar pieces with holes in them at the planned location of the shaft coupler and cutlass bearing. I have done this mainly so I don't waste time welding the outside of the keel seam at the location where the shaft tube will pass through, as a much larger hole will eventually have to be cut out.

    Maybe I have not been clear about the welding sequence I used on the inside, and plan to use on the outside - I do the keel seam first, starting midships and working towards the ends, alternating from bow to stern and waiting if I feel it is still too warm.
    Then, I do the chines, starting midships, working towards the ends, and alternating both port/ starboard and bow to stern.

    Is this not approriate??
     
    Last edited: Apr 5, 2015
  3. Ad Hoc
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    Ad Hoc Naval Architect

    I subscribe for free...just get electronic editions. Anyone can sign up fro free!
    I have the article in pdf format, but most likely breech copyright if i posted it here!

    Hmmmm...read the article then ask yourself that question :)
     
  4. Northeaster
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    Northeaster Senior Member

    Don't have access to the article yet, so in the meantime.

    I noticed in this Article from Kasten Marine (below) that they suggest weding the long stringers to the hull before welding the hull plates together (butts, keel, chines, etc - after tacking them however) - see step 2 below

    This is in contarst with what I have read in my Glen L guide as well as I believe in Stephen Pollard's book (which I do not have right in front of me.)
    I believe both these suggest wleding the hull seams first and then welding the long stringers to hull, and later stringers to frames.


    Kasten article:
    "Assuming that the frames, long'l stringers, and plates are all in place, using an aluminum hull as an example, the weld-up sequence will ideally be as follows:


    1. Tack weld all plate perimeters in place, i.e. to trim pipes, long'l seams, butts, edges, etc. This should be a regular sequence that is the minimum to assure that the plate edges are securely fixtured, but not so much as to induce any 'weld shrinkage' distortion of the plate. For example, on an 0.375" plate, this possibly means a 1" tack weld every 6 or 8 inches around the perimeter, more if needed, less if possible. This 'tack weld' sequence should ideally relate to the eventual weld length layout, i.e. if you eventually will make 3" final welds, then a 3; 6; 9; 12 increment would be appropriate, etc. In steel of course, the tack welds will be much smaller, and the final welding will probably not involve welds any longer than 1 inch (more or less, depending on plate thickness).

    2. Chain weld all long'l stringers to the hull plate, allowing a distance from any butt welds to the nearest long'l chain weld - say 12 inches to allow for shrinkage at the butt weld.

    3. Fixture all plate butts inside (with sister long's if needed) and outside (with temporary long's).

    4. Achieve all transverse butt welds, working in a measured incremental pattern over the whole vessel, much as is done when torqueing down a head. Usually this means working from the middle toward the perimeter (of the whole vessel). Within each butt, ordinarily it is most favorable to achieve the inside seam weld first - because the tendency is for the plate to shrink, causing an indent, but having been welded on the inside, there is some tendency to counter that force. Plus... you then have the whole outside weld to accomplish afterward, which allows you to thoroughly back-gouge down to the weld root.

    5. Fixture all longitudinal butt welds with internal and external fixturing as needed (usually outside on both sides of each long'l butt seam). This is especially important where long'l seam welds converge and the welds have the possibility of overcoming the local plate strength (causing distortion). In general, we prefer to allow the long's to converge in order to help resist that tendency.

    6. Treat all "insert plate" welds as being locally "butts" or "long'l seams" and include them in the weld sequence accordingly - inside first, then outside - fixturing as needed, inside and / or outside.

    7. After all plate butt welds have been accomplished, then begin welding the lengthwise edge seams using a regular, pre-planned sequence. This will also be like torqueing a head. It is usually best to start in the middle and work outward both lengthwise and vertically. Thus a radius chine or hard chine would receive the first sequence, followed by the sheer and rabbet line. Ordinarily it seems best to start amidships, working toward the ends for each sequence. Once you determine the best weld length, assuming it might be, say 3 inches on 3/8" aluminum plate, it is best to do a "back-step" sequence. Welds should be spread apart some distance, therefore something like making a 3 inch weld, then skip 24 inches, make another back-step weld, and so forth down the line. Next time you pass through, you can fill in at the 12 inch increment (but still laying down new welds at 24 inch increments). The next series would be at the 6 inch location, spaced 24 inches, etc. The specific layout increment you decide will be up to your own experience and what you observe locally. Plate of lesser thickness will require shorter welds, and possibly a longer interval between them. Steel will have less thickness, and requires shorter welds spaced farther apart.

    8. After all edge seam welds are completed, welds can be made from the long'l stringers to the frames - also introducing heat minimally at each joint so as to minimize the tendency of the long's to 'collapse' when heated. This could require local fixturing on the outside, in particular near any butt joints in the plating.

    9. At the very last, welds that attach the plating to the frames can be made. This must be done carefully, since these welds will cause more distortion than might be imagined, and whatever distortion they do cause will be much more visible to the eye. It is an advantage at this point to have made all the other "problem" welds first. It is helpful in terms of weld shrinkage / distortion to bias more of the welding toward the obtuse angle rather than the acute angle (the angle of frames to plates). This is most pronounced toward the bow and stern where the intersect between plate and frame deviates the greatest from being a 90 degree angle. In other words, in the ends of the vessel the welding schedule should not be too strictly adhered to in terms of exact weld lengths. In other words, if you need to bias more welds toward the open angle and fewer toward the acute angle side of the frame, that's expected, and very beneficial in terms of distortion. The goal will be to try to get the same overall amount of welding accomplished after adding both sides of the frame together. This is not strictly correct in terms of engineering, but it will help quite a lot in terms of eventual fairness.

    10. In some cases if there is noticeable distortion caused by the rigidity of the frames (the hungry horse look) it can be useful to locally 'relax' the frames. In steel, this can be done by 'line heating' across the frame locally so that it will shrink some to accommodate the overall plate shrinkage. In aluminum, this is not advised due to locally weakening the frame. Builders have developed a variety of strategies to address this particular issue, some even going so far as to very slightly "oversize" the plate girth when cutting out the shape, i.e. so the plate will 'shrink to fit' and end up snug against the frames without noticeable distortion. Whether this trick is used, and how much extra to allow along the plate edges will vary according to one's experience as well as the plate thickness. "
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Hmmmm..not really no.
    Now that you have the Proboat article....you'll see why.
     
  6. yofish

    yofish Previous Member

    I'm dying to see the 'why' over @ the ProBoat article, if anyone would kindly direct me to it with a URL.
     
  7. Northeaster
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    Northeaster Senior Member

    Well, the outside hull seams are now welded up, with little distortion - or at least an amount that I can certainly live with.
    Now, I am fitting the chine deflectors out of two pieces of flatbar. Plan called for 1 1/4" max flatbar or sheet in horizontal position and 2" max flatbar or sheet in vertical position.
    I did not have anything less than 1 1/2" in stock so my horizontal pieces are 1/4" wider than plans. I fnd the deflectors look a bit large or agressive, but I am new at this.
    If anyone woudl like to comment as to how they look or if the extra 1/4" would make a big difference in performance.. please do. (they are still only tacked on)

    Note. I had a bit of porosity in a few spots on my initial passes of welding chine seams and a few low spots. So I used die grinder to clean down and make sure any very tiny bubbles / air pockets were ground out and rewelded any low spots. I did not grind welds for appearance purposes...they looked better before grinding!! I was not really trying to keep a clean / fair chine line in grinding, but rather was trying to uncover any porosity that may have been hiding within the ripples of the welds.

    I tacked the chine deflectors on just next to the welded chine seam so that I could repair any leaks (instead of covering seam with deflector) and so the new weld will go over the seam as well. (plans showed it on or very close to the chine seam.

    If folks think the chine deflectors look OK... I will weld them up fully next weekend and then flip boat back over to start welding longs to hull, etc, etc.

    Note 2. Camera is upside down in one pic - as I wanted to see what the deflectors looked like upright... and temp longs are still on keel seam.
     

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  8. yofish

    yofish Previous Member

    So do we understand you are doing all this welding and have not done anything to attach the framing to plating?
     
  9. Northeaster
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    Northeaster Senior Member

    Yofish- for the most part that is correct. However, there are a few spots where I had no choice but to weld the plating to the structure, including:
    - at the stem - when I did my inside keel seam I had to fillet weld the hull plating to the stem. As well, om outside keel /stem weld, both side of hull bottom gets welded to stem, as well as welded together down centerline.
    - tacked hull bottom palte to a few frames.
    - tacked a few long stringers to hull but only wired the stringers to stay in frame slots - so boat woudl not fall off jig when inverted ( in addition to stem welds and few frame tacks mentioned above).
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    It has been our practice to train the welders in QA. Thus after the welders complete their roots, they dye-pen the root prior to capping. This immediately highlights any porosity (and other) issues. The welder must perform the dye-pen and repairs themselves.


    Your point being? (Other than my previous concern at lifting/turning)
     
  11. yofish

    yofish Previous Member

    "Your point being? (Other than my previous concern at lifting/turning)"

    Does everything need a point? I didn't understand his procedure. It was a question, I was not pointing out or pointing to or suggesting anything. I don't do it that way and look forward to his results.
     
  12. Northeaster
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    Northeaster Senior Member

    No new pics, as I forgot the camera at the shop. Likely won't have time to boat build for a week or two now.

    Finished welding on chine deflectors and I am happy with them.

    Bought a dye penetrant kit and tried it out on a few feet of one aft chine seam.
    I would like to hear advice to see what the recommended, normal or accepted methods are for dye testing seams on a boat. For example, I sprayed the dye and let sit (after cleaning well) on the outside seams and then after cleaning dye off, also sprayed developer on the outside seam - I believe this would be more benefitial if looking for cracks (in other applications). In my case, using both on the same side revealed some porosity.
    However, when I sprayed developer on the inside seam, trying to pick up any dye that passed through the weld to the other side, there was only one spot where this happened - it was a spot where I had partial ground an obvious porosity/ air entrapment, so it was thin there, and I had not finished grinding it out and rewelding.
    So, if someone could comment as to the best method I would appreciate it.

    Hoping to finish testing/ repairing any seam wleds in a couple of weeks, and then flipping then boat rightside up again, to begin welding long stringers to hull, and frames. Then looking forward to lowering engine/ trannie in for testfit and mockup of engine girders before flipping upside down again to begin building a box keel.
     
  13. yofish

    yofish Previous Member

    I've never used 'crack check' other than to describe the extent of a damaged area, usually an impact or flexure failure. If you are fearful of weld integrity at this stage of the game, you are completely upside down, IMO. Unfortunately, no alloy can save poor craftsmanship. Frankly, if your welding skills are that nominal you should have started smaller and learned that way rather than this way. There is no 'repairing seam welds' unless you've crashed into something! They are either right or not. There is no in between. Also, dye penetrants will not highlight anything other than surface porosity or a crack - nothing 'inside'. If you have through-and-through cracking in ANY fresh weld you have to stop because something is horribly wrong. If you have unacceptable internal porosity combined with poor penetration, then, you might as well start over. Checking for problems is just not what you should be doing. The fact that you are even doing it tells all. I have not read every post in this thread and forgive me if I've missed that perhaps you know someone that can set you straight? You will NEVER learn to weld or build boats by being avid on forums.

    You chose a steep path. Perhaps a little too steep.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    As I noted above, we trained every welder to dye their own roots prior to capping. What you've done so far is sufficient. Prevention rather than cure.

    Those with no appreciation for quality control would suggest otherwise; as has been noted several times. It shows the gulf between home builds to commercial Class standards. Nowt wrong with with ignoring quality if that's your bailiwick, but it is not what we do, nor recommend. Which ever method you elect to do is your choice, not theirs!
     

  15. Northeaster
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    Northeaster Senior Member

    Thanks for the replies.
    Yofish - I am not a professional welder, but have practiced quite a bit in the lats 2 years and did many bend tests.
    I see you asume that I have poor penetration???? I know the penetration is fine, and the weld are strong. I referred to "repairing" the weld seam as in grinding out a bit of surface porisity (and a couple of spots that went deeper) and rewelding in those area.
    There are no cracks throughout.
    I will be sure to tell you if the boat breaks in half on the first wave (or anyway after that).

    Adoc - thanks, I did consider it reasonable to spend a bit of tem and money checking for any irregularites and repairing where needed, before welding a box keel over top of the keel seam, for example.
    Busy with 2 young kids but hope to finish dye testing next weekend.
     
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