Conchfish AL 17.6T build

[m32825]

I loaded up the .035 wire and ran it with the same settings I was using for the .030: 480ipm and 20V. Less of the cold start look at the beginning, overspray seems better. I tried the racetrack beginning but have to work on getting a uniform bead, hung out too long trying to see what was happening before moving out.

Seems like my cleaning action is better on the bottom than the top. Thoughts on the cause?

-- Carl

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[kmorin]

Carl,
I think you can see how 20V's looks when burning 0.030" wire versus burning 0.035"? That small 0.005" diameter difference is a lot of added volume of metal - when its 'wrapped' around a 0.030" wire! The increased volume is what 'soaked' up the wattage and transferred more centrally to the puddle instead of overheating and flying off to the sides in a wider cone (weld over-spray footprint).

Still might try to get the arc a little shorter- maybe cut the contact tip back? I run the contact tip INSIDE the face of the gas cup typically with aluminum wire.  I like to keep part of the arc as covered by gas as I can.  And so I've always cut the longer tips back, or in the case of MK guns (cobra, python) I've purchased their short tips.

I don't watch or look at the first few puddle to confirm anything but the point of the wire before I light up.  The reason is that it takes my nervous system too long to make the start smooth.  I just have the habit (when doing short stitches/chain welding/non-continuous welds) of 'whipping' the tip/gas cup in the U turn I've tried to describe.  I don't have the recognition and reaction time to get going fast enough so I just do it by habit and not very guided by eye.  
5356 filler alloy has both a magnesium & manganese component (not exactly sure % but will be online somewhere) and those alloy elements when combined with oxygen create the 'black soot'/weld smut/smoke that forms as these two metals 'burn'/oxidize near the edges of the argon cover gas cone.  So if you can get the gas cup a little closer to the puddle? Not bad practice as the gas shield is bigger to work inside of to cover the puddle. 

Harder to see, yes; more crooking of the neck and wrists to see under the cup when its closer to the puddle, yes.  But that's MIG aluminum unless you turn up the cover gas to 65ft^3/hr. ! Closer cup to puddle, a little more lead angle, will help to improve cleaning  & angling the torch (body) angle down a few more degrees will help get the cleaned zone tracks to be a bit more evenly distributed. 

Bead looks nice, very serviceable for your skiff's scantlings and on the long seams you'd gouge the starts and stops before the next set of beads so the overall weld is great.  You can warp the ending puddle back over the next to last few fractions of an inch and that will avoid crater cracking when you let off the trigger and the arc stops when the puddle is molten from bottom to top.

Cheers,
Kevin Morin
Kenai, AK
 
 

[m32825]

This is a bad-news/good-news week. The bad news is that I inadvertently signed up for "the summer cold experience" somewhere. The good news is I get more time for welding practice.

My nervous system doesn't support waiting to see what happens at the beginning, either. I practiced race track starts and stops and tried your suggestions on gun angle and getting in closer.

My contact tip is recessed about 1/8". I got in close enough that I was starting to drag the insulating tip on the work piece.

I can see things getting hotter towards the end of the pass. I can imagine that turning into a problem on longer beads. How do I control that?

-- Carl

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[m32825]

Same as above, but turned the voltage down from 20 to 19.5. Got less overspray and more consistent heat from end to end. The u-turns are starting to feel more natural.

    -- Carl

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[m32825]

I've started working on the 12" coupons with corners. Just to see what would happen, I tried (operative word) an outside corner with the same settings I used above. I burned through within an inch a couple times, then started a pass and sprinted for the end. I know what "too hot" looks like.

I dialed the wire feed down from 480ipm to 330ipm, keeping the voltage at 19.5 and tried again with better results. I practiced trimming my tacks and gouging out ends for restarts. Restarts are on the fat side, working on trusting the u-turn more.

Next time I'll try turning the voltage down a bit, seems like the arc was sitting higher than it should.

-- Carl

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[m32825]

I tried a full length pass, things fell apart after a promising start. I was focused on following the joint and on speed, but not paying attention to the puddle. I cut out the bad part and tried again, came out pretty good.

-- Carl

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[m32825]

Flipped the piece above over, cranked the wire speed back up to 480ipm and welded the inside. Cut it up and did some bend testing.

-- Carl

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[kmorin]

Carl,
Nicely done.

I'd say those all show great progress, including the mistakes or 'not-for-sale' parts as you've concluded methods/techniques/adjustments to tune-up the errors, corrected what could be improved and moved ahead.  I can see clearly that most of what we've discussed shows up in your increased understanding of the MIG process in thinner aluminum.  I think you can see and feel the benefits of your many hours of practice before putting the final welds into you hull?  And now my standard whine about practicing "for a hundred hours before welding your boat" may seem a little less eccentric?

Notice that a joint that is back welded performs to the "ultimate failure" of the joint where a full back bend remains intact?  IF your boat was 'blown up' or hit a rock a 80 MPH, or was crushed by a 2ton wrecking ball - the boat would be crumpled but the welds would hold.  You beat the metal!  As a welder that is all you can hope to achieve.  (Well... that and nice appearance, uniformity, proportion and no distortion!)

If your chine seams hold up as well as your coupons, and they will; what more could anyone (anywhere) ask of your hull's integrity?  If you practice at 10" to 12" welds; when you weld the hull in shorter runs you'll have a clean, uniform hull with welds you're proud to have put down.

A note about one photo where you gouged out a stop to create the re-start puddle space/cup/puddle base.  See the tiny gas bubble remaining in the root of the weld? Those are common in 90% of aluminum MIG welds and why I advocate the 'wipe-out' ending technique if you're welding seams by chain or in stitches.  The wipe out ending you show in one or another of these nice images shows you're getting that idea well in hand as a technique you can use when its appropriate. These bubbles are also why MIG tie-in and starts are so critical, so is gouging the starts if the welds are part of a chain along a long hull seam.... but that photo shows why its good practice to get clean-to-the-root to start or stop your next passes' ends.

I also noticed you'd spent a few beads fine tuning the voltage on the inside fillet to reduce over-spray and that's another step in being able to correctly weld your skiff.  It is critically important to learn to make those fine adjustments and I'm glad you've spent time on coupons adjusting the many variables to tune your bead. Way too many first time builders settle for 'close enough nail it' in these welding refinements and end up with poorly welded boats.

I think you'll be glad you 'bit the bullet' and took the time, delaying your eventual build, to refine this critical skill by practicing the "right thing". Practicing a trade craft, but not doing the practice work correctly, only reinforces the poorly done work, unless; you practice doing the work to the best standard.  Those who're not well informed about what to do, who don't have an image in their mind's eye of a good weld; will settle for poorly done welds, and those don't hold together well.

You may not know this, but I'll share it in case?  In the wooden ship era, the Captain or Skipper of the ship was offered the chance, and in some Navy's of old, was expected to drive the "tre'nails" into his ship's planking.  "Tree Nails" are what we call dowels, maybe pegs, but they are cylinders of wood that were driven into the ends of the hulls planks- where metal nails might appear now. These dowels were slotted on the outer end to drive wedges into and that 'wedged end' would jamb the trenail into the planking. These held the planks to the frames of the hull.  "In a blow, the Cpt'n knew she was sound as he'd driven the trenail's wi' 'is own hand."  The tradition was to insure the work was done with ultimate care by the man whose life depended on the attention and skill given to fastening the planks to the frames. 

A little far afield, but you get my drift (no pun intended) in regards welding your own boat.  (Ultimate) Care was given to the many subtleties in driving in the 'trenails': as they should be, welding your own skiff.  He was using a specially designed hammer driving pieces of wood into holes sealed by various plant based 'goops' while you're using an electrical power supply to melt the hull together into a single piece of an alloy not even dreamed about by our historic Captain. However, the spirit of the original obligation remains on you as the builder and Skipper of your own boat.

I think you're upholding that tradition very nicely. Congratulations on your progress mastering aluminum welding. I look forward to seeing the skiff welded out and running in your home waters.

Cheers,
Kevin Morin
Kenai, AK


 
 
 

[m32825]

Thanks Kevin. In addition to your subject matter knowledge, you are gifted at both communicating and encouraging.

If my boat hits a rock at 80 mph, the rock will have to be be doing at least 50 mph. I take your point about strength though. It wasn't until I started doing bend tests that I began to appreciate how robust the welds can be. Bend tests provide honest, objective feedback every time. They also show what needs improvement!

Your hundred hours figure is accurate. I put in almost exactly that much time over the last three months. As I said early on, I was the poster child for the guy who doesn't have any business trying to weld a boat. I resisted putting the time in, but reached a point where I was starting to work around my lack of skills.

I agree with the importance of having a clear picture of "what good looks like" in your head. I also found it helpful to keep my best weld on the bench and try to improve some aspect next time. I feel like as a society we're becoming increasingly reluctant to portray ourselves as anything less than fully competent, but that fear gets in the way of learning. Everyone starts somewhere.

I like your trenail analogy, reminds me of one of Herman Melville's details about whaling life. You've got a bit of poet, or nostalgic, or romantic, or history professor in you. If my boat founders I can always walk back to shore but I do like the idea of knowing how everything was done and having a solid boat for fishing.

So, I noticed there's this boat sitting in my garage waiting for assembly...

-- Carl
 
 

[kmorin]

Carl,
Thanks for the kind words, glad you're a whaling history buff and didn't mind my far flung analogy about welding and building boats of wood.
Looking forward to learning your next steps and seeing your build progress.

A couple of tooling questions.  Do you have a router and carbide bits?  Are any of your bits V groove?  Just exploring how to prep the keel and maybe mid-bottom seams for a weld.  These tend to be hard to weld if not prepped additionally to just fitting together and tacking sheets with edges that are sawed or NC cut at 90 to the face. 

When joined in hull seams they tend to be 'tight' which is good for a fit but harder to get the weld inside to the best root face and obtain deeper fusion as you were able with a back to back fillet.   Part of this is due to the angle between the sheets/hull panels is almost 180 deg. and part is due to the fact they likely weren't beveled before tacking up?  Even if you left the flat bar back up longitudinals exposed.... the square instead of V'd or chamfered shoulders of the weld groove will 'pull' the arc and weld bead to the sides of the U shaped groove instead of allowing the bottom of the weld to be wetted.

Now that you see the travel speed implied by your practice coupons you fully realize that most of the hull welds are only a 'single shot' unless you cut them out and re-weld?  So seam prep becomes the next big hurdle and one that will contribute a great deal to effectively applying your welding practice gains in bead quality to your hull's final weld quality.

Cheers,
Kevin Morin
Kenai, AK

[m32825]

I am well supplied with ways to make glitter, is this the right kind of bit?
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I'm working towards longitudinal fit up, but there's something in the way. I need to weld and trim the front end of the lower chine pocket. The vertical plate has an inch or so of extra material to facilitate welding, once welded it will be trimmed so it tapers to a point. Then I'll be able to fit the bottom panel up against it corner to corner (and work on longitudinal fit on the opposite side of the bottom panel).

I know the goal is not to weld seams until everything is tacked, but I don't see a way around it. Here's a clip I took to show both sides of the joint.

video
 
 

[kmorin]

Carl,The router looks like it will do the job, they do well in aluminum but higher horse ratings seem to last longer? The bit is a 45 deg bit and is generally too wide for the seams but you’ll need to experiment and see? I use the shallower angle bit used (commonly) for solid counter top beveling bit like the 2307 Edge Bevel Bit with 22-1/2-Degree from Whiteside.

The job is to open the seam’s edges not to get a 90 opening that would result from 45 deg bit on both sides. The other item is the roller bearing guide- some times that has to come off and an external table edge guide has to be used to get the job done? It will depend on what work space is available? One technique that is helpful if the planks/plates/sheets are not on the boat is; clamp them edge to edge/back to back and use the roller on the lower panel- cutting the upper; then reverse this process.

It’s pretty rare to need to cut to a knife edge all that MIG requires is to cut 50-70% of the outer edge of the square cut. This will allow the arc to spread deeper into the weld zone without having to ‘penetrate’ by heat/amperage. Then, wetting by the arc will be deeper and single pass drag-type beads will go in much deeper with less buildup and the root faces will be more fully wetted/fused/welded. Remember the bevel is to increase the opening in a hull seam from square corners to slightly beveled edges so that instead of a U shape weld groove you have more V -but not trying to get the full outside corner 90 deg. V we'd see on an outside chine to topsides corner weld. 

The reason to take this time is shown when you try to weld plate thickness grooves without beveling.  Unless you "take off the shoulders" of the panel/plate's vertical edge cuts- the arc will 'run' to these closer points of metal instead of fanning out into the bottom of the weld zone. When the weld spray puddle is collected along the top of the two adjacent panels' edges; there will be a hollow below that bead and that's what you'd like to avoid.

Regarding the seam weld to get the vertical bar trimmed; This is where a nice small TIG weld would be appropriate for 6-8" to the right in your video (I'll assume that's aft?) . To get the weld to fuse the horizontal chine flat w/o overheating and melting I’d clamp a 1/4” flat bar inside under the joint shown, make the bar/heat sink longer than the weld area, wide as 1” wider than chine flat- if it can be fit and clamped well so the surfaces meet as much as possible to keep the net heat spread into a wider area/greater mass of metal.  You might find it helpful? to clamp a vertical heat sink to the pc to be trimmed?  All this can be tested on the bench before you have to put the welds on the hull.

 I’d say weld inside the vertical too, and each weld should be done when the parts are ambient (I recall it's pretty warm in your shop?). So it won’t work well to weld all three places, 2 vertical fillets, and 1 outside chine seam in a single time period.

I’d think that 1/2 hour between welds was needed -start with the TIG using the backing bar/heat sink and then move to the outer vertical fillet. That weld could also be TIG if you feel confident of putting down a bead small enough?

I would also use a ‘run-on’ block to the forward/open side/left in video end of the weld. The block can lay on top of the horizontal backing bar/heat sink and be trimmed out when done welding.  Run-on blocks allow you to use MIG, if preferred, and not suffer a cold start in what will become a critical weld joint as the hull’s remaining planks/plates are added. 

Hope this makes sense?

Cheers,
Kevin Morin
Kenai, AK
 
 
 

[m32825]

Hi Kevin,

I have a 1.5hp Craftsman router in reserve if the little guy can't do the job. I'll add a 22.5 degree bit to my glitter making arsenal, thanks for giving me a specific example.

The panels will be off the boat when I work on them. I've got a full length pallet topped with cardboard, so this will be a "crawling around" exercise.

Good description of the target joint geometry and goal. So when we've got that set up properly, is the goal to fill it all the way, maybe a little proud, in one pass? I mean just the section I'm working on, not end to end of boat.

I like your battle plan for the vertical at the front end of the lower chine. Pretty warm in my shop? Haha, you could say that: 84 to 104 lately! We'll start to get some relief soon, the edge is off the heat by the end of September.

This week I reviewed the build thread to remind myself where we left off. I picked up on a couple points that I glossed over first pass (or didn't sink in on the first exposure). Time well spent. Next step is to get the two outside longitudinals tacked down.

   -- Carl








 
 

[kmorin]

Carl,
I'm fairly described as 'pretty decrepit' since I worked too many 12's and 14's in my ill-spent youth and then slept "where ever I fell and got up to do it again."  Not wise choices for a man's youth or middle years and as a result of these poor choices; I get to enjoy the aches and pains of arthritis for my sunset years!  So a grain of salt..... to season my remarks.

First is; get that shipping pallet up on horses, or legs; just make it a 'table' - PLS, don't work like a 3rd-Worlder; on your knees. (maybe because mine don't work since I treated then poorly and disregarded their preservation??)  Working at waist ht. , instead of below your bent knees, is important for good skill applications for Westerners.  We didn't spend our youth and middle years "squatting" so we're not going to be as co-ordinated on our knees. 

If you can, it's well advised to get your work up to waist high and work as a bench top project.  Standing up so you're 'normally'  balancing the tools and tasks on a table top ht. is worth the effort to get the hull panels surfaces up there; IMO.  I my experience; "crawling around" should be reserved for those who don't know better OR can do that work at full skill levels down in the dirt.   So    I    say    just don't do it.

I have online posts about rotisseries to build boats, I have comment after comment about welding below your knees and unless you're a 'yoga instructor' level flexible and used to these contortions; JUST DON't do it.  I fully believe you will compromise the bodily guided skills needed to produce a clean and well formed welded boat.

[Between you and starbright55, I've been in rant mode a couple times in the same day! Sheesh, you guys are welcome to your own decisions, of course, but when they're in the full face of my extremely very long & detailed list of errors.... I feel obligated to at least mention something.  Then, when you come back to the thread and admit "you learned the same mistakes" I've learned.... well I don't feel as though I didn't try to help you avoid my list of mistakes.]

PLEASE!  Get off the floor, put legs under the shipping crate and work at waist height; like we're used to doing.  The results will be better than crawling around and if you need to get up on top of the table? You still can crawl around to suit your work. 

I'd like to ask you to consider that you've planned and practiced welding in different modes for weeks and many hours. The welding time on your boat may be less than the time it's taken you to get ready to put those welds in?  The critical path is those few seconds per weld that need to be controlled, skillfully applied and well prepared in order that both the skill and control are available.

The same is true for weld prep and that means getting off the floor, ground, "out of the dirt" & up to table height in order to perform skillful and clean edge prep for welds to go into properly formed joints.

Rant off.

Tip the crate/pallet up on edge, put your saw horses under/very near the ''stood up' pallet; tip the pallet over the horses and pull it up over to make a work table for long sheets.  Replace the cardboard to minimize scuffing and work at normal bench height to do your best work on your skiff's seam panel prep.

Cheers,
Kevin Morin
Kenai, AK

 
 

[gandrfab]

On that note.
Many welders will brag or rave about how many positions (difficult) they can or have welded in.
Comfort, always make your self comfortable before making that weld.

[m32825]

Good input guys, I'll get my pallet elevated. I've got sawhorses and blocking. I can see what you're saying about being able to see and control the router.

I've been doing physical therapy for frozen shoulder lately and it has been eating into my build time. That'll go on for the next couple months.

I got a chance to clean some of the smoke and smut left behind by whoever has been welding on my boat. I was starting to get that chimney sweep look, much better now.

Checked my center longitudinal, which is already tacked down. It was straight but had a high spot (1/16" too high) just back from the bow curve. A few cautious whacks with a dead blow hammer fixed it.

Still plugging away at getting the first outside longitudinal tacked. Getting closer!

-- Carl

[m32825]

Needs new cardboard, but now I have a 6x20 table.
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[gandrfab]

I'll recommend plywood, mig welding over cardboard has a tendency to start unnecessary fires, has been known to sit and smolder to find an unwanted fire and smoke finished sheet metal later.

[m32825]

I'll recommend plywood, mig welding over cardboard has a tendency to start unnecessary fires, has been known to sit and smolder to find an unwanted fire and smoke finished sheet metal later.

 

I'm with you on fire risk. Wasn't thinking of welding anything on it, just edge prep for the bottom hull panels. Might be short sighted though...

[kmorin]

 Carl,
I've mentioned before here (viewtopic.php?p=53719&hilit=rotisserie#p53719) and on other Forum's about using a rotisserie hull mounting jig to roll the boat while welding-out and doing other work on a welded hull. This link to another skiff's build shows an image of a scrap metal rotisserie I've used many times and rely on, in fact this same frame held up a 14k lb 34'er once it was modified a little.

I think its worth exploring given the relatively low cost for a rotisserie for a skiff as small as yours.

I'd expect the total skiff to weigh less than 200lb so a couple of these; Big Red T23401-1 Torin Engine Stand for 75.$ (on Amazon) seem like they'd more than hold up the skiff where two will hold 1,500 lb. and still roll the hull.  I'd turn them back-to-back so the wheels are 'out' and the skiff between the two rotating masts and then put a beam, box or I-beam, between the two pivots with an adjustable up/down leg so the load can be centered in the line of the pivots.

Such a rig will allow you to weld your best while getting the highest quality access to the hull's internals for welding. It is very much easier to stand flat footed on the shop floor and weld overhead, or in any position, than to try to put in decent welds when you're kneeling down inside the bilge and trying to get decent tight beads on the longs inside your hull. Further, trying to use the TIG torch is a real challenge while in odd positions since the two handed access as well as foot pedal control are both very compromised by the weld positions inside the hull- and for that matter being able to balance the weld patterns' contraction inside and out, fore and aft and allows you to put in short hull seam welds without much concern for rolling the boat.  IMO it is worth the few hundred $ it would cost to get the boat onto a rotisserie.

It depends on how you orient the hull on the rotisserie beam for support, but welding can be very relaxing, high quality, and easy using a rotisserie OR it can be very frustrating, not your best welds, and difficult as Olympic athletics to get into comfortable body position in order to put in decent welds. Leave the hull on the rotisserie and roll it outside and do the acid etching while it can be rolled on her beams ends and rinsed as easily as putting a lawn sprinkler on the entire hull. 

While it may seem like a lot of work to do? and perhaps unnecessary expense? once you look at your test coupons and realize they wouldn't necessarily look like that if you had to crouch under the weld table- reach overhead and put in the welds (for example).  Or, clamp a test coupon to the leg of your welding bench/work table and then kneel on the top of the table and reach down and weld the coupon!! It may take a little work to produce the rotisserie, but it will be worth the effort in returned quality of your skiff's weld-out.

Cheers,
Kevin Morin


 
 

[m32825]

Kevin,

You make a compelling case for a rotisserie, I'll plan on making one. I was trying to figure out how I was going to manipulate the hull for acid washing, so this is two birds with one stone.

My hull comes in around 500 pounds with the deck, I'm guessing closer to 400 without it. Still, to your point, not a huge amount of weight. More unwieldy than anything else. Seems like it would be a good idea to mount the hull with the keel towards the beam, for unobstructed access to the inside. Thoughts?

Let's make sure I'm tracking. I think the plan is to use my existing build table until the hull panels are tacked up and the outside seams are welded. Then mount the hull on a rotisserie to weld the inside seams. Is that right?

-- Carl

[kmorin]

Carl,
I've given my thoughts on order of weld-out in lots of different posts so I'll take a few lines here to summarize my view.

First, since you're considering a rotisserie, rolling the hull to weld, it need not be one side then the other - ie. outside vs inside first.  Because the reason for that welding sequence often has to to with the level of effort needed to roll the hull- and now that level of effort has/will drop to nearly nothing... I'd say it was best to get the hull on the rotisserie w/o welding the outside seams. 

I think it would be best to weld the 'end seams' or seam ends before moving to the rotisserie.  That is; 4-6" along each main hull seam from the transom forward and from the bow stem/keel weld aft.  The rest can remain tacked-only (except where the rotisserie's frames are) and the hull will be stiff enough to go onto the rotisserie's main beam.

Second, once on the rotisserie I'd weld inside & outside (or outside and inside) fore and aft in a series of 4" stringer/drag/single pass beads on the main seams as the first pass or 'lift'.  This will allow you to get the hull stiff enough to continue welding w/o distortion.  After these welds are in/on the hull seams then dress the ends and continue adding weld inside and outside. 

I'd say it will help you to make a rough hand drawn diagram of the overall boat and think of pulling the ends of a seine - drawing up a pouch of material- pulling the edges of a cup or bowl together and see if you can plan a 'balancing' set of forces. As the welds contract the boat's beam will try to increase as it pulls up the ends and that forces the beam outward.  By planning to add shorter spread out welds in the first two lifts then you'll avoid the 'long seam' contraction that tends to reshape a hull.  Also by keeping the welds to narrow, drag type welds you avoid panel distortion.

Design your welding pattern to minimize the contraction forces by tying-in short stringers first to longer stingers in the final passes.  Also, welding inside seams may require you to put SS bars outside the seam area to be welded to minimize burn through, and still put in single drag passes w/o using a patterned or whipped puddle.  It's typical for a SS bar to get 'stuck' to the outside or a seam and to form a backup of the weld if there's burn through.  Just tap the bar and it will drop off and then back-chip/gouge/hollow out the outside weld zone and it will weld just fine.

Once the overall hull seams are welded inside and outside w 4" stitches spaced a couple feet apart and staggered inside and outside; there's little risk of distortion beyond over-welding (bead cross section to large) or welding too long a pass in one place.

Third, the field welds inside the hull panels are those on the longs where tacks can fail easily if the sides of the panel are welded continuously from inside or outside as that perimeter weld will tend to 'cup' the panel by contracting the edges forming a 'bowl' or trying too.  Once on the rotisserie you're able to roll the hull anytime to make sure the longs' stitch located tacks aren't coming loose before you get to those welds in the middle of the panel. SO you can add the long's stitches to the overall welding pattern even if they're all inside on this design and that will also help you to balance the forces of weld contraction distortion. 

I'd estimate that with the small scantling and hull panel thickness that 2" stitches every 8-10" would be adequate? Not sure what your plans call for?  But over welding (too many welds, that are too wide on their face) doesn't make the hull stronger really it just distorts and wrinkles hull surfaces.

In my experience having the hull on the rotisserie for the entire weld-out process is a benefit not only to the quality of individual welds but also the improved control of the sequence of the welds and their shape distortion reduction.

Regardless where you mount the hull inside from frames or outside under the keel, you'll need to make sure you have welding access to any seam (keel) near the main beam and support frames. As small as your hull is, mounting under the keel would be pretty simple simple; two frames bolted to the main beam and reaching chine to chine and weld just inboard the outer chine and outside the keel a few inches should do fine.  1/4 x 4" flat bar welded to a V to approximate the hull w/ a couple of 'legs' reaching from frame to hull to weld too.... should hold the skiff w/o problem.  Weld a beam clamp to the center of the V of flat bar and you're ready to put the rotisserie onto the upside down skiff and weld the two frames to the hull.  It would be important to weld the chine seams and keel seam for 4-6" adjacent to the frames' attachment to the hull so that tacked seams aren't loaded with the hull wt.

Once the hull is tacked to the rotisserie, lift the end beams to lift the skiff off the wooden form, pull the wooden table apart and the skiff is ready to roll.

Cheers,
Kevin Morin
Kenai, AK
 

[m32825]

Hi Kevin,
​​​​
I've been studying your Davis Jig post and have a few questions...

What cross section and wall thickness is the main beam? Looks like you can unbolt the main beam for storage/transport? If you've got the boat's weight well centered, how much force does it take to turn it? How well does it stay put?

Lastly, what are the rounded wooden frames for on the shelf in the upper-middle of the picture below?

-- Carl

Screenshot_20240902-103225.png (486.13 KiB) Viewed 5610 times

 
 
 
 
 

[kmorin]

Carl,
This particular rotisserie does unbolt at all the beam and rotating joints.  Yes it needs to collapse for storage, transport or modification.  The main beam on this one is 6x4 x 1/4" wall.  But I don't think it was needed and think you could go with a slightly smaller size?  5x4 or 5x 3.5 - once the boat's support frames are tacked to the boat there is very little side to side  loading as the tacked up hull acts to remain stiff transversely.

I could turn each of the boats I've built on a rotisserie (that were centered well) by hand, standing flat footed near the chine or shear depending on which was closest handle.  If you look at the pivot pin socket's that are on the upper ends of 3" pipes (so the entire pivot center line could be raised if needed) there are flanges along the top of the pivot sockets.

The (3 1/2") pipe sockets were slit along their 12:00 o'clock line and about 3/16" to 1/4" of pipe wall removed. Then two 1/4" x 2" flat bars (which are drilled for four 1/2" bolts) were welded to the edges of the slits along the pivot pipe sockets.  This allows the 8 bolts per end to tighten these sleeves/bushings on the 3" pivot pipe.

By using Nyloc nuts on the compression bolts, the tension can be adjusted so the boat won't roll regardless of effort- the entire frame will lift but the boat won't roll if the bolts are tight.  On the other hand with a little tuning of the tension on those bolts; the skiff will roll by hand and stay where you leave it.  Sometimes, with the tension system shown, before or after rolling to given position I'd use an open end wrench to tighten or loosen those compression bolts but it was very manageable for skiffs much larger and heavier than yours. 

Therefore, I'd say you won't have any problems with your skiff even if your reduce your Davis Jig's scantlings; slightly smaller main beam, lose one bolt per clamp end and use the lighter wt. engine stands instead of my scarp pipe frames.

Another safety issue that I built in are the series of holes in the end verticals. These adjust the ht. of the beam and therefore the center of mass of the skiff in relation to the pivot pipes at the ends.  I didn't want to rely on compression to hold these so; used a mag foot drill to make those holes- think I used 11/16" dia. for 5/8" bolts?  Once the boat is lifted vertically they were pinned and the skiff would roll.  But if the skiff is 3' above the shop floor and not rolled (?) its harder to get in than if it were on the floor. 

I used overhead gantry, monorail or whatever lifting I could rig in whatever shop I was in then, to adjust the ht. of the skiff/main beam as this is a dead lift. At one time during my experimentation with the Davis Jig I included a lifting mast next to the first vertical leg of the end frames. The idea was to use a regular boat winch to manually crank the vertical leg up or lower it down using a wide nylon strap over a homemade pulley at the top of the mast. It worked but was removed due to have other lifts available making the built in system more effort and redundant.

I would typically go up or down a couple of holes in each end before pinning the first end and move to lifting the other end to pin the sleeve box steel welded to the pivot pins, to the (concentric) vertical rising square stock that holds the beam at the bolt on plate at the "outer" ends.

Re plywood in background.
I used those plywood formers to shape the stern of a skiff during a modification many years ago.  I converted the skiff from square stern to round (almost fan tail) just because I liked the look. ( I think there's a thread about that build somewhere around?) By dry-screwing small tabs of aluminum to the edges of the plywood formers I could tack the various metal parts to the outer rim of the plywood w/o spending any money on full sized metal formers. 

Cheers,
Kevin Morin
Kenai, AK

[m32825]

Kevin,

Thanks for the detailed description. I've got reconnaissance work to find out what my steel options are locally. You input will help me narrow the field of candidates. I was wondering about the beam not being square, so I'm glad you commented on it.

I don't have a dimensional diagram for the engine stands, looks like I might need blocking under them if the hull is on edge? I'm leaning towards fabricating the ends with pipe. In for a penny, in for a pound and all that. I like the idea of being able to adjust the height of the hull, I can see where that could be handy.

I also like being able to adjust the beam height to align the CG with the center of rotation. Nathan (plan guy) sent me the weight (a little shy of 300 pounds) and CG of the hull. In theory (haha) I should be able to calculate the offset I need, but it's always good to have a plan B.

Every time I want to make a hole in beefy steel my drill press cringes. It's not made for that kind of work, this will be a good excuse to add a mag drill to my collection of tools.
 
Clever idea using wood with bits of aluminum to tack onto. I'll add that to my mental toolbox for future reference!

    -- Carl