Conchfish AL 17.6T build

[m32825]

I plan to experiment more with the .045 wire to get it dialed in. I tried a couple inside corners on scrap but had the wire speed too high, it was hot hot hot. I don't know if I could ever move fast enough to do an outside corner with it, but it seems like a great tool for inside corners.

Love the story about your boat/brailer, the spirit of "git er done" was most definitely alive and well in Alaska that night!

-- Carl
 

[kmorin]

Carl,
wanted to mention or point out that I did the inside of the joints with this 'speed drag' technique.... and ONLY downhand. I just couldn't get enough speed in the horizontal, either left or right, to make the welds as consistent as I wanted.  I don't advocate the speed weld technique for outside corners, I usually whipped those puddles to allow a slower travel speed and to 'wrap' the edges of the chines, keels etc.

Physical note about torch and body movements.
IF you're welding horizontally you're likely rotating your shoulders/chest/pectoral girdle (as its called) about the center of your belt line at the hips. This rotation changes the angle of the arms/hands holding the torch to the work so the lead angle may not remain uniform.  That is; by holding your arms in an even steady triangle to the shoulder and chest the travel comes from rotating the above the hips in the waist.  So the angle of the gun to weld zone may well rotate or vary along the path of a longer bead.  This means the 'stick out' may vary as well.

Since V=IR where R is the wire stick out and gap to work .. ... you'd be using the power supply's monitor circuit that is trying to keep V constant... to crank the amperage as the R changes since you're moving the gun in an arc!  To avoid this event when welding horizontally to either side you have to practice keeping your elbows AWaY from your sides- many of us clamp them in to stabilize the arc/bead/stickout and wire gap.... IF you practice keeping the gun angle in exact lead of the puddle and using the back of one hand as a guide to the material, you can speed up the weld w/o sacrificing the uniformity by keeping all the variables limited to change during that bead.

Might be a bit esoteric, maybe I've mentioned this before (?) but using a constant voltage (CV) power supply requires thinking about each weld's deposition method/technique to avoid having your position and application technique conflict with the power supplies' control circuit design to keep the voltage constant.

I practiced for endless hours keeping my shoulders at a fixed angle to the work, while using my legs as a parallel carriage- not rotating as much as I could avoid.  BY working to keep the shoulders holding the torch as parallel to the work as possible and gliding along the weld instead of rotating at the waist... I was attempting to keep the angle of the torch to the work consistent and not changing over the length of the weld.  This allowed me to put down a little more uniform welds that were eventually longer w/o changing the weld's settings within the power supply.

However, using 0.045" on outside hull seams was done on boats with 3/16" or 1/4" bottoms, not 1/8" to 1/8" plates/hull panels.  I think that using the 0.035" wire on the outside seams would be fine if your power supply control circuit will give you enough WFS/IPS to keep up with a 'hot' setting for that size wire?  Your hull has so many chines, long-wise seams and deadrise angles between the various panels; that each seam will have to be experimented with a mock-up and prep then cataloged as settings for that seam's cross section.

98% of the skiffs I've built were 5 panel hulls with even 4 panels; where only 10-20% had two piece bottoms the rest had one piece 'warped' and cambered panels for bottoms.  Even though I did use reverse chines in most of a couple hundred skiffs, where the outer chine seams were very much like a 5-panel skiff's hard chine joint; the inner chine was similar but reversed; inboard was like (not exactly same angles) the outboard of a traditional chine joint cross section.

My remarks about welding this skiff's seams are based on lots of hull seams welded, however, NOT in the many variable angles your hull's design requires.  In all the couple hundred skiffs I've built; I haven't built any with such a complex shape. So, I'd want to prepare mock ups of each seam, get that collections of settings figured out and recorded and then only when I had decent series of settings and techniques for that seam's geometry would I put weld on the hull.

Still on the fence about the geometry and design of the sheer's various components; but the main hull will require more attention to detail than most skiffs this size- by far. Just a word of caution about not welding until you have a set of values tested and recorded for that particular joint's geometric arrangement in the seams of your hull.

I have a good supply of boat stories almost as many as the countless mistakes I made designing, building, repairing, and fishing the hundreds of boats I built.  Glad you didn't mind my inclusion of a boat building tale in the thread, thanks for your indulgence.

Cheers,
Kevin Morin
Kenai, AK

 
 
 

[m32825]

Got the other center panel prepped and tacked in the center. The front end is really pointy right now, reminds me of the Romulan ship from the 2009 Star Trek reboot. Maybe I should leave it that way to scare off jet skiers?

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[m32825]

Me, trimming panels to land on the longitudinals ...
​​​​​

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[gandrfab]

I cut it 3 times and it's still too short.

[m32825]

I cut it 3 times and it's still too short.

 

Haha, yes, exactly...

[kmorin]

Carl, I'm looking (more closely) at the photo of the VKB at the forefoot and the two inner bottom panels.  Are longs for the intra-bottom panel seam connected to the VKB? They look like they're floating/unattached?

Not sure what's up in that photo but just curious why the forward end of the longs appear to be unattached to VKB?  Lots of time in 'all gray' photography implied by images of aluminum going together I see things I don't understand so I'm just asking if my view is incorrect?

IF they Are floating and you're keeping them shaped or edge located by the inner bottom panel's outer edge?? Then pulling the two 'orange peels' the VKB all the way to their ( outer panels ) intersection at the bow stem (VKB) is very important before you begin fitting the outer two bottom panels. All edges of the inner bottom panel should be fully tacked out BEfore you begin the outer panels to insure you don't have fairing issues in the forefoot area. 

Keel seam, image 7196, looks good to go for a single pass seam.  How close are your tacks to one another?  IF too far apart they can allow one side of the other of the inner/keel edge of the bottom sheet to lift or curl just a head of your weld. OR in the worst case, contract and wrinkle when the weld is still molten resulting in a crack where tighter tack intervals will hold the edges of the VKB/keel seam together w/o distortion.

IF your tacks are more than 4" apart, fore and aft, you may want to tack inside along the VKB to bottom seam before you begin the outside VKB/bottom seam?  Rather than go back and put more tacks that will need clean-up and dressing in the outer keel weld; you could just break up the interval by tanking inside and serve the same purpose.

Another item of build sequence your photos reminded me to mention is about weld-out sequence.  The are transverse frames touching the hull panels and these points of contact need to be at least tacked before the outer hull seams are put in.  Welding around the perimeter of a sheet of metal will 'cup' the metal outward/concave on the inside.  IF the panels are not at least tacked to the transverse frames or bulkheads the that cup, from welding the outside seams first, will tend to put gaps from the hull/skin and the frames' edges.  If you weld to try to tack once the sheet is cupped you will further bow the hull sheet away from the xverse frame and likely tearing the tack.... making a bit of a mess of the nicely skinned hull.

It is best practice to mark the frames, before you cover their edges with hull panel, for welds and even bevel them for the weld area.  Since distortion mainly comes in the open areas (not directly supported by internal framing) as a result of the legs of a weld being on the flat hull sheet and not 'tucked' under/inside a beveled edge of the framing; making a layout for the stitch/chain welds and cutting a bevel on the edge of the xverse elements that will touch the hull plates reduces the fillet leg length on the flat hull plate.

By beveling the frames' edges weld root face width can be kept high, while keeping the weld length shorter and the outer face narrower to reduce contraction 'pull' or cooling pull on an open face of the hull sheathing/plate.

Further, tacking the inside welds at the beginning and ends of these beveled weld allowances gives a better control/uniformity of the weld-out sequence and results in a smoother hull.

Hope I've addressed your current questions? If not, or I'm not clear in what I've written please let me so I can help clarify my ideas.

Cheers,
Kevin Morin
Kenai, AK
 
 

[m32825]

Kevin,

The longs are floating at the front. My plan is to work the inside panels all the way to the front, tacking them on both edges before doing anything with the outside hull panels. I'm going to use the edge to place the floating portion of the longitudinals.

The center tacks are about 7 inches apart. I'll experiment with tacking on the bottom and do something to get them spaced more closely. Also, I know they need to be closer together as I approach the front.

I'm so glad you are looking ahead and thinking about issues that I would only discover after the fact. I was imagining the transverse frames as something the hull panels floated over, not thinking about what happens when the hull panels are welded. I don't think it would have occurred to me to tack the hull panels to the transverse frames before welding the seams.

Last week my posting was a little fragmented "stream of consciousness" on posts 248 - 250. I still have a question in 250 about the one inch stitch welds I'll be putting in before the curve. Tell me what you think?

I'm happy with the edge routing solution I have now, working off a guide on top of the metal. I can see I have a lot of beveling in my future. When I started trying to bevel the edge of the placed panel, the bearing (and Allen head screw holding it) interfered with the longitudinal. I could make it work if I lifted the panel enough, but that stresses the tacks. I struggled with finding the right combination of router/bit/guide then decided to build a fixture for my die grinder to follow the edge. It took half a day to build but knocked out my edges in no time. It can do any bevel angle, as long as it's 22.5 degrees!

-- Carl

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[gandrfab]

That sure is pretty, you can bevel with a hand grinder in a pinch.

[kmorin]

Carl,

The longs are floating at the front. My plan is to work the inside panels all the way to the front, tacking them on both edges before doing anything with the outside hull panels. I'm going to use the edge to place the floating portion of the longitudinals.


 

 I think this can lead to more work than needed and might leave some 'hoggs' in the inter-bottom seam?

The initial purpose of a frame on which to build a hull is rigidity or to provide fixed targets for all the hull panel seams.  By leaving these longs unattached I think you're fighting the purpose of all the work to create the rigid frame?

These longs have been bent to the curvature of the conic section of the bow (Right?)  and they will hold the inter-bottom seam in the surface of that conic surface section.  SO if they can flex inboard or outboard (floating between the VKB and next outboard chine) then they can lift out of the conic surface of the forefoot OR they can be pulled inward and fall below the conic surface.  Neither case is desirable for support of a weld seam that needs to be ON/in the conic surface in that area of the bow.

I think it will result in a better seam support of the panels' edges if they are determined to be in the surface of the bow cone by holding straight edges transverse to the keel from VKB to outer chine.  I'd suggest you either pull the ends of the seam-support longs to the VKB and tack-then fit the inner bottom panel to that edge OR put extensions (lapping sister bars to the existing longs) to reach the bow stem's curvature of the keel (VKB continued to bow stem). 

My reasoning is that the outer edge of the inner bottom panels- will not have an accurate 'target' and could hold the ends of the longs away from the VKB or pull it inboard so they need trimming to meet both the bottom panel's outer edges and this hull seam's intersection with the VKB?

Regarding the welds to the keel seam before pulling the two bottom inner panels to the VKB:

The welds are needed to avoid the bottom panel from lifting away or breaking tacks to the VKB. The area can be located pretty simply by eye but any straight edge will work as well.  The keel is straight (or nearly so) up to a tangent point where the forefoot begins to curve (eventually ) upward.  Now, because the hull is inverted- the curvature is downward.  Same point to locate. This tangent point is where the straight line of the keel begins to curve into the forefoot.  Once you locate that point you have pinpointed the point of beginning of maximum stress when pulling the two 'orange peel's' of the bottom panel shape into the VKB's outer edge.

When you pull those hull panels into the curvature of the bow cone you will induce the most stress OUTWARD at the keel immediately aft this tangent point.  The bottom will try to lift or separate from the key and 'pull outward'  or pull apart from the VKB.   The welds are just aft that tangent point, they are full keel weld stitches and fuse the VKB and the two sides in one pass.  They don't need to be long welds or more than a few welds in 18".  Their function is to resist the sheet's (vastly increased) tension that will be exerted on that edge against the keel when you pull the sheet's inner edge (and eventually outer edge) to the frame. 

Pulling the sheets inner edges to the VKB is the primary cause of this outward bending force.  But in your case, you'll need to pull/clamp/conform the outer edges to the (now floating) longs just behind/lagging/following the VKB tacks.  The reason both edges of the inner bottom sheets need to be pulled in the same operation is to avoid allowing the sheet's forward most tip (ends) to 'creep' up (now) the VKB instead of being extended to their correct location higher up (now, down; due to hull position) along the VKB.  Even allowing the tips to be 3/16" or a 1/4" 'short' of their 'correct' position along the VKB will create an UN-workable 'cup' to the outer seam as it will not lay to the longitudinal flat bar but will be raised off that edge UNLESS you keep tacking all four edges from stern to bow w/o getting too far ahead of any given series of tacks.

This will become apparent if you take you cardboard patterns, shown earlier, and tape the VKB edge slightly short of their correct position along the VKB; then the outer edge (which is to form the inter-bottom seam) will be curved too 'deep' or cupped too much to be pulled down to the long's inner edge.

I'd lead the edge of the bottom on the VKB by 2-4" compared to the outer longs' edge tacks but not much more, and I'd do them all in symmetry side to side, and closely transverse in order of tacking while keeping the VKB tacks leading the outer set of tacks. 

This text explanation my not be very clear w/o multiple review? But taken step by step will make physical sense when you get on the hull.

I think you'll need the longitudinals attached to the VKB so you can clamp the outer edge to them w/o pulling that seam up out of the conic surface that is the design intent of the forefoot of your hull.  The half dozen 1" long keel welds begin at the forefoot tangent point and extend aft for a foot or two to keep the bottom panels from totally relying on tacks to hold to the VKB in the area which become highest stress from curling the bottom panels in to the VKB/forefoot.

Nice bevel jig.  Looks very useful to do the bevels on the frame.  With just a base width change or a vertical guide addition to the base you could bevel the xverse frames with that rig.

Lots to think about but clearly you're taking time to do it right so I hope these details will further explain why I'm advocating the steps I've tried to explain.

Cheers,
Kevin Morin
Kenai, AK
 

[m32825]

Kevin,

I get what you are saying about the floating front on the longitudinals. I wasn't seeing the problem (yet) because cardboard doesn't pull on them like the hull panels. I will get them anchored before tacking the panels.

​​​I appreciate the additional detail on the keel welds, especially the tangent point. I was thinking about where the center edge departs from a straight line, which is about 18 inches closer to the bow. The tangent point is just short of five feet from the bow.

Let's see if I understand transverse frame attachment. Sounds like the transverse frames get tack welded or stitched prior to welding hull seams, but aren't themselves ever fully welded? What angle bevel do they need? Access to the edges under the tacked center panels is going to be a challenge. Is there a way to bevel them with a hull panel in place?

I'm working on dialing in the new welder for .045 wire. Got a decent keel weld but a bit  too shallow. My inside corner settings seem pretty close?

​​​​​​ -- Carl

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[kmorin]

Carl, I don't think we're using the same terminology for the lines references to the hull?

​​​I appreciate the additional detail on the keel welds, especially the tangent point. I was thinking about where the center edge departs from a straight line, which is about 18 inches closer to the bow. The tangent point is just short of five feet from the bow.








 

The tangent point, in my use of the term, is where the bow curvature begins to depart from a straight line.  That is the point where stresses will be highest to pull the bottom edges away from the keel when the forward 'orange peels' are pulled to the VKB's outer edge and tacked.  That point and aft of that point about 18" is where the short stitch-welds need to be added.



There will not be any measurable extra tension to pull the bottom panels' keel edges away from the VKB much aft of the tangent point -plus about 18"-2' aft of that point. No need to weld aft yet.

The bead should be like the weld you show, fusing both sides of the inner bottom panels to the VKB. It looks like your test shows you're getting good fusion of all three parts' edges in the bend test coupon.

Just slowing slightly on your travel speed (not giving a figure just a description) will allow the bead to fill in to a flat top. The keel weld bead top can be convex, bulging slightly, but that won't really change the strength as your test shows the welds you're putting down are more than adequate for the job to be done.

I agree that the inside fillets look good with nicely flowing puddle chill-lines flowing smoothly into the parent metal at toe and top of the bead.  To make these welds a little narrower you'd have to speed up your travel and even potentially ad more weld heat/wattage to get the fuse heat up in less deposit time.  Recall I usually tried to get these welds into a position other than horizontal in order to minimize bead cross section while maintaining good fusion.

Regarding bevels for the xverse frames to hull panels weld stitches;  Using a jig somewhat similar to the diegrinder jig you show.. you can use a small 'pine cone' round tipped burr or a small router bit with a ball, to excavate the bevels.  IF you do this care has to be taken not to get too deep into the thinner hull panels or you'll risk burning through when the weld is put in.

I've used a pc of angle welded to a short length of pipe. The pipe was at 90 to the inside of the angle.  The pipe was slit to allow the die grinder to be clamped (SS hose clamp) inside the slit pipe (beveled at the end to 90 to) fit inside the angle and welded in halves.

Then using UHMW tape as a sliding/gliding surface on the outside of both legs of the angle- a very controllable tool can gouge these bevels.



(looks like my photo bucket account is having trouble? not getting a very good image of what's in the storage?)  But you'll probably get the idea ? UHMW poly tape is available in all sorts of sizes and works pretty well.  This angle may be too short to keep the tool stable so just extend it a bit and the base will become more stable- but you can't get into corners as well.  Key here is to make a base, like your previous jig, that stabilizes an otherwise handheld tool; to make more controlled cuts.  

By lowering or raising the burr's tip inside/outside the angle's outer profile you can make gouges that reflect the cross section of the tip of the burr. SO that is why I'd suggest the pine cone shaped burr over the round one (shown in sketch) they have a smaller rounded tip to make a smaller cross section gouge.

Yes the transverse frames of all types and all but water tight bulkheads need to be stitched/chain welded to the hull panels- eventually. So too the hull longs that are not on/under seams need to be stitched/chain welded to the hull's skin/sheathing. The length of these welds varies but with the small scantlings of your hull I'd say they don't need to be any longer than 1-1/2" and most of them will work fine at 1" or so.

Hope this addresses current questions with usable answers?

Cheers,
Kevin Morin
Kenai, AK
 
 
 
 
 
 
 

[m32825]

Kevin,

I'm tracking on the tangent point of the keel. My initial confusion was because I was thinking about the tangent point of the center panel curving outwards. Wrong geometric plane!

I like your beveling fixture. I don't think I would have come up with that. Unless you talk me out of it, I'm leaning towards doing the bevels once the hull panels are on and I can flip the boat.

I think I've got my settings for .045 wire. Some pictures below. I managed to do the outside corner with it, but I don't think I can consistently go that fast when it counts.

Finally, my new welder has start slope and crater slope settings, I want to experiment with those.

    -- Carl

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[kmorin]

Hey Carl,
first and foremost; great looking welds and proof of their quality are your bend test coupons' images!  If the skiff runs over a anti-ship mine in the shallows of Florida (??-!) then the hull may be destroyed by deformation (!) but we know your welds will hold!

I can relate to your comment about being able to keep up the required speed for this weld method on all seams in all positions & weld conditions.  I'd say the heavier wire practice will make your welds using 0.035" wire outside the hull seem like 'easy street' where the higher amperage and faster travel will condition your reflexes so the smaller wire welds will improve and become higher quality as well. Using 0.035" wire outside with 0.045" inside is still going to result in high quality hull seams.

I'd say that any xverse frames' edges, still open to weld prep/beveling, would be better done now than later.  The reason is that the vertical bar of the frame is the only part of the weld joint that 'needs' to be beveled to gain the reduced face width of fillets inside the hull.  You can use a jig like I've shown to do 'mostly one sided' gouges- simply put the center pipe/tool body holding slit pipe off to one side- so the work can be done inside and still cut deeper into the frame bars.  But, no matter what you do, it's much less work and clean up to do these bevels on the xverse frames only- and not to gouge the flat sheet materials at all. Less risk of burn through as well- by burn through I'm not including 'print through' which will happen with all hull welds done on the framing away from the edges of the hull panels.

Not being familiar with your power supply's controls and not sure of the labels versus the graphic shown... I have used both controls, UPslope and Downslope/crater fill, on a Lincoln power supply. They did require testing a wide variety of settings and recording the settings to re-use them in the future as the Lincoln (I have) doesn't have a memory function to hold various re-callable settings in an internal file.

What I will remark about is that the most useful instance for carter-fill is when you're chain/stitch welding where the weld's will not end or begin on another but will have distinct starts and stops.  Seam welds, we've discussed somewhat before, are gouged at their starts or 'whipped out' to end so the final continuous welds don't have cold starts or craters.  But stitching/chaining means each weld has a distinct start and stop and this is where these controls are very helpful IF you spend time to learn how to incorporate their settings into this group of welds, which you've shown that you'd likely do thoroughly.

Cheers,
Kevin Morin
Kenai, AK


 
 

[m32825]

Kevin,

I have to be honest, I thought that weld was "too skinny" but decided to test it anyway... glad I did! Needless to say, my judgement got a calibration update. Nothing like seeing it to make one a believer!

The shallows of Florida that I frequent have limestone outcroppings and oyster bars. Deeper water has crab traps and manatees, but I don't spend much time there. This will be the perfect boat for that application.

Okay, let's do the transverse frames bevels. You are picturing 1 to 1-1/2 inch stitches. Is there just one stitch in the middle of where a hull panel crosses a transverse frame, or are there multiple stitches? If there are multiple stitches, how are they spaced?

    -- Carl

 
 

[kmorin]

I agree Carl,
break-bend tests are the best way to get in-shop, personal confirmation of what your weld quality is.  And glad to see you've spent the extra effort to confirm that huge wide, gorilla welds aren't needed and mainly cause oversized HAZ and distortion w/o really adding any functional strength to the boat.

Because the boat (most welded aluminum boats under 30' LOA) are very light compared to their size, they most often don't puncture when grounded- maybe once in a while we'll hear about a welded boat that ran onto something like a metal spike or re-rod in a piling... but for the most part these boats just slide off w some scratches.  50series aluminum usually has a yield strength, per square INCH, that exceeds the all-up wt. of the skiff.  I expect that your skiff will be essentially bullet-proof in the waters you're describing.

Planning stitch weld patterns can be done with all sorts of references but for your skiff's small scantlings I think a total pitch of 4" is workable.  This is the interval on your 'story stick' to layout the welds/weld zone prep.  Where 1-1.25" is welded and 2 3/4" is open (un-welded joint) and then another 1-to 1.25 " stitch on the other side of the frame. This pattern will keep the framed parts tight to the hull w/o much distortion- the welds will print though but not distort the hull sheets/skin/surface.

Once laid out and beveled (if you're going to) the tacks will happen at the beginning and end of each weld in pairs.
Then welds would be put down in a 'chained' pattern into the weld prepped areas between tacks.  To plan a chain you simple begin at the end/chine intersection of the frame (inboard or outboard) that is opposite your direction of travel for each weld.

Chain (putting links on) stitches along this line: (you're left handed) you'd begin on the right margin and weld toward the right end of the line.  Each weld begins from its left side & moves to the right side ending. The accumulated heat is headed in the direction of your welds.  You move away from the heat and weld direction to put in the next chained weld.  No frame (xverse) weld should be within 1-1/2" of the chines or long seams of the hull. NO need to make intersections of framing and long seam welds with your stitch layout.

Let's say you begin one space from the VKB; weld that stitch and move outboard to the next weld on the opposite side of the frame and continue all along that rib til it comes to the next 'chine'.  Hope this gives you a picture of how to plan the weld out of hull frame to skin? I'm not addressing the long seams. 

These welds would go on the xverse frames AND on the longs, however, on the longitudinals that don't back up weld seams, I would suggest you do them one stitch- skip four or five prepped weld zones and stitch again... then move to the opposite side of the keel and repeat- and finally after moving fore and aft- and working symmetrically about the keel you'd end up welded out.  I'm not advocating you get on a hull long and chain stitch weld it end to end. 

I'd weld out these frame welds before doing the hull long seams to reduce the shrinkage of the hull panels at their edges.  Breaking the panels into framed spacing sheets by welding the frame to skin/hull reduces the effects of edge contraction 'cupping' when welding perimeters of hull panels.  At the very least I'd want to tack all the frame elements inside to the hull/skin/sheeting before welding the outer long seams.

The 4" pitch is not written in stone, just my "eyeball" estimate of a pitch for this scantling set. To me, keeping these stitch welds narrow, hot and fast will govern how clean your hull ends the weld-out step of your build.

Hope I'm answering your questions with a text description that is useful? PLS Let me know if this makes sense?

Cheers,
Kevin Morin
Kenai, AK

 

[m32825]

Kevin,

Bulletproof is what I want. I thought about making the hull plates thicker than 1/8" but can see now that isn't necessary. Probably for a jet boat that's on rocks/logs all the time, but (navigational errors aside) my hull should only touch when I pull it ashore. I'm really happy it's not thicker as I get closer to forming the bow area, what a wrestling match that would be!

The hull panels are on the order of 12", 9", 6", and 4" where they cross transverse frames. So for a 12" length I'd have three stitches, 9" would have two, 6" and 4" would both have one? Towards the front where there is one stitch seems like it should be on the bow side, so any pull helps make the turn instead of fighting it?

The only longitudinals I've got are the three between the bottom hull panels. I was thinking those got continuously welded inside?

I decided to do the additional center tacks on top, where I can see them. They are at about 3-1/2" intervals. I got the keel stitches in and am starting to think about trimming and beveling further forward.

    -- Carl

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[m32825]

This thread has a nice rotisserie, but he's clearly on the wrong forum for aluminum boat building...

Macuch Craft build

[m32825]

Today's geometry appreciation exercise is complete!

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[kmorin]

Carl, replying to the #267 post; 
The strength-to-wt. ratio of small (under 30'-40') welded aluminum alloy boats is usually higher than needed to 'hold the water out' as a hull. So they tend to bounce off, slide off or skid off of groundings, and most underwater obstacles. 

One of the limits in boat building is effectively welding thinner than 1/8" for most welders and their equipment.  When we look at the market- we see a huge fleet of products that are pretty thin and still doing their jobs- keeping the water out.  Even those pressed and stretch-formed, super thin scantling boats, often riveted, will still hold up to lots of beaching abuse even underwater collisions.  Your skiff will be plenty strong for the uses you've described (IMExp). 

Yes, stitching the xverse frames to hull panels as you've described will work fine.  The key to that process is fast, hot, small face width welds to keep the contraction distortion minimized.  The wire most effective may be 0.035"? Experimenting/testing/mocked up bench welds will show the combination of bevel, wire, amperage and travel speed that will work best for your project.

Have to test weld a few gouged-T fillets to confirm?  Once welded, cut through and sand smooth then etch the sanded face with acid (hot vinegar will work OK, Naval Jelly too) to get a picture of the bead's root face fusion. 

I think your decreased tack spacing interval will be fine in prep for the keel weld. I agree the longs can be welded full length inside and outside but..... the outside welds are the more important welds to fuse all three edges in one pass. Inside welds are 'just' backup to the outside weld.  Your bend tests show that the outside weld- with your extensive prep and test welds will hold the entire seam together. 

#268 Rotisserie Fixture

That is a very nicely built rotisserie, dedicated parts of new metal with some good design features.  I've only built my rotisseries out of scrap; used oil production tubing for all the pipe and local metal store's off-cuts for parts.  So, designing from white paper - I'd say that design was very nice.  I found that using the pipe clamp style of tensioning/pivot bushings w/ variable friction I could adjust the pivots so they'd hold the rotated position I needed.  The pipe clamp style in my design allowed me to balance the skiff/load by lifting and lowering the vertical arm- as shown in the link. 

However, by having a variable clamp pressure sleeve/bushing for the horizontal pivot I was able to rotate the boat by hand, and leave it where I'd moved it and weld, then push/pull on the hull and reposition for another angle of rotation.  All while standing on the shop floor w my torch in hand.  This saved hours of re-positioning with overhead lifts and allowed for quite a bit of imbalance in the skiff's centering on the pivots- while still allowing hand rolling of the boat. 

I also notice that the triangular base of the ends have a leg under the main beam?  I found this to be in the way so my version has the triangular base outside the main beam's swing.  this allowed the main beam to be almost on the shop floor and eliminated any standing obstacles while welding.  In the same thought is the double mast or two pivots per end where the rotisserie's triangular wheel pattern has the second pivot over the outside apex of the wheels. 

I didn't have machined parts for the ends/pivoting pipe and sleeves.  I used concentric sized pipe so the fit was very loose- until the outer pipe was clamped around the pivot pipe. This allowed loose fitting parts to turn to roll the skiff while not requiring any machine fit parts or close tolerances.  So I think the design shown is great, I'd estimate it was much more expensive than my scrap-iron rotisseries and cost was my main concern.  Mine are both rust finished for example! 

#269
I like the die grinder fixture to get bevels on the frame elements.  I found that aluminum to aluminum can get hung up with chips and the drag or jump when being pulled. On the table of my skill saws, jig saws and various other power tools I've used UHMW tape to get a slick- non-binding surface to make tool control better. 

On the other hand you can use another product that works great- as well.  Velcro (tm) comes in sticky-back tape forms.  Take the loop side of the Velcro and put strips on the cutting tools' tables to make an easily slid but not slippery surface that will not get gouged by a chip and 'stopped'.  It also reduces the amount of scratching/scarring/marking that normal cutting tool tables leave on the metal- less to sand or grind out if you're painting or finishing.

You could add a couple of wedges to the base, taped on to create different angles, with the same original hardware. When you weld test you may find that a little steeper angle gives more thorough penetration at the root?  Either way I think the tool will work fine and even as few of these you need to cut-  you'll have them done rapidly and accurately so the weld settings and travel speed can remain the same and the replicated bevels will give uniform high quality results.  Slightly remodeling the reveal/exposure/extension of the carbide tip; you can use the same jig to gouge when the fillet is already formed.

Cheers,
Kevin Morin
Kenai, AK     
 

[m32825]

Kevin,

Good insights in your rotisserie commentary. I wonder if overall length limits were a consideration in his decision to put the legs inward? I might run into that myself. How much do the support legs do once everything is assembled?

You were right about aluminum on aluminum being sticky, and UHMW tape makes a huge difference! Thanks for that tip. I've beveled everything I can reach. The rest will have to be done once I have better access. I wish I had known about beveling the transverse frames before starting, it's trivial to do them on an open edge with good access. Router bit with a bearing and Bob's your uncle for those.

     -- Carl

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[starbright55]

You were right about aluminum on aluminum being sticky, and UHMW tape makes a huge difference! Thanks for that tip.
 
 


 

I ordered some today - even my router with a plastic base gets up.  I [thought I] had planned on sanding everything later, so I didn't care about scratches.  But, I think being able to move it smoothly will be sooo nice.
 

[m32825]

Marching along...

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[m32825]

So far, so good. Less than three feet to the bow. Might have to wait until after Christmas.
 

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[kmorin]

Carl,
couple general remarks about pulling the keel seam together on the inside edges of the 'orange-peel' cuts of the forefoot.

First, pulling the outer edges together will pull the inner edges together- so by putting pipe/furniture/Pony clamps from side to side on the outer most edges- and stopping them from sliding forward by using pliers-type vise grip pliers, you can gradually pull from aft-forward and slowly and more or less evenly bring the keel seam edges together.

Second, the work should progress evenly and smoothly not in steps or stages.  IF you put four to six clamps on from the 2x4 to the gloves - and put pressure on all of them- then you'd work aft to forward slowly add a turn or two - evenly in smooth 'layers' or passes; the center seam will come together evenly and the chines and bottom plates won't have kinks.

Third, generally, the center seam tacks should lead the outer seam tacks by 4-8" so there's still pull or leverage on the outside left to pull when the center tacks are in ready to be taken.

Fourth, as you have the longitudinal bar in the 'way' of furniture clamp pipes- I'd look at using nylon truck straps.  The hooks can go under the outer edges, vice grips will keep these hooks from sliding forward, and they can be moved away from the outer seam to bar joint- when the strap's end hook begins to hold the bottom sheet off the outer bar.

Some specific notes about tooling for what's immediately ahead.

Another away to pull the keel seam tight is to put an inverted angle on the top of the seam with a nylon truck strap under the VKB (using a wood slide or another aluminum fitting. On the apex of the 2" long pc of angle you'd tack a pc of small pipe or round stock so the nylon will slip while compressing the inner sheet edges. AT the two outer edges of the sheet a pc of wood with a slit or slit metal and round bar will also allow band clamps type of compression.

If the longs provide too much interference to grab the outer edges of these sheets and pull together ? you can weld a flat bar the keel and then put a series of 'tacked-on-crosses' or inverted V's) on the FB welded to the VKB.  This will be removed but gives a place to put wedges along the inner bottom sheet edges to pull them down to the VKB's edges for tacks.  This is the 'wedge-&-dog' method of plate fitting, and will allow tremendous force to brought to bear in a very tight space.

If you weld to the VKB the 'mast' or bar could have a cross pc that is 5-8" above the keel bar's surface and still have a lever or wedge to pull both (un-curved) bottom panels' edges downward to the keel. With a pair of bars like this you can use one to 'cinch up' the other.  Then removed the first cross pc and lower it down add wedges, repeat.... This may take a few sketches but is very commonly used for heavier plate and 'staged' adjustments to plate edges.

In this area it would be good to add many more tacks than to have the bottom unzip- breaking a whole series of tacks spaced too far apart.  I'd say 2" spacing was good and not too far apart.  3" may be OK but 4" is definitely too far between tacks- you can always dress them off/cut them out- but its a pain to have to replank the bow if they come undone.

I expect the next 18"-24" forward of the 2x4 will be pretty easy to fold and tack and I expect the process to much more slow, careful and require 10x the forces when you get to the forward 12-16". I would caution you not to forget the outer edge should progress right along with the keel seam.  Those tacks should trail but they are not a separate procedure to be added at some later time.  Planking when two edges are to be framed have to be tacker smoothly together.  Center seam first, then port, then starboard, needed catch 100% up to the keel seam's progress but not 10" behind either.

Just some thoughts looking at your photos.

Cheers,
Kevin Morin
Kenai, AK