Adapting the Console Skiff to aluminum

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Nclay
Posts: 3
Joined: Tue May 30, 2017 12:07 pm

Adapting the Console Skiff to aluminum

Postby Nclay » Tue May 30, 2017 12:48 pm

Hey guys, long story short...I've built a few stitch and glue skiffs, as well as cabins on large fiberglass hulls, and am tired of the chemicals, itch, fairing, and painting. I recently bought an aluminum capable mig and have been practicing daily for about a couple months and have been getting some nice results. I've been lurking around this website as well as others studying Kevin's posts and have read through pollards book. Im looking at starting on a small relatively simple center console skiff in the 15 foot range. Most aluminum cnc designs/online plans ive seen, seem to lack a pleasing sheer line ect... sooo, what are your guys thoughts on building the console skiff hull out of 1/8" 5052. Adding longitudinal topside stiffener along the chine in the form of a spray rail ect... do you guys think I could get the necessary bends in the forward portion of the hull in 1/8 5052?

Kevin Morin
Posts: 640
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Adapting the Console Skiff to aluminum

Postby Kevin Morin » Tue May 30, 2017 2:50 pm

Nclay,

Yes. if the skiff is designed to use ply, and you substitute 1/8" 5052 you can build it. Not saying there won't be some teething issues, but if it can be built in ply you can built it in aluminum. I'll assume looking at the pics its a set of large halves with a gore between the topsides and bottom panels at the chine line which is where the gore is cut -aft? This implies the keel to sheer piece of the bottom combine to topsides forward is one clean piece?

The skiff as shown will be wet- no spray rail, or chine rail for that matter. But adding the rails is almost like using separate topsides and bottom pieces with full length chine seam? But you can do what I understand you're asking.

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Nclay
Posts: 3
Joined: Tue May 30, 2017 12:07 pm

Re: Adapting the Console Skiff to aluminum

Postby Nclay » Tue May 30, 2017 7:00 pm

Hey Kevin, thanks for the prompt reply. I've semi-settled on that design and will add the optional raised bulwarks offered in the plans. I plan on finishing the gunwales with the 1/2 inch slit pipe style that you've detailed in another post. Do you think an angle extrusion chine cover would be a good idea in acting as a spray rail for that particular skiff? Also I'm a little unclear on Pollards description of butt welding the 1/8" 4/8 sheets to get the full length panels. How would you do it to achieve the best results? Thanks again- Nate

Kevin Morin
Posts: 640
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Adapting the Console Skiff to aluminum

Postby Kevin Morin » Wed May 31, 2017 8:25 am

Nate, depending on where you're located? aluminum is regularly available in 4'x20' sheets also 5' wide, 6' and even 8' depends on the metal distributor's policies - more than "do they make it"?

so, my first reaction is to buy big enough sheets to take the entire boat side out of one sheet? Next is welding the pieces together from smaller stock sizes and that's a question many builders do differently from one another.

There are two main groups- weld butts on the hull when tacked to shape, and the weld-before-and-then-sheet the frame or 'pull up' the panels' edges.

In the weld on the frame- tack sheets together camp- the advantages are that the shape stress - curves, cambers and framing help reduce weld distortion so welding after forming up means easier work flow -welding last. But the other side of that argument is that if you have weld distortion on the boat- while in the final position its harder to 'fair out' the wrinkles. And some of the welding can be harder to access once the sheets are put on the boat frame or pulled up into final shape.

There are builders who join sheets while on a bench-support frame of some kind. These builders want to be able to fair or smooth any wrinkles or waves induced into the sheet as a result of weld contraction. The gain here is the easy welding- usually flat, down hand, and in long fast 'drag' beads. ("drag" is the term for a 'machine' weld where there is no in-puddle actions- a simple point-n-shoot weld) In this method the joint is prepared- beveled or gapped depending on your preference and techniques (?) the sheets tacked to one another so that one edge is a line- and the weld is put in one one side then the other. Even in a 4' wide seam there are only 2 or at most 3 welds. (you could get by with 4 but its most common to try for as much length as possible)

The disadvantage, that some builders prefer to avoid, is the welded area does not bend/shape/"lay too" the framing exactly as the unwelded areas; the sheet gets a 'stiff spot' from the weld. Further, if there are wrinkles, due to weld contraction, then they have to be hammered or wheeled out to flatten the sheets back to fair smooth surfaces without waves.

The technique most often used in the weld-before-install builders is to make long fast narrow beads as far as their arms will reach. I've seen (only one) a builder who hung the sheets and tacked them up using clamping bars to keep the sheets flat to one another- then welded the two sides vertical down! He was very proficient in this technique and rarely had more than a slight cup as a result- that cup or camber from the sheet's original cooling can be used VERY positively in any builder's favor when planned for in the shape of the boat.

The key to these welds- and hard part of welding to practice - is the proportionality of the weld to parent metal. 75% of all aluminum welders I've worked with for many years tend to put in much more weld than needed. This will warp the hull plate butt seams more than anything- over sized welds.

What's hard to practice is, in order to use MIG, you'd need long strips of material- and they'd have to be more than a few inches wide or you'll end up with pretzels when they cooled. So having some strips sheared or saw some test pieces - then practice long fast beads that are only 1.2x the material- if you're using 1/8 then the bead need to say in the less than 3/16" wide/deep class! And that takes some practice.

Regardless if the skiff has a building jig or some type of framing (?) or it is self forming by pulling edges together - like the origami method- you can still choose either way to go regarding final sheet butt welds.

By using flat bars spot tacked on edge to the sheet face and 90deg across the seam- you can prep the seam, butt the edges- gap or bevel- then tack and finally using a few 1" x 1/8" or 3/16" flat bars 8" long- you'd reinforce that unwelded seam until the sheets were formed to the shape. These unwelded seams can be welded once formed to the hull's shape - especially if the hull form puts stress and twist or cup on the panels - that shape stress helps to resist weld cooling distortion.

Hope this helps?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Nclay
Posts: 3
Joined: Tue May 30, 2017 12:07 pm

Re: Adapting the Console Skiff to aluminum

Postby Nclay » Wed May 31, 2017 12:39 pm

Ok, that is making sense. Yeah the full length panels would be a luxury, and one of the perks of moving away from plywood.. but I live on Kauai, and the material has to be barged in from an Oahu distributor. 4/8 and 4/12 are their only offerings in the 1/8'' 5000 series.. so i guess butt welds it is. I"ll rip some strips today, and start practicing the longer runs. Do most builders then sand the panel's outer weld flush for cosmetics? or would that weaken it? Also, would welding one side, backing chipping the opposite side and welding it, be the appropriate technique for 1/8 inch material? or would you bevel?..leave a gap?...what is your preference? Thanks- Nate

PS Kevin by the way, I lived in Homer for a few years 2008-2010, I ran that aluminum landing craft the "Baylink" one season for homer ocean charters doing water taxi stuff. Still miss K-bay

Kevin Morin
Posts: 640
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Adapting the Console Skiff to aluminum

Postby Kevin Morin » Wed May 31, 2017 3:08 pm

Nate, I can see why you're working with small sheets sizes! That's a long way from the mill.

All the techniques you mention are used by someone! So making a choice is sort of prioritizing your results. First I'd weld and test my welds- then I'll mention it is considered poor practice to take the top off (sand down) a MIG weld in aluminum UNLESS..... you have a deep root area when you've beveled, or made some other gouging prep.

I'd want to weld the test strips, bend and break- then weld more and sand off the crown of the weld (if that is your intent) and bend again- noting the differences you can decide which is your preference?

I generally butt-tack sheets together or join them on the hull by putting one up and adding the other and tacking. I personally generally weld after the boat is shaped but: I generally always TIG weld the transverse seams- no MIG. I have done MIG butt seams in the past and I've used gapped plates with backers that are left permanently inside the hull- and I've done most other types.

I like the tack and weld after the boat is assembled due to the shape stresses or sheet tension I almost always draw in my skiffs. BUT... and this is not trivial-I'm the designer and the builder- so I've got a bit more leeway than using plans that I didn't draw. The leeway comes as the boat is shaped- I might make adjustments on the fly and that is not a good idea using plans you didn't draw. (Let's just say there are many dominoes of shape to knock over if you make a change to plans you didn't draw!)

Since the console skiff looks like the panels have a pretty high degree of stress or outside tension due to the pulling up the stem and chines(?) my thought is that I'd tend to butt and tack the seams then weld them in the finished form - but then I've not seen the plans and don't know the method of construction.

I bevel 1/8" using a Vixen file or belt sander- marking the edge -off set or cutback using a marker; then I fit to a knife edge - butt, tack, stiffen with bars. Once this sheet is on the hull- cambered outward and tensioned I weld the butt seams nearly last (using TIG) with a tiny bead- then I do the other side. If, there are framing elements that break up the weld then I'll do opposing sides of one stretch of seam in pairs before moving to other areas in the seam.

Homer and the K-Bay is sure a nice place to pilot a water taxi!

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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