Longer Aluminum Boats

[Bob La Londe]

First off I want to ask you all to remember Jim Isaac (rest in piece) for a moment. He's the one who first introduced me to this site some years ago. He was a proud tin boat owner and regular on my fishing forums.




Ok... Here is the setup and the question.

I want to build a medium to rough service super jon. I might build a shallow V, but that is the gist of it. Something in the 22-24 foot range designed for shallow running over sandbars. I think it would be best of the hull and bulkhead pieces were full length one piece or cut from full length one piece. I buy aluminum commercially (I run a one man custom mold shop), and I can buy a variety of bar, sheet, and structural at competitive (for this market) prices. From my primary supplier I get a flat rate drop off charge from them so shipping is pretty cheap. They have a wider variety sizes in stock than your local metal yards, and I just order aluminum sheet at the same time I order rectangular flat bar for my business. The problem is 22-24 foot length pieces are not among those sizes. I can special order longer pieces, but I have to buy a whole roll of aluminum. That amount gets me decent discount, but I'm not interested into going into the boat building business. I just want to build one boat. Well, two, but the second one is inconsequential and I already have the metal for that one.

I've read Pollards book on aluminum boat building, but most of the bigger craft he talks about are a different class of boat. I've welded aluminum before, but I could certainly use more practice. I don't have an issue with Pollards suggest method of welding from one side, back chipping and welding from the other side even if that is NOT the way most commercial aluminum boats are welded. For most commercial boats they do buy aluminum long enough to cut full length pieces, but that's just not a practical option for me. Some probably buy spools and have their own straightening and shearing setups. That's really outside of my capability. I am resigned that the most cost effective way to get the length I want is to butt weld a couple 12 foot sheets together.

What is the durability under real service of a welded seam across a long piece? Assume the welds are decent. LOL. I think my process would be to weld the one side, back chip and weld the other side, and then grind the first side flat for the outer hull. Stringers etc will help. Not sure I want to put ribs over a weld joint, bur a top hat shaped rib weld on either side of a seam would certainly reduce the strain on it. The problem is if there is a problem with the weld it can only be repaired from the outside then.

I know in groups like these there are always a few who want to jump to judgement or point people in a totally different direction. (It's why I refuse to talk about transom cores in these type groups) Please try to refrain from that, and go with me on this. This is not a project I thought of five minutes ago. I've been thinking my way through it for a few years now. I've got nearly all the tools for the job and a good relationship with a shop owner (not boat related) who has the one thing I might need that I do not have. I've got materials sources for the most part. I've done weld repairs from minor to major on watercraft that didn't sink after years of use, although I am not a boat builder and do not do boat repairs for hire. I've studied several boat plans over the years, and think I have worked up a pretty decent plan, but I won't share it for obvious liability reasons. Just go with my on my basic premise and question PLEASE. Thank you.

 

[MrGiggles]

What size material can you get, and what are your plans for the cuts?

I think it's relatively common for V hull boats to have welded seams that run longitudinal, not as much for perpendicular butt joints, since they aren't as strong.

 

[eeshaw]

There's a place in Louisiana that supplies boat material to anyone although I can't think of the name of them right off hand. I know they have just about anything you could want when it comes to boat metal. A lot of bowfishing guys go through them when they custom build their boats. They could probably supply you with anything you want. Personally I wouldn't do a butt weld on a hull bottom if I could avoid it.

 

[Bob La Londe]

FYI: My experience is that the hardness of 5052 goes away around the weld. Ie: the metal is softer, but the weld itself is plenty strong. The metal isn't "weaker" Its just softer.

What size material can you get, and what are your plans for the cuts?

I think it's relatively common for V hull boats to have welded seams that run longitudinal, not as much for perpendicular butt joints, since they aren't as strong.

144in (12ft) length or full coil.

There's a place in Louisiana that supplies boat material to anyone although I can't think of the name of them right off hand. I know they have just about anything you could want when it comes to boat metal. A lot of bowfishing guys go through them when they custom build their boats. They could probably supply you with anything you want. Personally I wouldn't do a butt weld on a hull bottom if I could avoid it.

Trucking from Louisiana would cost more than the material.

From my regular vendor I can get any size order (of what they sell) delivered for $50 to my door and their driver will help me unload. Larger orders they deliver for free.

 

[MrGiggles]

FYI: My experience is that the hardness of 5052 goes away around the weld. Ie: the metal is softer, but the weld itself is plenty strong. The metal isn't "weaker" Its just softer.

What size material can you get, and what are your plans for the cuts?

I think it's relatively common for V hull boats to have welded seams that run longitudinal, not as much for perpendicular butt joints, since they aren't as strong.

144in (12ft) length or full coil.

There's a place in Louisiana that supplies boat material to anyone although I can't think of the name of them right off hand. I know they have just about anything you could want when it comes to boat metal. A lot of bowfishing guys go through them when they custom build their boats. They could probably supply you with anything you want. Personally I wouldn't do a butt weld on a hull bottom if I could avoid it.

Trucking from Louisiana would cost more than the material.

From my regular vendor I can get any size order (of what they sell) delivered for $50 to my door and their driver will help me unload. Larger orders they deliver for free.

From what I understand aluminum welds are almost always weaker than the base material. But there is at least one welder on here that may know more.

One thing you could do is angle your butt joints, essentially making them longer. Spread the load over more weld.

 

[Bob La Londe]

FYI: My experience is that the hardness of 5052 goes away around the weld. Ie: the metal is softer, but the weld itself is plenty strong. The metal isn't "weaker" Its just softer.

What size material can you get, and what are your plans for the cuts?

I think it's relatively common for V hull boats to have welded seams that run longitudinal, not as much for perpendicular butt joints, since they aren't as strong.

144in (12ft) length or full coil.

There's a place in Louisiana that supplies boat material to anyone although I can't think of the name of them right off hand. I know they have just about anything you could want when it comes to boat metal. A lot of bowfishing guys go through them when they custom build their boats. They could probably supply you with anything you want. Personally I wouldn't do a butt weld on a hull bottom if I could avoid it.

Trucking from Louisiana would cost more than the material.

From my regular vendor I can get any size order (of what they sell) delivered for $50 to my door and their driver will help me unload. Larger orders they deliver for free.

From what I understand aluminum welds are almost always weaker than the base material. But there is at least one welder on here that may know more.

One thing you could do is angle your butt joints, essentially making them longer. Spread the load over more weld.

The base metal becomes softer. It is annealed by the heat of the weld process in the HAZ (heat affected zone).

 

[sonny.barile]

Have you given any thought to a lapstrake design using coil on a roll? You will have many more welds but all longitudinal.The strakes overlap so your inside and outside welds are not aligned. Between the inside and outside weld (the overlap) Is double thick.

The older heavy duty Quintrex boats were lapstrake.

 

[Kismet]

I'm sure you've thought of this, but have you considered exploring some of the boat makers that supply the swamp boats featured in SWAMP PEOPLE?
As I'm picturing your desired creation, it seems to sort of fit into the long jon-ish, semi-v=ish, heavy duty, take=a=lot=of=abuse craft that they use.

Might be worth an inquiry, if for nothing else than to discuss the strength of the welds and variations they have used, and others that they have found fault with.

Best wishes.

 

[Bob_esper]

Several vendors in LA can get at least 20' long sheets. But like you said, shipping will eat you alive. You can certainly splice sheets together though if you're determined. My first boat was made up of (4) 5x10 sheets of metal. I had a seam up the middle and on the sides. Was it ideal? No, but it's survived 9 years now at this point so can't ask for much more. I would advise using 5086 for the hull. It's a little stiffer than 5052 and will give you a bit more rigid boat. Also it'll have better corrosion resistance if you every take it to the ocean.

 

[Weldorthemagnificent]

There is weakness in the heat affected zone with any material. That being said, aluminum is used structurally in many applications. If the weld is placed in an area that is braced well and not as subject to flexing, it should be fine. They make aluminum dump truck boxes and they aren't one piece. I'm assuming you'll be using 1/8 to 3/16 because of the size and application. As you have mentioned, back gouging to sound metal and welding is a good plan. Have you considered welding from one side with backing? Use a same thickness backing strip welded intermittently on one side of the joint. On the groove weld side use a 1/4" root opening with one side bevel prepped. Once completed and ground flush, this should be a sound weld and the backing should add rigidity and you can hide it under a cross brace. Just a thought. Either method you'll want fusion at the root. A small, infinitesimal lack of fusion can propogate into a crack especially on a cyclically loaded structure like a boat. I recommend a qualified welder although guys with an aluminum ticket are scarce. You could always have an inspection done to ensure no defects. Radiography likely. This would give you an opportunity to gouge out any defects and repair before it becomes a crack in a boat.
Good luck with the project!

Sent from my CLT-L04 using Tapatalk

 

[thill]

From what I remember of a friend extending a boat, the weld was put BETWEEN the strakes/supports and not right on a support that could act as a "hinge" that would promote cracking. I think it was a simple butt-weld, too, no lap or support. A weld in the middle of a panel just doesn't have much stress on it. His boat is still going strong, with no issues, as far as I know. He did it with a spool gun on a Mig/Argon setup, but he is a professional welder.

Also, if I remember correctly, he heated the metal up quite a bit before welding to help with annealing/thermo issues. Turned out great, of course.

That being said, do your own research, as my memory might be faulty.

 

[cyclops2]

I would just get a wide 16' long boat and cut it in the middle widest part. Add in 8' long sheets with simple creases done at a press shop. Then do 2 " over lapped welding seams . Piece of cake job then. No tricky hidden welds.
I have no Patent Rights to simple modifications.

 

[CarpCommander]

Pierce aluminum is where a lot of guys get long continuous sheets. It’s in LA. You can get the bottom, sides, and quite a bit of bracing for around $5k. Get creative on shipping options, or rent/borrow a trailer and take a road trip.

5052 is already butter soft, and is not heat treatable, so no worries about welding. As Bob mentioned, 5086 is probably a better option for the hull. I’d recommend NOT piecing together a 20+ foot hull, especially if you ‘could use more practice’ welding aluminum.

One option to consider is buying a bare hull from a commercial builder like SeaArk and building it how you like. That’s what I’ve done, and it’s honestly the best way to go ‘custom’ without doing a full ground-up project. Longer boats require very specific bracing, and if you’ve never built a complete hull, a 20+ footer is gonna be quite the project....

 

[beagle]

What about scabbing a lateral seam, basically a strap lap jointed on the inside of your butt joint?

 

[Driftless]

a top hat shaped rib weld on either side of a seam would certainly reduce the strain on it. The problem is if there is a problem with the weld it can only be repaired from the outside then.

I'd do some research on who around you would be using the lengths of aluminum you want. The manufacturers of aluminum would know who uses it as the ship it to them. The distributors also. Widen your search until you find it as there's not too many aluminum manufacturers.

For input to what you asked, my two cents.
You could put hat channels on both sides of the weld, then connect the tops of them to each other with a thicker piece of alum, welded to the channels. On the outside, weld an alum 'strap' bridging the joint, wider than the width of the hat channels.

As with any structural framing, avoid joints all in one spot from different planes. Stagger them.