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Hey everyone,

I was wondering if anyone know's if a Tubby Tug has ever been built in aluminum? I'm curious if it's even possible. I wonder how the plans would have to be altered to accomplish this. Also, what type of alumimum should be used for freshwater applications and what gauge. Any thoughts would be greatly appreciated. Hope everyone enjoys the new year!

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If the women don't find you handsome, they better find you handy....

There is a company that builds something similar. I have no idea if the extra 5 feet of length on this boat makes it doable in aluminum, or if that is not a factor at all.

wingnut2840,
At the risk of learning more about plywood than I really want to know, you might say that any boat that could be built in plywood COULD be built in sheet aluminum. If the shape required lots of planks and edge joints that could be cold glued in plywood but would have to be welded; then my rule of thumb is probably 'true' while being impracticable. Many full length weld seams between 'planks' designed for a wooden boat, that were built in thin aluminum, would invite excessive distortion and cancel some of the material's benefits to the small boat builder.

I'm mainly talking about the type of design shown the Dai-San's image of the Berkley Engineering tug built of welded aluminum. [which should be cleaned soon or it will begin to pit!] Those designs with large panels keel to chine and chine to sheer that are designed for ply CAN be built in aluminum.

With that said, I'm only dealing with the possibility not the desirability of such a design change.

5052 alloy is completely adequate for fresh water BUTTTTT!!!! thickness is another entire discussion that I'll try to make as short as I can without leaving out the main problems.

The largest problem with thin [below 0.125" or 1/8"] metal welded aluminum is; aluminum MIG welds are not evenly proportional to the metal thickness. MIG wire is fed through a hollow copper tip with welding voltage and current connected to the copper tip. The filler/feed wire becomes 'hot' and an arc is established just beyond the tip fed by the continuous stream of wire that becomes molten in the arc and melts the parent metal. The molten droplets of feed/filler wire pool under an argon gas covered puddle and help melt the metal being welded [parent] and when the whole show cools- the metal is fused.

This is called a related rate, where the rate of wire being fed into the arc through the tip has to balance the amount of voltage so the arc doesn't melt the copper tip AND the welder must move this tiny hot spray of metal along the weld seam at a different rate for different thicknesses of metal combined with the right wire speed, voltage, gas coverage for any given THICKNESS of parent metal. Someone balancing all these rates is an aluminum MIG welder, learning to recognize the balance of all these related rates takes time and practice.

Thicker metal allows more heat to be added so more molten wire at a slower travel can be cooled by the heavier metal before the entire weld area drops on the floor. Slower travel speeds are significantly easier for our nervous systems to do. Thinner metal requires smaller diameter filler, at higher speeds to make a weld that is closer to proportional to the parent metal.

It is "ten times" easier to weld 3/16" [0.187"] metal with 0.035" diameter wire than it is to weld 0.080" thick metal with 0.030" wire. The difficulty comes from the amount of time the puddle can be applied to any given length of weld. If you used the same travel speed to weld the thinner example as you do for the thicker one: the puddle will melt the parent metal and splash on the floor - there will be a hole not a weld bead.

Now comes the problem. Because of the nature of the wire limits to MIG you would need a wire much too thin to feed in a mechanical/electric MIG torch [wire feeder] to make a 'proportional' weld. The second reason this is such a problem is that welding power supplies are not designed or built to provide full weld control at the very very very low voltages and amperage levels needed to burn the wire you cannot buy!

Last but not least is the lack of proportionality of the voltage needed to arc/burn/vaporize the feed or filler wire. The amount of energy needed to start and hold and arc are not proportional to the cross section of the wire- even small wires need more weld heat than very thin metal can cool fast enough to weld slowly.

The obvious idea of 'just turn the machine down' to adjust for thin metal is not [very] applicable below 0.125" metal. Below that thickness you'll pretty much have to add high travel speed to get minimum sized wires (0.025" or 0.030") to weld at minimum power supply settings and it will still be 'too hot' for 0.080", 0.060" and 0.040" sheet aluminum.

To [hopefully] summarize all this; since thin metals require high travel speeds coupled with very exact system settings - the welding dexterity is much higher than thicker materials where the heat dissipation of the energy needed to fuse the metal can be applied more slowly and still remain a weld bead. Because the skills required are much more practiced, thinner aluminum is much harder than thicker aluminum to build for the less experienced welder.

These thin materials are all commonly riveted for the reasons I hope to have helped you understand, if you didn't already?

You could built a boat this small of 0.080" and 0.100" but I would recommend you stay with 0.125" for the hull plates/panels in order to provide a welding environment that was more controllable.

Cheers,

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Kevin Morin

Kevin; Always look forward to your input on the forum.....and as usual your response is excellent. Well thought out and informative.
Thanks, Doug

Building (slowly) a Titan ...out of plywood

That small tug was built by Dearden marine in Canada.

Totally (well sorta ) unrelated, but I live near Cobourg Ontario on Lake Ontario, and often visit the marine there. This summer there was an aluminum boat at the dock. Turns out it was a Union Jack built 12 years ago by Connor Marine/Stanley Marine in Parry Sound On. It looked brand new! They build some beautifull aluminum boats there, and are the preferred boat for Georgian Bay.
Doug