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"Canuck57" wrote in message
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"Eisboch" wrote in message
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"Eisboch" wrote in message
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First, rivets are used on aircraft for the following reasons, not all
of value on a boat:

- low weight per attached foot of seam than welding
- cheap and manufacturing ease of use
- thermal expansion and flex
- can be drilled out for access/repair/inspection
- welding is more expensive per attached foot than rivets


Are other opinions welcome, yes.

I think aluminum welds are fine as long as they are reinforced or the
sheets are relatively thick. Thin sheet (seam) welding of aluminum is
prone to cracking when subjected to even a little flex as compared to
other metals. Maybe someone with knowledge of metallurgy can explain
the crystalline structure, etc. My opinion is based on experience in
industry.

BTW, I think flex is much more important in airplane wings than you
give it credit for. Next time you fly, note the location of a wing
tip as the airplane begins it's take-off run and watch it as you
become airborne. While flying in turbulence, watch the tip of the wing
again. There's quite a bit of wobbling around going on out there.
Welded aluminum panels wouldn't last long, nor would the wings if they
were designed to be stiff rather than being allowed to flex.

Eisboch

But my point being, do you want that much flex on a 17-19' boat?

I would think not. But on an aircraft, this is good. The wings are in
effect shock absorbers for up/down drafts and air density changes. But
I don't think this level of flex is needed nor desirable on a small
boat.


The wings of an aircraft are *not* designed to be shock absorbers. They
may be, by default of their ability to bend without breaking, but that's
not the design purpose. The design purpose is to allow them to bend and
flex (which they are going to do, welded or riveted) without breaking
off. Rivets allow the bending and flexing without exceeding the yield of
the aluminum. Welding would make them so stiff that they would snap near
the welds.

But, that's not the issue. It's the fact that even a small, thin
skinned aluminum boat *will* want to flex. If it can't (because the
seams are welded) it's likely that one or more of the relatively weak
welds will break whereas a riveted construction allows the bending or
flex without damage.

Even large, welded steel ships have expansion joints built into the hull
structure to allow for flexing, otherwise it would crack in half in
rough seas.

Eisboch

While I don't profess to be an aircraft engineer, I done believe the
sales hype about boats are better because we build then like aircraft.
The needs of the two are different. Even the rivets are different.

You mean like Edmund Fitzgerald? Me, I don't plan on being in anything
remotely as hazardous as Lake Superior and have no intention of amidships
being over a 35' wave. Michigan, no problem. Koocanusa, Lake of the
Woods, Rainy River, nice. But I just have a thing about Superior...used
to live by that lake and I would sooner hit the Pacific.

But how much does a 17-20' boat need to flex? If we look at fibreglass
in this size, not much hull flex at all.


For some boats, the rigors of trailering on awful roads might be worse
than the pounding they get in the water.

Good point. The amount of support on some trailers looks kind of pretty
small in the square foots department. At least in the water it is
distributed over a much larger area. And Canadian roads... 'nuf said.