Welding the skin to the frames demystified

[tazmann]

Originally Posted by Ad Hoc

3mm plate with frames/stringers at 6mm...if not done carefully the welder will just over cook it all too...he'll see 6mm, lots of 6mm in his mind....too much heat, too much weld bead etc too...

Yep aint that the truth and to complicate things more I am going to use galvanized material, LOL

[Brent Swain]

My last boat had a stern that was too wide and a bow too narrow. She was a bitch on the helm and hard to control downwind, despite a full length keel. For my current boat I widened the waterlines foreward by about three inches and fined down the stern lines by about three inches. The improvement was huge. Instead of fighting the helm she would self steer in a 15 knot quartering wind and I can leave the helm free for long periods without her wandering much , even under power. Harrison Butler had the same experience with his designs many times. This just doesn't happen with wide sterns and lean bows. Perhaps this explains why designers of such boats are so fond of hydraulic steering.
Brent

[Brent Swain]

Originally Posted by MikeJohns

Take a deep breath Brent and please stop driving off on enraged tangents.

Your 26 footer flimsy? please try and read the posts properly. Also anecdotal marketing doesn't prove anything, anecdotal tales can be very misleading.

Arguments such as the pressure vessel are not even remotely applicable and has nothing whatsoever to do with hull structure and global strength, you are quite confused here. Neither is your design remotely related to a gas bottle. If you really want a better analogy take a frameless hull and a framed hull and then apply a partial vaccuum (not pressure) and see how the shape collapses.

Of course panel shape has an influence, if you want to be more scientific just read some of the modern scantling rules eg 12215-5 which go into detail on just how much support you can count from the shape, but for the full effect you have to stop this shape collapsing which comes back to the elastic instability I was talking of earlier.

'My sailing hulls, with every part being curved, would fare far better in a partial vacuum than a framed boat with flat surfaces, especialy the conic bow and stern sections.
Brent

Originally Posted by Brent Swain

'My sailing hulls, with every part being curved, would fare far better in a partial vacuum than a framed boat with flat surfaces, especialy the conic bow and stern sections.
Brent

May I doubt that a bit?
Regards
Richard

[MikeJohns]

Originally Posted by Brent Swain

'My sailing hulls, with every part being curved, would fare far better in a partial vacuum than a framed boat with flat surfaces, especialy the conic bow and stern sections.
Brent

I doubt that too

If a plate collapses structurally through elastic instability due to an applied load( what we term buckling ) then you need to consider what happens next, because the load increases on adjacent structural elements. If this is adjacent unsupported plating already under the same load and close to failing itself then you start a chain reaction of localised stress that exceeds yield.

Framing limits the extent of buckling considerably as the load is transferred to the framing and in some collisions even a pair of transverse frames can be substantially bent, this also absorbs energy that would otherwise go into distorting more of the structure.

Here's an analogy;
A drink can collapses easily, but some transverse bulkheads in the can and it becomes much stronger.

Cheers

[drmiller100]

Why did they quit making cars with frames, and go to that new fangled unibody stuff???

[Ad Hoc]

weight and money

[welder/fitter]

Originally Posted by whoosh

thats ridiculous Mike, whoever heard of a beer can without stringers

LOL
Too funny, buddy, too funny!

[drmiller100]

Originally Posted by Ad Hoc

weight and money

Ok.

So it isn't that framed cars are "better" then unibody cars, they are just lighter and cheaper.

If they are lighter, wouldn't they be faster? Get better mileage? Have more cargo capacity? Stronger for a given weight?

This sounds much too radical to me. People have been making boats for thousands of years very successfully. It seems pretty radical to me to be now making them out of metal. It seems way too radical to take advantage of SHEETS of metal instead of cutting the sheets into board sizes so we can build boats the way we've been doing it for thousands of years.

[Ad Hoc]

Boats have been made out of metal for thousands of years. Only just over 150 years.

Lighter to add more luxuries such as a/c, GPS, tinny holders, and oh yeah, what is it now..er..um...good old safety issues too, such as side impact bags, air bags, etc etc..all add weight. Hence their need to reduce weight to try and maintain some kind of equilibrium.

As for better mileage, yup they sure are. But I've noticed you're in US. Not known for its fuel efficient cars!

[welder/fitter]

"So it isn't that framed cars are "better" then unibody cars, they are just lighter and cheaper."

I think that Ad Hoc was saying the opposite.

"If they are lighter, wouldn't they be faster? Get better mileage? Have more cargo capacity? Stronger for a given weight?"

No, No, No, yes. I have a fully framed '65 Plymouth in my shop, with a 426 Wedge, that will blow the doors off of a 'glass 'vette. I have a '59 Chev Apache w/235 inline 6 that gets better mileage than my 2002 Mazda v6. My Plymouth can carry more than a 'vette & my Apache can carry more than my Mazda. Yup, unibody stronger for a given weight, definitely. However, you're forgetting that there are other variables. Newer vehicles have internal, built-in, transverse roll cages.

"This sounds much too radical to me. People have been making boats for thousands of years very successfully. It seems pretty radical to me to be now making them out of metal. It seems way too radical to take advantage of SHEETS of metal instead of cutting the sheets into board sizes so we can build boats the way we've been doing it for thousands of years."

Facetious & of little value. A proper weld joining mild steel sheets or plates is 100% of the parent material. What's your point? Sounds more like you've got a stick up your ass. Either that, or Brent's moved to Idaho, which I highly doubt!

[MikeJohns]

Hello Stu,
....Beer can with bulkheads ...

DMiller

Originally Posted by drmiller100

Ok… So it isn't that framed cars are "better" then unibody cars, …….wouldn't they be faster? Get better mileage? Have more cargo capacity? Stronger for a given weight? ....It seems way too radical to take advantage of SHEETS of metal instead of cutting the sheets into board sizes so we can build boats the way we've been doing it for thousands of years..

What happens when you stretch that car into a truck or a bus? You quickly see the limits of this analogy. Also cars are meant to collapse in pre-determined ways and are then unusable, unsafe and are written off. I’m not at all sure this is remotely applicable to blue water - distance cruisers.

Look at the structure of an alloy aircraft, the skin is monocoque and carries significant stress but the frames hold it all in shape too.

If you want to get unconventional then look at something more ‘modern’ The pressure hull of a steel submarine is another good example of an optimized structure but it has substantial and closely spaced transverse framing. The German U-boats for example had close to 20mm thick 3m diameter pressure hulls ( a tube) and closely spaced ring frames 900mm apart to keep that hull from buckling. Nothing about convention here, just plain utility and maximum strength from the material used.

Sheet metal can be used to very good advantage and there are many chined boat designs too but that is not the issue, Brent was questioning transverse framing requirements. But that is wandering off the original topic too.

[drmiller100]

my point is cars are successful with unibody. Unibody is a designed structure that doesn't have a "frame", yet is very strong.

To suggest a boat must have a "frame" to be strong is an interesting proposition to me.

Further, it seems obvious to me a "unibody" boat makes sense.

The advantage of a "unibody" boat would probably only be that it would be lighter and cheaper for a given strength.

[drmiller100]

Originally Posted by MikeJohns

[color=black]
Sheet metal can be used to very good advantage and there are many chined boat designs too but that is not the issue, Brent was questioning transverse framing requirements. But that is wandering off the original topic too.

Let me try this another way. So what exactly does the transverse framing "do"????

Originally Posted by drmiller100

my point is cars are successful with unibody. Unibody is a designed structure that doesn't have a "frame", yet is very strong.
To suggest a boat must have a "frame" to be strong is an interesting proposition to me.
Further, it seems obvious to me a "unibody" boat makes sense.
The advantage of a "unibody" boat would probably only be that it would be lighter and cheaper for a given strength.

A car body is designed to collapse! If optimised, in a predictable manner. A car body is NOT free of transverse framing, it´s quite the opposite. Just open the hood and have a look how many parts there are to form a sort of integrated framing. (sorry cannot express that better).

Boats, as far as I know, are NOT designed to collapse on a collision, to protect the passengers.

The Picture in my post above shows a German SAR vessel hull structure. These vessels, worldwide famous for their outstanding ability, survive multiple capsizing in breaking groundwaves without any damage of the structure. Not only theoretically, unfortunately that happened in real life, with all souls lost. But the boat was soon on service again, after erecting a new mast.
http://www.dgzrs.de/
If this... see attachment... is daily routine, you do´nt play idiotic games with scantlings. Why should we cruisers do?


The origami method is valid.............

on Ponds...............period
Further Questions?

Regards
Richard