Welding a steel hull

It might pay you to read stuff a bit more carefully

I repeat

"However, because the stress levels generally remain in the elastic region, and because the loading is non-fatigue, the HAZ should not affect performance. "

In two syllable words it means - yes, the HAZ area is created by an arc strike, (which we can agree on) but it doesnt matter "because the loading is non-fatigue, the HAZ should not affect performance."

Once again - I still have no examples of it being a problem in your standard steel boat hull.

 

Please don't bring turbine manufacturers into it They even ask what type of marker pen you are using, as some of them have been proven to crack turbine blades, well thats what they say.

 

i didnt know boats spun at thousands of rpm

 

murdomack

OPPPSS, sorry. Just confuses the issue further for that that find it hard to follow IACS...doh!

 

rwatson, the reason that you will not find discussion on arc strikes on a 5mm plate is simple; this is considered a defect in the welding process, as is porosity, slag inclusion, lack of penetration/fusion, etc., and is not specific to a singular metal, thickness or weldment.

Now, I'm not saying that the type of material is not a consideration. arc strikes on more brittle metals/alloys than mild steel can be much more damaging.

The initial contention was that this - dragging rods across plates to burn down to flux coating - is not considered to be an acceptable welding practice. If you read the initial post, you will note that I listed many poor practices that Brent Swain promotes. If you are going to build, or are in the process of building, a steel boat, why not do so with quality in mind? Not only will you have more faith in the finished product's ability to serve it's purpose, you will have a boat that is easier to sell to someone who knows what they are looking at. Some suggest that these boats are over-built. Perhaps, but that doesn't excuse shoddy workmanship or gambling on "good enough" or "no big deal".

 

i have a 20v 130 amp 30% duty cycle mig welder with which i use flux core wire

i have a farm so that has been adequate for anything iv built

how good would it be for boat building?

 

Welds on stiffeners inside a boat are under compression, not tension, so it is, as I have pointed out , irrellevant to the welding of stringers inside. We are talking about a material which is 45,000 lbs yield strength for a boat which has traditionally survived when built of wood with a compression and tensile strength of 1500 psi. 3/16 plate has the same tensile strength as 7 1/2 inch douglas fir, and you say a slight loss of stength would make it too weak? Give your head a shake.
There were plenty of arc strikes on the first 36 I did, as the owner, who did all his own welding, was a first time welder, with no previous welding experience. Yet she survived 16 days pounding on a lee shore in 8 to 12 foot surf on the west coast of the Baja, without a single weld failure , then was pulled off thru a quarter mile of 8 ft surf, being lifted and dropped 8 ft on to hard packed sand every wave for 1/4 mile ,yet not a single weld failed. The same boat T boned a steel barge at hull speed and a log boom at 14 knots with no dammage. Can you imagine what that would have done to your Lloyds or otherwise approved fibreglass or wooden boat? Yet you say arc drags made her too weak? Give your head a shake! No, maybe not. Something may fall out.
What welders are trying to tellus is " Better fill my pockets for the welding job, as if you do it, it may be too weak." What self serving bull! Welders commonly try to put themselves on a pedestal by spouting this kind of crap. I don't do the welding on my boats . I show the owner how to do it and encourage them to do it. Despite their having done everything from circumnavigations, pounding across 300 yards of Fijian coral reef, a collision with a freighter in Gibralter, to a single season passage thru the NW pasage , none has suffered a single weld failure. And you say your "approved" fibreglass boat is stronger, because you have a piece of paper that says so? So lets have a demolition derby between your approved fibreglass boat and my unapproved steel boat. No takers? Shows how much confidence you have in your own bull.
These are small steel sailboats , grossly overstrength whatever you do, not marginally designed turbine blades, or bridges. Reminds me of the fisherman who told me " I used to weld caterpillar parts so I know all about steel boat building."
Duhh! Sound familiar?
Brent

 

"..Welds on stiffeners inside a boat are under compression, not tension,.."

Hmmm..let me see. So a stiffener that runs between frames on the hull bottom is being compressed, and never in tension.

Ok, lets look at this. A boat hits a wave, what happens to the hull plate, does that plate get 'pushed' into the hull or does the plate get 'pushed' out from the hull. Well, clearly only an uneducated person would say the hull plate is moving 'out of the hull', since that requires an internally applied force; the wave is an externally applied load/force, hence the plate moves 'into' the hull.

Ok..so plate moves into the hull, what is attached to the hull plate...ah yes,the stiffener. The frames are significantly stiffer than the stiffener, or longitudinal. So the stiffener moves into the hull as well. What happens next...well, the hull plate and stiffener is being force into the hull and since the frames, relatively speaking, do not move, the stiffener now takes up a slight curve between frames, ie deflection into the hull.

So, on the attachment of the stiffener to the hull plate, one can calculate the modulus and moment of inertia. There exists a location called the neutral axis. This is where no bending stress occurs. However below this axis, is where the lower part of stiffener is being pushed, so this is in compression, correct.

Err..what about what is above this neutral axis??..ah yes, good point!...well above this axis the stiffener is also being bent into a curve. But the top edge of the stiffener is being stretched it is being stretched beyond its normal static length, since the stiffener is bending....so what does this mean...it is in tension.

So, the lower part of the stiffener is in compression and the upper part is in tension.

See it is not rocket science, just requires less myopia. The same people that teach you quality, welding, fabrication are those same people that teach you how to analysis structures, fatigue analysis and more....funny that! But all these people that teach say the same thing..some people learn some do not...some people understand and comprehend, some do not. It is a funny world.

 

I don't recall anyone suggesting that an arc strike would cause a boat to sink. I am convinced that there are numerous defects in all of the boats Brent has built or, more correctly, helped tack together. To suggest, however, that someone follow such poor welding practices is irresponsible & shows a lack of knowledge in steelwork.

 

Not knowing your welding experience, forgive me if I comment on a few things you already know.

I'm guessing that you use self-shielding wire, based on the 20V limit. When using self-shielding wire, a seemingly decent bead can be swiss cheese inside, so finding the sweet spot when setting your machine is crucial. I think that you'd find that the speed would be slow, causing a lot of heat about the welded area. I also think that you'd find need for more juice & a higher duty cycle, especially for areas that use thicker plate. I should state, however, that the smallest wire welder I use is a 28v/250A @ 100%, so I really don't have much experience with the lighter welders, other than for auto body work, where I deal with 16-18 ga. sheet. Hope this helps.

 

i wasnt referring to my expertise as that would need to improve

so far i havnt had to worry about water leakage just getting it to hang together

i was curious about the machines ability to weld a boat, dosnt look promising without an upgrade

 

If you don't mind spending the money and have other opportunities to use one, I'd suggest something along the lines of the Miller or Lincoln models that run about 210A-215A. That leaves you the choice of GMAW or FCAW with
CO2 shielding. If you want to keep costs down, a stick welder will do.

I'd avoid self-shielding flux-core as it can be temperamental as hell. I've seen very experienced shipyard welders have all kinds of trouble with this, and wouldn't use it for below waterline welds, myself. With a wire welder, even though most of your welds are stitches, duty cycle is more important than with stick. I seem to recall that you are a tool & die man. if you work for a large company, you could probably buy your machine through the company & save some money that way. Just a thought.

 

im a farmer now

at the moment i do all my welding outside and though ive built some fancy machines such as the one that picks up stones off my horse training track , pretty wasnt what i was worried about, my philosophy is if you cant do it plenty good, do it good and plenty so far that has worked

 

This is the crux really, the engineers are concerned with best practice and many of these deficiencies are a problem in more highly stressed structures and plating. On a 36 foot boat the plating will be relatively immune since it's overly thick for other reasons.
However this would still be a concern on fittings such as chain plates and engine mounts and maybe the higher stressed sections of some framing in some designs.

Murielle posted before on bug strikes in her arc something I never considered before, that would be a big worry too, BAZ Bug Affected Zone.

 

Having worked many years as a brake press operator I could see how arc strikes would affect the strength of high tensile , not too ductile, steel . With AR or T1 plate, or some of the high tensile aluminium we bent for tank trucks, a scratch or a centrepunch mark on the outside of the bend would result in a crack. If the plate were bent in the wrong axis, it would crack.
However, with mild steel, it didn't matter how many cracks, arc strikes , or centre punch marks you put on the back of the bend , it would still take a 90 degree bend with no problems. If you bent it the wrong way, you could flatten it out and bend it the other way with no problems . Done that many times. With higher tensile or stainless , it would crack any time you straightened it out.
I've bent a lot of mild steel away from arc strikes and never saw it even begin to crack. One can see a clear example of this watching a glazier cut glass. A slight score down one side and a bit of pressure, and it will break cleanly on the score . Now go try this with poly propelene sheet. It doesn't work on more ductile material.
I doubt very much that turbine blades are made of common mild steel.
There is no comparing the properties of a ductile material like mild steel with those of high tensile steel. Different rules apply to different materials.
Go do a few arc drags over a piece of mild steel flatbar, put it in a vise and bend it back and forth until it breaks exactly on an arc strike, before you waste a lot of time worrying about them. It won't break exactly on an arc strike. In fact, you will find the arc strike ehas nothing to do with where it eventually breaks.
On Origami boats, the bows, and stern are a conic sections, one piece, with no welding or seams within 8 ft of either end.Each half the hull is made form a single 8 ft by 36 ft sheet of steel. Thus , any water pressure on them is pure compression. With no welds outside there is zero chance of arc drag there.
I find it hard to imagine that any one would believe that 3/16th plate with an arc drag would be weaker than the 1/8th plate commonly used on boats the same size, with no arc drag.
I find it equally hard to imagine that anyone would seriously believe that decks on a 36 footer which have the same tensile and compression strength as 5 inch douglass fir, are not strong enough.
I sailed a boat ,designed by someone who was consiered a top guru , tested in the top tank testing facility in the world , from BC to New Zealand singlehanded, and two years cruising around the South Pacific. The boat's design was an abortion. That blew any blind faith I may have had in gurus, and their infallibility.
Those who refuse to question, or think outside the box, have contributed nothing, and never will. If we had followed their ' Do it the proper way, the way it has always been done" we would have never made it out of the stone age.
Brent