Welding the skin to the frames demystified

[Brent Swain]

Originally Posted by whoosh

as usual I have great respect for what Mike says, but really this is all a bit strange, small steel boats do not break, well unless they are so poorly built, like ICEBIRD, Lewis boat that split her coamings in the Antartic there are simply squillions of small(under 60ft) that are amatuer built and welded, that have survived for years and years
honest Injun pro boatbuilders rarely even think too much abt engineering equations, we just do it♠
Myself, I build transverse as you know, I fully weld floors forewards, lightly, acontinuous small weld is better than a triple pass staggered or chain
As I work aft and up the topsides I lighten up, same as the pl lightens up

steel requires more care as it pulls far more so leg and throat size do make a difference,
By the way I am ticketed
on fast powerboats this cont welding is a must forewards
groundings dont break welds fatigue does
it is interesting that the Euros have never taken to stringers, and I go along with them, , water traps,
A skilled builder wont get a hungry horse, and all first class metal boats need some filler
i maintain, and I am entitled to, given the VERY strong opinions here, that people build that way because they have neither the skill or patience to do otherwise.
Sorry if that offends but so be it
Mr Swain, I notice you take the Caveman hollow log principal, take some plate, weld it up, bung in some frames and what you see is what you get
But boatbuilding is not like that, its an exact art, in metal, requiring skill patience, feeling,
now prey why are there no examples of your work in the gallery?

There is no harm in closer stringers as they do far more work structuraly than transverse frames, and drasticaly reduce the chance of distortion, while transverse frames add to distortion and hungry horse looks.
3mm decks are more work, and not neccesarily much weight saving over heavier deck plating and less framing? Absolutley true. Applys to hulls as well. That is exactly the principle I use in origami frameless boatbuilding. I have seen 30 footers with 3,000 lbs of framing and ten guage plate, the same weight as 3/8th plate and no framing. Which would be more resistant to holing? Corrosion? Easier to build?
All steel boats need filler? Bullshit! None of mine have needed any and most are as fair as any fibreglass boat. That is the price of such foolishness as totally redundant transverse framing on small boats.
Do more stringer welds make a boat stronger. Once the stringer welds are strong enough to enable you to totally mangle the plate without the stringer separating from the plate, ( as strong as the cross section of the stringer) more weld is a waste of time and money.
None of the engine beds on any of my boats has broken. Out of roughly 200 , only one had paint failure from movement at the ends of one transeverse web. It was extended a few inches and there has been no problem since. It's just a matter of extending them wide enough.
If you are installing a ten hp engine, make the beds strong enough for 150 hp, and the engine will be that much quieter.
It's interesting that anyone would compare origami boatbuilding methods to caveman boatbuilding, while clinging dogmatically to methods of boatbuilding originally devised to build boats out of a stone age material like wood( Dead vegitation) . If we had listened to them we would still be in the stone age. Nothing more primitive than taking a modern material like mild steel and treating it as if it were a stone age material like wood, and throwing away the many advantages and options we have in it's use, just for dogma's sake. It reminds me of the conservative thinker who told me " Invention is dead. There is nothing left to invent anymore. Everything there is to invent has already been invented. " That was in the sixties. That comment has been made for centuries, and each time it was accompanied with " Yeah, but this time is different . This time everything really has already been invented."
A wooden boatbuilder once asked me " Why does everyone always want to re-invent boatbuilding . He had just spent a year setting uo frames , and was ready to plank. A couple of days later I had just pulled together my first origami hull, in two days. I did the entire 26 ft hull, decks , keels , skeg ,cockpit and rudder , handrails, engine mounts, lifelines, hatches, pulpit, pushpit, and bow roller in 21 days. Then I asked him
"Well , have you now figured out why we want to reinvent boatbuilding?"
Boats are far more expensive , and time consuming than they need to be, and exclude far too many people from their cruising dreams (Unless you are an elitist who believe only the rich should be allowed to cruise , something I reject) Steel allows us to drastically simplify boatbuilding and produce better boats as well, boats that don't need fillers to make up for outdated building methods and outdated attitudes to new advancements . Critics of origami boatbuilding simply are unable to grasp the geometric principles involved. They are in effect saying the equivalent of " I don' t understand Chinese therefore chinese is uncomprehensible and is thus not a language."
If we let those who are incapable of undertanding geometric principles set the pace , progress will be held back to the comprehension level of the slowest student, to the great detriment of the progress of metal boatbuilding.
Given the huge addition to structural stiffeness given by shape, any calculations which don't take shape into account are grossly inaccurate. An example of this would be calculations that treat the sides of a sailing hull as if they were flat surfaces. It's been said that shape has only a minor effect on structural stiffness.Bullshit!
One way to test this out is to weld up a square propane bottle then hook it up to a water tap , with a pressure guage on it,and turn the tap on gradually to see how much pressure it takes to blow it. As propane bottles are 16 guage plate, use 16 guage for your square propane bottle. After blowing it, put your pressure guage on a full propane bottle that has been left out in the sun, and see what it reads. Then double that number for the safety factor. You'll find the square one takes a tiny fraction the pressure of the round propane bottle to blow it. So what keeps the propane bottle in shape and prevents it from blowing? Framing on the bottle? Show me some. No, shape is the huge difference.
The same is true of the difference between conic ends and chined ends, or cylindrical shapes on a sailing hull and the flat surfaces of a powerboat hull. The same rules don't apply to both.
Limber holes in stringers, while very important on un foamed steel, become irelevant once a boat is sprayfoamed.
There is nothing wrong with welding longitudinals to transverse frames, just don't do it before all the rest of the welding is done, and all the resulting shrinkage is finished, or you will get distortion and the "Hungry Horse" look.
Brent

[Ad Hoc]

Brent
Interesting post

You said "...There is nothing wrong with welding longitudinals to transverse frames, just don't do it before all the rest of the welding is done.."

Long.t's are or should be, always the first welded joint, ie to the frames, via their shear tab connection. The sequence in which you weld the long.t to the plate affects the look and distortion, as well as the heat input, weld length and and throat size.

But hey, more than one way to skin a cat...

[plebusmaximus]

Are we talking aluminium or steel here?

Stitch hull, frames, stringers 20mm stitch

5mm bottom reduces distortion. Its all in the skill of the welder that deletes the need for any bog.

The architect who designed the hull should be able to tell you what should be done according to their design.

[plebusmaximus]

A naked hull shows no mercy

[Brent Swain]

Most hungry horse problems come from welding the longitudinals and frames to the hull plate , before welding the long chine and deck welds , shrinking the edges of the plate in the proccess. Shrink the edges without the plate being attached to the frames or longitudinals and the shrinkage gives you a smooth outward compound curve in the plates. Shrink the edges withthe plate attatched to the frames and it can't do that , so you get hungry horse bumps and hollows between the frames. Do it without logitudinals and you have a disaster. I've seen some real disasters done that way.
Such mistakes are why some are misled to believe that all steel boats need fillers. Do it properly and you don't need fillers.

[Ad Hoc]

Exactly.
All shell plating must be fully welded prior to welding the frames and long.ts to the shell.

[whoosh]

Originally Posted by Ad Hoc

Exactly.
All shell plating must be fully welded prior to welding the frames and long.ts to the shell.

This man has not a clue, he has nothing on his profile, will not tell us who who works for, or his exp, which quite obviously is none I have asked him in other threads
he makes the most randon, and incorrect statement, has no gallery and generally novices should not listen to one word, it will certainly make them do all thing the wrong way
there is no totally (correct way) but this guy has not posted one true thing
some of my early trailer boats, the trailers are 6061 t6, 130x75x6 box I gave 5 years warranty on both, all these boats are 15 years old
There was no filler used on the painted one, the joggle in the plate was from a machine i made, frames were 90x35x6 t, at 1200 with 4 full length girders through bottom and floors at 600 up to girder tops, they all have fine entRy to fish offshore in NZ The whote one 4cyl volvo, the other2 6 cyl diesels all, walk around the eng on white boat, they do a lot stand up gamefishing

[M&M Ovenden]

Originally Posted by whoosh

When you have non floating frames(and I never heard this term before now) and the frame is a close fit, you can use a piece of mig wire, jam it UNDER The frame and then when you stitch the weld will not pull the plate over the frame,
make up a weld stick, and mark off your weld space and then use that stick template everywhere Tidy welding is a plus,
welding has nothing to do with hull stiffness, ( soory if others replied that)
adn if all gets too much then here is something for you'
* 4 tablespoons Dijon or spicy deli-style mustard
* 6 cloves garlic, crushed
* 6 tablespoons extra virgin olive oil
* 4 tablespoons fresh lemon juice
* 1 1 / 2 teaspoons ground black pepper
* 1 / 2 teaspoon salt
* cayenne pepper to taste
a great salad dressing
good luck

Whooshy boy,

It's unfortunate that today's communications are such that I can't respond as I would of if you had insulted me in person. Let me just tell you that my response would of not come flat handed but rather with bare knuckles. Note that even though I am loosing my political correctness the time of a post, I have the guts to do it signing my real name.

Now excuse me, I have to get back to the kitchen...because yes, I do enjoy my kitchen time once I'm done in the shop.

Murielle Ovenden

[whoosh]

we have a misunderstanding, I thought Murielle was a lady and the recipe was a smile thingie
WE have sorted things out privately, and we are sharing salads

[M&M Ovenden]

Fortunately, a misunderstanding over the web delays consequences of some peoples temper, in occurrence, me this time. Some explanations and apologies later, Stu and I are friends again. My apologies for my rather strong temperament.

[Dudley Dix]

Mike, in response to your post of 01-21-09.

The rules are based on a number of assumptions and even observations of other vessels that did indeed break. You don’t need your own design to break to prove the design is inadequate you can extrapolate this from some-one else’s prolonged heavy weather experience and learn from the damage.

Yacht design and scantling rules have the same origins, they have developed empirically over a long period, with the same objective. That is to build boats that will not break.

The rules used by the inspection societies have their roots in the yacht design scantling rules. They did not start from scratch with the intention of writing a new scantling rule, they borrowed from what was historically successful.

If the topsides are overly weak for docking and bend easily it’s an insurance claim and the dent is fixed. I think designers very seldom get sufficient feedback or are sufficiently objective to qualify this themselves.

The commercial field is a very good indicator of the strengths and weaknesses of design and building practices for commercial craft. Deficiencies in construction quickly become apparent through the mandatory scantling societies inspection process. The rules are altered if failures occur and of course every design has an unblemished record up until the first failure.

Pleasure craft are handled and maintained differently by their owners and are built to slightly different standards as a result. There is no need for a pleasure yacht to be built to the same standard as a commercial boat that is going to do very different service. I don't see many owners driving their boats into docks and marinas but when they do the boats still seem to come through virtually unscathed. My car is not built to stay unbent when I bump into something but somehow my boat does withstand it. If it does bend when I bump a dock too hard, why should that count as a structural failure? That falls into the category of operator error.

When a boat has sailed around the world and continues to sail without any apparent signs of stress, surely it must have proven something. By your reasoning it may have broken and we just don't know that it has broken.

The preferred design process now amongst engineers is to design to the applied loads rather than follow a suggested minimum framing requirement. FEA analysis has radically simplified the design process for grillage based structural design. Scantling societies also accept this type of analysis when vetting a submitted design.

As I said in my original post, boat structures are not as easily put through this process as a static building. In the end the result is basically the same, the structure needs to pass the standards of the inspection societies. Whether that structure was designed by FEA or using the scantling rules the final test is passing the scrutiny. Some of my metal boats that were designed using ABS as the basis have been through scrutiny, mostly without change. The scantling rules provide only a reference point for designing the scantlings, they don't design the structure. From there the detailing provides the rest of the story to produce a strong boat.

The way that I use the ABS rule is to calculate minimums in various parts of the boat to find the worst case situation. That information forms the basis from which I design the structure. From there, most of the structure ends up somewhat over-strength because it is impractical to change framing sizes and spacings to suit moderate reductions in loadings elsewhere in the structure. Higher loads are carried by local increases in scantlings where needed.

My opinion would be that with experience you use it as a steel design guide but preferably have an engineer check the design assumptions since the society will not.

I once had a client ask me to design a rig for his boat. It was a rig concept that was covered by international patents, so I refused unless the client bought rights to use the design. He went to an engineer, who designed the rig for him. When it was stepped on the boat he asked me to look at it and comment. I did not need to do any calculations, I told him that it was going to fall down. That is what it did, in the middle of the Atlantic.

I knew that it would fall down because of my experience with sailboat rigs. The engineer knew that it would not fall down because of his experience of structures.

I did 3 years of structural engineering courses at university in my training before I studied yacht design. I am not an engineer. However, I know that I would rather design a boat structure that is based on centuries of history rather than ask a structural engineer to do it for me. If he was a structural engineer and a boat designer then he would be qualified to do it.

In South Africa my neighbour was a naval architect, with his experience all in commercial craft. He could design an excellent tug or service vessel but would not be able to design a successful sailboat. To him, brute strength is everything, even if it is more than needed by that boat. In sailboat design we look for maximum efficiency in the structure, so that there is minimal wasted material draining power.

I am not knocking engineers. All that I say is that an engineer does not always reach the correct answer or conclusion. He must have experience in the right field.

The Volvo Race is being sailed right now, in the fastest monohull sailboats of their size that have ever been built. I am sure that all have been designed with the highest level of technical input available, beyond the reach of most designers and owners. Yet, these boats are breaking.

The problem comes back to what I said in an earlier post. Racing crews no longer sail within the limits of the boat. They just sail as fast as they can, no-matter what the weather and sea conditions. If the boats get broken then the next generation is built stronger based on the data of the previous generation. The result will be boats that are pushed even harder until they also break. So the cycle starts again.

The boats that most of us are designing are for cruising. They have to be strong but they will never be pushed to their limits in the same way as modern racers.

[Brent Swain]

Originally Posted by Ad Hoc

Exactly.
All shell plating must be fully welded prior to welding the frames and long.ts to the shell.

Absolutely true, when it comes to frames, less true when it comes to logitudinals. John Dearborn, who builds fine round bilged aluminium boats in Gibson's BC, said that even if a frame touches an aluminium skin, without welding it in , you can still see it on the outside of the plating. The wire trick sounds like a good one.
Woosh, don't look a gift salad recipe in the mouth. You sound like you need it.
Brent

[Ad Hoc]

Brent
"..Absolutely true, when it comes to frames, less true when it comes to logitudinals..."

Once all the shrinkage and distortion has taken place in the shell alone, unstressed by any attachments such as frames and longts. The long.ts should be the last structural member welded to shell plate. In the correct sequence too, not just from aft to fwd or vice versa!

Dudley Dix

Well said. Far too many "engineers" who are not naval architects. Not saying they cant do the job, but they need some 'marine experience' to qualify their statements.
I took over a job for a client who used an engineering consultancy to sort out a structural problem with LR. It went on and on, endless FEAs, arguments about the mesh size, continuity, extent of the foam core and on it when. My client asked me to assist. I read the replies from LR, the original request, looked at the FEA reports and their replies. I looked at the structural dwgs. I then called LR explain that their request already existed, the surveyor couldn't or didn't read the dwg correctly. One phone call and 2 hours of reading the emails sorted it out. The engineering consultancy charged nearly $20,000 and got nowhere!
Experience in design, in the marine field is essential. FEA is just a tool...rather like giving a welder a saw and saying weld that...wrong tools for the job. Only experience tells you that...as well as a modicum of common sense!

[Ilan Voyager]

All depends on the background and formation of the engineer.

To use the services of a structural engineer that have background only in civil engineering for a boat structure is pointless. He has no idea how a boat works, and worst he has no feeling or instinct on this subject, things you acquire by experience and formation.

The thing gets worst with "exotic" materials as composites and sandwiches which are unknown by the common engineer outside boatbuilding and aviation (and some other very small fields). I have worked for NA on structural design but I'm a naval engineer -ie ship design engineer- so I have some knowledge of the field. I wouldn't have worked in a field outside my knowledge and experience.

For small boats specially yachts, unless you're in racing and building with very innovative materials and designs, rules like ABS, DNV and others plus the sum of the accumulated experience is enough to get a safe and good structure at good weight. I do not see the necessity of hours of FEA, or calculations which are mental masturbation if you do not have a solid database obtained by a costly campaign of measures. That has been done rather extensively by major Navies and some civilian institutes for shipbuilding. These database are not public, and are practically useless on small boats.

At my knowledge such database are nonexistent or very small in yacht design; the CRAIN in France did a campaign of simplified measures that has given nothing truly interesting.

I've bought the Gerr book on boat strength and I think that this book is largely enough to design the structure of a small boat in "ordinary" materials. Maybe a bit conservative sometimes, but it's not a bad thing. Better to stay in the strong side (without exaggeration) in cruising boats. So, as engineer, I do not see the need of spending money and time in "masturbation" engineering for deceiving results in this field.

[welder/fitter]

Boy, I've sure been enjoying this discussion.

Wynand, others:
a couple of questions:

1. Do you round the outboard edges of your frames & longs?
2. What is the minimum overlap that you allow between your longs & frames?

Last year, at about this time, I was trying to resurrect a nightmare of a Roberts345 - Brent knows the boat(xWandling) - for the new owner. I wish I still had my pictures, as this was truly a sight to behold. longt.s like over-cooked spaghetti, only enough overlap between stringers & frames to allow for tacks, and a stbd. bow only a mother could love. Deck plates that looked like a breaking surf, the list went on & on. When replacing the longs & frames - frames were crooked & inconsistent in midships area - I rounded all outboard edges & allowed only enough gap between longs & plate to allow the tacks to be the interface between them, let's say about 1 to 2mm. welding strongbacks from frame to frame allowed me to wedge out the plate in places to a more uniform shape. Due to the time/costs overun on a ferry that was being built, I had to switch from the drydock to the shipyard to push 7-12s, meaning no time for this side project. Hopefully, the owner continued in the same vein & all works out well for him. Can a boat be over-welded? Structurally; no, cosmetically; you bet.

It sure is easier to build from scratch, than to try and repair a project gone wrong.
Mike