Origami steel yacht construction

Keep in mind that I'm NOT an engineer. I used to be a marine population ecologist which means I knew quite a bit of statistics then I moved into software development and this led me into designing/writing data logging systems and data analysis and eventually management of a marine R&D group. I don't have the training or the math that an engineer has.

Anyway. A ship mast is moving in 3 dimensions and the amount & direction of any loads are constantly changing. Those loads are transferred from the mast into the hull. Sometimes through the hull as David Lewis found out.

Next thing I keep in mind is, EVERYTHING flexes with varying load. If might flex much, you might not see it, but it flexes. I had a sheave block with strain gauge on a 1/4" wire at one time because we had $300K in equipment on the end of the wire and needed to know how close we were coming to the wire's breaking strain. This was a diminishing returns problem because we were deploying equipment in over 5000m of water. The wire loads varied from the static weight of the package up to 5 TIMES the static weight depending on depth, drag, heave & pitch. This stuff gets complex and without numbers you're just guessing.

Next stiffness increases far more rapidly with section depth than it does with thickness. A piece of 65x6 flat bar is easily bent if it's laid flat between 2 objects. Turn it on its edge and its resistance to bending increases a lot. Ask the engineers for the formula I just look up a book or rely on a designer. Now a flat bar on edge is unstable; once it goes out of vertical it keeps right on going until it's flat, bent or broken. If you weld that flat bar to another flat bar to form a T section or H section, you get resistance to bending and better stability when side loads are applied.

Now we've got a flat bar frame welded to the hull plate. The bar resists bending, the hull plate keeps the bar vertical, both work better to keep shape and resist deformation than either by themselves.

Getting back to the pipe mast support in Brent's design, it's only supported by the hull plate with a local increase in thickness via a doubler plate. If you took that same doubler plate and welded it on top of a frame/longitudinal cross then you're transferring the load to a hell of a lot more area than otherwise. I wouldn't do that because getting underneath it for maintenance would be difficult, I'd raise it up on a bracket that allowed a paint brush and a wire brush to get in there. Or you could weld the doubler to the hull plate then relieve the flat bar where it crossed the doubler for a neat fit, slit the pipe vertically and fit it over the frame etc. Lots of ways to skin a cat.

My understanding of the mast structure and its loads is, the shroud plates & shrouds are under tension, the mast is under compression, the ring of steel immediately under the mast (on a hull skin) is under compression and the hull skin itself around the mast (or doubler, just a bigger mast section in effect) is under shear. You have to design for the WEAKEST one to be adequate which is why saying that X is Y and therefore its tensile strength is Z is totally pointless. It may be true, but that doesn't make it relevant.

Thing to keep in mind is, whatever you put on a boat is going to move whether you can see that movement or not. If it moves enough to reach the material's fatigue limit, it's going to tear or break. If it's a poorly designed joint you're allowing it to move more than otherwise is possible. Add to that a less than perfect weld with hidden flaws that you might have gotten away with and - how's your insurance???

I chose not to build out of aluminium because it's a lot more notch sensitive, less abrasion resistant, has a lower fatigue limit and reaches its plastic limit on deformation (ie it stretches less before it tears) a lot quicker than steel.

Got to get back to welding now, lunch break is over.

PDW

 

[

Next thing I keep in mind is, EVERYTHING flexes with varying load. If might flex much, you might not see it, but it flexes. I had a sheave block with strain gauge on a 1/4" wire at one time because we had $300K in equipment on the end of the wire and needed to know how close we were coming to the wire's breaking strain. This was a diminishing returns problem because we were deploying equipment in over 5000m of water. The wire loads varied from the static weight of the package up to 5 TIMES the static weight depending on depth, drag, heave & pitch. This stuff gets complex and without numbers you're just guessing.

At any rate, they don't ever exceed the breaking loads of the shrouds, or they simply break, which is far below the breaking strength of the support

Next stiffness increases far more rapidly with section depth than it does with thickness. A piece of 65x6 flat bar is easily bent if it's laid flat between 2 objects. Turn it on its edge and its resistance to bending increases a lot. Ask the engineers for the formula I just look up a book or rely on a designer. Now a flat bar on edge is unstable; once it goes out of vertical it keeps right on going until it's flat, bent or broken. If you weld that flat bar to another flat bar to form a T section or H section, you get resistance to bending and better stability when side loads are applied.

That is why I went from flat bar to angle. The greater the distance between supports, the greater the likelihood of them bending. Thus, going from chine to tank edge is a far shorter distance than from chine to centreline , and the tanktop edge is stronger than the centreline.

Now we've got a flat bar frame welded to the hull plate. The bar resists bending, the hull plate keeps the bar vertical, both work better to keep shape and resist deformation than either by themselves.

Getting back to the pipe mast support in Brent's design, it's only supported by the hull plate with a local increase in thickness via a doubler plate. If you took that same doubler plate and welded it on top of a frame/longitudinal cross then you're transferring the load to a hell of a lot more area than otherwise. I wouldn't do that because getting underneath it for maintenance would be difficult, I'd raise it up on a bracket that allowed a paint brush and a wire brush to get in there. Or you could weld the doubler to the hull plate then relieve the flat bar where it crossed the doubler for a neat fit, slit the pipe vertically and fit it over the frame etc. Lots of ways to skin a cat.

You have a huge longitudinal supporting it, the topsides plate.

My understanding of the mast structure and its loads is, the shroud plates & shrouds are under tension, the mast is under compression, the ring of steel immediately under the mast (on a hull skin) is under compression and the hull skin itself around the mast (or doubler, just a bigger mast section in effect) is under shear. You have to design for the WEAKEST one to be adequate which is why saying that X is Y and therefore its tensile strength is Z is totally pointless. It may be true, but that doesn't make it relevant.

The weakest ones are the shrouds, far weaker than the mast support I use.

Thing to keep in mind is, whatever you put on a boat is going to move whether you can see that movement or not. If it moves enough to reach the material's fatigue limit, it's going to tear or break. If it's a poorly designed joint you're allowing it to move more than otherwise is possible. Add to that a less than perfect weld with hidden flaws that you might have gotten away with and - how's your insurance???

The huge angle that is the combination of topside and bottom plate, at the chine, doesn't move measurably, far less than the fatigue limit. In fact, nowhere near the fatigue limit.

I chose not to build out of aluminium because it's a lot more notch sensitive, less abrasion resistant, has a lower fatigue limit and reaches its plastic limit on deformation (ie it stretches less before it tears) a lot quicker than steel.

Got to get back to welding now, lunch break is over.

The weakest point is still the windward shrouds along with forstay and back stay. That is far below the yield point or fatigue limit of the two mast support pipe, or their connection point at the chines.. The yield is still 75% of the tensile strength, which puts it many times the strength of any weight which could possibly be put on it, before the rigging breaks.The support pipes are on the chine, which flexes a lot less than simple hull plate. Being two chines instead of one centreline, doubles the resistance to flexing.
Any welds there are under compression, and not likely to squish out of the way.

/4

 

The design I'm building which Brent derides has this load fed directly to the keel which is a 7.6m length of 200x40 flat bar welded to 6mm deadwood plates forming a hollow box.

I don't deride the structural strength of what you have at all., supporting the mast by putting it on the keel, the sides of which are steel bulkheads on egde, their tops prevented forom going anywhere by their attchment to the hull plate and the bottoms prevented from going anywhere by their attachement to the bottom plate . It is one of the strongest methods there is. With the mast supported by the chines, the hull plates become the bulkheads on edge , supported on the top by the decks and on the bottom by the bottom plate, along with their fore and aft curves. It is the same thing , structurally. The difference is the support pipes are far shorter, and you don't have to plan your interior around the mast suport.
With the cramped interior of the saugeen witcch , you ned to do everythign possible to increase interior space and eliminating the mast support going right thru the middle of it would be a huge improvement, especially when it can be done with no loss of strength..
Even when people plan to put a bulkhead there, I prefer to leave them option of other layouts, should they change their interior in the future.
Sheer strength depends on what is doing the sheering. Its much harder to cut anythign with dull scissors than with sharp scissors.
The resistance to sheering depends on how sharp and how hard the blade doing the sheering. The end of two inch pipes, with a well radiused weld on the ends, is not excactly the same as the hardened ,sharp edges of a plate shear.


How would you do it with a fin keel with no keel under the mast?

 

. They could simply be cleaned with a twisted wire wheel prior to welding. By the same token, since we're talking about 3/16" plate here, gouging the seam with a 1/8" disc (your recommendation) isn't going to clean out all the slag, especially on the more acute angle joints like the bow.

A twisted wire wheel will do absolutely nothing to a freshly cut edge, but bounce off. It won't even begin to move slag.
The 1/8th wheel grinds her out well, anything thicker wont get right in, and will leave too big a V to fill.


Nevermind the poor fitup because of high and low spots on the unground edges and slag holding the joint apart like here.

It's only slag holdijng it apart. A whack with the sledge hammer will pull the seam tight, every time. You can grind the slag of after the plate is trimed flush and ground
I find that using a heavy piece of half inch plate with a sheerd edge removes slag far beter and quicker than any grinder

Gives good full penetration to the inside uphand weld. Then I trim the outside flush, grind it flush, goudge out the seam and only then do an uphand weld.


Besides that, you can't possibly maintain that it's easier to to grind seams overhead fighting gravity than grinding on the flat. Grinding the centerline lying on your back between the keels would be a terrible job.

It is , but far quicker and easier than flipping the 8x36 plate over to grind it.
Give it up Brent, why don't you just admit that the seams end up not being ground properly on boats you tacked together?

They are all properly done. Funny how you, who have never seen one of my hulls built ,know more than those who have, despite your knowing little about the process, or steel working in general.

 

The 34 foot Van de Stadts Wynand shows are all origamiboats, only with many times the seam welding, cutting , fitting and grinding of my designs, and far more visible chines.. The outside framing is only a slight modification in the building process, which are totally uneccessary to get the same shapes.

I just met another couple who bought a Gazelle for super cheap, which, according to some, sets the resale price of all gazelles at super cheap. Again it is a case of yet another older hull which suffered major corrosion inside ,which, had the hull been 3/16th instead of 1/8th, wouldn't have been a serious problem , as there would have been enough steel left to make it a non issue. With 1/8th , you have very little margin for corrosion, especially in the tropics, where corrosion rates double for every ten degrees rise in temperature.
I have seen a lot of ten gauge write offs, which would have been easily repaintable, and could have been cruised in safely for decades more, had they been 3/16th instead of 1/8th.
In my youth, I never had much interest in steel ,as long as I believed they had to be 1/8th plate. When I fist saw Ganleys Snowbird , 30 ft , 3/16th plate, with very little transverse framing, and logitudinals for strength. I was suddenly interested in steel .
Having worked in steel shops for years to that point, I knew well the liabilities of 1/8th plate.

 

Heres my 31, 1 month from start to launching, April to October, start to sailing and living aboard, despite my having pulled together two more 36 footers in that time

 

Ummm....from April to October is six months, not one month.

 

What? I use them for this all the time. Are you thinking of a cup brush maybe?

Or you could grind the plates first and have a perfect V to fill, no slag, and less effort overall.

If you need a gap to get penetration on an uphand 3/16" inside corner joint with 6011 you're doing it wrong. Besides, I thought you never weld the hulls you tack up because your customers can hire people of lesser intelligence?

Who said anything about flipping the plates? If you had ever ground an edge in your life you would know that it's obvious when the slag has been severed and any that clings to the underside can be simply knocked off by running a piece of scrap flat bar or similar along the edge. Beveling the aft centerline could be easily done by blocking up that part of the plate a ways.

Sure

I'm pretty sure I do despite being a layman but if I'm making eroneous statements here I hope the pro welders will step in and correct me, my ego can take it and I'm happy to learn. Is Brent's supposed strategy of fitting without dressing the plate edges sensible?

 

My apologies if I have misunderstood you in some post.. Thou I'm sure I read about the bus windows in some other thread, but obviously it was just a miss quote thing, which is exactly what makes it worth the effort to use "quote" in a proper way..
By the way.. is it easy to see in this messege who wrote what part?

 

No, it is not. As well, even those not-flame-cut edges that will have something welded to them should be ground(lightly) to remove mill scale. Btw, I'm sure you already know that it really doesn't matter whether one has worked on a Brent boat, or not, the same good steelwork practices are used when doing any fabrication.
Mike

 

Thanks, good point about the factory edges, I hadn't thought of that. I know I'm pretty much beating a dead horse with this but Brent is a slippery character and I don't want him to get away with promoting fab techniques that I know aren't even adequate for less critical structures like truck bodies.

 

And the bugger was 57ft LOA to top it all:!: . Here is a picture of the boat with the markings of the X Ray inspector clearly visible on the hull.

Apologies for a bit off topic...

 

there are no frames-only confusion

 

Well,I can't let you go without saying thanks!

 

EDITED and out of context
That's an interesting idea.sort of a girder?ie: giving stiffening dimension...

...I should say that in my own soggy fg boat (and in any other where I feel the need!) I go for'ard and feel around when I'm banging along up to windward.I do this with the idea that "if it's stiff enough,it's strong enough" Of course,I know now thanks to my professors' excellent posts!that this is not going to save me in a metal boat especially in the interior welds!Plus,there's maybe the foam inside.(I dislike sprayin foam! because access to the hull is a peeve of mine)
I was thinking too that there'd be some deformation (outside) in some boats that'd indicate whether or not the opinions here about Brent's maststep were valid.In the punchthrough fatiguing,I'm not convinced there'd NEVER be "seeable" deformation and Brent says never has been.The welding is not something I know enough (but I'm learning as much as I can without the "Doing"!)about but I still think it's unfair to take pictures of boats under construction and attack Brent's skills.I can say that Brent's own boat is not a tangle of pitted,poxy welds. but I haven't paid enough attention to say if they're a "roll of dimes"....


It'll explain my pursuit here (where I haven't much to contribute so I'm going to back far away)that One of the mods I've done in my own boat are TWO STRUTS VERY SIMILAR TO BRENT'S before I ever saw this detail in his....But my intent was a little different.
The trunk top seemed to be generating cracks in the gelcoat at its corners and so,my struts come down from these to pads on hull.(There wasn't any other "structure" worthy of the name to put em).These're made in fg and wood.My mast is stepped on keel ,so of course the analogy is very loose
They seem to be working or at least do no harm!Touch hull!