Transverse frame calculation

Have a look at this:

www.ieindia.org/publish/cv/0503/may03cv13.pdf

Although applied to the design of a bridge the principle is similar.

 

If you bend a strip fix it in place, bend another and glue them together you have much lower pre-stresses than if you glued the two strips together then bent them. When you take a laminated frame out of the mold it stays the same shape so it's neutral. If you sprung those same frames into place then you should be able to realise that It's the global pre-stress that makes it weaker. The in-built stress is trying to straighten the frame out and this acts counter to the requirements for stiffness.

The frames hold the plating in position the plate inturn holds the frames in position so your reasoning is valid but structurally if we look at structural failure the plate isn't that great.
The plate buckles easily since it's such a slender structure on it's own, that's why framing is added, it's perfectly valid to look at the frame and some attached plating when looking at load paths and deflection. The plating 'shures up' the framing to some extent but if the frame collapses then so to does the plate in quick succession. It's a very valid exercise to analyse the frame and some attached plating, not the entire hull since it's the framing we are looking at.

The comparison between a pre-stressed frame and a pre-fabricated frame can be made on this basis to judge the stiffness and impact resist ability.

Again the proven 36 footers get away with weaker framing methods, but the hard brutal message is that Brents structural arguments not just incorrect it is significantly misleading.

Then if you start trying to convince people that this is a valid method for larger structures - bigger scaled up boats without any transverses what's going to happen?

 

I step the mast on deck on a massively strong arc, which is supported by pipes from the inside deck edges to the chines making the structural equivalent of a ring frame ,without the weight and bulk of one. For the chainplates to come together, the decks , massively strong longitudinal bulkheads, would have to stretch on their inside edges , edges which are supported by the cabin sides, which would also have to stretch longitudinaly. Once you have pulled together an origami hull, these conections become self evident.

 

That's interesting, even though it's just a proposal not a detailed study. He is however proposing an easily constructed arch which is taking it's load in compression, the same observations apply. If the arch was just a shallow variable arc it would promptly collapse.

This is where Brent was confused with his arch arguments. Except that he won't admit it and just arches his back and spits vitriolic abuse that gets deleted by the moderator.

 

No they are called decks, bulkheads are transverses

 

For the 36 the arc is made of half inch plate on edge , three incheas deep in the middle and curving down into two knees at the cabinsides. We have put the suide decks under on a 36 without the lee shrouds even showing the slightest signs of slackening in any way. On a fibreglass or wooden boat,this level of stiffness is impossible to achieve.
If you wanted even more strength , you could weld a flat bar along the bottom of this arch , making it into an I beam , with a huge increase in strength. That flat bar could be as thick as you want to make it with few drawbacks.
Pre stress steel in concrete is common practise. Tell them that they are doing it all wrong.
I used to put he longitudinals in after pulling the hull together . Doibng it on the flat was light years easier.
If the longitudinal you want to use is too stiff, stacking a second long on top of an existing one, after the hull is together, is an option which would give a huge increase in stiffness.

 

You are talking the mast step frame . Thats fine, it was the hull longitudinal framing and your reasoning that the rest of this is about.

 

Doesn't matter what you call them, their structural effect is the same.

 

There you go again. Mixing apples and pears..

To compare the "stiffness" of structural memebers, you need to use the correct definitions.

The structural stiffness is the "EI"...in otherwords, the product of the second moment of inertia (I) and the Youngs modulus (E).

Fibre Glass has an E of roughly 20GPa
Wood has an E of roughly 10GPa
Steel has an E of 208GPa.

So, given two structural members of the same 'shape and depth', it is not rocket science to see that steel has more than 20 times the stiffness under a given load than wood and ten times that of Glass. That has NOTHING to do with any argeument you are using for your "..lets roll the thing up.." method.

This Relgion based science is the same as offerd by another here, yet when questioned to demonstrate his "claims", a deafening silence:
http://www.boatdesign.net/forums/boat-design/compromise-31901-7.html#post352558

Trust me, believe me, don't question me.....this has no place in science and engineering. Utter nonsense...

 

Let me see if I can sum this thing up for myself.

The argument for compressive loads on arches seems in my mind to fall all to pieces when the arch is moved from a force of linear gravity onto the roiling surface of wind and waves with twists and turns in all directions.

The buckling loads are very valid and must be taken into account by designers. The only way around the buckling loads without frames is by compound curve and that only works to a certain degree and is therefore restricted by size.

So what does all this mean?

I have no doubt that Brents boats are sailing the oceans and doing fine BUT there would need to be many restrictions on size and design to keep the hull within the limits that can be handled by the compound curves needed. In other words, the designs would be very limited and generally all look the same. If that is acceptable to the builder, then I have no argument. That acceptance of design limitations is what Brent is hanging his hat on.

Where I would part company is when the illusion is given that this building method has a wider application in building the many small boat designs that we see. No it will not build them unless you want a design with continuous curves that pinch the boat at both ends in sizes under 55'. The guy reading about the simplicity of contruction who wants a nice wide stern and a higher Cp ratio is plain screwed and wastes time exploring this method.

So it appears that Brents designs are an intergal part of the building method and are therefore a one trick pony so to speak. Brent has found a niche. More power to him. If you want his pony with its inherent compromises, then you have a winner and it seems he finds enough people willing to accept the compromise in the name of the all mighty buck.

I guess the other problem I see in these threads is the zeal with which Brent pushes his methods without the disclaimer of the one trick pony detail. A niche market is just that and to sweep aside the bulk of the market with cliches to make your niche seem mainstream is a marketing type plan that always raises a few hackles. In the end you get more flies with honey than with vinegar.

 

I guess the other problem I see in these threads is the zeal with which Brent pushes his methods without the disclaimer of the one trick pony detail. A niche market is just that and to sweep aside the bulk of the market with cliches to make your niche seem mainstream is a marketing type plan that always raises a few hackles. In the end you get more flies with honey than with vinegar.[/QUOTE]
thats rather well and diplomatically put,
Brent has a nice and free advertising platform hereThe thing is this (advertising) has been going on as long as I have been here, (twice) and the record is kinda stuck in the groove ( 2004)
However if enough people want a cheapo boat and google such, then the name will come up
I was told many times here that Origama boats had no frames, so that is why I questioned the frameless 60
I think before I did a 60 , with 5/8 caps holding up 40 tonne of boat , I would certainly not be considering MASSIVE LONGTITUDINAL B/Hs cos that would slice up the accomadation)
Go sailing Brent, you only have so many years in you lfe, and you are just stressing trying to preach stuff to people who will never be converted

 

Quote: they are called decks, bulkheads are transverses

No it isn't !

you can fix the sheer to the concrete floor if you want with the hull turned keel up and load a side till it collapses. A transverse support bulkhead or frame will make it a lot stronger. The deck is not a transverse frame.

 

I knew that I had seen something well written on this subject before so I went searching and found this article on Michael Kasten's web site. I am sure that being on the same area of the globe Michael has crossed paths with Brent.
http://www.kastenmarine.com/frames_first.htm

 

LyndonJ arguing about the naming of something hardly moves the debate along. The deck is part of the support structure and if you rolled the boat over and looked at it, you could say that it looked like a ring frame. Ok it’s not a transverse frame but it does constrain the hull edge
http://origamimagic.com/images/Image2.jpg
If you are going to make judgements about the suitability of structure you have to know about what forces are acting on it, so as to ascertain whether it will fail and when. So far it’s been established that the structure as pre stress but we don’t how much and where, a part from the longitudinal frame that mike did.
It seems to me that this building method treats the whole side of the boat, as one piece with localised stiffening, so should be modelled that way.
As for boat size!
http://www.submarineboat.com/pauls_boat.htm

 

Hey bhnautika

If you look at the first 2 posts of this thread you'll see that the transverses we are taslking about are transverse frames , bulkheads are also transverse frames. Brent states clearly that they are irrelevant in boats up to 60 feet.

How is a deck a transverse frame ??? Brent said a deck was a bulkhead, just a horizontal one. I think the definition is very important. Bulkheads are transverse frames.

Pauls boat looks interesting, a couple of comments there. They cut the longitudinals and added the lower transverses later, the topsides will be weak in collision and there are some nasty hard spots where those large brackets end abruptly on the topside plate.
From experience a class society would not accept that design nor could you support it with FEA and convince them otherwise. A high cycle fatigue analysis would show a lot of hot spots in their structure.

[Edit added]


Just becasue it has been built doesn't mean its safe or durable or best use of material. Those brackets would be much more sensible as angle bar frames between a continuation of the lower transverse and the deck beam. Would probably be a similar amount of material and a much better design.

I posted some of te following in the origami threrad too:

I think we need to come back to transverse framing. Brents logic is that transverse framing is not required becasue his method produces stronger longitudinal frames. That would have been nice but it's based on misunderstanding.

Unfortunately it makes the resulting frame 'floppier'. Thats a fact. Brent beleived it made it stiffer, that beleif is esaily shown to be wrong and clearly has been.

Now the danger (once again) is that someone preaches a message that this method is lighter easier and stronger and will work on boats twice the length without scaling the actual real structure that keeps it intact.
In reality for the boat to be as strong you'd need to scale the plate and frame dimensions along with the displacment (or thereabouts).