Sean`s Pods....

I was looking at Sean Herron`s modular boat.

Is there a torsional issue with bolting these "pods " together like this ?

I was thinking of 4 x 8 ft modules bolted to make 32 ft by 8 ft.

I like it a lot.

SNG maybe ?

 

Not if you do the calculations to prove it.

If you haven't or can't do the calculations,....then you'll never know!

 

Thanks ...for nothing....

 

boat fan

I don't get it? You ask a simple question which provides no data absolutely zip other than a simple concept thus:
"..Is there a torsional issue with bolting these "pods " together like this ?.."

So, if the reply was to your liking, such as "yes great wonderful no problems"...i wonder what you're reaction would have been?

If you do not calculate the structural strength of a design that you have "designed", how else are you to know? Or do you prefer to guess? I do not know what your rationale is! Unless of course you wish to absolve yourself of such and expect others to take that responsibility for you?

Designing, is not a matter of just drawing...the two are very different disciplines.

 

I have a great idea !!!!

What not ask SEAN the designer !!!!!!!!!! Yaaaaayyyyyy

duuhhhh

 

Firstly I`m not a designer.
It`s probably why I did not ask the right question.


"Designing, is not a matter of just drawing"

Who said otherwise ?

"Unless of course you wish to absolve yourself of such and expect others to take that responsibility for you?"

Once again , said who ? I don`t recall anything about " expecting " anything from anyone.


I had 2 years of study in civil engineering a long, long ,time ago , so I could still work out the sheer force and bending moments on supported or cantilevered beams, rsjs , or box girders ( which this boat is ).As well as shear on bolts plates etc...

What I guess I should have asked is how does a boat bolted together like this act AS A WHOLE , do you calculate for a UDL ( uniform distributed load ? Partially Cantilevered Girder ? That IS THE REALM OF A NAVAL ARCHITECT . Knowing how to calculate vector forces or drawing a shear force or bending moment diagram is one thing , but knowing WHAT to design for in a boat is another.

Any actual " data " is irrelevant to the question. The numbers change with the dimensions.


Good god ...its 8 ft wide 32 ft long maybe 7500 lbs .We are not talking super tanker here people.

As an aside : I designed NOTHING .This " design" already exists (I guess.)
Sean Herron drew this.Hopefully Sean will answer.

 

Have done....

Yesterday in fact .....

 

boat fan.

Progress. Since the original question, could have been, "..i have seen a picture of this apple, is it tasty??.."...everything needs context!

So:
"..What I guess I should have asked is how does a boat bolted together like this act AS A WHOLE.."

Well, since you have already pointed out you have a modicum of structural grounding.
Firstly,
you must establish the magnitude of the applied loads and where to apply them.
This relates to your comment thus:
"..Good god ...its 8 ft wide we are not talking super tanker here people..."
It matters not whether it is 8cm long or 80m long or a super tanker, one must establish the magnitude and location of the applied loads. How else will you know if it is stiff/strong enough??
This leads to your:
"..That IS THE REALM OF A NAVAL ARCHITECT.."

To establish the magnitude and load path, once must first say what the design is intended for?
For example, i ahve no idea about the box you have shown. Is it to be bolted to a monohull...or welded between to small hulls, like a catamaran...i simply have no idea. However, in each case, of these two examples, each has a very very different load path and magnitude of the said loads for analysis.

Which is why i said, what is it "designed" for?

Once you have established the magnitude of the loads and the "type of loading", the load paths can also be established.

the rest is just simply analysing the member, or box you have, in 3 ways
1) Globally....so, where these 'global' loads are applied, what happens to the box. This depends on how your box is attached and to what.
For example, if just placed onto the deck of a mono, if the mono is short, there will be no long.t bending, per se, assuming the mono is stiff enough anyway (again no data). So it will all be local loading. If the box is between two hulls, you have a torsional moment from each hull either side. The magnitude depends upon the final displacement, speed, and the sea conditions it shall experience;
2) Secondary,
From the global loads, how are these forces resisted, frames. The framing transfers the loads from the monohull/catamaran/whatever into the box. In addition, any internal loads, such as mass/passengers/fuel/whatever...will also influence the design/analysis, since there maybe a combination of load cases;
3)Tertiary,
Plate and stiffeners which are attached to the frames, how do these react under said conditions from 1) and 2)?

So, going back to your statement
"..Any actual " data " is irrelevant to the question..."
Without seeing knowing the mass, thicknesses, how this box is arranged and onto what and what the whole design is 'designed' for etc etc, how is one to analyse the box?

If you wish to reduce this to a one liner, that is fair enough and your prerogative. But, structural design, whilst not terribly difficult, requires more than just "does it act as a whole".

The simple answer is yes...but how it is "designed" will determine how it works and if it works at all. If it is not stiff enough, it wont work. But conceptually it does, when designed for the application at hand.

I realise this doesn't help you much, but if you want a one liner...ask someone that is not a naval architect. But with more data, yes, answers can be provided.

However, as you have now gone back to the designer, you should get the answer you seek.

 

4 x 8 ft modules . 8 ft wide.

32 ft x 8ft x 7500lbs . 30 - 75 hp O/B

10 mm ( 3/8 ) Plywood , ( 12 mm (or ) 1/2 inch optional ) .12 mm ( 1/2 inch ) Bulkheads .Stitch and glue .Biax glass / ply / glass sandwich .

Intended use should be obvious to all.

( Or , would you build this to cross oceans ???...I think not ....)

 

In answer to your Q
Is there a torsional issue with bolting these "pods " together like this
Each box, has four sides and 2 ends, and what "appears" to be a shear load path between each. This needs to be calculated if sufficient, since the mullions look 'weak', but what load??. How many rivets are required at the ends, again...the applied load is required to answer this Q. However, as such each module, has torsional stiffness. But what load do you expect it to experience? Is this boat on a canal..hence a low external load, say 10cm wave only, or crossing the ocean in 10m Hs seas? Where it goes determines what loads to apply and hence, is it fit for purpose.

The main question to ask, is how each model is join/connected together. Once any external load is applied to a module, how does it transfer the load to the adjacent module? This is done by the method of fixity you decide to use. Again, no data. But you need to determine your loads to ascertain how the type of "fixing" is influenced.

As for your UDL etc...is all the eqpt centred in one mass in the centre of the module, or is it evenly spread out....do passengers sit in one location or anywhere. The mass of these 'items' are required. Then you can design the internal structure to ensure that when someone stands in the centre, it doesn't collapse.

Like i said before, drawing a boat and designing a boat are two very different disciplines!

 

No need to repeat: " Like i said before, drawing a boat and designing a boat are two very different disciplines! "

I have always understood that.

So , how does a naval architect tackle the question of crew moving about in this vessel ?
I understand that you design for tankage etc ( max static ) ( And disregardiing free surface / baffles etc ) for now , how do you approach the moving crew issue ?


PLEASE , AD HOC ,Lets be sensible here ...about use.

Blind Freddy can "see " that this is a sheltered water boat. This brings up another question , : What does " sheltered water " use mean to a N/A as far as design criteria is concerned ?

Just trying to fill in some blanks about approaching this the RIGHT WAY.

 

If you are concerned with just crew moving about, one can use a value of 5kn/m^2 as a design pressure. This is the default min allowable with DNV and i have used this successfully for 20 years.

So, you have your spans, and your frame spacing, you have your UDL (above)and then you establish a modulus based upon this data. Then, once you have drawn your section, you then check the deflection. But this only satisfies local loading, it does not address any external 'global' loads, since these modules are all 'linked' together.

 

Thank you I understand .

 

You will have to ask DNV.
I don't understand why this is necessary. A safety factor is applied to this value (if required), not taken away from it! It is the minimum allowable.

LR's ends up a lower value, and it is wrong. I keep meaning to get them to correct it.