styrofoam sail boat idea, have questions.

Cenkaetaya, you're making nothing but guesses, which designers and engineers find annoying to say the least.

You're structure as designed is overly complex, considering the current crop of cored structures available, which will just serve to drive up cost, not down. Your estimates of it being cheap are irrelevant (and quite debatable) because, again the total effort and cost associated with the hull of a 42' sailboat is a small percentage of the total effort and cost of the project. So what if you save 5%, you can do this with good material usage or clever cut files.

You haven't considered the loads imposed by the sea, the rig, the engine or anything else that affects the boat. Without a reasonable set of load paths, you're suggestion it will be strong is literally a crap shoot.

Maybe you have 30 to 50k to toss at an experiment, but I don't. Personally, I don't think you have any concept of how this "new system" can handle the loads, let alone how to transfer them. For example how will you attach the rigging hard points, without folding you boat in half when you tighten up the headstay turnbuckle?

Again, without a firm grasp of the concepts and principles of yacht design and structural engineering, you're hopelessly out of your league. This isn't a personal assault, but an observation based on the extreme lack of statistical data you've offered so far about this thing. Statements such as:

or

suggests you haven't a clue what it takes to design a ocean capable structure, that will take you and those you love farther from shore then they can swim back to.

For example what plastic would you use for your inner whatever? I'll assume you'll want a closed cell type of foam (do you know why I make this assumsion?), but what type will it be? What about your netting, what material will this be? You don't even have a grasp on the physical requirements of the materials involved, let alone have made material choices, so it's difficult to take this very seriously without considerably more thought.

 

You also need a plastic that will take antifouling paint

 

I’m curious as to why you want to build a boat this way? what are the advantages?

 

The immortal fear a boat could sink. That´s all.

Go and get some sealegs, you will feel much more comfortable or find another hobby.

The entire commercial fleet, and about 99% of the yachts (I guess) are not unsinkable, but miilions of people are going to sea, every day again.

 

My background is in decades of Enginenring, designing different structures, automated machinery etc...

The last three years I spent on my computer, lovingly designing a large power triamaran.
This triamaran was on my mind for well over 40 years... full with my (and other people's) innovations and ideas and although it is still only in the design stage, from all the preliminary calculations it seems like a fast and light cruser with many proprietory ideas incorporated.

Despite my background, I am here ...lurking and picking up bits of information, just in case if I missed something. Just in case somebody has a better idea to do the same thing.
This is a good chance to see what other people do, what worked and what failed. (Becaue in everything, there are trade secrets that you must learn by practical experience!)

So ...This probably gives me the right to throw in my voice of caution into this thread.

Your suggested structure would end up on the bottom of the sea, before leaving the Marina!

Never mind the unsinkable bit. Parts may be unsinkable, but the structure would fail!

If you add foam filled floatational spaces and foam filled amas to your boat, you may end up with a something that will float even when most parts are filled with water.

Foam cored hulls are OK, but they must be sandwitched in-between rigid panels.
Lots of money was spent on R&D by various copmpanies to find the right type of foam to create the best sandwitch panels.

The real strength comes from the surface sheets. This sheet gives you that strong extreme fibre!!!
The foam is there only to separate the two sheets to increase the "cross section's moment of inertia" in bending.

A couple things of interest:

The actual loads on the walls are the same for the same size, shape and displacement boat, regardless of the materials used!

The pounding can be reduced by a fine hull shape, the weight can be reduced by expensive materials and building processes.

An extremely simple approach is to conclude that, the loads are in some sort of "bending" therefore only the modulus of elasticity of the surface panel and the section's moment of inertia that matters!
The strength can only be increased, by reducing the overall weight or by increasing the structural strength at the same time.
Structural strength can be increased by a different shape, bulkheads etc...

The center of the sandwitch material is a lot more that just simple foam. This filling must withstand the pressure from the surface panel and must not collapse. It must bond to the surface panel even after millions of poundings and reverse cyclic loading!

Otherwise the load equation is out of the window and you boat is on the bottom of the sea!

Just check out the sandwitch panels for decks or roofs with balsa core! The balsa wood must be glued between the panels with the grain in a certain way or the sandwitch would collapse!
The shear strength between your foam and the surface panels would be almost non existent! You coudn't keep the surface panels glued to the foam!

One more point; foam hulls as you sketched them, (with canvas on the outside) even if you coat the canvas with something, would cave in at the first big slap from the water!
You would need lots of internal braces at the right points and at the right sections, supporting the hull as one giant structure, to keep the water pressure out.

The longer the structure is, the more intensified is the overall bending moment on the hull when you are riding on peaks! (The load will go up by the third power!)

To be honest, it would be possible to build a boat as you suggest at a considerable expense, but I would not venture using it!

Regards,

Stephen I. M.

 

nice, thats what were talking about.

Thanks to all the people who provided long replies, I enjoyed reading them!

I must say the last guy has explained it the best.



what would you say in terms of that guys {plastiki} boat?
I dont know if you saw it, just search google.

What i thought is that this foam style design may be possible to do with a catamaran, but with a single hull boat it would be very hard.

 

Well, plastiki hasn't sailed yet so we will have to wait on those results. He keeps delaying the launch but I think it's a publicity thing. If he does, the first ruff sea he hits, we'll see 12,000 plastic bottles cast adrift. Just my Opinion. http://earthfirst.com/wp-content/uploads/2009/03/plastiki.jpg

 

Let's hope not..there's enuff of those damn bottles laying around and floating around already and it gets worse all the time...

 

In response to the OP I will fall back on the old homily: We don't know what we don't know.

 

I think cenkaetaya's idea could work with a few minor changes. Firstly, swap the styrofoam for closed cell foam. Change the netting to fibreglass, and as long as the plastic on the outside layer is epoxy, i see no problem with this either (might want to add a layer of plastic on the inside of the foam as well). Add some stringers and frames, a new designer, and voila! Instant boat

 

Could you make a small dinghy out of polystyrene first? That way you will get used to working with the material.

When the dinghy floats you will be able to see how it handles on a small scale and make any changes to the design. You will encounter many of the problems of a full size boat, though probably not all.

If it works you will now have a dinghy to put on your completed boat.

If it doesn't work you will have saved time and money and will get a bit wet in a lake as opposed to somewhere out at sea.

Take lots of pictures, if it works or fails everyone learns.

Mark

I should stress that the only reason I am not telling you to give up on the idea is that I have no experience building boats, which is probably why I clicked on the thread in the first place.

Newbies like me get very excited by the idea of doing something either on the cheap or ground breakingly novel.

It is probably best to bear in mind that just about everybody who has ever been on a boat is aware that polystyrene floats, if it was cheap and easy to use someone would have done it many times over by now.

Could you get cheap enough insurance for such a novel idea?

 

Displacement increase with the cube of the increase in length. That means that the impact/crushing force against the hull increases greatly. If the dinghy does OK, the force on a hull 12 times longer will be 1728times harder.

 

I'm not an expert but I can see the problems and agree with everyone here.

The problems are fundamental material strength, size of the boat and seams if any. The bigger the size the more tension or torque forces will occure anywhere and break up any weak spot. Waves alone will do that thanks to gravity and load weights.

Although, I think it's a pointless exercise, and costly in the long run, I think there are two designs you could try:

-one man vietnamese bowl boat, essentially a floating barrel for one person

-catamaran, where you can use strong wood board for top plating and boarding, and use the styrofoam for the bulk of the outboard hull (whole)body. You still have to use many layers of plastic wrappers. Wrap until the thickness is at least about a millimeter. The problem is getting bulk foam. But since it will be a thick bound mass of foam it's somewhat better than just some hull wall.
Note that glue or pretoleum based fluid will dissolve the foam.
Surfboard construction knowledge might help you further.

As to the bottle boat, I bet it will break 100% of the time.
Each bottle wall is thin such that the forces of the binding string or ropes necessary to keep the boats form will likely destroy the bottles. Not to mention when they have to carry a person on them.

 

There is a very simple way to put this foam theory to rest, or to the bottom of the sea, where it belongs!

Anybody who thinks it is possible to do what was suggested originally, should get a small chunk of the foam core sandwich material from a boat builder.. (Only a small scrap piece!)

Compare the copmpression strength of that sandwich core to any other foam material and you will immediately see the difference. Watch how the regular styrofoam crumbles between your fingers! Even the highest density will do that!

It is somewhat of a misleading name to call the "boat building material" a foam core sandwitch panel.

Well, it is a sandwitch type construction, but there is quite a different of a foam molded betweeen the two strong but light plates...

It is great for light weight construction, but don't hit the rocks!
Same goes for the carbon fibre material.

The pounding of the water can tear even the traditionally constructed monohulls apart.
Even steal hulls are occasionally torn open like tin cans!

Multi hull cruisers will have a few very highly stressed joints.
Just imagine the force generated by a 40-50' hull slammed into heavy seas by a gale force wind. All that force is concentrated on one point where the bridge meats the hull or where the bridge is tied to the amas!

One hull may want to go up, while the other is in the air.. the force might be acting on a 10 to 20 feet arm...
It doesn't matter how you slice it, the weight of the water is 1 kg per liter.

Fact: Forget about any previous education in other fields, the more I learn about boat design, the more I realise that "my revoluitionary new idea" might not be a good idea at all!

I had arguments with people over simple things... one of those tall tales, people telling me that their "X" length mono hull sail boat was sailing much faster then the hull speed...try pulling a sail boat with a high speed power boat and see what happens if you have enough horse power!

Never copy a military design.. they just put in another 10 000 or 50 000 HP...
if they need to.
There is no free lunch, if it would be possible to make a boat to fly on water running on solar power and carry 100 tons, it probably would have been invented by lots of other smart people.

Early on when I just finished my education, frequently I felt that the estabilishment restricted my inventive streak! (My youthful ignorance combined with arrogance!)

I had my nose rubbed in it a few times and once a really smart engineer who was my mentor told me: "Next time when you feel irreplacable, just take a walk in the cemetery. All those big shots have been replaced!"

Now all this had nothing to do with the subject at hand, but I put it in here just to show how important it is to stay with both feet on the ground and not get carried away with dreams based on wishful thinking and not solid practical science.

With respect,

Stephen I. M.