Boxy Fisher Catamaran idea

Pericles, I'm sure polistirene is usable for boatbuilding if it can be treated somehow to eliminate the known issues. It's cheap, light, rigit, and can be worked with easily. Maybe they forgot some ingrediant to it ?

Richard, a difficult question. Obviously if you use a rigit material like wood with fibreglass it would be stronger than using the polistirene foam that I use, but only the short term in my opinion. Once the wood gets a sniff of water the problems start, adding even more weight and strength deminish. Wood is also heavy, but for many people it is an acceptable media to work with and some woods are better than others. For my app wood would be much too heavy and personally I don't like wood in boats.

I use the polistirene foam for many reasons, insulation, fire retardent, buoyancy, lightweight, easy to work with, long term stability, bonds well to fibreglass and so on.

To answer your question. When sandwitched you get some stiffness. To gain strength you have to be a bit more clever with the structure especially if it is going to be a large construction. A 90 degree bend in fiberglass always flexes, to eliminate this a triangular strip of foam glued in the 90 degree bent that also gets glassed over stiffens as well as add tremendous strength. Check the eifel tower, all triangles.

If you take a shoe box without the lid, it flexes really easy when you twist it. Now put the lid on and suddenly it is rigit. You can now cut holes in the side of the box, and it remains rigit. This same effect is achieved when you create bulkheads (those funny roundish hull entrances) in hulls. So a hull is nothing else than a series of connected shoe boxes with holes in them

Having say three bulkheads in a hull would increase trength and stiffness over having less bulkheads, because the one box would help the attached one not to flex. Glassed in cupboards, berthing etc all adds to the strength and stiffness. If you are going to have them you can just as well utilize them to the advantage. The entrance hole to the hull for instance, if you add thickness to the outer rim it is nicer to the touch and it provides strength and stiffness.
Small things, but it makes a lot of difference. The trick would be to distribute the hull with features that would enhance the functionality of the space(s) and at the same time add strength and stiffness. If you have a piece of hull that is barren, ad something to it, ie a strip with holes that you can place the drinking glasses in... simple example , but it will add strength and stiffness. Ok, and some weight unless you overdo it.

Any area of glass is flexible, but by adding some feature you strenthen and stiffen it. If you look at John Schuttleworth's boat hulls, the nice sleek features running along the hull length is to strengthen and stiffen the hull... not only for looks, that's just a spinoff.

Lots of details eh !

 

Fanie, the only solution for your cabin weight I can think of is to use "canvas" of something LIGHTER, and a frame of aluminium as is used for bimini covers etc for small 18ft recreational open fishing boats.??? and hard stow items in boxes set on the inboard sides of the hulls. That would mean that to transport, one hull would face stern first, the other bow first so these "boxes" would ride on the top of the other hull & be offset a bit - is that clearer than mud? otherwlse I will rough sketch what I am thinking?

 

As I understand it polystyrene foam is dissolved by the styrene in polyester resin. Is is cheaper to build EPS foam with epoxy resins or conventional boatbuilding foam and polyester resin?

 

Masalai,

I have considered a canvas cabin, but one of the things I want to get away from is pitching tents and tent poles My first drawed attempt actually had such a concotion, but I didn't like it and neither did the other guys.

Tents are cold, and not strong enough. In stormy weather the weaving, flapping, windy canvas will drive you nuts, and our coastal areas have just those winds. It would be much nicer to retire to a nice comfy protective cabin after a hard day's fishing.

The cabin could also be split in a top and bottom part, but would have a few issues of it's own.

 

Richard,

You are asking for trade secrets, however. I am a generous man and will give you the information, so long as you keep it to yourself. Please bear with me here.

Foam core is quite expensive. There are a number of manufacturers, whose track records are very good. http://www.proboat.com/ That being the case, the searches for alternatives have been unremitting. I, for one, am guilty of failure in this instance.

http://boatdesign.net/forums/showthread.php?t=19932&highlight=Foamglas

Polystyrene EPS has its drawbacks, although Fanie has to be admired for his persistence.

http://boatdesign.net/forums/showthread.php?p=182741&highlight=Pericles#post182741

Closed cell, two part, polyurethane buoyancy foam has its admirers, me amongst them! Here is a British manufacturer that states their product is impervious to moisture. Mind you, I do wonder if that is the same as being waterproof. The foam retains its closed cell structure, even after being sawn into blocks.

http://www.spray-insulation.co.uk/buoyancy foam.htm

When foamed into cavities or onto boards it sticks like the proverbial to a blanket but, not to polyester film. Neither does epoxy for that matter.

http://duckworksmagazine.com/03/r/articles/glass/bottom.htm

Here's another UK manufacturer who supplies me. The prices are good.

http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__Polyester_Film_87.html

I make blocks of foam inside a box lined with polyester film. It cures, I remove the sides of the box and slice up strips or planks or carve components. Is it as good as http://www.boatdesign.net/articles/foam-core/index.htm ?

I can only really answer this question empirically.The proof of concept composite panels constructed with 800 gsm biaxial fabric and WEST SYSTEM have not delaminated so far.

Would this be a really quick way to build a catamaran? Yes, because correctly organised, the foam core can be produced to specification in thicknesses to suit the construction and being much less expensive, funding the project requires fewer months to save up the dosh.

Do with it what you will,

Pericles

 

Hi Deepsix,

Keeping an eye on costing is defenately an issue, however, there are things you just don't compromise. The hulls and beams are the lifeline when you're out there. Pretty much everything else can go wrong and you would still be relative safe as long as the hulls and beams hold up.

If the EPS foam you refer to is the same stuff we have here - I don't like it. It is easy and fast to pour and work with, but the fact that it is actually brittle and once deformed if does not go back to it's original position, and once broken loose inside it's cavity it keeps on scharfing when there's movement and eventually becomes like a powder. Maybe I'm too crytical on this, it is used for bouyancy in a lot of boats here and most of them still floats. It is much easier to pour the liquid into a cavity than to fill the cavity by cutting and fitting blocks of foam, so the boat builders of course usually take the easy cheap way out.

I have seen various boats cut open for becomming too heavy using the wrong kind of floatation under deck. Worst is milk bottles !! Can you believe that ? Fist wave you bump the lids bust open and from then on they just start filling up. Second was polistirene blocks, some were as heavy as bricks and if you squish them they pour water out. Third was EPS foam blocks. No more square corners due to scharfing and deformed but they were better than the polistirene.

Sorry, I know this is off topic, but the best under hull flotation I've seen was coke bottles, and of course like the foam I'm using. The drawback of the coke bottles are the cavities between the round bottles, but then you can count on about 2kg for each bottle you can get stuffed in there. On hot days the coke bottles can be noisy too as they push each other around expanding with heat.

The PE foam I use, I have pieces here that has been lying outside in the wind and wather for more than 5 years. It is difficult to distinguish between them and the new foam I bought recently. The pieces that was glass covered and unpainted have the fibreglass strands beginning to come off since the UV of the sun destroys the exposed resin, the foam however remained beautifully intact and retained it's bondage with the fiberglass.

The PE foam has only one disatvantage, it is not rigit enough, so you have to make a form or support for the type off app to keep it in place untill you have glassed it over. Looking at most of the cat hulls a form is used in any case, so.

 

Fanie,

You seem to differentiate between Polystyrene and EPS and you mention PE foam, for which I need some clarification as to what it is. Please help.

From http://en.wikipedia.org/wiki/Polystyrene

Polystyrene's most common use is as expanded polystyrene (EPS). Expanded polystyrene is produced from a mixture of about 90-95% polystyrene and 5-10% gaseous blowing agent, most commonly pentane or carbon dioxide.[citation needed] The solid plastic is expanded into a foam through the use of heat, usually steam.

Extruded polystyrene (XPS), which is different from expanded polystyrene (EPS), is commonly known by the trade name Styrofoam. The voids filled with trapped air give it low thermal conductivity. This makes it ideal as a construction material and it is therefore sometimes used in structural insulated panel building systems. It is also used as insulation in building structures, as molded packing material for cushioning fragile equipment inside boxes, as packing "peanuts", as non-weight-bearing architectural structures (such as pillars), and also in crafts and model building, particularly architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for corrugated cardboard, tradenamed Fome-Cor. A more unexpected use for the material is as a lightweight fill for embankments in the civil engineering industry [4].

Expanded polystyrene used to contain CFCs, but other, more environmentally-safe blowing agents are now used. Because it is an aromatic hydrocarbon, it burns with an orange-yellow flame, giving off soot, as opposed to non-aromatic hydrocarbon polymers such as polyethylene, which burn with a light yellow flame (often with a blue tinge) and no soot.

Production methods include sheet stamping (PS) and injection molding (both PS and HIPS).

The density of expanded polystyrene varies greatly from around 25 kg/m³ to 200 kg/m³ depending on how much gas was admixed to create the foam. A density of 200 kg/m³ is typical for the expanded polystyrene used in surfboards.[5]

From http://en.wikipedia.org/wiki/Polyurethane#Watercraft

Watercraft

Some surfboards are made with a solid polyurethane core. A rigid foam blank is molded, shaped to specification, then covered with fiberglass cloth and polyester resin.

The hull of the Boston Whaler motorboat is polyurethane foam sandwiched in a fiberglass skin. The foam provides strength, buoyancy, and sound deadening.

Best regards,

Pericles

 

Wow Pericles ! I wish we got that pro mag here. One can pick up a LOT of hints and tip from something like that.

When I tested the little tri's centre hull and other parts in the pool it was something else. You can fill everything up with water but it refuses to go under... Here's the aft beam in some cool (since it's on water) pictures and a pic of a hole saw cut piece that was ripped appart, it's fill of dust hence the white. 100% buoyancy ? Sure, why not ?

 

Have a look here
http://www.sondor.co.za/index.php
check under materials, SPX, the density I use is the 33kg/m3 or SPX33.

I'm sure you would have a similar type of material available since Sondor is not the only manufacturer of this in the world.

 

You will know polyethilene as the white tough plastic they make bread? cutting boards from. The windrider is also made from polyethilene. The foam I use is polyethilene, closed cell, black, uv etc, check the spec sheet.

The EPS foam we get from Rigifoam - http://www.rigifoam.com/

Note - PolyETHILENE and PolySTIRENE

 

Thanks for that Pericles. Fanie, when I asked that question, I ment to write XPS not EPS, was just momentarily confused. It just seems strange to me to combine XPS foam, which is very cheap but has low sheer strength with expensive epoxy resin. It may be ok for low load applications but in higher load situations the core might fail. You are clearly using PE foam but im not sure what the sheer strength is. I will have a look at the site.

Thanks

 

Hi Deepsix, I am not mistaken, I do use XPS. It may shear if only a small surface, but the size of a hull ? No way hozay. It doesn't shear that easy either. The XPS is not that cheap either - it is going to cost me double what the glass and resin is going to cost. Even if I seriously bend a piece of laminated foam, it does not tear or delaminate. The fibreglass breaks before the foam delaminates from the fibreglass !

 

Fanie,

You can catch up on many back numbers.

http://www.proboat.com/digital_issues.html

Happy reading.

Pericles

PS

Including the very latest issue. http://www.proboat-digital.com/proboat/20080203/

PPS

I am going off line to read.

 

OK guys....back to basics now...and I mean basics.
Foam, foam, foam. What is the foam for? Is it to provide thermal insulation, and the sandwich system is to provide an extra barrier incase of a leak? aswell as extra strength?
Which brings me to another point. Is it common for cruising boats to leak?

As you can see....I don't know much about boatbuilding!

Would it be crazy to build a boat without any sandwich?

 

Fanie, would you mind posting a jpeg or freeship file showing the cabin attached to the hulls?
It would be nice to see it more clearly.