Spaceframe boats?

Are there reasons why the use of spaceframes for a boat would be a good or bad idea? Assuming you had a mostly open deck and didn't mind having modular deck pieces you could pull back out, you could literally have a boat that gets longer or wider, then shorter and narrower under different conditions with a bit of wrench turning. Heck maybe even split into two separate boats! (if you had say separate cat hulls to attach to the second)

In theory spaceframes are super strong for distributing loads across the entire structure - but i'm wondering whether there are unpredictabilities in the forces of wind and waves and especially high sea state conditions that make me wonder whether using them would be brilliant or stupid.

 

Can you explain how the hull skin would conform to the changing shapes? Also, how would you change the geometry of the spaceframes, which are trusses?

 

FWIW, all boats and ships are either spaceframe (i.e. internal structure supports the skin) or monocoque (the skin structure is self supporting). The decision to go one or the other is based on the loads ( a function of size, speed, weight, and environment)and construction material (which rolls back into the weight). So a 10 foot FRP tender can be monocoque while a 30 foot FRP cigarette hull is a spaceframe.

Now some may argue that there is a third case where the skin supports the structural load only because of some secondary structure/means (i.e. an inflatable or large tanker). But really those are only optimized examples of the first two.

Modular vessels? Sure, look up nesting hulls or sectional floating dry docks. But why? The more compromises you make in a hull, the less primary capability it has. Keep hulls as simple as possible as required to meet design needs. Of course, if the design need is to be as complicated as possible (i.e. kinetic sculpture racing), the sky is only the starting point.

 

I have often wondered if a triangular spaceframe truss would work as a cross beam for a catamaran.

 

Sure, you just need to engineer it for the loads.

 

Yep, that's the part I can't do

 

Well first separate the hulls from the rest of the boat itself, like a catamaran with demountable cats. So that the trusses you have between the cats are what is changing in length and width.

Then consider that the cats might be themselves modular, say I made them in ten foot sections. (since having multiple bulkheads to prevent sinking is beneficial anyways, I say why not have them actually able to separate at the bulkheads) So in one configuration I might have 40 feet of cat hull under there. And later if I decided to lengthen the boat I add two per side so now there is 60 feet of cat hull under there, to support 50% more weight, because i'm making the deckhouse and such a bit longer and wider. Yet later I might shorten it to 50 feet or even 30 feet and shrink the deckhouse back down again, just putting my spare parts in storage.

In short the skins arent stretching or changing, you just have modules that are pretty close to water tight. (potentially to the level of just painting over the seams, razorblading them apart if youre adding cats, then repainting if a super-thin gap makes that much hydrodynamic difference) I'm not necessarily suggesting that the whole boat changes it's dimensions multiple times per day or during a race (though i'm not suggesting that's forbidden!) just that it's possible with some wrenching to alter the whole design.


And to jehardiman, i'm not sure if were exactly on the same wavelength. I'm not referring to monocoque vs framed members, but framed members vs spaceframes.



Or what i'm trying to mean is the deliberate use of smaller more easily handled tesselated members in a lattice, as opposed to having large heavy trusses or substantially varying sizes or very large members. If I disassembled framing on a large boat I might have members 20 or 30 or 40 feet long, a spaceframe might be a bunch of 4 foot sections hand carried with connectors like you see in a geodesic dome the kids play around on the playground.

 

The flat panels you show will be much heavier than curved ones. Boats are very sensitive to weight, particularly multihulls. I fail to see the advantage of a truss system that makes the interior unusable for habitation.

 

You know you can use spaceframe, the challenge is making something superior with the capability. Space frames benefit from more direct and predictable loading which allows more efficient material use. The negative is that space frames are a huge waste of space (no useful space) and add surface area. Another negative is that space frames are single point failure structures. Lets say you do the math and calculate an optimal truss for a beam of a catamaran that is made of thin wall tubes. The you drop an anchor or bump something that bends or even dents one skinny compression tube -you just lost half your strength and rigidity.

 

See my gallery for modular concept. Could be space frames.

 

There is no difference except the framing pattern you chose is inefficient in space use. Space frames do not have to be tetrahedrons, that is only a requirement of the lack of end fixity. In fact, using a skin panel that can support face shear, or allow end fixity, and triangular support is structurally inefficient. Take a good structures class and you will have this all explained.

 

I'm not necessarily assuming I had a superior idea on how to use it yet, in part I was wondering if anyone else had used it for it's strengths and found it worth doing. Sometimes solutions pop up in my head that I don't yet have a perfect problem for yet... Maybe a way to uprate a hull to ice-rated inside the cat for a cold weather adventure while being easily disassembled to keep the weight out for the normal use in the tropics? Assuming there was an existing frame strong enough for normal duties, using the spaceframe to augment instead of replace.

I suppose one additional problem I realize when I think about it is that a spaceframe is strong in compression loading but in tension there could be problems - and wave forces pushing the catamarans in opposing directions could damage the lattice, hmm...


I wasn't too worried about 'usable space' because I wanted to keep the cats and any support framing between the cats strictly functional - the cats can be as narrow and long as possible without regard to habitation or storing anything besides tanks. Then everything humans live in or need to access in the big broad long overwide deckhouse where they are more accessible anyways. I hate futzing around in cramped quarters.

 

Mirabaud was done about 10+ years ago and is still the largest bi-foil monofoiler:

No Hull:


Mini Hull:

 

I suppose a skin-on-frame boat, such as a kayak or canoe can be considered a space frame boat of the most extreme sort. The skin has no bending or compression strength of its own. That is provided by the frame. It does tension have strength, and of course, it keeps the water out.

A more personal example is a frame I made to turn a vinyl four man raft into a sailboat.

(See attachments)

The frame took all the rigging and most of the other sailing loads, leaving the raft with just compression loads.

It did actually sail and was able to sail upwind surprisingly well.

Other than a skin-on-frame boat, the space frame concept tends to add extra weight, over a more conventional design.

This is because the space frame itself tends to impose point loads on the rest of the structure, which have to buffered and/or distributed some how.

The large plywood pads on my raft design are an example of this.