Shark cage

General Composites Discussions Composites Talk
#1

Hi Ladies and Gents,

I am very new to the world of composites, ive only had a play with some fibreglass but wouldnt mind having a go with some carbon fibre which got me thinking.

I dive a lot here in South Australia, which is home to some very large things with teeth. When doing deep dives it requires decompression stops which means im hanging in the middle of nowhere under my boat with no idea of whats around me so for piece of mind a cage for this would be great.

So heres my question (which ive emailed numerous suppliers but never got a response).

Do you think composites would hold up against an attack from a shark?
The angle of attack would be random and if they chomped down on it would it compromise the strength to where it would fail? could it be patched up.

I have welded up one out of alloy but the weight and storage of it on the boat is a major hassle so i tend to leave it behind. something light yet strong would ideal.

Any advise would be much appreciated.

#2

Now that is a unique application. Well I guess the main technical constraints in this case are blunt force impact (eg a nose or tail whacking it) and sharp point impact (teeth). The point impact will be the most difficult to design against but certainly not impossible.
Im assuming the design needs to be similar to my mental image of current ones where there are lots of small metallic bars in a mesh format?
If this was me doing it and having to use a similar geometrical design to existing cages, I would use a multitude of materials in the bars and not just one. For example, aramids (or another similar type cloth eg diolen), glass and possibly a light metallic layer (eg aluminium) also to aid with the puncture resistance. The combination should give better properties than using any one individually. Then an epoxy resin coated perhaps to limit moisture ingress

#3

I was going to suggest something similar ^

Use thin walled ali tube to keep the weight down, and then wrap it with Kevlar to get the strength and impact resistance. Certainly wouldn’t be simple to make though, it could be quite tricky. I think my approach would be to get the ali tube and cut it to the respective sizes for all the pieces you need. Then because thin walled ali is difficult to weld, I would wrap it all with the Kevlar while they are individual pieces. Use shrink tube for compaction. Then cut notches into them where they need to intersect, use a high strength epoxy adhesive like Araldite 2015 to bond them together, and once that has cured wrap more Kevlar around the joints to reinforce it.

That is my line of thinking anyway, but I’m in the automotive composites business so this is a bit out of my field! Interesting project though, so I’ll keep an eye on this thread!

#4

Hi mr berry

I’d keep it simple , and maybe portable or easy to break down ??

Few joints and some carbon or Kevlar tube and " she’ll be right mate" :D:D

Also I’d maybe use a threaded solid aluminium insert where the joint’s are to give plenty of strength so you can have it bolt it together in certain joints for easy storage.

Just thinking out loud :slight_smile:

Tim
http://www.rockwestcomposites.com/browse/tube-accessories/aluminum-speed-rail-joints

Kevlar tube.
http://www.rockwestcomposites.com/browse/round-kevlar-tubing

#5

Hi,

Thanks all for the swift replies, it is a unique use for it but a pretty important one.

My design would only be for protection,yet have the least drag in the water as possible. My old one was roughly 80cm x 80cm x 180cm light alloy made out of pool fencing.

I like the rock west joiners and maybe a modular design is the go, no point making it but it being too hard to use.

It could be 4 frames 80cm x 180cm with a 80x80 square with an X . the frames only need to stop a sharks teeth from taking a chunk out of me. so maybe one piece in the middle of the up right frame and a couple of cross bracings.

I did think of the light alloy wrapped with kevlar, id probably drill the alloy and slot the other bits inside and wrap with kevlar.

Any other thoughts would be great, keep it coming