[Dr_Snapid]

Who knows much about aluminium? This is a question for any of the engineers, professional welders etc out there in auszooker land

I have a 14 foot catamaran. I tow it with my suzuki therefore I am permitted to ask this question of the knowledgable folk here on 'zookers, correct?

I want to replace my catamaran's trampoline (or what's left of it) with a sheet of aluminium. The aluminium will be essentially hanging just like the original tramp was

So basically, sitting in between the four bars that make the frame, with 5cm or so to spare on each side, holes drilled every 5cm or so right round the outside of the sheet, and roped into place around all 4 edges. Just like a trampoline mat, only not soft and stretchy.

I will then cover with the stuff excercise mats / camping floor mats are made of to make it more comfortable to sit on. Holes for drainage bla bla bla

My question then. Given that the aluminium sheet would be roped every few cm (lets say 5cm) do you think the aluminium would stretch under the strain of a couple of people shuffling around on top? Even standing on it?

I was considering using 1.2mm thick or 1.6mm thick sheet. The weight of such a sheet would be roughly 11kg for 1.6mm, even less for 1.2mm.

Let the headscratching begin...

[Fatzook]

Do the current nets fall to the centre from all 4 sides? Metal won't like this at all. The ally will stretch, buckle, crease, and fatigue from the constant shifting weight. Also, you would need to use a 5083 or other marine grade material, which usually does not come in sizes under 3mm thick.

If it were me, I'd be making a frame to support the ally sheet, so that it cannot sag at all, then chuck the matts onto that.

[atari4x4]

you trying to reduce the amount of spray coming up or is the tramp just rooted?

the old boy replaced one of the trampolines on a hobie that was originally the mesh style with a solid thick vinyl tramp & it was so much nicer to sail.

[Dr_Snapid]

Yes tramp rooted. The boat was a freeby from a mate's inlaws.

The idea for not going with a tramp was stability for fishing gear and such on the deck. I thought there would be a better surface than a tramp, when someone moves, the whole tramp will move, spilling your bait/gear/BEER etc

I'm not a huge fisherman anyway but my dad is and the boat is hopefully a Dad and I quality time thing, he's on chemo for cancer at the moment but will never be an old man I suspect.

Framing is certainly an option now that I have this aluminium brazing thing sorted but the hanging sheet seemed like a possibility to consider, very easy and cheaper.

[Fatzook]

Dr_Snapid wrote:

but the hanging sheet seemed like a possibility to consider, very easy and cheaper.

Not gonna last mate. Not to mention the potential for unjury with sharp edges.

Go get a piece of 1.2 ally offcut and try to bend it by hand. Its effortless.

Do what Gus said. Vinyl, or make a solid floor for it.

[Dr_Snapid]

Thx for the input so far guys.

I think for now a tramp will go on while I consider options.

[got_bar_work]

Add 2 more beams across between the hulls and use 12mm marine ply
It will be light and have a bit of flex in it as the hulls will flex quite alot under sail

[cairns27]

Exterior ply will do the job.They only use marine ply for under the water line now.


bye

[Dr_Snapid]

I'm about to start work on a plywood box for the Cat's trailer. Since i'll have some ply around, I might have a fiddle and see how ply would work out.

PS: My understanding when it comes to ply and boats is that Marine ply is not any more waterproof than normal structural ply. The timber of a boat should never ever get wet anyway. It should be properly sealed.

Marine ply just has no voids/weak spots etc so it can be bent to a uniform curve without having it snap at a weak spot or curve unevenly. So going by that, as long as you arent curving the ply, you dont need marine ply, although for strength you would want to be careful where you have voids.

I think the ply idea does have merit, i'll keep it in mind

[tonyevans]

Dr_Snapid wrote:

I'm about to start work on a plywood box for the Cat's trailer. Since i'll have some ply around, I might have a fiddle and see how ply would work out.

PS: My understanding when it comes to ply and boats is that Marine ply is not any more waterproof than normal structural ply. The timber of a boat should never ever get wet anyway. It should be properly sealed.

Marine ply just has no voids/weak spots etc so it can be bent to a uniform curve without having it snap at a weak spot or curve unevenly. So going by that, as long as you arent curving the ply, you dont need marine ply, although for strength you would want to be careful where you have voids.

I think the ply idea does have merit, i'll keep it in mind

Use MARINE ply - It has VERY different specs than exterior of building ply.

[Dr_Snapid]

Which specs Tony?

[tonyevans]

Put a piece of Building ply - Exterior Ply - and Marine ply in a bucket of water - leave it for a few months and then tell me which you would rather go to sea in.

Google is you friend.

[Dr_Snapid]

One of many results tony, there ya go. You gonna tell em they're wrong?

http://www.misterplywood.com.au/Product ... ywood.aspx

Also Austral's website lists structural ply and marine as same bond and same stress rating.

I know the thickness of the veneers on a structural are different to marine as well but how this affects your construction depends on the job.

Plywood should never get wet. (or any timber in a boat for that matter)

I'm not saying you arent right about using marine ply for boats, only that dropping them in water to see which one is waterproof is pointless, because it should NEVER EVER GET WET

[tonyevans]

Dr_Snapid wrote:

One of many results tony, there ya go. You gonna tell em they're wrong?

http://www.misterplywood.com.au/Product ... ywood.aspx

Also Austral's website lists structural ply and marine as same bond and same stress rating.

I know the thickness of the veneers on a structural are different to marine as well but how this affects your construction depends on the job.

Plywood should never get wet. (or any timber in a boat for that matter)

I'm not saying you arent right about using marine ply for boats, only that dropping them in water to see which one is waterproof is pointless, because it should NEVER EVER GET WET

When I was building boats from 8' Sabots to 30' Fishing boats the one of spec's for "Marine" ply was submersion in boiling water for 72hrs without any effects or penetration past the first glue line. I guess like everything else these days no one cares about things lasting - just so long as it stays together long enough to get the money and move on.

[Dr_Snapid]

Ok Ok I hear you although...

WHY SHOULD YOU CARE ABOUT WATERPROOFING IF IT ISNT GONNA GET WET?

It makes NO SENSE to give a shit about waterproof glue when the glue wont get wet. I'd sure be glad of glue that can survive 72 hours of boiling water if I was to attempt to cross a boiling lake atop a steaming volcano in an unpainted plywood sabot. A big boiling lake. 4 days sailing wide.

However.

If the timber is sealed, painted and maintained, it would not need to be waterproof. A boat made from 100% marine ply WILL ROT LIKE SHIT if not sealed and painted. Not in 72 hours perhaps... Same as 100% of non smokers will die, I guess...

The ply used for any purpose would however have to satisfy all the other requirements of the proposed purpose such as suitability for bending, strength etc... and marine ply is generally well suited to marine applications but it is not because it's waterproof.

[Trypt]

Dr_Snapid wrote:

Ok Ok I hear you although...

WHY SHOULD YOU CARE ABOUT WATERPROOFING IF IT ISNT GONNA GET WET?

It makes NO SENSE to give a shit about waterproof glue when the glue wont get wet. I'd sure be glad of glue that can survive 72 hours of boiling water if I was to attempt to cross a boiling lake atop a steaming volcano in an unpainted plywood sabot. A big boiling lake. 4 days sailing wide.

However.

If the timber is sealed, painted and maintained, it would not need to be waterproof. A boat made from 100% marine ply WILL ROT LIKE SHIT if not sealed and painted. Not in 72 hours perhaps... Same as 100% of non smokers will die, I guess...

The ply used for any purpose would however have to satisfy all the other requirements of the proposed purpose such as suitability for bending, strength etc... and marine ply is generally well suited to marine applications but it is not because it's waterproof.

X2

[tonyevans]

Yes - Of course you are right - Paint is 100% waterproof and infallibly so. So use rice paper glued togeather with flour paste as long as you paint it

[Dr_Snapid]

Yeah your point is well taken. That isnt what i'm saying... what i'm saying is that if it's marine ply under there it will still turn to shit when it gets wet, because it is not waterproof.

You must maintain the sealing surface on marine ply at 100% same as structural. The glue is the same, the wood is the same. The only difference is the marine ply has met a standard for voids (or lack thereof) that exceeds the standards required for structural, also it's ply thinknesses will be optimised for bending (all plys are the same from memory) rather than thicker surface plys like structural (if memory serves)

I seem to be repeating myself so I think i'll leave it at that, I appreciate your input though.

[got_bar_work]

This crappy timber thing is All to hard
Just lay a foam filled fiberglass sheet

[Dr_Snapid]

got_bar_work wrote:

This crappy timber thing is All to hard
Just lay a foam filled fiberglass sheet

I dont think that sounds easier!

[tonyevans]

got_bar_work wrote:

This crappy timber thing is All to hard
Just lay a foam filled fiberglass sheet

Bin there - done that - It stinks - Literally