Lightest hard center deck for a small cat

If price is not a too much of an object you migh want to investigate monopan as a possibility. It's construction is similar to a standard honeycomb panel, however that is where the similarity ends. The core consists of extrude polystyrene and face sheet are glassfibre impreganted with thermoplastics. I came across the product about 2 years ago looking for a protection system for honeycomb flooring in a helicopter. Our testing showed that for impacts it out performed plywood at a fraction of the weight. I have often considered if it was feasible to maufacture a whole cat out of the stuff.

link
http://www.monopan.ca

 

No doubt foam sandwich of one kind or another will be stiffest for any given thickness and weight. But there's the coast, and the whole baggage of the non-renewable materials.

I am doing the exact same thing in the conversion of my old A-cat into a cruising solar powered cat, and have opted for a hybrid of the hit-tech with the old school...

I have built a hollow honeycomb cored ply box using 4mm Hoop Pine ply (Arukaria Cunninghamii, plantation grown, FSC Certified, BB grade to save cost coz I won't be admiring the grain or colour). 40mm thick for my 2.1m x 2.3m span, with Western Red Cedar egg crate for the core at 150mm x 150mm centres. The Cedar is ok to use now that the logging practice has got sorted out.

It will be clad with a layer of symmetrical carbon/vinyl ester as a stress skin. There will be a little local deflection on the top skin under foot, but I'd rather have that and keep the weight down.

This is going to cost about A$450, and weigh in at about 40kg. In foam/epoxy it would cost 3 or 4 times that, and weigh maybe 15kg. You get what you pay for - sort of in reverse with boats, eh!

 

Yes there is the coast - but I really meant the COST.

 

Maybe ditch the glass altogether and epoxy a door skin on either side of a foam core. If you think it necessary maybe run a few fir stringers through the foam like in a surfboard for some strength and stiffness. Maybe just glass the bottom so there will be little fairing but the top will be smooth.

Or you could lay this up on a mica table too and that would give you a fair finish one side, could jack a little camber into it too which is good for several reasons, strength being a good one.

I made a much larger hard deck for a Mac Gregor 36 many years ago, used end grain balsa with a light laminate of glass either side and a grid of two 1 x 6fir stringers fore and aft and two atwarth. I had about 10" of camber in both directions. Was excellent for strength, we used to sit in deck chairs with a cooler between us and the tunes cranking, was a great improvement and total weight was around 300lbs , but more than twice as big as what you're looking at and a much larger span.

Steve

 

Just curious - what is this "door skin" material you American fellas keep talking about? I mean, yeah we do have doors in Oz, but they aren't usually skinned with anything you can build boats out of!

 

doorskin?

1/8" Lauan Plywood is commonly referred to here as doorskin.

http://www.clcboats.com/shoptips/stitch_glue/lauan_plywood.html

 

Foam is cheaper than wood

Gday Bad dog

I have found foam to be cheaper than timber now. That's why foam stripping is more popular than cedar strip. Shop around for your foam. I found a big variation in price for the same stuff. Still like ply though.

cheers

Phil

 

Maybe we're getting ripped off on foam over here!

 

pvc foam core

I would avoid polystyrene core (expanded and extruded) at (almost) any cost.
Probably the best core is Corecell (SAN) which has tremendous elongation to break and provides incredibly tough laminates when coupled with postcured epoxies in the skins. But this is contrary to the cost requirement.
Any of the PVC foam cores will do the trick, I have had some nice results with navicel, and we get it at really good prices in South Africa.
It compares favorably (albeit slightly lower) on mechanical properties to Herex C70-75, but seems (to me at least) to bend slightly better when heated with a heatgun for shaping round tight corners. Nice stuff.

The variations in local stiffness between PS core and wood stringers just feels like trouble in the long run. The first hand heel on the foam part of the laminate will leave a dent, and if close to a stiff shearweb in the form of a wood stringer, may cause the skin to crack.
PS foan is not closed cell, so this will ceratinly get waterlogged with time.

I once (audaciously) did floorboards for a racing rib using exactly this method.

Never got feedback from the customer. Never got any money either, so maybe the answer lies therein

On the subject of small little tiny multi's, can anyone please comment on the attached views of a 17 footer I'm working on?

 

In 1979 I made two hinged panels for a Crowther International 23 from 10mm Klegicell, coated with 10 oz f/glass cloth set in epoxy. Worked well.
I heard from the present owner and he said they are holding up fine.

 

The international 23 (in the background) had a collapsing beam arrangement looks like nested tubes have you considered that method of folding (sliding) for your cat Ray? You could easily integrate your hard deck with that system.

 

Yes. My two panels were hinged in the centre with a brass hinge strip.
When the hulls were slid inwards the panels folded Up.

 

Yes, I did. I might be wrong about this, but I seem to remember stories of tubing seizing up and being difficult to slide. If you've seen the L-7 trimaran, you've seen a better version of this idea. I'm trying to develop a system where there is no friction to overcome, so that the boat can be folded easily and quickly while on the water.

I think I'm going to use 1/4" ply stiffened with stringers, and filled with cheap foam for flotation. I used ply with stringers for a deck on another boat, and while it had a small amount of bounce, it was fine. Not the lightest solution, but cheap and strong and light enough.

 

No problem. I lubricated mine with Teflon spray.

 

need foam? go to nida-core

http://nida-core.com/english/nidaprod_foam.htm

I've used some of their honeycomb products, neat stuff...