Plywood replacements

[knobblyoldjimbo]

Just out of idle curiosity (and with absolutely no intention of doing anything about it) I was looking at alternative products to use instead of ply.

 

My interest was piqued by two things, one was a response in SA, can't find it now but it was either related to Moth building or International Canoe building.  The other was a conversation with a Paper Tiger guy, Steve (Dipsy Dan) where he said that finding good quality marine ply that was also light was getting harder.

 

So, what I found (so far) was this list: 

1. Duflex from ATL Composites. (http://www.duflex.com.au/duflex2/)  looks the part but seems to be wickedly exy, 
2. PolyCore. (http://www.polycore-australia.com.au/News--and--Events.php) This stuff seems to be good too, the linky shows a large cat that someone built using it.  The website is a little confusing but if you google it there are some threads in boatbuilding forums where they are saying that you can now get polycore with .5 or 1mm layers of epoxy/fibreglass mat on each side.
3. Dragonplate.  A US company but I especially like the downloadable CAD plans that have the designs for you to make your own desk in cf tubing!  http://www.dragonplate.com/sections/Download-CAD-Models.asp

It seems to me that with something like polycore which seems to cost about $80 for a 6mm 2400x1200 sheet (1mm glass) you could build something like a PT for little or no more than ply.  Another thing is that, as far as I can see one of these sheets weighs 2.5kg compared to 4mm ply at 5.5kgs (gaboon).  This could mean that you could make a boat that is down to weight and can therefore add more stuff inside to stiffen the hull up.

 

Someone also talks about using a router to remove all but the layer of fibreglass thus leaving a layer to interface to the next panel.

 

Also it seems that you can buy the product in larger sizes, what about 4.8m x 1.2 - you wouldn't need to do much scarfing on a PT hull with that sort of sizing for example.  Maybe someone can generate a cutting schedule that has all the edges cut to the right angles for simple people like me to just butt and glue - just send off the schedule and get it all laser cut - job nearly done.

 

Someone also showed a veneered product, you could have a PT/Mozzie deck with walnut veneer and not waste too much in terms of weight.

 

KO

[korwich]

You're bored aren't you James?

[knobblyoldjimbo]

Yup! Fnnnng stiff!

Still I could be building a PT

[QB2]

someone on gumtree or ebay had about at least a dozen sheets of 2400 x 1200 marine ply for $50 .. unfortunately it was 10,mm and not 4mm otherwise i would have snapped it up

[CTMD]

I got very close to building a Duflex Paper Tiger when I lived in NZ as it was the biggest single handed cat class in the country at the time and we were designing a lot of Duflex cruising cats.  The cool thing about Duflex is they have a standard detail for joining sheets that is easy to do and works well resulting in minimal fairing.  The other advantage is that you can model the developable hull shapes and they will cut it out for you taking the joins into account.  So basically your kit will arrive as four 2.4x1.2m pre-laminated sheets with all your hull panels, bulkheads etc cut out but held in with small tags (or you could get them to join them for you into one big sheet (2.4x4.8m) before it leaves the factory .  Assuming you've prebuilt a nice big work bench it'll take you about an hour to glue the 4 sheets together.  Then the next day you can knock the parts out and start putting your puzzle together.

 

Ask nicely and I could even dig up the cutfiles for you.

[knobblyoldjimbo]

Interesting, do you remember what the costings were?

[CTMD]

Wouldn't have a clue (was going to tack it onto an order for a 50' cat) and it was 9 years ago.  Most the sheets we used to use had much thicker cores and heavier laminates and averaged out to about $600 per sheet although I have just found one old quote that used mainly Balsa Core and slightly lighter skins that comes out at about $350 per sheet.  Give them a call and ask what sheets would cost a good starting point for an unbreakable Paper Tiger would be DF1006X4 (I think) which would be 400GSM double bias either side of 6mm corecell foam.  With this laminate you wouldn't have to glass the whole hull just the seams and the boat would be a brick shithouse (but not a shithouse brick).  A better structure would come with 100gsm unis either side of the foam then you would assemble the hull and sheave the whole thing inside and out with 200gsm Double Bias.

[knobblyoldjimbo]

CTMD, so with the PT, Where you can adjust the shape of the boat to fit your requirements how does that work with these standard drawings? Also if you're using say 15mm Duflex then do you take that into account in the cutting file or do you have to make manual adjustments to the provided kit.

[CTMD]

It was modelled in 3d in the shape I felt was optimum at the time which basically had minimum deadrise in the bottom panels and max beam aft. You take the thickness into account when developing the panels so aside from some edge detailing you can build the whole boat without cutting or measuring a thing.

[knobblyoldjimbo]

Neat

[korwich]

There you go James, something to ease the boredom, you could glue it altogether in the lounge room while watching General Hospital and Days of our Lives. Just make sure you can fit it all out the door when you are finished.

[knobblyoldjimbo]

It is an interesting concept though.  For a lightweight like me the PT is a good fit.  Having a kit form that really did just need glueing together also makes a great deal of sense.  Using man made materials also avoids the pitfalls of trying to find the lightest piece of marine ply (and also hoping that it does stay stuck together since apparently the quality of most ply these days is questionable).

 

Using material that is lighter than ply would also allow one to make it stiffer by putting in more internal brackets (whatever they're called). Using material that comes already skinned using 'proper' pre-preg products also makes sense as it removes the variations in standard production techniques (including the need to use gel-coat).

 

Still, no job, no money to do this so I'll just have to leave it to others.  I don't understand why the PT association doesn't push this but there seems to be a lot of activity in the class (like a fleet of 20 PT's in Tasmania!) but not much on their forums.

 

If you can get 'kit' form PT's like this then there'd still be a lot of work, like the foils, but I bet CTMD has a CAD design that would cut the foam blanks all ready for skinning!