Alternatives to plywood?

Kelpie

Kelpie

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I'm toying with the idea of building a stitch-and-glue dinghy, and, just to prevent it being too straightforward, I'm wondering about using some sort of composite sheet rather than plywood.
One option would be 'Nidaplast'. People have built boats from it before, but I'd like to get an idea of how it actually compares to plywood in stiffness etc.
There is a data sheet here:
http://www.ecfibreglasssupplies.co.uk/images/TechnicalDataSheet/576.pdf
but I don't know enough about how to interpret it and compare it to plywood- could any of the resident material scientists enlighten me at all?
And are there any other sheet materials I should be considering? Or should I just be sensible and stick to plywood...?
Many thanks
 
It's a core material.
The stiffness comes from being sandwiched between two layers of GRP, carbon or whatever.
Do you actually need a lot of stiffness for your dinghy?
 
lw395 said:
It's a core material.
The stiffness comes from being sandwiched between two layers of GRP, carbon or whatever.
Do you actually need a lot of stiffness for your dinghy?
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I'm not sure. People have built them using this stuff with carbon skins. Presumably you can achieve the same thing at a much lower cost, but extra weight, in glass. As the dinghy is designed for plywood construction I would want to aim for materials with similar performance.
 
When I was at school one of the students (aged 15-16)built a pram dinghy in the woodwork class out of good quality oil tempered hardboard ( not the mushy stuff from B & Q!!). Very light when done. All went together easily. He did it in the evenings over one term & painted it when complete.
I expect that these days he could have epoxied it. Possibly cover the outside in a glass mat such as 300 grm cloth.
Seems to me an adult with a garage could build one in a few evenings & looked after would save a lot of money. Even if it did not last so long as one built from hi-tech material one could always knock up another really quick once one had the plans & a couple of patterns.
 
Fibreglass sheets (instead of plywood) would be the way to go - but you would have to laminate them yourself (which is pretty easy really) unless you can find a supplier in the UK.

McMaster Carr in the USA sell them - McMaster-Carr
Maybe somebody in the UK does something similar?
 
Bajansailor said:
Fibreglass sheets (instead of plywood) would be the way to go - but you would have to laminate them yourself (which is pretty easy really) unless you can find a supplier in the UK.

McMaster Carr in the USA sell them - McMaster-Carr
Maybe somebody in the UK does something similar?
Click to expand...
Fibre glass sheet material is very expensive in the uk e.g 3ftx2ft 5mm about £80, so a dinghy about £600, less discount for quantity.
 
If you can get hold of a large sheet of glass, from an old shop front or similar you can make your own sheets.
I have seen a trailer manufacturer (small Luton vans etc) who just made sheets of varying thicknesses with differing numbers of mat to suit the job.They were all just laid over the glass so came up perfectly flat. I do not know if the gel coat was applied first or last but one could experiment with that & also if a release agent was needed
 
C08 said:
Fibre glass sheet material is very expensive in the uk e.g 3ftx2ft 5mm about £80, so a dinghy about £600, less discount for quantity.
Click to expand...

The logical thing to do then is to laminate some sheets up yourself - it is not difficult.
Just need a suitable mould surface - this could be an 8' x 4' sheet of Arborite / Formica glued to something to make it more stiff (eg a sheet of chipboard if cost is a priority).
Or a sheet of glass as mentioned by DB above - but glass is fairly easily breakable......

I made some 12' long x approx 3'6" wide fibreglass sheets for a dinghy using a 12' length of galvanized steel sheet - bought from a roofing company before they put the corrugations in it. This resulted in a fairly ideal mould surface.
You would still have to apply mould release wax first to ensure that the fibreglass sheet releases easily.

I would not worry to use gelcoat to make these sheets - if you will be using them like plywood for a chined dinghy then you will still have to overlaminate the joints on the outside with glass tape and resin. You could coat the dinghy with gelcoat afterwards, although it would probably be easier to simply paint it.
 
Bajansailor said:
The logical thing to do then is to laminate some sheets up yourself - it is not difficult.
Just need a suitable mould surface - this could be an 8' x 4' sheet of Arborite / Formica glued to something to make it more stiff (eg a sheet of chipboard if cost is a priority).
Or a sheet of glass as mentioned by DB above - but glass is fairly easily breakable......

I made some 12' long x approx 3'6" wide fibreglass sheets for a dinghy using a 12' length of galvanized steel sheet - bought from a roofing company before they put the corrugations in it. This resulted in a fairly ideal mould surface.
You would still have to apply mould release wax first to ensure that the fibreglass sheet releases easily.

I would not worry to use gelcoat to make these sheets - if you will be using them like plywood for a chined dinghy then you will still have to overlaminate the joints on the outside with glass tape and resin. You could coat the dinghy with gelcoat afterwards, although it would probably be easier to simply paint it.
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If you want it light and stiff you could make up your own sandwich panels using a layer of cloth for the inside face and a couple of layers for the outside face. Use Airex core or similar. You get stiffness, lightness and floatation.
 
geem said:
If you want it light and stiff you could make up your own sandwich panels using a layer of cloth for the inside face and a couple of layers for the outside face. Use Airex core or similar. You get stiffness, lightness and floatation.
Click to expand...

Trouble is, if you make up the foam sandwich panels beforehand they might end up being too stiff, and it would be very difficult to bend them around the curvature of the hull.
I have started to build a dinghy (just under 12' long) using single skin fibreglass sheets - I hope to one day finish it.
It has two chines each side, hence the widths of the panels are fairly small; the widest at the bottom panels.
And if they seem to be too 'floppy' I will just glass in some foam stiffeners as required.
 
Nick Turner made a Merlin Rocket from foam sandwich planks, so it is definitely do-able.

I believe one method is to lay up glass and resin on one side of the foam to make sheets. Then build the boat, then glass the inside.

Also look at the UK Cherub website.
 
Tape together the design as a female mould in hardboard with the shiney face inside. Wax it lavishly. Laminate the hull with cheepo mat and resin, then rip off the hardboard and tidy up. You have a boat.
Personally, I like ply, having grown up in that type of construction (and still doing it..) it is quite stiff, more so than GRP, but getting expensive for even half decent stuff.
 
You would have a very flexible boat. It would definitely want a core, which could still be done in the manner you're suggesting. I'd love to see it don't with a rib/inflatable dinghy.

The fibreglass work would be laborious and expensive. Polyester rather than epoxy would save some cash, but you'd still need some form of barrier coat.
 
Derek Kelsall has been building boats of flat sheet, foam cored fibreglass for about 40 years. Everything is laminated on a flat formica table and then joined with secondary bonding.,
 
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