nidacore vs plywood

Hi. I am planning the build of a 20' powerbost for aea fishing in the caribbean. I was planning on using 1/2" marine plywood fiberglassed onto a 2"x6" keelson and 2"x4" stringers and ribs. A good friend suggested i use 1/2" nidacore instead of plywood.
1)What are your suggestions on that advice?
2) if nidacore is used, how are the sheets fastened to the ribs? In the case of plywood, it is swrewed onto the ribs.

 

If you dont know how to fasten Nidacore = should you be designing for it ?


Some typical comments :-

"I wouldn't use it in hulls. Maybe in non structural parts like pilothouse roofs etc.

The trouble is that the core is made of polypropylene, which is very difficult to bond to. There is a fiberglass scrim that bonds to that but then you are relying on the bond to that, not to the core itself.

In short, it's not my favorite core. Plywood is also a fair bit cheaper usually.

.... A good foam would be better but NidaCore will work for deck and sole.
"

http://forums.bateau2.com/forum/viewtopic.php?f=8&t=3362

 

You can always make an emergency patch or repair in plywood with a few hand tools and some screws. If you are in St Lucia, materials are harder to get for foam core repairs. Also, it requires a lot more skills and controlled climate to get a good job.

 

yeah, but repairs in Foam will be a lot easier to get, and do, than in Nidacore -which is what the initial proposal was about.

If anyone bothers to read the discussion in the link, NidaCore is much more problematic to bond to most resins than foam.

 

Ok. Thanks for the most valuable reply. I have decided to govwith plywood. Another question is do you think I would be able to get away with using exterior 1/2" ply vs marine ply? I will be glassing inside and outside surfaces. I am looking at the huge cost difference as out here not even ply is cheap.

 

This has been said a lot, but here it goes again.

Do the math - lets say a 20 foot powerboat uses say 20 sheets of marine ply

Lets say you can get Exterior Ply for um, guessing here, $50 per sheet, and marine ply for $120 per sheet. You are saving $60 * 20, or $1,200.

Guessing again - now for a $1,200 saving , you are hanging a $12,000 motor, $2000 of paintwork, $ 6000 of epoxy and fibre, and say $5,000 of electric, fittings etc etc and say $10,000 of labour, consumables, overheads etc.

The plywood holds the whole thing together - and if it starts going wrong, you are risking the whole shooting match on say 5% of savings. ( $30,000 for $1,200 )

In two years, when the paintwork starts showing cracks, and you cant see delamination happening - and don't know if the hull is going to open up under heavy pounding in bad weather, you will curse the small amount you saved in ply.

Do the sums, using that kind of analysis, and you will see that its a false saving.

While you are at it, consider the small investment of proper plans - its the same deal.

 

What Mr Watson said, the structure is permanent, all the other crap can be unbolted and replaced but the **** plywood is permanent and fundamental.
False economy.

 

The difference in marine ply and house ply is not in the glue , there all the same.

It is claimed that marine ply is built with no interior voids , thats BS I can show you lots of so called MP with voids.

The difference is in both the wood chosen , and more importantly the numbers of plies in a thickness.

1/2 inch marine or aviation ply that is 5 or 7 layers is far stiffer than simple 3 layer house plywood.

The longevity of the boat depends on a certain stiffness , that only comes from many plies of wood.

 

Rwatson and Fred have given you the answers. The basic boat is what supports all the other stuff. To skimp on the foundation is false economy.