marine plywood + alternative material

[TimStewart]

With reference to my question yesterday about deckhead repair of my achilles 24. I have 2 further questions.
1 what is the difference between marine plywood and ordinary plywood, plus how to tell the difference.
2 What alternative material could I use in place of marine plywood, which doesn't have the potential to absorb water over the years.
Thanks again in advance to anybody who replies.
Tim. /forums/images/graemlins/smile.gif

 

[William_H]

Marine plywood I believe has the better water resistant glue to exterior grade. don't know how to tell the difference except in the markings on the wood itself. There really isn't much alternative to plywood in practice and that is why it is used cos it is cheapest.
fibreglass could be used however to get the stiffness you need thickness. This can be acheived by using a foam balsawood or honeycomb sandwich.
These materials would need wood or solid reinforcing at places where bolts go through for things like chain plates or similar structural members.
if you used cheaper plywood with fibreglass over both faces you would need to make sure you sealed all edges against moisture ingress which can cause delamination (and use epoxy resin).
regards olewill

 

[mainmarine]

Marine ply and WBP [exterior ply] plywood use the same glue but the veneers used in marine ply are better and have fewer voids. Depending on the thickness needed, you could use a nonferrous metal or hardwood, to add strength instead of ply.
Malc

 

[KRG]

These people can help, I've seen a lot of plywood referred to as 'marine ply' which is really just exterior grade ply but a specialist supplier like these should see you ok.

 

[m1taylor]

Look for BS1088 which is the standard for marine ply - anything that isn't from a reputable supplier without that standard isn't likely to be marine ply.

 

[Graham_Wright]

1088 now has an alternative reference (which unhelpfully I can't remember) but neither guarantee the suitability of the plys for marine use. If you can find a friendly timber merchant, specify 1088, tell them it is for marine use, explain whether it will be immersed/wet and then look at the number of plys and feel the weight.

I have used 1088 for cabin interior work but the differences in weights and number of plys has varied considerably.

If the intended area is wet, you really need proper marine ply which will have rot resistant plys and cost you slightly more than double standard 1088.

 

[snowleopard]

A good quality 'exterior' ply is indistinguishable from the more expensive 'marine' type. A poor quality 'exterior' will have fewer layers and large gaps in the laminate. The trick is to look at the edges all round the sheet before buying.

Alternatives include acrylic - like window material but it can also be opaque. Vetus do a material they call 'plastic wood' designed for wet applications. It comes in sheets and is machined like wood. It's not cheap.

Solid or foam-filled GRP is longer-lasting than wood and, in the latter case, much lighter. It can't be bought off the shelf but you can make your own panels by laying them up on a sheet of melamine-surfaced chipboard which gives a good finish.

 

[Blueboatman]

Re:Alternatives to ply -under mast foot

Marine ply as discussed.

Close cell foam-will not take compression so thats only for cabintop and deck,ditto end grain balsa.Specialist plastic cores-ditto plus expensive and best with epoxy(more expensive again)....

Hardwood(Not Mahogany).Oak/Iroko is excellent so long as it is not totally encapsulated with grp-If you were to get moisture in it(any deck leak) it will remain wet,swell up and rupture the grp and/or eventually blacken and rot. So...
You could laminate a solid section of fibreglass/resin to the thickness of the old plywood beam on a table and then trim it to size and bond it in place.
Replacing the ply with ply is probably the easiest and most cost effective, user friendly way to go ,imho.
If you seal the edges of the ply with resin AND SEAL ALL THROUGHHOLES TOO (before inserting any throughbolts etc) ,then you will probably be going a long way toward removing the reason why the original piece became saturated in the first place.
Hope that helps.

 

[oldharry]

Sadly BS 1088 no longer guarantees good quality marine ply, and is as has been said, often indistinguishable from wpb. Generally speaking the difference is that the inner veneers are of inferior quality, and are thicker than the skin veneer, also there will be larger voids in wpb or exterior grade plys.

The only type of ply suitable for immersion and boatbuilding has all the veneers made of the same hardwood as the surface veneer, and all veneers of equal thickness including the surface sheets. Look carefully at the edge of the sheet, and if there is any difference between inner and outer veneers, walk away.

And it is not easy to find 'proper' marine ply these days.

 

[bilbobaggins]

As 'Muchy' has suggested, Robbins of Bristol are certainly able to provide the quality of ply you need, and guide you appropriately. They have a good reputation, and they stand by their standards.
However, do make sure that you 'know what you want' and tell them exactly so in your written order.

You will also be able to purchase from them the 'Gougeon Brothers On Boat Construction' book on using the West System of epoxy resin products, and other very useful data sheets. In there, you will find all the know-how you will need.

However, don't 'spoil the ship for a ha'p'worth of tar'. Use good materials, in the recommended ways, and you will have a satisfactory outcome.

 

[boatmike]

Tim,
Stick to marine plywood. All the advice on suppliers is valid but as you only need a small piece the trick is not to have to but a whole sheet to get it. When you know thickness and size post again and somebody will let you have a bit I am sure. (I may have some myself)
When you drill through for the mast bolts drill oversize holes and liberally coat holes and bolts with sikaflex. This will stop water ingress. Probably where it got in before.

 

[hylass]

alternative material

"What alternative material could I use in place of marine plywood, which doesn't have the potential to absorb water over the years"

Do you know a material called "Alucobond" and "Alucore"

I have used Alucobond to make interior furnitures and I like it: nice, clean, light, and very easy to work..

see on: www.alucobond.com