Marine Ply

[Cameron]

What exactly is marine ply like as a boat building material. Is it closer to GRP than traditional wood as my landlubberly upbringing siggests to me?

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[ccscott49]

Marine plywood, is Plywood, that will resist boiling in water, for so many minutes, it is meant to be a waterproof material, but in my experience is anything but! There are BS numbers etc and CE marks and all that guff. For interior work its fine, but IMHO for outside it's an abomination! The water doesnt dissolve the glue, but it does wick up the fibres of the plywood and delaminate the material and rots like hell. It can be made to resist a lot better, by sealing the edges and all over, with epoxy, which helps it a lot, but doesn't stop the material deteriorating. By the way, it is not made with epoxy glues, as they will not resist boiling. I even seal interior pieces with epoxy first. It is not like GRP atall, and only a little like solid timber. It does have its uses.

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[scarlett]

I was told by the dealer in Ply that it is the same as builders 'waterproof' ply but without voids and other faults on the internal ply layers----- which makes it twice the price.

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[tcm]

yep i agree. Long term, a bit useless cos of the delamination. So, fine for making sailing dinghies and erm landing craft i suppose. It has good dimensional stability so can be used for one-off fabrications, but there's nearly always a better material option, either aestheitically (real wood) or structurally (metal, grp). Main advantgae of marine ply: cheap!

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[Cameron]

Thanks for this. I also guess that a lot of evils can be covered up by a recent epoxy treatment?

By the way good tip from this site about the boats and outboards for sale website. The prices are pretty obviously without commission.

Cameron

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[kds]

I have a lot of good experiences with marine ply - but you do need to pay for good quality stuff. Value for effort, it is good, but like any wood - it does need protection.
Ken

<hr width=100% size=1><A target="_blank" HREF=http://www.canongrange.co.uk>Bed and Breakfast, cathedral Green Wells, Somerset Canon Grange</A>

 

[Talbot]

I think you are over criticising marine plywood, but you do have to make sure that what you have is the real deal, as some that is sold as marine ply is just standard building WBP with an inflated price. Thee have been some good long term builds using this material, which lends itself to the home builder for strength and utility. Good examples of this are the bob cats some of which are still going strong after more than 30 years (I know of one that has made it as far as Australia in the last 5 years) IMHO the cedar strip has replaced marine ply for most decent large boat building, cause even with tortured ply, you cant make the shapes that you can with the strips.

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[aitchw]

That's correct. The higher price of marine ply reflects the supposed selection of materials without the faults. In all other aspects it is the same.

As stated in other posts, ply needs careful treatment with epoxy if it is to survive any length of time. Initially, copious amounts of thinned epoxy until it just won't absorb any more and then less thinned, high build coats until there is no grain texture at the surface. Scrapes and gouges need immediate treatment to prevent moisture absorption.

It also suffers badly from flaking and chipping when being cut. Little bits of wood will flick up either side of the cut making a real mess of the finished appearance. Very fine blades, prescoring the cut line and patience help but it is always likely to happen.

I don't regard it as a cheap building material especially when you take account of the essential epoxy treatment and the care you have to take working with it but it does provide a very strong, light construction method for the home builder.

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[dickh]

The BS standard is BS1088 - which is just about to be dropped according to BS. Look at this website <A target="_blank" HREF=http://www.marineply.com/welcome1.htm>http://www.marineply.com/welcome1.htm</A> for all the info on marine plywood. Years ago you could get good marine plywood made from decay resistant wood, but not now. Can be faced with teak or to simulate the stripey floors on big yachts. Ideal for making bulkheads which can be glassed onto the hull. If the end grain is exposed water WILL get in and eventually start rotting. Traditionally all edges were faced with solid timber and nowadays as has been said, epoxy is used for sealing.

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[cliff]

Correct, so if you get good quality exterior ply it can be as good as maring ply at a fraction of the price.

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[leapfrog]

good quality marine ply is not cheap, we used to pay £ 150 a sheet for 12mm, it is in 1/1.5mm lamiations and is harder and heavier than anything your likly to find in builders merchants,
There was a place in witham. Essex, i think it was called brunzelles or somethink like that. i still have some of cuts that have been outside for ten years with no treatment on them and there is no delamiation, like all things in life, you pays your money and takes your choice.

Leapfrog

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[wagenaar]

You probably mean Bruynzeel, which is a dutch company that makes probably the best marineply. They use the name "Hechthout" for this ply. Try a google-search for it and maybe you can buy it directly in Holland if the quantity is large enough. I am certain, though, that they have a british importer.

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[robind]

Unfortunately, now a days, a lot of imported ply is poorly manufactured to low standards, and that includes both WBP and Marine grade standards. recently I purchased a sheet of "Marine" ply from a well known builders merchant/wood yard/hire shop/plumbers merchant, ad infinitum, which when cut manifested both problems with voids and compressed chips in its core. the blue stamped "label" on this sheet clearly stated that it was marine ply and made in Malaysia. When I took it back, in bits I might say, they weren`t keen to refund my cash as "they weren`t in the middle of this sheet so how could they know" but were persuaded to do so with some pressure regarding the SOG act and inclusion of the trading standards people )) I dont know what the answer is, to ensuring that you get only good quality. I would like to say that you should deal only with established specialist in the business and pay a lot of money! but I fear that this is not the answer.
Rob

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[floatything]

Do not confuse WBP (water and boil proof (I think)) with marine ply. Marine ply has no voids in the endgrain, and is also made up of layers of similar wood of a superior quality. Unfortunately it is also quite a bit more expensive. I have used WBP for non-critical work, but were I to be working on a ply hull then I would pay the extra and get proper marine ply.

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[mireland]

Good source is Robbins Timber in Bristol. See their good website for details

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[kds]

"Robbins"
Yes - but you still need to check every sheet as best you can as not all their ply is up to the standard shown on the label, IMHO.
Ken

<hr width=100% size=1><A target="_blank" HREF=http://www.canongrange.co.uk>Bed and Breakfast, cathedral Green Wells, Somerset Canon Grange</A>

 

[ccscott49]

I am not getting confused, marine ply has to be also WBP. The marine ply available today is not as good as it was some years ago, Bruynzeel as somebody has mentioned is very good, but the water WILL get into the end grain, if not sealed with something, preferably an epoxy or cascamite/urea formaldehyde type glue. It is a wondeful material for making furniture out of, but I wouldnt use it for anything which may get wet. This is a personal opinion, the only rot I found in Englander after 39 years, was in a ply roof which has now been replaced. Sorry I just dont trust the stuff.

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[rjp]

I can certainly second that, I got some real rubbish from them a couple of years ago. Some offcuts got rained on and literally fell apart - turned out there was very little glue between some of the laminates! To be fair they did replace 3 sheets for me, but wouldn't do anything for the time and labour spent removing sections of deck that I'd already cut and fitted. Oh, and it transpired that the advertised British Standard didn't mean that the material had been manufactured to British Standard at all. One to watch out for. Marine ply is a minefield!

John

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[oldharry]

It is extremely difficult nowadays to obtain good quality true Marine Ply. BS1088 is rubbish and is little more than WPB with a hardwood exterior veneer. But if you can get good stuff - and its a big 'if' nowadays - then it is a very good boat building material, provided the construction entirely covers all end grains, or they are protected with suitable sealant such as epoxy.

Modern plywoods are simply rubbish, and the BS1088 stamp which we used to rely on in the 60s is now virtually meaningless. Huge voids in the laminations, inferior glues inadequately applied, inferior grades of both the external veneer, and the internals all lead to 'ordinary' ply being a total disaster if used on a boat.

However a great many boats were built in the 50s, 60s and 70s using decent grades of marine ply, and while most of them have failed because of neglect - they MUST have a meticulous ongoing maintenance programme if they are to survive - there are still some quite old ones (my own Eventide 26 being one) still going strong in both senses of the word, and likely to last for as long as they continue to receive plenty of TLC. The great advantage of a properly built ply boat is that they are infinitely repairable on a DIY basis. Punch a hole in one, and it is a pretty straightforward job just to remove a section and replace it - well within a competent DIYers scope. A bit of rot somewhere? chop it out and glue a new piece in. A whole lot easier generally speaking than any other material used in boat building, with the added advantage over conventional wood construction that a well designed hull can be built to much lighter scantlings than her carvel or clinker counterpart without loss of strength. The natural curves of the hull impart considerable strength without the need for the large number of supporting frames found in conventional timber constructions. But they do need carefull maintainance.



The only real problem for the Plywood boat enthusiast is sourcing plywood of sufficiently good quality.

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[charles_reed]

Bruynzeel

Dick van der Stadt started designing under old man Dirk's aegis after the War.

Still, as far as I know, in business and probably the best-known manufacturer of plywood.

Apart from timber-type and quality the adhesive and processing are different.

Marine ply costs about x5 the price of usual indoor ply obtained in DIY sheds.
An alternative for out-of-water marine use is birch-faced external ply.

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