Marine Ply vs Exterior WBP

Little Rascal

Little Rascal

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Is marine ply worth the extra cost?

I'm replacing half a bulkhead on a Hunter Europa. It's 9mm thick and not really loadbearing as far as I can see, or at least low load. It's in the cabin so always dry (hopefully!) - although water damage is the reason for replacing it, I think I've solved the leak that caused it.

Looking at Robbins Timber, their Elite Marine ply is 45 quid more per sheet than their exterior hardwood WBP.

Is it worth the extra?

I know it's nice to say "marine ply...rubarb, rubarb... proper job... rubarb... nothin' but the best" when it comes to selling her on, but is there a real/structural reason why I shouldn't use a quality WBP?
 
FWIW, Sea Rush's saloon was clad in veneered MDF (yes, MBF, FFS!) when I bought her. It actually looked quite nice, so I decided to let it lie for a few years untill it all dissolved before ripping it out. That was some 24 years ago & it still looks much as it did when I bought her!

I've lost interest in replacing it now - it will do for a few more years yet and it definitely looks better than white GRP everywhere.
 
An often asked question and as many answers as you like.
It very much depends on the quality of the product, there is a lot of very poor quality marine ply [BS1088] and some very good WBP, often the birch faced ones. Internally WBP should be more than adequate.
How are you going to finish it? If you want to varnish go for a hardwood veneer, birch faced is good for painting.
 
Certainly WBP will be quite adequate for interior use.

Like all things quality varies.

My dinghy is made of WBP. It lives outside, although covered during the winter, and is still as good now as it was when made 32 years ago.
The box on my camping trailer, a few years younger and made of some cheap wbp, is delaminating!
 
It varies.
Even the cheap exterior ply from B&Q can be good. I made a thwart and bulkhead for my tender from it and i was fine.
OTOH, an offcut of a different B&Q 'exterior' sheet delaminated when I left it wet overnight. I was using it as a sanding block with w&d paper.

I think I would hope that the wood would stay dry anyway, inside a boat with an epoxy coating?
 
Just had birch faced reccomended by a supplier...

As you say, what concerns me is the variability of quality!
I used some Far Eastern from a 'Build Centre' a while ago but wasn't that impressed.

I shall go and look at it and muse...

Also need something for washboards - any thoughts?

Edit:

No epoxy coating, it's to be glassed in (polyester resin) and varnished/painted.
 
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IIRC, marine ply uses similar veneers and the same glues as marine ply, but is likely to have voids which may allow water to penetrate and do damage. You could prevent this if you sheath the edges all round and the sides in the bilges with a light glass cloth & epoxy.

Doing this you could use a cheaper ply, but I'd be inclined to spend the money on getting ply with a decent veneer to match the rest of the wood in the boat. You'll appreciate the superior appearance long after you've recovered from the heart attack the price gave you! :eek:

One final thought. I don't know how your boat is constructed, but bulkheads on most boats are structural, helping the grp mouldings to keep their shape and adding rigidity. If you replace half a one-piece bulkhead, the result may not be as strong as if you replace the whole in one go.
 
Stemar said:
...You'll appreciate the superior appearance long after you've recovered from the heart attack the price gave you! :eek: .
Click to expand...

Hmm... appearance rather a secondary consideration after function and price with this wee boat. A sheet of Robbins Super Elite represents about 8% of the value of the boat! Let's just say simple and workable is fine...

Stemar said:
...One final thought. I don't know how your boat is constructed, but bulkheads on most boats are structural, helping the grp mouldings to keep their shape and adding rigidity. If you replace half a one-piece bulkhead, the result may not be as strong as if you replace the whole in one go.
Click to expand...

The reason I say not especially structural is that the previous iteration - the Hunter 19 - simply had hanging knees at the deck join which didn't extend to the floors/berth height bulkhead. The thickness of the bulkhead as it meets the floor is only an inch or two - most of its rigidity is provided by the lengthwise side of the berth/locker. The floors themselves are a very thick lay up of glass where the ply seems to act only as a distance spacer. The bulkhead is effectively in two parts.

Some pics below.... the first show a locker I've taken out since.

The lower part of the bulkhead shown has gone soft through water damage. I had considered a quick fix of adding a doubler but I think the whole lot has to come out. :(
 
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OK, it isn't a huge piece and, as you say, appearance isn't the most important thing.

Looking at the photos, I reckon a half-sheet of ply will be more than enough to do the whole bulkhead and won't cost much more from a timber merchant than a bit to do a half job from B&Q.

What I'd do is use the old bulkead as a template and cut the new one from a bit of BWP. I'd then look at the edge that goes against the hull and, if there are any nasty voids, I'd seal them with a bit of epoxy & the same cloth you're going to use to fit the bulkhead to the hull. I'd then paint the whole piece with epoxy before fitting. Once it's all done, a lick of paint will look fine and the job will see you out!
 
Don't know if he is still selling but my son bought several sheets of faced marine ply from an Ebay dealer somewhere in the Southampton/Portsmouth area. He buys reject timber seconds from Oyster and much of it is virtually perfect. He had skips full of really good stuff, all sizes, and very reasonably priced.
 
Well I've just been to the timber merchant and also the boat.

The birch ply is good quality indeed, very consistant veneer thickness and no voids - just the finish is a little 'Ikea'!

In fact it's better quality than what is already there - which looks like Far Eastern WBP or similar with quite thin face veneers.

So on balance I'll use Hardwood WBP after all!

Thanks to all for the input!

Jon
 
As you are probably aware the usual build practice is not to bond the edges of the bulkhead directly to the hull sides. If done this can form a visible ridge on the exterior of the hull where the hull flexes during sailing. Probably could use some newspaper rolled, or polystyrene strip fitted between the edges of the bulkhead ply to make a 'bridge' then filleting as normal.

ianat182
 
Mdf

Searush said:
FWIW, Sea Rush's saloon was clad in veneered MDF (yes, MBF, FFS!) when I bought her. It actually looked quite nice, so I decided to let it lie for a few years untill it all dissolved before ripping it out. That was some 24 years ago & it still looks much as it did when I bought her!

I've lost interest in replacing it now - it will do for a few more years yet and it definitely looks better than white GRP everywhere.
Click to expand...

just for ref : tho mdf is no brill there are grades of mdf , or there used to be, completely waterproof grades.There are intermediate grades used for waterproof flooring bathrooms etc
 
Getting decent marine ply is difficult these days. Although most of the stuff I have looked at is stamped BS1088 I think I know what the BS stands for and it's not British Standard. If you look at the make up of the sheets only the ones running across an 8*4 sheet are thick ones. The ones running length wise Are the same thickness as the outer facing with the result that the sheet warps which as my old woodwork teacher told me many years ago should not happen. Robbins seem to be the only place left to get good stuff and it's now two arms and a leg for it.
 
There is some absolute rubbish around labelled WBP- I made a couple of hatch covers using this. They looked great, with 5 coats of varnish- but de-laminated in six months! Beware!
 
de-laminating

From experience ashore on buildings WBP ply can fail in a very short time, in one case a roof deck over 1 weekend while waiting for the felt roof. However a lot of builders merchants also keep marine ply, not perhaps the quality of Robbins but at a much mors sensible price.
 
If I need to test ply; I used to do a few boil cycles, now I just leave a bit in the dishwasher for a few days. Marineplyonline have good stuff at much lower prices than Robbins, esp for jobs such as this.
A
 
IIRC WBP (Weather & Boil Proof) is a grading which refers only to the type of adhesive used in the plywood. Not to the type of timber, not the quality of inner or outer veneers, not to the absence of voids, not to the resistance to delamination, not to the number of laminations etc etc not to anything except the type of adhesive. That is why anything from pine shuttering ply to far eastern destroyed rain forest rubbish to baltic birch ply to almost best marine grade will all have the label WBP.

It is not necessary to use certified marine ply for work inside a hull but it should be of good quality so you are right to select with care. Baltic birch for instance is often very strong, sound and well manufactured but the wood itself has very little resistance to decay.

Tim w
 
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