Thread: Stupid question..... or is it????

I think... gotta love that ... ahem.. I think

What your missing is not so much the encapsulation of the plys... but rather the plys themselves... okay so recommendation of most if not the majority of boat designers is for the use of Marine grade ply in their boats... some say its okay to use exterior grade... but NONE say its okay to use less than those two

Now the question is why not?... simple answer is... the marine grade ply and to a slightly lesser extent the construction grade (exterior) ply are made with few to no voids between the layers whilst the lesser grade ply doesnt discriminate and are often rife with voids and lapses in glue making for pockets where the plys will come apart or be missing... so whats that say?

It basically says that yes you could cut and make your ply panels for the boat or the planks if you will... and use inferior grade plys no problem BUT even with epoxy coating and a pre coat to seal the ply ON THE OUTSIDE... the ply interior will still contain those voids and missing glue... now what WILL happen sooner rather than later is that those voids and missing glues WILL make the ply laminates separate... this WILL cause failure of the ply and therefore the plank and therefore the boat itself.

Now on the other hand by using a superior grade ply preferably Marine but perhaps construction... there will be few to no voids and the glue used WILL cover the entire ply veneers in the making and thus there will be less to no chance of failure OF THE PLY... sealed and coated with epoxy and epoxy and glass will create a solid ALMOST indestructable peice of boat hull material with little to no chance of ply failure.

Okay so given that... one when purchasing the ply must take into account the use and intention of the boat to be built right?... so is it just going to be a boat for a couple of seasons? say a ply canoe... if so then use whatevers at hand seal with silicone and paint... actually thats just what I did about 4 years ago and it was till it flew of the roof out in Kal going great guns after then 3 seasons of use AND definantly abuse... but it was never meant to be perfect nor to last longer than one at the most 2 seasons it lasted 3 and I think probably with a bit of maintenance here and there lasted a few years more... now however if its a nice sized boat your intending to build or something that you intend to last for many years and be used by you AND your family on water deeper than say a foot or two... use the better grade be reasured by spending the money on a more reliable ply structure and enjoy it for as many years as you and your family look after it.

For anything less than a throw away bung it together ply canoe Id think... there I go again ... Id think that one would be better advised to use the best grade ply one can afford after all its the safety of you and your family or friends your putting on the line... buy the construction grade or if a larger boat then the marine grade

The epoxy when applied to the ply BEFORE construction begins or even after but before the application of the glass... is used as a sealer then with the addition of the glass it forms a hard outer covering which when combined with the same on the interior (although few glass the interior) will give an impenatrable surface for the hull for water ingress (which is the intent) which will take all but the most punishing of abuse... this is not so if inferior less than construction grade ply is used due to the instability of the nature of that ply via the voids and lack of glue in some areas... thus to gain the most from the whole experience and for longitivity the idea promoted by most if not all designers is for the better quality yes and dearer Marine or construction plys

Says he with thoughts that this same thing can be related to tools... buy the best you can afford and upgrade as you can.

Howd I get on Mik? Midge? daddles?

note... apologize to the guru of wooden ply double canoe building James Wharram for disagreeing with him on this matter

Shane, that's a horrible post. It's short (by your standards), to the point (amazing, did they change your drugs?) and accurate (I'll allow you to get away with it this time)

Marine plys also use a waterproof glue, cheap plys don't. If you search enough of the net, you'll find 'boil' tests where bods have dunked innoffensive pieces of plywood into pots and then boiled them to see what happens - cheap plys fall apart, marine doesn't.

Boat building materials are very much a case of 'you get what you pay for' and sadly, not a lot of it is cheap. In the past, timbers had to be chosen for their rot resistance - if it's in a boat, it's going to get wet. With the modern epoxies, it's possible to encapsulate the timber, thus keeping the water at bay. This enables us to use a lot of timbers that weren't appropriate before, but you do need to remember that any sheathing can be broken, thus letting in the water.

There's more to timber selection (including plywood) than rot resistance - strength, flexibility, weight, colour, all come into the mix as well but in general, coating with a good marine epoxy (which is bloody expensive) means you have a larger choice of timbers.

Me, I'm trying to give up guessing about this. Everytime someone like Mik starts talking about timbers, my brain goes into a death spin and not because Mik lacks the ability to explain things simply (the man is a marvel that way - he could teach my dog to build boats). So, when it comes to timbers, I listen to the designer (or someone with similar credibility like Mik) and take his recommendation ... even when it appears he's wrong.

If you did through the PD racer thread, you'll find a discussion there of what happened when Midge and Mik tried to use very cheap ply for their first boats

My two Mouseboats are made of pacific maple exterior ply - cost about $25 a sheet. One is over three years old, poxy coated and painted with high quality enamel - she's still going strong. The other is a couple of years old and painted with crap house paint onto the bare ply - she's still going strong too, but guess which one I expect to fail first

Richard

maybe you should get Mik to teach your dog how to build boats then the Yellowtail might have a chance of getting finished, You do leave your self open Daddles

So..... at the end of the day this wasn't so stupid question I was just missing all those things very nicely explained by you guys.

Thanking you very much. Some things are more clear now. Sun is shining at my "knowledge horisons"

Well done Ding!

And Alex, always remember, you can replace fittings that you decided to "cheap out" on, but it's really really hard to replace the ply!

cheers,

P

No, no..... I didn't want to go cheap, I was just wandering what was the secret in using exclusively marine and exterior ply. By all means I would go as directed by desinger but I just didn't understand all those things. Now I know.

Originally Posted by STEPHEN MILLER

maybe you should get Mik to teach your dog how to build boats then the Yellowtail might have a chance of getting finished, You do leave your self open Daddles

I'm happy to teach Dogs, but draw the line at cats.

You can't teach a cat Nuthing!

Hey Daddles, has your cat jumped up on wet epoxy recently - it had a number of habits incompatible with epoxy didn't it?

MIK

Originally Posted by Daddles

Shane, that's a horrible post. It's short (by your standards), to the point (amazing, did they change your drugs?) and accurate (I'll allow you to get away with it this time)

Marine plys also use a waterproof glue, cheap plys don't.

Richard

I KNEW THAT!! I was running outta breath is all

Theres a huge MASSIVE conglomeration of info out there on this net thing mate... some acurate and some not... even on some of the dedicated to boat building sites its amazing how wrong some people can be when they seek to educate and extrapolate on something while trying to big note themselves... which is why I come here... here you will probably get a verbose answer from some the likes of young daddleydaddles up there and probably get some short responses as he says "short, accurate and to the point" such as my small effort... but always lurking just under the keel are the ones who ACTUALLY KNOW stuff... like Mik and some would say Midgey ...no seriously hes cool and knows stuff too... well you dont built as many ply boats as midgey has and not know stuff eh!... and we must always be able to accept criticism of our peers... some places on the net they dont... they would post something like I did only wrong like I didnt and then argue fume froth an carry on like raw pork chops at a barbie to anyone who says the slightest thing contrary to their own words.

So be carefull when you read "advice" on the net particularily in forums... sometimes its bloody so far wrong to be damned dangerous... so check it out look it up from preferably the manufactures sites and definantly ask the designer why they recommend a particular thing... ahem if the designer is still breathing and contactable that is... I once had a bunch of boat plans that were like that damned nuisance when designers kick the bucket like 100 years ago

oh and another thing... if the plans you have are by a US or other international designer its sure as shyte the timbers they ask for recommend or suggest are for their own part of the globe... what Ive found is that they dont know shyte about our timbers down here (apologize to the US an international mobs yer excused from those comments ) so get yourself a good book on Aussie timbers in boatbuilding from somewhere (Mik? you know of one? I know a bloke from Melborne ahem now Canberra who sent me some info some time ago that I could probably scan again and zap to you in an email if you want) but anyways just check the timbers in relation to our own if you can BEFORE you start getting it all together... sorta saves some heart ache that way if you know what I mean?

Anyways seems I was right... AMAZIN!!!

Oh good, he's back on the green pills

Richard

Originally Posted by Daddles

Oh good, he's back on the green pills

Richard

Nah the red ones! cause everyone knows red makes yer go faster!!

which probably explains all those flamin pesky traffic tickets that keep piling up in the glove box eh?