Likes Likes:  0
Needs Pictures Needs Pictures:  0
Picture(s) thanks Picture(s) thanks:  0
Page 1 of 3 123 LastLast
Results 1 to 15 of 37
  1. #1
    Join Date
    Apr 2012
    Location
    Southern Califorinia
    Posts
    40

    Default Marine Ply vs Standard Ply test

    Hello. I just registered and this is my first thread.

    I am planning on building my first canoe, but have not yet decided between electric or standard quick canoe.

    Most forums and articles I have come across recommend the use of marine grade plywood due to its superior quality of construction when compared to standard plywood. I came across a youtube video, presented in two parts, that disputes this recommendation.

    In Summary (of the videos):

    22"x6"x3/4" plys are used. They are gradually loaded to failure.
    Standard ply failed at 617 #s.
    Marine ply failed at 680 #s.

    Marine ply is only 10% stronger but 3 times the cost.

    Two plys are coated with 1 coat of epoxy then placed outside in water for 54 days. The water froze during part of the test. Also, due to evaporation, parts of the boards were exposed to atmosphere.

    The plys are then again tested.
    Standard ply failed at 520 #s.
    Marine ply failed at 481 #s.

    Based on these tests there does not appear to be any reason to buy the marine ply.
    The videos can be found at the following links.

    Part 1

    [ame="http://www.youtube.com/watch?v=_ymEoivrrK0"]Marine Plywood and Construction Adhesive Testing - Part 1of 2 - YouTube[/ame]

    Part 2

    [ame="http://www.youtube.com/watch?v=IY7hkCexNVY"]Marine Plywood and Construction Adhesive Testing - Part 2 of 2 - YouTube[/ame]

    The second half of Part 2 compares 4 adhesives: liquid nails, PL heavy duty, PL premium, and AeroMarine Epoxy.

    AeroMarine Epoxy was declared the winner. However both AeroMarine and PL premium were shown to be stronger then the adhesive used to bind the layer of the of the Marine ply.

    I am hoping that the experts on this forum would view the videos and share their thoughts on the matter. If contrary evidence is not presented then it makes no sense to purchase the marine grade ply.

  2. # ADS
    Google Adsense Advertisement
    Join Date
    Always
    Location
    Advertising world
    Posts
    Many





     
  3. #2
    Join Date
    Jan 2005
    Location
    Melbourne
    Age
    65
    Posts
    11,997

    Default

    I love practical comparisons like this - great stuff!

  4. #3
    Join Date
    Oct 2011
    Location
    Victoria, BC, Canada
    Posts
    76

    Default

    I've built a couple quick dinghies out of exterior grade fir plywood and for anything that takes more than a few days to build I'd definitely spend the extra for real marine plywood. I went with top quality Joubert Okoume plywood for my sailing canoe and if I'd gone with the cheap lumberyard stuff I'd have saved about $300 on a $1600 project. For me it's worth the extra many times over because marine ply is far, far nicer to work with, looks better and is more reliable. Fir plywood tends to check (crack) and get a rough surface after a while in use. It, at least around here, comes with lots of filler "footballs" to plug knots and as a result likes to break in a tight bend. There also tend to be many voids on the inside that can greatly affect strength in those areas. Those stress tests might make the woods appear similar but in actual practice there is a big difference. Plus, ultimate breaking strength is only one of many characteristics that matter.

    I've also used Meranti marine plywood which is about 60% of the cost of Okoume while still being nice to work with and more rot resistant. The downside it that it's heavier.

    I'd say it really comes down to what you're looking for: if you want to slap something together quickly and get out on the water then fir and PL premium can work fine but in my experience it's a false economy and makes the build harder, the boat heavier and generally isn't worth it for anything that you're going to put significant time into.

  5. #4
    Join Date
    Apr 2012
    Location
    Southern Califorinia
    Posts
    40

    Default

    I have been thinking about why the marine ply would lose more strength after exposure to the elements then the standard ply. During the testing of the adhesives, the failure point, at least with the PL premium and the AeroMarine, occurred at the adhesive between the laminates of the ply. The Marine ply has 7 layers and the standard ply has 5, which means that there is more adhesive used in the marine ply. If the adhesive is the weak link in the chain, then that might explain why the marine ply failed at a lower load. I guess the only way to confirm this is to test both plys with the same # of laminates.

    In regards to appearance. In Southern Califorinia, my local Home Depot carries Sandeply hardwood plywood. I saw it yesterday at the store. it was very uniform in color and appearance. I did not find any fillers. it was priced at $20 a sheet. Do you know anything about this wood?

    In regards to the adhesive. I am planning on using the PL premium as the filler (fillet?) for the joints. I will be using epoxy inside and outside. The interior joints will be protected with fiberglass tape and for the outside i will use fiberglass cloth. Do you know if PL premium is compatible with epoxy? If it is, do i need to wait for the PL to completey cure before applying the epoxy and fiberglass?

  6. #5
    Join Date
    Jun 2007
    Location
    Aberfoyle Park SA
    Age
    63
    Posts
    1,787

    Default

    G'day Blue
    I see you are in USA.
    You'd need to look at the actual specs of the two bits of plywood under test,
    and I don't know what your equivalent standards would be.
    There are several thread in this forum about plywood - this post is especially informative:
    https://www.woodworkforums.com/f32/au...ml#post1139226

    I guess the key thing about the two standards in use here - BS 1088 & AS/NZS 2272 -
    is that the genuine article cuts no corners in the core veneers.
    High grade construction plywood goes close to marine but, at least in AU, it
    isn't much cheaper. Here, your average, off-the-shelf sheet of 'exterior'
    plywood can be a huge step down in quality & still cost the same or more
    than genuine BS 1088 from Asia. So price difference is less of an issue here.

    Also, as you are building a canoe, may I suggest you don't have the luxury
    of 1/2" of timber between you & the briny. You should be building out of 1/8",
    3/16" or 1/4" at thickest. If you are doing more than building a cheap disposable
    canoe (the Quick Canoe's design brief), those plys had better be good ones!
    The time you find out the core of your 3-ply is filled with putty, is the time it
    (and you) are under most stress... For this reason, and having built several
    kayaks over the years, both in marine ply & selected construction ply, I'm
    happy to cough up the extra for marine.
    cheers
    Alan J

  7. #6
    Join Date
    Jun 2007
    Location
    Aberfoyle Park SA
    Age
    63
    Posts
    1,787

    Default

    Re-read your initial post.
    IIRC, MIK's spec for Quick Canoe is 1/4", so ignore the 1/8 & 3/16
    In construction, that's probably 3-ply vs 5-ply in marine.
    You'd probably see a somewhat bigger difference in performance between
    3-ply & 5-ply than between the 5-ply & 7-ply in the videos, Especially for
    loading across the outer veneer grain rather than along it. The 5-ply will
    withstand point loading like hanging on a rock much better than 3-ply.

    It would be interesting to see those tests repeated with a square of ply
    suspended only at the 4 corners, and the load applied to a small diameter circle
    in the middle. I expect the panels would break in their 'weak' direction rather earlier...

    Also must comment that the single coat of epoxy in the video test is
    inappropriate application of the product. Pox should always have 3 coats
    applied to guarantee the moisture barrier. Any less, and there's really not
    much point in spending the $$ applying it.

    cheers
    Alan J

  8. #7
    Join Date
    Jul 2005
    Location
    'Delaide, Australia
    Age
    65
    Posts
    8,138

    Default

    Howdy,

    Before I take it to pieces ... this is a really nice clip. I am all for people actually trying things to see what happens. Great stuff.

    BASIC UNDERSTANDING OF MATERIAL SPECIFICATION

    The biggest determinant of plywood strength are
    1. Timber density as an approximate check of strength and stiffness
    2. The relative thickness of the veneer layers
    3. The absence of voids


    The only part that the marine ply standard controls are the voids.

    Marine plywood controls
    1/ the size of the allowable voids and patches and the allowable materials for repairing them.
    2/ the type of glue

    Basically marine ply allows a smaller size of void and a smaller size of patch. So the timber veneers have to be better quality.

    Exterior, Marine and Aircraft ply all use the same glue. So no difference

    So from this we know we need to check
    1/ the weight of each piece of ply.
    2/ the relative thickness of the veneers - if the outer veneer with timber grain running the length of the test piece is thicker compared to the other veneers - doubling the thickness of the outer veneer will very roughly double the strength. However you lose that same strength in the other direction. In recent years we have seen plywood manufacturers reduce the thickness of the outside veneers to almost paper thickness. This can make a huge difference in strength.

    The standards for the different plywoods are also MINIMUMS! This means that some exterior plywoods can be WAY better than a bad marine ply in terms of voids.

    For example the Hoop Ply plywood manufactured in Australia ... the exterior ply used to be just amazing ... you could look at a metre thick stack of it and see not a single void on any plywood edge - better than most marine plywood. The problem of course is that the Hoop pine ply is about the only plywood in the world that is just shy of 8ft by 4 ft which can mean that some boats don't fit on the smaller sheets.

    STATISTICAL RESULTS FROM USING MULTIPLE SAMPLES

    Ok ... now for the methodology. The two pieces are within 10 percent in terms of weight bearing

    I've spent a reasonable amount of time in labs ... you never trust a test that relies on a single sample.

    Typically for this type of test you would do maybe 20 pieces. Then see how they look on a graph - get rid of any anomalous results that are too far different from all the others.

    Typically for tests like this you might find out of your 20 pieces of each type of plywood ... that most of the exterior ply samples would have weight bearing and deflections within around 10 percent of each other. However it is really common that out of 20 samples you might have one or two that are 50% stronger or weaker.

    However if you test just one piece ... then you never know whether it is near the average or one of the ones significantly stronger or weaker.

    And that is just the exterior ply ... now was the piece for the marine ply a strong one or weak one or ... what?

    EXPERIMENT METHODOLOGY
    One of the good things about breaking and bending lots of pieces is that it is a good test of how good your experiment design is.

    If you find a really big variation in sample strengths for the same ply then it means that your experiment is poorly designed. Maybe the supports move around a bit ... or the location of the weights added varies a bit each time or some other factor.

    With a good experiment maybe the strengths will stay within a narrow band. But if every piece varies between plus 50 percent of the average and minus 50 percent of the average .. then the experiment is wrong.

    So multiple samples are a test of your experiment too.

    EXPERIMENT DESIGN 2
    The other missing part is that there is no test for when the plywood starts failing.

    The normal way is that initially as you add weight ... the deflection varies directly with the weight.

    twice the weight is twice the deflection. This means that if you remove the weight then the plywood will resume its original shape.

    So the piece hasn't failed ... yet.

    However at some point the two go out of kilter. You add a bit more weight and the deflection increases more than expected. This usually means the plywood is starting to fail.

    In fact .. for boatbuilding this is EXACTLY what we want to know! We don't want the piece to break .. we want it to behave perfectly and resume its original shape.

    But breaking it ... proves nothing really. Because there are so many ways that something can fail. Is it the weight or a bit of a hard edge on a couple of the lead pieces creasing the top veneer of the ply. Or some flaw in the ply in that particular location.

    CONCLUSION
    Well ... it is interesting ... but more work is needed to come up with a real comparison that is truly useful.

    But you can look at what I have written above and get some idea of how to set it up to be a real test.

    Best wishes
    Michael Storer

  9. #8
    Join Date
    Jul 2005
    Location
    'Delaide, Australia
    Age
    65
    Posts
    8,138

    Default

    Now for Glues.

    From my perspective there are interesting new glues ... usually water based to some extent ... usually polyurethane or crosslinked PVA (yellow glue). There are lots of different brands.

    I will group them together as "alternative glues". This is only for my own convenience, but I will explain my position.

    1/ All glues except epoxy are non gap filling and

    2/ require high clamping pressures
    High clamping pressures only make sense if the fits are very good.

    The labels say this.

    2/ They also say the glues are not waterproof enough for marine environments.

    This doesn't mean you can't use them at all .. just to know where and how they can be used.

    GAP FILLING
    It means more than filling gaps .. it means that the glue can fill a wider space and carry load across the joint.

    All the alternative glues rely on close fits. Surface to surface contact. With pressure. This almost inevitable means using clamps.

    With epoxy you can use drywall/plasterboard screws as temporary fasteners with full bonding strength between ply and the framing or ply to ply or whatever. Some building methods depend on this - such as epoxy filleting or some boats that have a modified clinker where there is a vee shaped gap where the planks overlap .. and it is just simply filled with epoxy paste.

    The masts on my boats are epoxy glued .. and the spar is held together by working along clamping, then wrapping packaging tape around the spar next to the clamp .. then releasing the clamp and moving it 200mm up the mast and doing it again.

    You don't need a truck load of expensive clamps for epoxy boatbuilding.

    Wherever you can get good tight fits and good clamping pressure the alternative glues can be very good indeed. But you need lots of gear. Nice if you have it already. Then there are places where it is hard to get a clamp on ... like when the bottom goes on the boat after the side ply is on .. there is not edge to put a clamp on.

    I'll explain more a bit lower about what it means.

    HISTORY
    Before epoxy there were two common marine glues. Urea formaldehyde and resorcinol. Some also used casein glues for areas that were not subject to tooo much water.

    These were also gap filling glues that required high clamping pressures.

    The racing boats I sailed in the '70s were built with these glues.

    You could buy a boat two or three years old that was a bit leaky. It would be good to start sailing with. You could improve it a bit using glass tape with POLYESTER resin (EPOXY is much better because it actually bonds to the wood for fibreglassing). That would stop the leaks for maybe a season or two ... but they would gradually start up again. Also the paint would require work every couple of years as the ply sucked in moisture and released in cracking the paint in that period.

    I got into plywood boat building more professionally in the late '80s. Lots of people started building because epoxy ... being gap filling and requiring low clamping pressures reduced the risks of a miscut or slight sloppiness in assembly. Also as above you just needed a cordless driver and a roll of brown packaging tape rather than a couple of dozen or four dozen metal clamps.

    So that was the building advantage.

    However there was a more important difference ... instead of the boats deteriorating over two or three years of hard sailing (there were exceptions ... but speak to anyone who bought second hand boats over this period) ... the epoxy ones ...

    Never leak when launched
    Never start leaking with hard use
    Never break
    The paint and varnish go on for two three or four times longer than if you used alternative glues and conventional paints.

    USES OF ALTERNATIVE GLUES
    So ... places where you can use alternative glues are

    Any place you can clamp .. if you have clamps
    Any place where you can get a good fit. A good place is laminating or spars or when putting flat framing on flat plywood.
    Also where you are happy for the boat to go well for a couple of years without serious maintenance or maybe substantially longer with luck.

    Epoxy is great for my work as a designer ... because the boats end up absolutely reliable regardless of the builder's skill level.

    Regardless of where they are built.

    You can see more discussion about specific epoxy info on my FAQ ... have a look at doing repairs because of no fastenings.
    www.storerboatplans.com/Faq/faqindex.html

    Great questions and observations BLUE SAILOR!

    Michael

  10. #9
    Join Date
    Apr 2012
    Location
    Southern Califorinia
    Posts
    40

    Default

    Thank you gentlemen for the very thorough and informative replies.

    Mik, after reading what you posted and then reading the FAQ's page, my mind went numb.

    After a few phone calls i found a local lumber yard that sells marine grade ply. they have it in 1/4" thickness for $54 per sheet with a rating of A-A. The wood used is douglas fir.

    I didnt realize that buying good quality standard ply was such a hit or miss (more miss then hit i suppose). Hate to find my self in the middle of a lake with a leak. And i will go with epoxy all around and leave the PL out.

    I have specific questions about the quick canoe, but I will ask them in the quick canoe thread.

    thanks again.

  11. #10
    Join Date
    Apr 2008
    Location
    Connecticut, USA
    Posts
    414

    Default

    I feel silly adding to what MIK has already written, but I will say this:

    Most non-marine plywood, even exterior grade, is designed for rectilinear buildings. Flat faces on polyhedra. Very few buildings have curvy walls.

    Marine plywood is designed with the knowledge that it will probably be bent when used. Not too many flat surfaces on a hull. Good behavior when stressed is built in.

    Good non-marine ply is surely better than bad marine ply. I've seen some Chinese crap which I would not trust to keep my family safe at sea. But if you stick to the good marine stuff, European-made and Lloyd's-approved, you are much more likely to get fair curves and strong hulls. Totally worth the extra cost up-front.

  12. #11
    Join Date
    Apr 2012
    Location
    Southern Califorinia
    Posts
    40

    Default

    Thanks for the additional info paulie. Considering the wonderful replies i have received i am very glad i registered on this forum.

    I agree that spending the few extra dollars upfront significantly reduces the potential for future problems. And as we know, problems tend to show up at the most inconvenient time.

  13. #12
    Join Date
    Feb 2008
    Location
    Eustis, FL, USA
    Posts
    2,270

    Default

    Well, Mik beat me to it, but the videos, noble effort and all, are flawed across several of the usual practices we use in testing, so the data is essentially meaningless.

    Considerations in panel usage in the marine environment, typically require dynamically capabilities. Construction grade panels are intended for static loads. The construction of the panels bears this out by the use of more uniform veneer quality, thicknesses and most importantly count.

    A 1/4" (6 mm) BS 1088 or 6566 sheet will have 5 equal thickness veneers. These veneers will be tightly arranged, free of notable defects (6566 does permit slightly larger internal defects), they will not be over lapping each other and assembly pressures regulated during the cure. A 1/4" construction grade (APA "Exposure 1" grade) will have 3 veneers and the middle veneer will typically by substantially thicker than the two outer veneers. This internal veneer does have to have good rot resistance, but doesn't have to be the same species, plus it can have substantial gaps, voids, juvenile wood, pith, checks, splits and other significant defects. The outer faces are graded by quality.

    The AA grade your local supplier has suggested, says absolutely nothing about the construction of the sheet, just that it should have two, perfect, sanded faces, free from defects (that's what the AA grade means).

    The only acceptable marine grade with a USA marking is the APA PS1-07 stamp. Actually this grade has been recently changed, but I haven't looked up the designation that replaced it, though your supplier should know.

    Back to the dynamic loading thing. If you take a construction grade panel and bend it into shape on a boat, then ask it to flex repeatedly during it's life, you can expect it to fail pretty quickly. It just doesn't have enough veneers or enough quality in it's construction to tolerate these types of loads for very long. This said, you surely can us a construction grade on a canoe or kayak with good success, mostly because these boats are lightly loaded. I know many that use "underlayment" panels for just these types of builds.

    On larger boats, particularity powerboats with some speed potential or stayed sailboats with high aspect rigs, you'll quickly find out why we insist on the marine grades. I've seen construction grade literally explode after being hung on a boat and screwed into place.

    Simply put, the hull's planking is often some of the best material on the boat, partly because it's what keeps your socks dry, but mostly because loading is almost always transferred to the hull shell somehow, so it has to be up to the job. You can cut costs with bulkheads, furniture, cabinets, lockers, cockpit seats, etc. These are areas were loading is often local and you can get away with it.

    The price they've given you for that AA sheet is high, so maybe you need to shop around. Also, Douglas fir in an AA sheet is a waste of time, you can't finish it. As soon as you touch it with a sander, it turns into a washboard and you'll never smooth it out without gallons of filler. A good quality 1/4" meranti BS-6566 sheet (typically called Aquatech) will run about $40. It's faces will be perfect or nearly so and it can take a finish without going insane. A better grade would be what's commonly called Hydrotech and it's also a meranti sheet, but to the BS-1088 standard, which is the best. This sheet should be about $50 and it's the usual recommendation for hull panels, unless light weight is desired (isn't it always). If you need a light, strong, quality panel, then you want Okoume sheets. These are often from Joubert Marine and are very good (what I usually buy). They'll runabout $80 a sheet for 1/4". There's also some Lloyd's stamped (the BS-1088 stuff) stock I've been getting from Italy that's also very good and about the same price.

    What's all this stuff mean? Well lets say you have a canoe design and it calls for Okoume panels and weighs 30 pounds. Well if you build it exactly the same way, but use Meranti, it'll be a 37.5 pound canoe. If it's Douglas fir slightly more and if you are toting this canoe around the woods, looking for a place with thick enough water to splash it in, you'll pretty soon wish you'd used Okoume.

  14. #13
    Join Date
    Oct 2007
    Location
    Poland
    Age
    67
    Posts
    805

    Default

    And my two words :

    In Poland we often uses local (domestic) plywood without "marine" label for boatbuilding but for this purpose plywood must be waterproof!!! We often uses an "external" class of plywood, which has really similar parameters to the "marine" plywood, but it's price is low - you can boil a piece of this plywood by many hours (over 24 hours) without delamination.

    My BETH is built from domestic production "external" (waterproof) class birch plywood - with success!
    Aloha!
    Robert Hoffman
    http://robhosailor.blogspot.com/


  15. #14
    Join Date
    Feb 2009
    Location
    Adelaide - outer south
    Age
    67
    Posts
    935

    Default

    Veneer thickness was discussed earlier but one other point on that is that for a clear finish a thicker outside ply reduces the risk of sanding through it which significantly affects the appearance.

    As an illustration of voids the picture below shows the bottom of a stitch and glue kayak hull with a 120 watt floodlight inside it. The horizontal lines and dots are joints and stitch holes which have been filled with epoxy/wood flour and it is expected that a strong light will shine through them.

    The vertical lines are voids in the ply . Yes it is an exterior grade, 4mm, with thin exterior veneers. I got away with it because it is a small hull and sandwiched between layers of glass/epoxy. In a larger boat, who knows?
    Attached Images Attached Images
    Cheers, Bob the labrat

    Measure once and.... the phone rings!

  16. #15
    Join Date
    Oct 2007
    Location
    Poland
    Age
    67
    Posts
    805

    Default

    Quote Originally Posted by labr@ View Post
    Veneer thickness was discussed earlier but one other point on that is that for a clear finish a thicker outside ply reduces the risk of sanding through it which significantly affects the appearance.

    As an illustration of voids the picture below shows the bottom of a stitch and glue kayak hull with a 120 watt floodlight inside it. The horizontal lines and dots are joints and stitch holes which have been filled with epoxy/wood flour and it is expected that a strong light will shine through them.

    The vertical lines are voids in the ply . Yes it is an exterior grade, 4mm, with thin exterior veneers. I got away with it because it is a small hull and sandwiched between layers of glass/epoxy. In a larger boat, who knows?
    In Poland we have 4 classes of plywood of domestic production. 1st is excellent and 2nd class may have little knots, but they must be filled and covered/plugged with veneers, and the outer layers of veneer are pre-sanded and smooth. Any veneer defects in any of the layers are not permitted. I've used class 1by2 (different classes both sides of sheet) and it is really great for boatbuilding and not expensive.

    Plywood surface grinding was not necessary and similar effects, such as your, not stated.

    BTW, Much depends on the species of wood of which the layers of plywood - indigenous birch is strong and dense, but quite heavy, and therefore sometimes boatbuilders choose okoume plywood.
    Aloha!
    Robert Hoffman
    http://robhosailor.blogspot.com/


Page 1 of 3 123 LastLast

Similar Threads

  1. Marine ply
    By HELLICONIA54 in forum Michael Storer Wooden Boat Plans
    Replies: 8
    Last Post: 19th February 2011, 07:06 PM
  2. Standard
    By skankstro in forum MUSICAL INSTRUMENTS
    Replies: 5
    Last Post: 27th July 2010, 12:08 PM
  3. Looking for marine ply
    By Linda Bowden in forum BOAT RESOURCES / PRODUCT SEARCH
    Replies: 5
    Last Post: 12th June 2008, 10:30 PM
  4. RE: Marine ply
    By coogzilla in forum Michael Storer Wooden Boat Plans
    Replies: 7
    Last Post: 11th April 2008, 12:51 PM
  5. Marine Ply
    By AlexB in forum BOAT RESOURCES / PRODUCT SEARCH
    Replies: 5
    Last Post: 19th April 2005, 09:49 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •