Durability of marine plywood based on different coating options

Discussion in 'Materials' started by Alex80, Jan 24, 2014.

  1. Alex80
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    Alex80 Junior Member

    Assuming a displacement hull boat is left in the water year round (tropics) what is the durability of the hull if made of:

    - Marine plywood (no further treatment)
    - Marine plywood with epoxy coating
    - Marine plywood fibercloth and epoxy?
     
  2. upchurchmr
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    upchurchmr Senior Member

    Alex,

    I have no "facts" to use in comparison, but here is what I have experienced.

    1. I assure you that marine plywood rots when the end grain is not protected, but the wood will hold together well while it rots.
    2. Epoxy coats should improve things, but epoxy without glass or some other reinforcement is easily damaged by abrasion.
    3. Fiberglass and epoxy will protect from moisture and therefore rot very well, so long as you repair any damage without waiting too long. Water in the wood from damage has to be dried out before a repair or you risk rot. Abrasion is significantly less likely to get thru to the wood. Use of Glass makes it easy to build up enough thickness of epoxy to prevent water from coming thru to the wood.
     
  3. pescaloco
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    pescaloco Senior Member

    You wouldn't want a plywood boat with no coating on the wood it wouldn't last too long

    Glass over ply can be a long lasting boat building technique if done properly

    With plywood you have to seal all penetrations into the wood, if water can get in it will rot
     
  4. PAR
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    PAR Yacht Designer/Builder

    There are lots of examples of uncoated and unsheathed plywood boats, that have survived many decades including two of mine - 54 years old Douglas fir plywood and the other 57 year old mahogany faced birch plywood. The Douglas fir boat has spent extended periods in the wet and the garboards have been replaced, but the rest of the planking is as built in 1960, with assorted repairs and maintenance of the last half century, as you'd expect. This is the point. They wouldn't be alive had they experienced much long term neglect.

    Treatments, no treatments are frankly irrelevant. When it comes to wooden boats, the only thing that is relevant is regular care and upkeep, regardless of coatings or sheathing presence.
     
  5. michael pierzga
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    michael pierzga Senior Member

    When you use modern methods..epoxy...it is possible to build a whole boat with no metal fasteners. Fasteners are the reason plywood boats fall apart.

    How durable is epoxy sealed plywood ? Well, 18 years ago a client asked me to mount a swim ladder to the face of a concrete wall. The concrete wall face was irregular so I mounted the ladder on a piece of marine ply then mixed up a bucket of concrete to use as bedding compound and lag bolted the ladder ply assembly to the face of the seawall.
    This marine plywood had two coats epoxy then a couple coats of marine paint. The ladder assembly is frequently submerged during flood tides

    No sign of delamination after 18 years.

    The lesson is ....seal the ply with epoxy.

    As far as build scantlings...eglass skins...follow the build scantlings that the designer specified. Many times designers call for sheathing. This sheathing insures the the epoxy film thickness is correct and it protects the surface from physical abuse. A workman scraping barnacles from the bottom with instantly damage unsheathed plywood.
     
  6. Alex80
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    Alex80 Junior Member

    Dear all,

    Thank you for your insights so far, I greatly value the practical experiences shares as I have virtually no experience what so ever with wood in a marine environment.

    To give you a better idea where I am coming from, allow me to explain the following: I do not have the expertise and even less so the time to build the boat myself. However, as I am based in Singapore I can make use of the small backyard "wharfs" in Malaysia. These of course have ample experience with wood (and sealing with epoxy does not appear to be rocket since) but are not very apt at fibreglassing boats.

    Of course there are also professional wharfs building pleasure crafts and these are very good at all kind of fibreglass works but also a lot more costly compared with the backyard boat builders.

    The 24' boot I intend to have build would cost me about USD 2,500 - 3,000 in labour from a backyard wharf but about USD 15,000 - 20,000 from one of the industrial wharfs.

    Of course the price for the fibreglassing materials is not so much an issue at this size but if fibreglassed it has to be done properly and my budget doesn't allow me to make use of an industrial wharf.

    So essentially my question might be rephrased as follows: If I build a boat out of marine plywood with epoxy coating and leave it in the water year round:

    - how long would it last if I only do the usual surface maintenance (cleaning of hull, antifouling etc. but no wood works).

    - how often would you advise me to scrap the growth from the boat and put new antifouling?

    Thank you so much for your comments, I want to start the building process next month but before I need to have a clear idea what kind of durability I can expect (eg. fibreglass last about 25 - 30 years here in Singapore, how long will my epoxy covered wood boat last, 3 years? 5 years? may be even 10 years?
     
  7. michael pierzga
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    michael pierzga Senior Member

  8. PAR
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    PAR Yacht Designer/Builder

    Fasteners aren't the reason plywood fails and frankly it's an absurd statement. Plywood boats have been built for quite a few generations now and only the last generation has epoxy coated plywood really gained favor. This isn't to say epoxy coating and/or sheathing isn't a good idea, but it is to say it's not the end all of plywood boats.

    As to your question about durability, well the only real answer is up keep. A coated and/or sheathed boat will offer a longer margin of neglect, but not an appreciable amount. Simply put, plywood's durability is maintenance based, not material or coating based. If you take care of the boat, it doesn't matter if you smear cream cheese all over the planking. On the other hand, if you drop it in the water and forget about it until you've got a leak, well, no coating and/or sheathing is going to help.

    If you find inexperienced builders that haven't used epoxy, you'd be best advised to not let them touch the boat with this material. It's not rocket science, but does require good procedures and technique, or you're just wasting money on a coating/sheathing that will fail.

    Wooden boats, regardless of the planking type, can tolerate the least amount of neglect, so if you want a wooden boat, you have to stay on top of any and all issues that arise or it will quickly spiral up the seriousness of the issues faced.

    Fiberglass boats can last a lot longer then 20 - 30 years. I've seen them at 60 years, working just fine. I don't know why they seem to (die?) live shorter lives in your area. I have built boats since the 1960's, most from wood and the choice of hull material, has much less to do with longevity than the amount of care it received. As I previously mentioned, wooden structures can't tolerate neglect for very long, before bad things happen, so if you're looking to just splash and hope for the best, there are other materials that are much better suited for this treatment, such as alloys and FRP.

    Anti fouling paint is usually applied each year, depending on how your area tends to be, you might be able to stretch this out to every other year, in a relatively benign location.
     
  9. Alex80
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    Alex80 Junior Member

    Thanks PAR.

    But what exactly is the "upkeep" we are talking about?

    With my fibreglass boats all I had to do was to make sure they always had a decent coat of paint on and of course antifouling under the water line.

    I am still wondering what additional upkeep wooden boats require?
     
  10. PAR
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    PAR Yacht Designer/Builder

    This is just the point I'm getting at. Wooden boats can't be treated like 'glass boats or you'll have a pile of mush in fairly short order.

    In the olden days before epoxy, there were two basic approaches. the first and most common was to make a fairly massive structure, that could absorb neglect for many years before it fell apart. This is how work boats are built. The other method was to assume you where only getting a limited amount of time and the boat was tossed, in favor of a new one when the time came. Race boats where typical of this. Now, if you took good care of the boat, you could double, triple or quadruple their life span.

    It sounds like you want a splash an forget it type of boat. You show up when you want to use it, park it when the afternoon sail is over and it'll sit for a month, until your next outing. Wooden boats aren't well suited to this type of treatment, which is why they fell out of favor, with the advent of 'glass boats in the 1950's. If you want a forget about it boat, then forget about wood as the hull material, even if epoxied and sheathed. You'll just be disappointed.
     
  11. Alex80
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    Alex80 Junior Member

    This is not too far off. Once a month is effectively the average amount of boating I am doing.

    So what exactly should I do to maintain the wood boat after each outing and possibly in between?
     
  12. SukiSolo
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    SukiSolo Senior Member

    Having been to Singapore, I would very wary of applying epoxy sheathing in that climate. The standard humidity must be approaching 90% with plenty of heat. This means the wood is not actually dry and epoxy absorbs moisture during cure. You will need a humidity controlled environment to firstly dry the wood properly and secondly apply the epoxy. Just be aware of that issue and note that the ideal moisture content of the timber should be sub 10%.

    Have to say though having sailed a 28' FRP racer/cruiser boat there it was like an oven inside whereas a wooden one would have been a little cooler especially with white decks. The sun really is strong so painting over the epoxy for UV protection is also recommended.
     
  13. PAR
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    PAR Yacht Designer/Builder

    There's no doubt an epoxy sheathing will have beneficial results on a plywood hull. If the boat is to be moored or berthed seasonally, then you'll need a heavy sheathing, much heavier then typical for a trailer borne boat. I'd recommend at least 18 ounces (600 GSM) total thickness of the sheathing on the bottom (preferably in multiple layers), which can be tapered to 6 ounces (200 GSM) at the rail. This will provide some protection against grounding and strikes. If you launched and did nothing except paint her at haul outs, you'll get 10 years, before major issues need to be addressed, which will be soft spots in the planking that have to be cut out and replaced.

    I'm not sure of Singapore's climate, but I'm in Florida, where it's tropical in the summer. It's hotter than a hooker outside a Ford automotive assembly plant on payday, with humidity at 90+ percent most of time and I epoxy regularly. Plywood is fairly stable, even under these conditions. If it's kept covered and ventilated, the moisture content will be below 15% which is safe, though epoxy formulators will prefer 12%. Of course, you need epoxy formulated for these conditions and you need to use well established procedures, but it's commonly performed in un-climate controlled shops all over the world in these (and worse) conditions.

    The problem I see with your project is inexperienced builders, in regard to epoxy. Again, it's not rocket science, but if you don't have experience and proper technique, you'll just waste a lot of expensive goo and fabric, requiring repairs much sooner (maybe as soon as a couple of seasons). This is why I say pick your poison carefully, as you might just get what you didn't wish for.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Possible, but is it as strong ? And it must have a high degree of difficulty in some cases, keeping stuff in place while the glue cures.
     

  15. Alex80
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    Alex80 Junior Member

    Once again thank you PAR, your insights are very valuable.

    That said, I feel that I should mention that the boat will not only be in the water seasonally but year round (with the exception of when it is hauled out to be painted).

    The heat and humidity in Singapore corresponds to summer in Florida year round with the exception of the period from late December to the end of February. Lot's of tropical rain showers too.

    The marine biology is highly aggressive to an extend that dry berthing is more expensive than wet berthing and many of those wet berthing keep their boats on inflatable tubes in the water.

    To use a more practical example: anti-fouling will never ever last a whole season for a boat which is in the water year round in Singapore. New anti-fouling every six months is a must.

    Given these circumstances I fear that 10 years in Florida may amount to 3 years, may be 4 years in Singapore. That is to short, even for the low construction costs.

    So I will definitely look at having a layer of fibreglass cloth included when epoxy is applied.

    Would this make a notable difference? Or is it in the end disproportionate to the additional costs. Of course I am aware that a layer of fibreglass cloth has nothing in common with an actual fibreglass hull. But I would like to know the degree of protection it affords the plywood beneath. Now, obviously I am not talking about running aground or scratching alongside the berth. Just the usual exposure to the elements.
     
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