planking or plywood and glassing a hull

Discussion in 'Boat Design' started by verboon, Feb 6, 2008.

  1. verboon
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    verboon Junior Member

    hello I was wondering what is more durable: planking a boat hull, or plywood and fiberglass, and what is cheapest of the two.
     
  2. rwatson
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    rwatson Senior Member

    Are you going to coat the planks with fibreglass/epoxy as well?
    If not, the key will be the type of wood you use. The better the quality of the timber, the more it will increase the cost.
    The other factor is - does "cheap" include labour time as well?
     
  3. verboon
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    verboon Junior Member

    If I planked the hull I would paint, varnish, or epoxy the planks and put cotten in between. The cost will only be affected by quality of materials because I will be building the boat myself.
     
  4. rwatson
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    rwatson Senior Member

    So its only materials you are calculating.

    I would imagine the sums would start with something like
    Option 1) Good quality timber plus good paint job
    Option 2) Soft timber with fibreglass/epoxy inside and out
    Option 3) Plywood with Epoxy on outside
    Option 4) Plywood with epoxy inside and out

    The next question is in regards to the methods requiring fibreglass (2,3,4)
    How much Fibre and Epoxy will you need for each option?
    Option 2 will need more because it becomes a major structural part of the hull.
    Fibreglass in Options 3 and 4 will depend on high thick the plywood is.

    The calculations can only be accurate if you designer can specify the "scantlings" required.

    One major cost to consider is the final painting method. My little 16' strip plank canoe cost more to paint the outside with a 2 part paint system than the wood for the entire canoe.

    I am having to go through this exercise myself in the next month or so on a 28 footer, so I have an interest in the answers you are seeking too. I have shelved Option 1 because of the high maintenance effort and skill level required, and because suitable timber is impossible to get for a decent price any more where I live.
     
  5. verboon
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    verboon Junior Member

    well I would probably plank it with some sort of hard wood, I am leening towards marine ply and glass for simplicity and less maintenance, but is there any advantages of a planked and cotton caulked haul to a marine ply and glasses haul. And you said that I glass over a planked hull but I thought that rotted quite easily.
     
    Last edited: Feb 7, 2008
  6. PAR
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    PAR Yacht Designer/Builder

    Neither is more durable if you provide the same level of care and upkeep.

    The type of upkeep will be dependant on the building methods and techniques employed. The hull's planking is generally some of the best, if not the very best material you use on the boat, for obvious reasons. Secondly, the planking of a hull accounts for a small percentage of the total build in the vast majority of craft.

    The moment the epoxy decision is made, especially on small boats, your costs and build effort rise dramatically. This is solely because for epoxy to be effective as a moisture vapor coating, it must encapsulate the wood. Just coating one side isn't much more then painting your surface with plastic, which will eventually trap moisture under it.

    The only "cheap" planking material or method is stuff you don't expect to last very long.
     
  7. verboon
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    verboon Junior Member

    so if I planked a boat and epoxied the planks I would have to epoxy all sides of the plank, what if I sheeted the hull with marine plywood and glassed the outside your saying that I would have to coat the inside of the marine ply with a layer of glass or just epoxy too.
     
  8. rwatson
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    rwatson Senior Member

    Pars comments, are right on the mark, but there are a couple of not stated options.
    1) Total encapsulation with fibre and epoxy is the only reliable method of preserving TIMBER THAT ISNT GOOD ENOUGH TO SURVIVE ON ITS OWN. This would include Balsa, western red cedar, all type of softwoods etc
    In reality, the timber component is largely ignored in most strength calculations, its just a "filler" to hold the epoxy apart. Timber has the advantage over foam material in that it is easy to work, fair and shape, and is cheaper.

    2) Quality timber, including marine ply will survive very well, epoxied on the outside and painted on the inside. But if you use planks, they need to be glued together, not caulked. Unglued planks will just "work" and create cracks in the fibreglass coating.

    You can also infer that even "good" planking will rot if it is totally covered with epoxy, but not well enough to prevent moisture entry.
    For example, you could have the very best of timber, and even epoxy it both sides, but if a flaw lets water in, even the best timber will suffer.
    Gougen Brothers state that you need three things to create rot in coated timber 1) Moisture, 2) Oxygen, 3) Light.

    The last point about ply and fibre/epoxy, is that it is very easy to layup the epoxy before the sheet is placed on the frame. By laying up fibreglass on a flat ply surface ( both sides if you want), and perhaps using peel ply, you dramatically cut the finishing time and waste of materials through sanding and fairing.

    And regarding your last question verboon - is there any advantage to planks and caulking. yes - no bloody fumes and itchy fibreglass. Depending on the cost of timber, it has the potential for being cheaper, but standard hardwood makes a heavy boat, and the caulked seams are a constant bother and expense over the life of the boat.

    When there was plenty of light and robust boat building timber, it would certainly have been a great option to consider. Now such timber is around $2000 per cubic metre, and decent lengths are much harder to come by.

    I am leaning to doing my hull in marine ply where the hull is fairly flat, and use glued planks where curves on the chines occur. I plan to fibreglass and epoxy both sides, but not have to use so much fibre on the plywood above the waterline. It may not be the cheapest method, but I bet it will go very close, and the result will be a long lasting and quality product with a bit of luck.
     
  9. BOATMIK
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    BOATMIK Deeply flawed human being

    You can build a boat well enough with both methods that will last perfectly and beautifully until you are ready to pass it on to someone else.

    Do either the cheap way and you reduce the potential life and increase the maintenance.

    Why are you asking this question? What sorts of skills do you have? What sort of time do you have. Is the point to learn boatbuilding skills or just get a boat in the water?

    If money is a problem maybe it is a good idea to build the largest boat you can afford good quality materials for - which means build something smaller.

    However there is an alternative way of building REALLY cheap and expecting the boat to hang round for a few years. While not dealing totally with this direction you could look at Duckworks, Michelak, The cheap pages.

    So many possibilities out there.

    Best wishes
    Michael
     
  10. PAR
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    PAR Yacht Designer/Builder

    Total encapsulation is just as the term suggests, every exterior surface, including fastener holes. This embalms the wood, creating a moisture stabilized material. You don't need fiber reinforcement on most wood species (to stabilize moisture content), though a few have checking issues which require a fiber reinforcement to provide a structural element to the process.

    If the epoxy coating is kept intact, the wood can survive indefinitely, which of course, is a very optimistic view. In reality, the epoxy coating gets breached by dings, nicks, scratches, etc., which lets moisture into the wood. If not addressed, you're eventually going to have problems.

    Epoxy alone will add very little strength or abrasion resistance to wood. This is why reinforcements, such as different types of filler and/or fabrics are used. It is this reason that epoxy use adds so much to a build effort and cost, the related materials, besides resin and hardener and the effort to apply.
     
  11. BOATMIK
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    BOATMIK Deeply flawed human being

    Howdy PAR,

    I think you are overstating the problems of nicks and scratches with damaging the epoxy and reducing the life of the boat.

    The boat in the picture below was 13 years old when the pic was taken and had little maintenance. It is epoxy coated and the only glassing is tape over the chines and stem and on the centreboard and rudder blades.

    While I agree that it is "very optimistic" that minor damage damage like nicks and scratches will not happen it doesn't seem to have as big an effect as you seem to indicate - there are plenty of long lived epoxy boats round now and many or maybe most will require only a little maintenance to keep looking good.

    Regarding nicks and scratches - you just fix 'em as they appear. You wouldnt leave wood exposed on a conventionally built painted boat either. Realistically you do have a bit of time to do something about it - but ignore it on any construction or painting/varnish method and there will be bigger repercussions the longer it is left.

    Regarding the labour ... there is a labour increase - but with good planning and some of the methods that epoxy boatbuilders have used that can be minimised or even may save time over more conventional means. For example precoating and sanding plywood can be done. The sheets themselves can be epoxied and sanded or the parts.

    With a plywood boat this might only add two and a bit days to the building process (using wet on wet application it adds a day per side of ply), but might save several days in varnishing and painting later as you don't need primers for paint and with varnish if it is an interior you can probably get away with a couple of coats of varnish - varnishing or painting the interior of a finished boat is VERY time consuming compared to precoating.

    Be aware that if an area is exposed to direct sunlight frequently then if it is clear finished you will need the full normal six coat of varnish - but there are savings on interiors and for dinghies/canoes/kayaks that are stored out of the sun.

    The reduction of paint and varnish coats can save many days of complicated sanding, cleaning and painting for some boats.

    With maintenance ... a properly built epoxy glass boat can save so much time and money over maintenance cycles that it is crazy.

    When I was racing dinghies regularly in the 70's and 80s we would usually get a couple of seasons (maybe 3) before the boat needed serious maintenance - a good sanding, maybe some parts stripped and started again. With epoxy boats the boat I use the most is now at the 13 year mark with only minor work around the gunwales and some problems with the varnish on the floor requiring work - the epoxy on the floor is intact but the varnish has problems. Most of the boats I have been involved with professionally are similarly low maintenance - the quality of the initial job is everything.

    That last is good advice for ANY construction method.

    [​IMG]

    It still looks pretty good - photo was at 12 years old - the main thing that helps any boat is to keep the sun off as much as possible. Epoxy will take care of most water problems ...

    We did put a cover over it when it was stored outside for extended periods - the local yacht club - where it sat several times with a bit of water inside - maybe for a few months at a time. The curious thing is that water has gone through the varnish and allowed a fungus to grow between varnish and epoxy - so that will have to be fixed for cosmetic reasons - but at least the fungus is not in the wood.

    There are a whole lot of ways that you can reduce the extra processes if building an epoxy boat ... I have put many of them on this page
    http://www.storerboatplans.com/Faq/faqindex.html

    By the way as you could see from my post above this one I am not necessarily advocating using epoxy for Verboon's build - it depends on what he likes the sound of in terms of building process, what he wants to learn and what seems to make the best sense.

    As far as expense goes - epoxy is competitive as initial cost is not the only cost of owning a boat.

    And there is probably some advantage for resale in the long run too - which also cuts the cost of ownership.

    Best wishes
    Michael Storer
     
  12. verboon
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    verboon Junior Member

    thankyou everybody for all of your usefull information, I have narrowed the materials that I am considering down to: red cedar(plank method) or marine plywood(sheeting method). For both of these methods I want to coat the inside of the red cedar, or the marine ply with epoxy and then glass the outside of them to make the hull very durable.
     
  13. PAR
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    PAR Yacht Designer/Builder

    Any building method, using epoxy or not, if well cared for will last fairly well.

    A small skiff of my design requires a few sheets of plywood, and several lengths of solid lumber. It's a glue and screw design with minimal epoxy use, which is primarily used as an adhesive on the chine logs, keel batten and the few frames. Costs for all the materials including fasteners and a quart of goo can be less then 400 bucks.

    Toss in enough epoxy to replace the chine logs and keel batten with fillets and tape, then sheath the exterior, plus encapsulation of the other components, the skiff has now nearly doubled in cost and effort to build. Will it be longer lived - possibly. Will it be harder to repair - yep, you bet.

    Dings and nicks on a carvel hull are just part of doing business and not a real consideration, unless it's an appearance or structural issue that needs to be addressed. This is typical of most traditional building methods.

    Most of the restorers I know are shying away from as much epoxy use, preferring to rely on more traditional methods. I've personally seen what unattended moisture pockets, as a result of old battle scares will do to a sheathing, particularly in areas where freeze/thaw cycling will occur or in berthed/moored vessels. It's less an issue on trailer boats that will dry below moisture content levels that promote decay.

    For the most part Michael, I think we're in agreement, in that you have to care for the boat, regardless of the techniques employed in their build. I'm willing to sheath boats, use thickened goo for structural applications, but do admit that I cringe when I need to remove a damaged filleted piece, without disturbing the lovely pieces attached to it.

    My basic issue is it's not a cure all, just a exceptional adhesive/sealant. It can increase the value of some build methods, but if you tell a prospective buyer that your lapstrake beauty has just had a epoxy/cloth sheathing put on its bottom, you can kiss off anyone familiar with what happens when those planks do what their designed to do (move). I've seen many a sale go down the dumper when a 'glassed bottom was mentioned. A good friend has a pretty Constellation that he can't sell, because it's bottom has 12 ounces of cloth on it.

    On the other hand, it's pretty hard not to sheath a Douglas fur plywood boat. New construction benefits most from epoxy use. Repair also can benefit, but has several limitations.

    I just want this caveat to be mentioned, I'll still build with it, repair with it when applicable and currently I'm drawing up a new taped seam design, but it has limitations and does increase effort and build costs, especially in small craft.
     
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  14. BOATMIK
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    BOATMIK Deeply flawed human being

    Howdy PAR,

    I agree - more than you think perhaps .... I only have one epoxy filleted boat on my list of designs too. The rest have good old wood in the corners.

    I agree with almost everything else you say .. the only difference is that I probably go in the direction of encapsulation - but only if it can be done before the boat is assembled as far as possible.

    I don't think the cost increase is dramatic - the boat above is around $2500 for everything to go sailing except the glue.

    Including glue is highly recommended by the designer.

    Not encapsulated you would be up for $95 for epoxy (if you were careful - 3 litres)
    Encapsulated about $360 (12 litres without the need to be too careful - some left over).
    Total difference $265.

    Around 10%

    Encapsulating a finished boat is a terrible idea :) Can be done but at great cost of labour and materials for a poorer result than thinking it through from the start. Just as crazy as putting plywood over traditional laid decks - it's all backwards!!!

    It is a matter of a consistent approach - not necessarily meaning that every boat has to be epoxied, but that whatever method is chosen that it is consistent and makes use of the advantages of the particular materials.

    And I am sure we agree about that too!

    Good Stuff and good discussion!

    Cheers
    MIK
     
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