A Question About Planking

Discussion in 'Wooden Boat Building and Restoration' started by Windship277, Jul 7, 2017.

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  1. Windship277

    Windship277 Previous Member

    I want to build a Sea Bright 18 for coastal use but can only find clinker built plans for that model boat. My second option is a Whitehall 17. I dont trust a clinker build to the open ocean for long periods of time and I dont like the added wetted surface. Is it possible to carvel build a meant to be clinker built boat by drawing the edge of the frames smooth? Then proceed with a carvel build??
    Sea Bright 18 https://www.woodenboat.com/boat-plans-kits/sea-bright-18
     
  2. PAR
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    PAR Yacht Designer/Builder

    Carvel builds can be converted into other build types. There's nothing wrong with lapstrake construction. There's two types; traditional planking hung on frames, riveted, bolted or clenched down. The traditional type of build can greatly benefit from polysulfide in the laps, making them much more water tight. The other is glued seam, which is absolutely water tight and doesn't have any of the issues traditional lapstrake builds do. In fact, you can toss out most of the frames too, with this method.

    Yep, you can convert a lapstrake to a carvel build. The scantling change a little, but otherwise it's the same type of build, unless a glued seam, in which case the scantlings change a lot.

    The Ruel Parker build you've linked is a glued seam build, no frames and modern construction techniques, so none of the usual lapstrake issues.
     
  3. TANSL
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    TANSL Senior Member

    I ask this question because, honestly, I do not know the reason for these changes. Intuitively, it would appear that they would not have to change, for example, the thickness of the lining. Do the scantlings actually change with a glued seam, and why? Thank you very much in advance for the clarification.
     
  4. Windship277

    Windship277 Previous Member

    Ok. Thank you for your response. I dont know much about building a wooden hull. I have read that clinker is a weaker build but... I dont see the reason for lap strake build except for tradition. It IS beautiful. I dont like the added wetted surface especially in a small craft and the added weight. Weight and speed is a big concern for cruising. Your life can depend on the performance of your boat. With a small ccraft, I dont want to cut any corners.
     
  5. Windship277

    Windship277 Previous Member

    Yeah, I had fig the scantlings might change a lil. The cut out on in the frame allows prob about half of the plank to be out side of the line I would draw to strip plank so, prob not change significantly. Ive never built a wooden boat and I need input, lol. I DO have a lot of marine carpentry exp. I was a frozen snot man before, lol. Theres nothin like wood.
     
  6. messabout
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    messabout Senior Member

    If I remember rightly (questionable) the Atkins had a nice little Seabright they called Surprise. They made some boastful claims about her speed with a dinky little Palmer or other inboard. It was not a lap straker and it appeared to be a simple enough build. Chapelle wrote wrote at some length about the Seabrights. Explore some of his writing perhaps to find what you have in mind.

    A lap strake boat is no more vulnerable than a carvel build. In fact, pound for pound it is probably more rigid than alternative build methods. There are lot of old lap strake Thompsons and Lymans still holding forth after 60 years and more. I once crossed the Gulf Stream in a Chris Craft Sea Skiff, a lap strake ply design, when a nor easter was in full song. That is to say the waves were of prodigious size and confusion, some of them 25+ feet from trough to crest. The boat survived the ordeal quite nicely. All that being said, I would opt for a design in sheet ply, not clinker.

    Why would you build a Seabright with strips? An Adirondack or Whitehall,.....yes a stripper.
     
  7. Angélique
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    Angélique aka Angel (only by name)

    You remembered rightly, she's still out there . . :cool:

    Surprise 19' High-Speed V-Bottom Seabright Skiff Motorsailer By William & John Atkin

    [​IMG]

    [​IMG]

    [​IMG]

    ‘‘ The lines of Surprise are designed for speeds under power up to 20 m.p.h.; it is therefore important to bear in mind the matter of weight of materials and equipment, especially that of the engine. I would not advise the installation of an engine weighing more than 270 to 290 pounds with its complete equipment. The weight of the following engines come within this range: Universal Fisherman, 8 h.p. at 1,200 r.p.m., 220 pounds; speed 14.5 m.p.h.; Nadler 8 h.p. two cylinder two cycle at 1,000 r.p.m., 210 pounds, speed 15.5 m.p.h.; Red Wing Meteor, 18 h.p. at 2,800 r.p.m., 225 pounds, speed 18.5 m.p.h.; Universal Atomic Four, 22 h.p. at 3,000 r.p.m., 286 pounds, speed 20 m.p.h. There are other engines which might be installed including several of the air-cooled type all of which will weigh something below the maximum figures mentioned. ’’

    [​IMG]

    [​IMG]

    [​IMG]
     
  8. PAR
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    PAR Yacht Designer/Builder

    Your have some misconceptions about lapstrake (clinker is just a lapstrake attachment method). Lapstrake hulls are generally slightly stiffer, particularly longitudinally, than most other wooden build types. The glued lap version is stiffer, stronger and much lighter than most other wooden build methods. Think of each lap as a glued (or fastened, as in a traditional build) stringer on plank width spacing (pretty tight as stringers go). This is why it's light and stiff in traditional builds and stronger in glued lap builds. In a glued lap build the hull becomes homogeneous in nature with built in roughly water line shaped longitudinals. Glued lap builds can be designed with a single frame, while the traditional builds do require them to maintain athwart stiffness.

    Yes, the laps do add a very modest amount of wetted surface, but they also add to rolling or heeling resistance, which can be beneficial in sail and rowed craft. Because of the weight savings over other build types, your performance envelop improves in sail and man powered vessels. It's also not as hard to do as it looks, though you do need to get your head around the process which is different than others.

    The Vikings seemed to do quite well in open ocean and open lapstrake boats, so this nonsense about not being as seaworthy as other types, is literally ridiculous.

    About the SeaBrites. You need to be careful about these, particularly the Atkins development of them. Simply put, some are better than others and you do want to get the ones John did, who continued his father's development research on the type. Basically, you'll want the newest of the series, not the early ones, as they were learning about the type's quirks. You must remember these are still half a century old designs (at best) and coastal cruisers of modern design and build methods abound.

    In the end, you'll need to much more closely define your needs, before you can justify a SeaBrite design. SeaBrites also have a fair bit of wetted area, because of the box aft. They do tend to max out in the low 20's (MPH) range on the better ones, but in their defence they usually do so with very modest power. The big selling point for most is the ability to carry the engine, very low in the hull and the shaft angle can be very low, which is good for efficiency and fuel consumption. As a pulling boat, it'll suck compared to more traditional shapes, though it'll have more capacity and initial stability.

    TANSL, in practical terms often carvel planking can be the same thickness as lapstrake, though this is because plywood is only available in certain sizes (thicknesses). In a technical sense, because of the plank interface (overlap) in lapstrake builds, the thickness of the planking can be slightly finer, while still retaining the strength and stiffness of the carvel build, assuming the same planking material and general build parameters (frames spacing and other structural dimensions. This was taken to extremes in racers back in the golden age of sail, but a mechanically sound engineering approuch. The only way to get a lighter (wooden) build is molding, but molding is generally harder and more costly than lapstrake builds. As a rule molded has the highest weight savings potential, with glued lapstrake being a close second. It can get pretty complex in these compairsons once some of the composites build methods entry the mix, but in the end it typically falls on practicality. Molded builds tend to be laborious and costly, strip plank tends to also be high on labor, though materials costs are usually much lower. Carvel is likely the fastest way to get a hull, though material choices and selection can dominate the process. Lapstrake with plywood if fairly fat, being just under carvel and material costs are compairtivly low.
     
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  9. TANSL
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    TANSL Senior Member

    Thanks, PAR, for your explanations. I was thinking of constructions like those of the figure and, of course, I had never thought of using plywood boards but solid wood boards in both cases.
    Snap9.jpg
    I still do not understand why one method or another need larger scantlings or why the fact that the tables are glued gives rise to much larger scantlings. It is very likely that the "clinker" will produce heavier hulls. In order to be able to affirm it would have to consider all the structure, not only the planks of the shell. But I, who have no experience in this type of construction, I can not know. I only ask questions and I question what I do not see clear.
    I found the following on the internet:
    “Using carvel planks to construct a hull is when planks are fixed to frames with their edges butting up against each other. This method of construction produces a smooth hull, however, the seams tend to require caulking (except in the case of very small boats) and generally it is heavier to similarly sized clinker boats. The construction detail does make a strong hull.”
    See also : http://www.yachtpaint.com/usa/diy/ask-the-experts/what-is-the-difference-between-clinker-and-carvel-construction.aspxClinker built vessels are lighter”
    Which seems to go against some other opinions. In short, I still do not understand. Anyway, many thanks for the explanations.
     
    Last edited: Jul 9, 2017
  10. Angélique
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    Angélique aka Angel (only by name)

    No, not with modern build methods, because when you bound-the-laps-strong-enough1 then all the overlappings become structural-elements2 which all add to the overall strength and stiffness of the boat, and this in such a way that can be saved on materials as frames and stringers and plank thickness, compared to more traditional build methods which don't use epoxy.

    1 Like in glued lapstrake plywood is possible.

    2 Each overlap acting as an angled longitudinal solid piece of extra thickness that also acts as one solid piece with the angled-to-each-other-planking3, making the whole a kinda monocoque structure with the overlaps acting as build in stiffeners integral with the hull.

    3 Which is another element that adds to the strength and stiffness of the hull structure as a whole.

    Edit = added footnotes.
     
    Last edited: Jul 9, 2017
  11. Angélique
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)


    [​IMG]

    Not exactly the same, but one can imagine that this flat-V-flat profile is stronger-and-stiffer-in-all-directions1 than any piece of the same material in the same amount and length but just flat, which also goes for the obtained overlaps profile in glued lapstrake plywood, which becomes as one piece in the build process.

    1 Except for pure tensile load, because then both will perform equally since the cross-section of the tensile loaded area remains to keep the same value in this case where the amount of material and the length are not changed.
    Edit 1 = added footnote.
    Edit 2 = enlarged the footnote a bit in an attempt to enhance TANSL's understanding of this matter.
     
    Last edited: Jul 11, 2017
  12. Rumars
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    Rumars Senior Member

    TANSL I think you missunderstud. Traditional clinker construction is usually lighter then carveel, and glued ply lapstrake is a lot lighter. To make an analogy if 1000g/m2 E-glass was specified and you use S-glass instead, you either use less glass or end up with a stronger boat. Glued lapstrake using plywood would be like substituting carbon for E-glass. This is because plywood is a quasi-isotropic material and wood is anisotropic. Using glued plywood you can eliminate most or all of the framing necessary with traditional build methods. So when converting carveel to traditional lapstrake one can use carveel scantlings and the result is more or less the same (clinker beeing stronger) when converting to glued lap the scantlings need more radical changing or else you have an overstrenght and possibly overweight structure. This is like converting wooden construction to fiberglass, you can use wooden boat scantlings but the resulting structures are over the top.
     
  13. PAR
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    PAR Yacht Designer/Builder

    These types of conversions are pretty common place and I get several requests for this each year. There's no debate about lapstrake, regardless of type being lighter than carvel as well as other methods, such as batten seam, double planked, etc. With the exception of molded veneer builds and of course the introduction of manmade fabrics, lapstrake is the lightest of the traditional builds and glue lapstrake much lighter.

    Plywood as planking is actually weaker than solid wood planking, but being much more dimensionally stable and coupled with glued seams, permits the same thickness planking, while the gross reduction of other structural elements, (no frames, no stringers, etc.). In fact, it's generally accepted that you should use the same thickness plywood as the original planking was in a carvel build. This is because of the weaker longitudinal stiffness of plywood, compaired to solid stock. In a traditional build comparison, keeping things relatively equal, (solid stock planks, typical frame arrangements and spacing), there's little difference, in fact possible a slight disadvantage to lapstrake. On the other hand, if you take the longitudinal stiffness the laps bring to the mix, you can decrease the size of the framing elements and the planking slightly, allowing the hull shell bare more of the loading. This is usually accomplished by increasing frame spacing, though can (has) be carried out to extremes on some racers.

    Lastly, given a choice, plywood planking is simply a better material than solid, for several reasons. It is heavier than solid of the same physical dimensions and isn't as stiff longitudinally as solid, but cross grain stiffness and strength is much higher, plus the dimensional stability and if coupled with glued laps, makes the end result considerably lighter. Of course typical plywood is quite ugly, compared to solid, but sliced veneer plywood is available if you need the bright finish.
     
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  14. TANSL
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    TANSL Senior Member

    @Rumars :
    TANSL I think you missunderstud : I agree, there are several things I misunderstud.
    plywood is a quasi-isotropic material : This is a surprise to me because, in my opinion, plywood is a non-isotropic material. When calculating the scantlings, the mechanical properties of the material must be taken into account, depending on the composition of the layers.
    Is this is a quasi-isotropic material? :
    Plywood.jpg
    I am convinced that it is not, and should be calculated in a similar way to any non-homogeneous material.
    Using glued plywood you can eliminate most or all of the framing : This would be great but I would like to understand why.
    when converting to glued lap the scantlings need more radical changing … : why?
    …. or else you have an overstrenght and possibly overweight structure : Some experts say otherwise. This is what I do not understand.
    This is like converting wooden construction to fiberglass, you can use wooden boat scantlings … : This, with all due respect, is a tremendous mistake.
    @Angélique :
    Except for pure tensile load….. Sorry to say that in my opinion that LOAD does not exist.
    …both will perform equally since the cross sectional load area remains to keep the same value. I don´t know what is a “cross sectional load area”. In any case, the cross-sectional area of a reinforcement is very decisive when studying shear stresses, but may be not so decisive when studying tension or compression stresses. Its distribution is more important than its total value. That is why the V-profile you have shown in the photo may be totally inappropriate in many cases. With "inappropriate" I mean it brings a lot of weight and little module (first moment of area) on its top.
    @PAR :
    I know that some of you speak to me with the authority that gives the experience but, behind the facts contrasted by the practice always there is a theorical explanation, technical, of these facts. Knowing this explanation is what leads you to understand what you are doing and why and, therefore, to apply a method correctly or to avoid applying it when it is not correct. That is why I ask my questions, to understand. I do not mind knowing what my neighbor does, I want to know why.
    I have not said that plywood can not be used with clinker or carvel methods, what I meant is that I was thinking of solid wood strips, overlapping or not.
    I ask again why, within the same method of construction, with the same material, gluing the joints can greatly increase the scantlings. I can not understand it.

    As all of this, I think, goes beyond the initial objective of the OP, if you decide not to answer me, I will understand perfectly. Thank you, everyone, for trying to get me out of my ignorance.
     
    Last edited: Jul 10, 2017

  15. Rumars
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    Rumars Senior Member

    Plywood has longitudinal and transversal layers and as such has strenght in two directions. Yes it is not a real isotropic material, but for boat construction it has strenght in the two directions that matter most and is regarded as quasi-isotropic. Marine ply with 5, 7 or more layers of equal thickness venner and no voids meets this criteria in my opinion. The cheap 3 layer ply with thin faces and a thick middle veneer is of course another thing.
    A long time ago the russians made special plywoods with alternating +/-45 in addition to the +/-90 degree layers, as well as unidirectional plywood. As far as I know those plys are now unobtanium and the only similar product on the market is Vendia plank, a unidirectional laminate designed for traditional lapstrake construction.

    PAR explained why the glued construction can eliminate most or all of the framing. The forces are carried by the skin because the skin is able to do it. In traditional construction with riveted overlaps the skin is not able to carry all of the forces and still needs frames, but fewer or smaller then carveel. If you maintain carveel scantlings (frame dimensions and spacing, stringers) the resulting structure will be heavier because you have more material in the boat (the material at the overlaps and their fasteners).

    Yes I agree using wooden scantlings for fiberglass is a mistake, the resulting structure would be to heavy, but that does not mean it was not tried. For example the folkboat association wanted to assure viable competition between wooden and fiberglass boats, so the fiberglass boats had to look and weigh the same. As a result the fiberglass version has lapstrakes and there is way more laminate in the structure then actually needed, because it was required to meet the weight criteria.
     
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