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Thread: Converting design from lapstrake plank to lapstrake ply???

  1. #1
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    Default Converting design from lapstrake plank to lapstrake ply???

    Hi folks,

    Getting a bit confused when attempting to dig out info on this, I guess the period when everyone was doing it was pre-online. I get a lot of "designed for ply lapstrake" stuff, and the ply lapstrake methods developed since, which don't really give me much clue on conversion.

    The older designs I'm looking at, designed for home builders, mostly Science and Mechanics, Popular Mechanics, type designs, are mostly single chine, and use wide planks, some of them saying things like use a 14" plank for the sides, but if you can't get one, 2x 8" planks... which are also not easy to find clear grained examples of at reasonable pricing in local yards/stores these days. For an heirloom quality boat, fully round bilge, yeah, I'd pays the money and takes the trouble, (And most of that type in small boats you can do with narrower planks apart from maybe a fat ended garboard.)

    Anyway, these types of designs, look like they should adapt to ply, but not really finding much to help. Current ply lapstrake seems almost a completely different method, a variety of stitch and glue, dispensing with chine logs etc. Using the fillet instead of stringers/battens.

    Theoretically in the 14" plank thing above, all I need is to swap 14" swath of ply for that plank, one side done, complications arise though for something like a 2 a side plank bottom, when it's unclear whether there is a 2 way twist that single piece ply won't cope with. What's around for free or free to try software, I can loft the lines into and figure what can be done with single piece and what can't?

    Also hard to find guidance other than "ply can be thinner than plank" for suitable thicknesses of ply equivalent to given thickness of planking.

    I used to be pretty good at winkling info out of google, but the more "helpful" it gets, the more useless it gets for winnowing out all the crap it "helpfully" included that you don't want. So maybe there's a magic word or phrase related to this that I'm not hitting on. (Optional, insert rant/diatribe about how useless google is these days, with removed operators and results enhanced by artificial stupidity.)

  2. #2
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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    IANANA, but it is my understanding that it is only sometimes possible, after considerable number-crunching & juggling of specs, to do it. I think it is in John Gardner's _The_Dory_Book_ where he discusses how building a lightweight plywood dory to a heavy traditional design can create a dangerously unstable boat. It does not sound like something to try without professional designer and/or builder advice.

    Here are a couple of reads for you:

    Ply Lap -vs- Traditional Lap

    boatdesign.net

    Hope the voyage is a long one.
    May there be many a summer morning when,
    with what pleasure, what joy,
    you come into harbors seen for the first time...

    Ithaka, by Cavafy
    (Keeley - Sherrard translation)

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    You've discovered the major reason that folks today don't bother with these older magazine designs -- they're worth every penny you paid for 'em! This is just one reason many of us pay designers (many of whom are on this Forum) for their plans.

    Yes there is a way to convert most of these designs to ply from solid wood, but it involves years of experience with all types of construction and materials, and won't work well for some of the more "interesting" designs - some of which are better left unbuilt. But there are so many of these free designs that you can't really make generalizations about conversion unless discussing a particular type of boat, or better yet, a particular design.

    In the very vague general sense, particularly if the free design didn't require any steaming of the wood planks, you can replace solid wood strakes with ply strakes. Whether is is best to go for glued laps, stitch n' goo, batten-seam, or whatever is up to you. Making a scale model may be the best way for you to answer your questions about twist.


    You might learn something looking at designs that have gone the other way, as some Oughtred and Vivier boats have been built from solid wood strakes rather than ply.

    Have fun!
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Plyboy, I think I followed a path very similar to yours when trying to choose which boat to build and how. I started with a thread that complained about how over-priced the plans seem to be.

    Then I bought the "New Instant Boats" book by Dynamite Payson which has plans for several simple-to-build plywood boats. I think it was a good value. Next I bought John Gardner's books: the Dory Book, and also the combined Building Classic Small Craft, vols 1 & 2 in one bound paperback. The plans in Gardner's books have nice drawings and offsets; the plans in Payson's book give construction details for beginners. The Payson book drawings are so small you need a magnifying glass AND keen vision to decipher the dimensions. Gardner's book is also a solid investment, but some of the plans lack enough information to build directly unless you have enough experience to fill in the details on your own.

    THEN, I bought the plans for Bolger's Gypsy, drawn full size. $40. So far this adds up to about $100, plans and books. All good investments and necessary information for a first time builder. And lots of plans to choose from. In other words, if you know everything you think you need to know, you could plop down the same $100 for plans from a designer, and get started right away. For example, Karl Stambaugh sells plans for sharpie designs around $80. The Goat Island Skiff plans are $120 and they come with a 100 page manual, in addition to the drawings.

    The Gypsy plans are solid plans, but the finishing details are rather plebian. So I'm adopting some details from other similar boats, and adapting as I go. I've learned a thing or two in the process. I like to think I've learned things I wouldn't have if I'd just bought a set of plans for $100. And I'm approaching it as though this is the FIRST boat, rather than THE boat.

    BTW, it was about a year and a half from when I first started looking at plans to when I first started cutting wood. My wife thinks I should do less thinking and more doing.

    Good luck in your search!

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    You have to be careful of plans designed with solid wood in mind. Even hard chine ones probably won't adapt readily to plywood, unless they were designed for it in the first place. And hard chine is NOT lapstrake. Totally different beast. No chine logs, for instance, unless they are lapstrake topsides to a hard chine and flat bottom. But no guarantee that topsides can be gotten out of a single piece of ply, or that the bottom can be either. It is all about developable surfaces.

    You can probably just swap in plywood for solid lumber for traditional lapstrake design, but you still have to seal all the plywood edges really well, and you lose the lighter, simpler framing that glued lap plywood permits. Which is why the smart thing to do is buy plans to build the boat you like in the material you can obtain, until you have built enough you can play around with them at your will.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Quote Originally Posted by Thorne View Post
    Yes there is a way to convert most of these designs to ply from solid wood, but it involves years of experience with all types of construction and materials, and won't work well for some of the more "interesting" designs - some of which are better left unbuilt. But there are so many of these free designs that you can't really make generalizations about conversion unless discussing a particular type of boat, or better yet, a particular design.

    In the very vague general sense, particularly if the free design didn't require any steaming of the wood planks, you can replace solid wood strakes with ply strakes. Whether is is best to go for glued laps, stitch n' goo, batten-seam, or whatever is up to you. Making a scale model may be the best way for you to answer your questions about twist.
    Right, I'm leaving the "interesting" alone, mostly wondering about the ones that seem like the designer just wanted a slab to cover the gap twixt gunwhale and chine or chine and keel. I would guess it's a particular era of 30s and 40s designs where there were simplified construction designs for homebuild but plywood hadn't taken over completely. Seemingly transitional between fully framed traditional lapstrake and batten on seam plywood over removable former.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Quote Originally Posted by robm View Post
    unless they are lapstrake topsides to a hard chine and flat bottom. But no guarantee that topsides can be gotten out of a single piece of ply, or that the bottom can be either. It is all about developable surfaces.
    Yeah there's a couple of skiff-ish things I'm eyeballing that have crossplanked bottom.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    It may help if you post some links to a few free designs that you are considering; chances are that someone put them on the net, like here: http://boatplans-online.com/

    I've been doing my design work on FreeShip Plus 3.4 but there is a version 3.5 out now. It isn't great for recreating existing hulls, because the control points fall outside of the hull and you have to drag them to where the hull falls on the measurements you want, you cannot just type in a table of offsets for the hull itself. There is a feature for importing line drawings and creating a hull to match, but I haven't worked with that much yet.

    I think in general ply will be more twistable than solid lumber of equal strength. I don't think a design calling for a 14" wide strake of solid lumber will have much in the way of twist in that strake, and definitely not bends in different directions. But I don't get the mention of lapstrake and a hard chine in the same design, unless it is just for the topsides above the chine in case that you cannot find lumber wide enough to make it out of a single strake. The only time I've ever seen a 14" wide board (actually even wider) was under the tin roof of an old building in a pioneer village. Back then they used to "waste" such lumber for construction. The guy at my local lumberyard saved some clear 1x7 in 16' length but even those don't come up every day, I could not just walk in there and expect to find nice lumber except expensive select eastern white pine.

    I'm not sure I'd trust a computer design program to tell you wheter a boat is buildable or not. The boat design program may tell you that something isn't developable by making it a red colour in the developability check, but when you click on the "develop panel layouts" button it will spit out a panel layout anyway (you can make it display stressed areas). If there are any curved station lines on your panel expansion output that means there is distortion going on. For thick ply his may mean that it isn't buildable, but for thin ply (4mm) it can be twisted and tortured into many shapes the computer cannot predict. This means that if you build with those strakes you'll still make a boat, just shaped slightly differently from the one in the computer program. I have in fact built a hull from such thin plywood and cannot get even close to reproducing it in the computer.

    For a boat of any size or a motor boat I wouldn't even look at those old freebie plans, and just go with a modern design for plywood. Trying to design and build my own I am finding out more and more what I have to make up on the fly that would be specified in a proper plan. Many modern plans have a lot more detail than what's in those articles. A little dinghy or rowboat would probably be more forgiving of substitution of materials or be amenable to a home design. For thickness of ply to potentially substitute, look at similarly sized designs made for ply. Whatever you doctor up yourself, it will be an experiment, and will probably behave differently due to different weight unless it is more ballasted to compensate for the lighter materials. Also, those old designs probably have less flotation in them (or none) but you'd probably want some for safety.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Im sure there is a programme that highlights where panel stress is highest and possibly likely to have issues.....but then not all plywood will bend the same way, different number of plys, thickness of core material and species all play a part. I do not recall the name of it though. I only ever used one programme for design that is no longer available, Plyboats, it was basic enough where the learning curve was not difficult, but good enough to give you diplacement calcs, heeling moments etc. I have tried to get to grips with freeship, but my patience expires. I usually end up making scale models if i want to find something out. Is there anything like the old "basic" Plyboats programme still available?
    Sam Rabl and others got to grips with conic-projection, and designed boats that could be planked with plywood in large sheets. But even today, some very shapely Vivier boats are being built with ply, though it does mean rippng the ply into much smaller peices to do so.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Quote Originally Posted by BOI View Post
    It may help if you post some links to a few free designs that you are considering; chances are that someone put them on the net, like here: http://boatplans-online.com/
    Yes, I've been trying, I own a number of the boats books, and several dozen magazines, also "encylcopedias" and annuals of various sorts, the ones I'm really really interested in are not online it seems. I was looking for "similar" construction, but that tends toward making it a straw man, like for example the Biloxi dinghy, but not the bottom.

    For a boat of any size or a motor boat I wouldn't even look at those old freebie plans, and just go with a modern design for plywood. Trying to design and build my own I am finding out more and more what I have to make up on the fly that would be specified in a proper plan. Many modern plans have a lot more detail than what's in those articles. A little dinghy or rowboat would probably be more forgiving of substitution of materials or be amenable to a home design.
    Yes, definitely, anything over about 20ish feet, needing more than 10HP or planing speed over 20mph, I don't want to mess around with.

    Thanks for the tip about FreeShip, I'll look it out.

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    Default

    .zaz.
    Hove to off Swan Point......

  12. #12

    Default Re: Converting design from lapstrake plank to lapstrake ply???

    I know that this thread has long been inactive... However I just am going to weigh in. There is a traditional design and built lap peapod in the Maine Maritime museum or Penobscot MM, built in 1940's or 50's. using all traditional methods and design. except the planking is of plywood.
    I am planning to soon built a traditional pod this way myself.
    And regarding sealing the edges. I have a 40 year old plywood Thompson runabout and it is planked with DF MDO. The edges are fine with just paint on the outboard side and varnish on the inboard sides. even after years of just sitting in a shed some where.
    Last edited by robertlawrence; 10-10-2018 at 04:07 PM.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    recently bought plans for atkin's "little water" and plan on using plywood planks. it is near 25'.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    I have two boats, that I aquired in a trade, an eight foot lapstrake sailing pram and a twelve foot Pea Pod. They are built of eighth inch mahogany plywood, also known as doorskin and lapstrake planked The boats have several objectionable characteristics. First, they are extremely flexible and have an unnerrving way of showing this flaw out when ever one shifts position while sailing or rowing! The boats will both twist and bend in a manner that a normal lapstrake planked hull of cedar will not. In addition both boats are surprisingly heavy, much heavier than a traditional cedar planked boat of the same size would be. This weight comes from the fact that the plywood is heavier than normal planking material per cubic foot. It is a bit surprizing to find how heavy these little boats are when they must be picked up and loaded or launched!
    I for one, prefier a cedar planked lapstrake hull.
    Jay
    Last edited by Jay Greer; 10-12-2018 at 07:49 PM.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    This is not advice, but just to share my experience; a few years ago I built a Yankee Tender from Joel White's plans (purchased from the WB store), which is actually a modification of a John Atkins design.
    The plans called for solid wood construction, cross-planked bottom, 3/8" WRC strakes, etc all put together with clench nails or rivets etc. A friend and very experienced boat builder suggested I use the Oughtred method of epoxy/ply construction. So I built her to Joel White's plans quite faithfully except that I substituted 1/2" ply for the bottom and 1/4" ply for the planks (all marine grade meranti). All the rest- chine logs, knees, braces, thwarts etc- was mahogany and fir. Except I think the keel and skeg were white oak.
    So except for the bottom and planking she was built pretty faithfully to the plans. And -if I do say so myself- she's a beautiful little boat! 12'4"x42" beam. She rows beautifully, is very stable, feels very solid and sturdy, and is a delight to fish from or spend time on the water with my wife watching birds and wildlife or having tuna sandwiches and cookies for one of our now famous picnics
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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    That my friend is a proper wooden rowing boat! Bravo! Well done!
    Jay

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Conventionaly built excepting glued (and riveted) 12mm Sapele plywood on mahogany frames/keel. (Original design was probably intended to be carvel) I think using hign quality plywood with conventional construction is a proven technique.


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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Thanks Jay, I appreciate the comment.
    Addendum; she's 4'2" beam, not 42"
    regards
    pvg

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    Quote Originally Posted by Canoeyawl View Post
    Conventionaly built excepting glued (and riveted) 12mm Sapele plywood on mahogany frames/keel. (Original design was probably intended to be carvel) I think using hign quality plywood with conventional construction is a proven technique.

    It may be a proven technique but, in my humble opinion, it is not a proven material! Especially for planking!
    I have surveyed and been forced to do too many corrective surgeries on vessels built in that manner to condone such foolishness!
    There was one boat that was experimental and built by Chris Craft that cost more to repair than the boat was worth. Still the owner insisted on repairing it. It was a bitch to fix and those of us who were stuck with the job hated what we were forced to do! In truth I suffer both a physical and mental allergy when boat construction calls for plywood to be used! But, if it is considered to be a disposable boat it can be excused as long as the owner is aware of what he faces in the future! The crack Transpac ocean racer "Ragtime " is built of plywood. The maintenance of that boat has proven to be very, very costly over the years!
    Jay
    Last edited by Jay Greer; 10-13-2018 at 05:07 PM.

  20. #20
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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    It's no big deal to replace a plank, whatever kind of wood it is...

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    No, spiling and hanging a plank or two is no big deal to those of us who know how to do it. Even a full planking job is no challenge if the framing is fair and no stealers have to be calculated in at the stem or tuck! But pity the poor owner of a vessel that was put together by a "Jerry Builder" and the cost of correcting his or her shoddy work, when it proves to be a problem down the line!
    Jay
    Last edited by Jay Greer; 10-14-2018 at 03:52 PM.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    My dory tender was designed for cedar, built in glued lap ply. She's a peach.

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    Default Re: Converting design from lapstrake plank to lapstrake ply???

    My little six foot loa pram tender to "Red Witch" is made of 1/4" fir marine plywood. It was built to fit inverted over the Witch'es deck house.
    The plywood has required special care, over the years, that a normally planked boat would not need. The little "Hex" pram has had three new bottoms and one new port side plank, plus one stringer that rotted out as it was red oak in a stack of white oak that was over looked. The plywood needed replacement due to checking, rot and delamination. If it were not a labor of love to maintain her she would have been trashed forty years ago!
    Jay
    Last edited by Jay Greer; 10-15-2018 at 12:44 PM.

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