50ft strip plank sailer - producing the strips for planking

Discussion in 'Boatbuilding' started by TOALL, Sep 29, 2016.

  1. TOALL
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    TOALL Junior Member

    Machining of the mould sections by cnc next week so my thoughts are turning to producing the strips for planking.

    Lots of pros and cons for producing moulded planks many differing opinions.
    I'm thinking of a slightly different approach. Planking is 27mm thick so loosing maybe 10mm from each edge amounts to a lot of sawdust going down the extraction pipes. I'm thinking of using loose tongues to make plank alignments more reliable. if I machine say a 8mm grove down both edges of the planks and separately produce the matching tongue.
    This also helps in alignment at end to end joints in the planking. I plan to zig zag cut the ends and glue them together as planking precedes. I will be able to make sure at these joints the loose tongue bridges this point.
    Taking this further, if the tongue is machined slightly oversized a constant gap could be left between the planks.( I've looked at the dry method of planking, pushing epoxy between the boards which does seem, on the face of it, a great idea)
    I like the idea of working the stripping dry, although unless I glue the loose tongs in I will have 8mm line running through which is unglued. No doubt this has all been tried. would really like opinions
     
  2. waikikin
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    waikikin Senior Member

  3. rwatson
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    rwatson Senior Member

    This guy is the dry strip "king". He had a couple of videos on the method. There's a construction photo on his home page.
    http://www.bowdidgemarinedesigns.com/index.html

    If you do dry strip, the edge machining is totally redundant, as they never touch using Bowdidges technique. His boats are quite small however.

    I have my doubts about the cost and bother of edge machining. On the sections of hull that are 'straight', keeping the planks aligned is not that hard. A few temporary 'patches' should do it until you get the gap glued if the timber is a bit wavy.
    On the sections of hull where the curve happens, often the bead cant seat in the cove, and neither can the 'tongue' in a groove, and certainly not a bevel. just makes. Where you need to shape the planks, you have to plane off the machined edge anyway.

    This guy has some uncomplimentary comments on large strip planked boats, and suggests diagonal planking is the go. For example
    "It is worth noting that ABS (American Bureau of Shipping) rules do not recognize solid wood, fully encapsulated, as structural below the waterline. This means they do not recognize the wood as contributing to the strength of the structure, because is is not likely to last"
    http://www.gartsideboats.com/faq/more-on-strip-planking-pauls-opinion.html
     
  4. PAR
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    PAR Yacht Designer/Builder

    The only real advantage to strip planking is its friendliness to the novice builder. It's not particularly fast as build types go, it's tedious, if milling your own stock has lots of waste, tends to be heavier than other build types and in larger sizes, just isn't as well suited as other methods. Of course, it all depends on which strip plank method you're going to use, as there about a dozen different kinds.

    The way to do strip is to use a method that doesn't rely on self alignment so much as good technique. For example, lots of little strippers employ cove and bead edges, but when these are planked up, there's still a lot of material removed in fairing, so what was the advantage of the cove and bead stuff. The same would be true of a tongue and groove approuch. The dry plank method that Mark has championed is interesting, but produces a heavy hull. The epoxy needs for this type of build triple because of the gaps, though it does help in other areas (fairing).

    The best use of strip planking is if the strips are little more than a core, over which veneers are laid. This means you can use lower grade strips and the fits don't have to be particularly precise, as the veneers will hide and fill all of this. Conversely and again, if the strips are considered a core and fabric skins, instead of veneers are used, you get similar benefits. These types of build are true composites and can produce lighter and stronger hull shells.

    I find it much easier and faster to not "edge dress" the strips, but do this by hand, as the strips are applied to the molds. A few swipes with a small plane and you can match a rolling bevel pretty well, certainly well enough that epoxy will fill any minor gaps. After a dozen linear yards of strip beveling by hand, you'll get a feel for it and it goes much quicker. You also save a lot of goo with this approuch, because of the tighter fits.

    As to milling the strip stock, just buy 16' - 2x12's (40x300) and rip the edge off at 27mm on a table saw. The long, wide boards will have to come from older, bigger trees, so the grain will be straighter and tighter, with far fewer defects. This is also the cheap way of getting strips.
     
  5. rwatson
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    rwatson Senior Member

    You have made this assertion a few times, but without showing any calculations.

    I investigated the method for an 8.5 meter boat, ( attached) and on an 8,5 meter, 4.5 meter circumference hull, not allowing for any reduction of a tapering bow, I got an extra 13 kilos of epoxy for a ridiculously wide plank gap of 20 mm ( more likely averaging 6 mm). Also, 50% of the "glue" is much lighter microfibre.

    That's hardly a "heavy hull", and I bet its nowhere near "3 times the epoxy".
     

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  6. PAR
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    PAR Yacht Designer/Builder

    We have a builder that's used this method, currently working on the fitout of the interior of a 26' sailer. The hull is essentially completed. His gaps ranged, as you'd imagine, but rough averages would be ~1/8" tall, across the thickness of the strip. So, a 3/4" thick strip, with a 1/8" tall gap of goo, the amount of epoxy is pretty easy to figure out. This would be compaired to a typically glued (epoxy) strip and approximately 4 times the adhesive material, assuming a nice tight 1/32" glue line. He estimates 4 - 5 times the amount of goo over a traditional glued and nailed strip job. He used a few different spacers, nails, wedges, finally settling on tongue depressors.
     
  7. Barra
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    Barra Junior Member

    PAR what on earth are you talking about. Firstly the glue has to be no stronger than the wood it glues so low density filler is fine, AND LIGHT. The OP is talking 50 ft hull so unless he is a goose he won't be using 3/4 in planks. With a round bilge hull the gaps will be "V" shaped. Even an 8.5 meter hull will use a range of plank widths, maybe as wide as 90 mm on the topsides.

    As for edge dressing planks on the job , you must be joking unless you are going to turn the job into a life times work. Rough sawn edges are fine, just get on with the job.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

  9. waikikin
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    waikikin Senior Member

    Hi RW,
    Can you show your calcs, the attachment isn't clear to me in the assumptions.
    Regards from Jeff.
     
  10. TeddyDiver
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    TeddyDiver Gollywobbler

    Reckon you have missed a zero at some point. 130kg would be more accurate.

    BR Teddy
     
  11. TOALL
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    TOALL Junior Member

    50ft strip plank sailer

    Like the ribbet idea, presuming its placed in line with a station mould.

    My stock is all 50mm thick so I was planning to cut all my planks 50mm wide and 29mm thick . Then putting it through the 4 side planer to achieve 48 x 26mm.
    My stock is 50mm thick and random width, cutting it this way will reduce wastage and give me a kind of quarter sawn cut. It will mean I am stripping the entire boat in 48mm strips. Without doubt I'm not looking foreword to fitting this many planks but on the upside fairing should be easier.

    If I choose not to fit a tongue I think I have to scarf and glue all the end joints before fitting the planks. This is not a pleasant thought as 1/5 of my stock is 8ft lengths. I really need a way to assemble and glue this joint as planking is applied. I can Tenon the ends in a zig zag fashion but with out the tongue I think I will get flat spots at the joint.

    In a ideal world I would love to plank the mould without glue, using square edged boards and without scarfing and gluing the planks prior to assembly
    But I cant see this as a practical method,

    I think the only combination is, grove the planks on both edges and use a loose tongue to edge align, zig zag Tenon all the ends of the planks and rely on the tongue to eliminate flat spots at the join.

    By the way my construction material is kd Brazilian Cedar.
     
  12. PAR
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    PAR Yacht Designer/Builder

    My 3/4" plank dimension was an example only. I'm not sure how many builds you have under your belt or designs you've mustered up, but I have been around the block a few times and can assure you, strip planking a hull of this size (as described) is a heavy way to build. The only advantage is the small plank size. I can bevel a 50' long 2" plank with a hand plane in a few minutes. It doesn't have to be particularly neat, unless using something other than epoxy. Of course, the strips will become trapezoidal, that's a given on a round bilge, but working down a 2" plank with a plane or belt sander is simple, fast and tightens up the gaps, so you don't have to make a career out of filling them in.

    There's no need to scarf strips in a strip plank build, just wasting time. A 45 degree cut does help alignment a bit, though butt joints are just as acceptable.

    I use "U" shaped alignment pieces, cut from scraps. They're placed over the freshly laid strip, sandwiching it with the one below. It helps with alignment, until a nail can be placed. I just pound them on, as I place the strip. Also a small block, with a screw in it, driven at an angle, from above the freshly placed strip, screwing to the mold edge works well and is fast. In reality, strip planking alignment isn't as critical as most think. You're going to have to shave quite bit, to fair it up anyway, so don't go crazy with alignment methods. Just get it close and plane the offending strips down once it's planked up.

    Tongue and groove sounds like a big waste of time and materials for less than a pretty fair result. Strip planking is best treated two ways: as a narrow plank width carvel or as a cored composite. As a carvel, you don't need to focus so much on the fits (unless it's to be bright), which makes things go together faster, though is still tedious. As a cored structure, hell you can use French fried potatoes as the strips, assuming a sufficient inner and outer sheathing schedule is employed. Again, the only advantage to strip planking is novice builder friendliness. You can also get away with lesser grades of planking stock, but these are the only things that make strip planking viable. On a 50' hull, I'd use a thinner stripped core, skin both sides with veneers and an exterior (minimum) fabric sheathing. In reality, I'd never strip a 50' hull, but would consider molding or other more weight/labor friendly approuch.
     
  13. TeddyDiver
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    TeddyDiver Gollywobbler

    I didn't and don't bother to plane the strips just sawing them square and close enough. The surfaces must be sanded anyway and with a belt sander it's easy enough. Anyway there's a lot of time to saw the next patch of strips and sand the completed area while waiting the epoxy to cure. Same with left overs and extrudings of the goo just use to fil any voids on the sanded area.
    Reckon working time to saw, set the planks and sand a 50 footer is about 500h give or take..

    BR Teddy
     
  14. PAR
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    PAR Yacht Designer/Builder

    Yeah, that's about it, strip planking is a pretty sloppy and relatively slow way, to build on a hull of this size. Assuming a typical beam, with these strip dimensions, it'll be in the 90 to 95 strips per side range, for this hull. Working alone, the average backyard builder would be hard pressed, to get more than a few strips per day, unless working full time, per week on the project. This makes Teddy's estimate quite accurate.
     

  15. rwatson
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    rwatson Senior Member

    Fair enough, that's why I posted it, so others can check the calculations. I am not the biggest math head. I spotted 2 serious errors in my calculations already so I will work it out again, using some realistic figures, because I want to seriously consider the option.

    Say the hull is 8.5 meters long, and 4.5 meters in circumference
    Lets make the gaps something realistic at say 6mm wide , (.006 meters width )
    Say the planks are .019 deep (that's a usual thickness when glass is going on both sides)

    So each "gap" is 8.5m x .006 m x .019 m = .00097 cubic meters per "gap".
    .............................................................................................................

    The circumference around the widest part of the hull is 4.5 meters, when divided by a wood strip of .025 = 180 strips, so 180 "gaps"
    ........................................................................................................


    180 "gaps" at .00097 = .174 cubic meters of resin
    Resin is 1.2 Kilos per Liter, so 1200 kilos per cubic meter
    So a pure resin fill would = 210 kilos of resin if you were building a barrel.

    But, reduce the number of gaps to allow for bow and some stern taper , say x 2/3, and reduce the resin mix by 1/3 to allow for the lighter filler, and it would come to

    less "gaps"
    120 "gaps" at .00097 = .13 cubic meters of resin

    less resin with filler
    .13 cubic meters x 2/3 = .098 cubic meters of resin (99 litres)

    would weigh around 117 kilos.

    But then take off the timber you save,
    .1164 cubic meters of a light timber like WRC at 350 kilos per cubic metre
    = ~ 35 kilos.
    ...............................................................................................................

    So extra weight overall on boat = 98 kilos.
    The resin coverage on a boat that size is around 120 liters, so you might say you double the resin.

    The planned bare hull weight was around 500 kilos, so you could say you increase the boat weight by nearly a fifth. BUT there needs to be over 200 kilos of permanent ballast, so at least 1/2 of the extra 98 kilos can come off that figure. So an "extra 41 kilos". The other benefit is that the timber strips are separated by a thick glue line, which may be handy from a longevity point of view. Since the extra resin is around $2,000, you would hope so.

    So, its not as good as my previous attempt, but not nearly as bad as Pars estimates looked.

    You would never use this technique on a hull that wasn't going to be fully encapsulated with glass/epoxy. Even Mark Bowdidge says his engineering calcs just consider the wood and filler to be a high density core, which is in line with all commercial standards.

    But being able to lay out and fit all the planks, fit in the stealer planks ahead of time then have a one time "glue-up", seems to merit serious consideration.
     

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