Dry Strip Planking

Discussion in 'Multihulls' started by Wrekin, Feb 16, 2025.

  1. Rumars
    Joined: Mar 2013
    Posts: 1,996
    Likes: 1,271, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    I don't have a dog in the fight between foam vs. wood, male or female, etc. so I try to stay objective.

    PET foam has lower sheer strenght then PVC of the same weight. The solution is to increase the weight until the properties match. 135kg/cum PET is slightly better in sheer then 80kg/cum PVC. This is still 150kg lighter per cubic meter then paulownia, so not an anathema for someone considering wood.
    Price varies locally but it can be said that the more processed the wood is at the time of buying, the more it resembles foam. With foam one can also use polyester wich can bring the cost down. You need to make a comparation based on real local prices, including transport and tools, and you need to normalize prices to a common unit like for example square meter (preferably finished, including paint), even if the wood was sold per cubic meter.
    Just to give an example of internet prices, the spanish site sells rough sawn 15mm boards for 30€/sqm, wich incidentally is the same price/sqm as 150kg/cum 15mm PET foam from Germany. If you can get by with 100kg/cum PET the price drops to 23€/cum, and if you buy the wood planed on two sides it jumps to 41€/sqm.

    Female molds can work well with strip if they are employed correctly. For a big boat the molds need to be either spaced wide enough for a person to fit between them or closed spaced and sturdy enough for a person to climb into the hull. Building a canoe or thin outrigger where you can reach the middle from both sides by streching your arm is completely different from the wide main hull of a bigger multi. Strip thickness is also a factor if you need to climb in for fairing before glassing.
    Using plastic or wooden nails as fasteners also changes things, the strips stay firmly attached to the mold during fairing and glassing (this is also true for male molds), you could glass one side, turn the whole mold (or get under it), glass between stations and only then remove it.

    If I would dry strip on horizontal female molds I would probably want
    my body to fit between molds, nail down a batch of strips that's not wider then my forearm, glue them up then immediately fair them.
    I know some builders who find it very easy to do an approximate rolling bevel by hand on each strip and use minimal glue amounts and others who find it tedious and butter up wide gaps with copious amounts of thickened epoxy.
    That's why the time and expense of doing a few test panels is so important, you discover what you like doing.

    Just as a hint, there are mobile bandsaws that use 100 or 120mm wide blades and hydraulic turners wich can turn a log into nice strips for under 100€/h, one just has to ask around.
     
  2. fallguy
    Joined: Dec 2016
    Posts: 8,218
    Likes: 1,881, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Boat Builder

    Yes, but.

    It doesn’t work that way for all hull forms.

    You asked. I answered. Now you want to prove me wrong? It ain’t an argument Gonzo. Each hull type has a preferred way to fly.
     
  3. fallguy
    Joined: Dec 2016
    Posts: 8,218
    Likes: 1,881, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Boat Builder

    To the OP.

    I built a foam sandwich hull in a female. No one instructed me, but I made the bottom form walkable. Basically 2x material with ply planking. I walked into the hull and did the transom last. Make sure to make allowances as needed. I messed up and got permission to apply the battens to the face of the mould and lost over 400 pounds displacement for it. Also, the right side of the female here was made splittable due to a 13’ ceiling limit to get it out of the mould.
    IMG_2873.jpeg

    Everything is about facilitation. You count steps. If it takes you 100 steps and 15 minutes to plank a 1”x12’ stick; you’ll quickly be able to determine it’ll fail, so you need to shoot for efficiency.

    If the designer specified female; disregard all other comments because we may be totally missing something relevant.
     
  4. Wrekin
    Joined: Nov 2023
    Posts: 9
    Likes: 3, Points: 3
    Location: France

    Wrekin Junior Member

    Rob Denney - Thanks for adding your experience. Great to hear that Kiri boats are still going strong, especially with the same glass schedule as specc'ed! Do you know, more or less, how accurate the strips have to join to be able to use PU glue? I'm buying used float frames from a Dutch builder, so as you suggest will test out the female mold on the floats before deciding what to do on the main hull. Yes planning to glass the other side as quick as possible - Normandy is great butter and cream country so the wood needs to be stabilised fast.

    Rumars - I was quoted by Ipaulownia rough cut planks - 23 euros/m2, after tax, and French supplier is quoting me - 600 euros/m3. Out of interest who is your German supplier?

    Would it be right to think I have to order twice as much as wood to account for milling it into strips?

    Fallguy - thanks for sharing your experiences.
     
  5. Wrekin
    Joined: Nov 2023
    Posts: 9
    Likes: 3, Points: 3
    Location: France

    Wrekin Junior Member

    Rob - do you know if the 'dry' builders were using pure epoxy or putty?
     
  6. Rumars
    Joined: Mar 2013
    Posts: 1,996
    Likes: 1,271, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    For paulownia I used the Ipaulownia site, 3000x120x15mm packets of 10 boards. Rough cut 91.80€ + 21%VAT, planed 152.40€ + 21% VAT. https://www.ipaulownia.com/en/shop/paulownia-boards/
    Each packet has 3.6 square meter of area and a volume of 0.054 cubic meter wixh means 25.5€/sqm and 1700€/cum before VAT. With spanish VAT it's 30.85€/sqm and 2057€/cum.
    These are parallel edge boards, it's easier to calculate the strips, you must add the blade thickness to each strip (1.2 or 3mm), so for 14x25mm it comes out to 4 full strips per board plus a 15mm one for the thin cut blade.
    With slab cut boards (more or less conical, depending on the tree), you loose some material with the live edge and strips have different usable lenghts.
    14x25mm strips can also be cut from 25mm thick boards if it fits you better. It's difficult to determine the exact waste percentage without knowing the initial dimensions, because of so many factors, for example do you need to plane the wood, some of the non standard strips are actually advantageous to have (14x14 for example fit high curvature areas better then 14x25mm, sometimes you actually need tapered strips). I always calculate with at least 50% waste. A good trick is to not mill all the strips at once, this way even if you overbuy the remaining wood is in board form and can be sold or used for something else.
    The french supplier seems a lot cheaper then Ipaulownia, even with their lower direct quote.

    For the PET foam I used Time Out: Kernmaterial | Hartschaumplatten günstig online kaufen - Time Out Online-Shop https://www.timeout.de/verbundwerkstoffe/kernmaterial/schaum

    The composites expo is in Paris in march if it interests you, JEC World 2025 - Le salon de référence mondiale dédié aux composites https://www.jec-world.events/fr/
    Timeout offers a free entry code, don't know if it's still valid: Messetermine - Time Out Online-Shop https://www.timeout.de/messetermine/
     
  7. Dave G 9N
    Joined: Jan 2024
    Posts: 159
    Likes: 68, Points: 28
    Location: Lindstrom MN

    Dave G 9N Senior Member

    Paulownia doesn't always demonstrate much resistance to decay. It may, like a number of other woods depend on the age of the tree and the location or climate where the tree was grown. There is some evidence that the rot resistance is not very good: 4 Common Paulownia Siding Problems (Explained) https://www.builditfine.com/paulownia-siding-problems/
    Cedar has a better, more consistent reputation. As I type this, I am reminded that the 18 year old cedar trim outside the window is rotten while the 30 year old cedar trim in other parts of the house is quite sound. There is always a bad batch of anything you can think of.
     
  8. Wrekin
    Joined: Nov 2023
    Posts: 9
    Likes: 3, Points: 3
    Location: France

    Wrekin Junior Member

    Hi Dave, thanks for sharing that link.

    I sent an email a while ago to David Evans asking about Paulownia's qualities. He sells Paulownia planks and strips in Australia for marine applications. He sent me this reply

    " Asia was years ago harvasting at 6 years and the trees grew so fast they were like straw with similar qualities to straw but that was 25 years ago and much has imporved since then."

    He advised avoiding trees under 15 years old....
     
  9. skaraborgcraft
    Joined: Dec 2020
    Posts: 766
    Likes: 247, Points: 43
    Location: sweden

    skaraborgcraft Senior Member

    Had i known it could survive and grow in minus 20, I would have been better planting that over the Larch trees, which i probably wont live long enough to make any use of.

    Spruce has been used up here for many strip boats, even if its rot resistance is low, better than balsa in that respect.
     
  10. skaraborgcraft
    Joined: Dec 2020
    Posts: 766
    Likes: 247, Points: 43
    Location: sweden

    skaraborgcraft Senior Member

  11. Dave G 9N
    Joined: Jan 2024
    Posts: 159
    Likes: 68, Points: 28
    Location: Lindstrom MN

    Dave G 9N Senior Member

    Warning TLDR and not exactly on topic, You are free to skip to the next post.
    It sounds like you might be able to count the rings per inch (or mm per ring if that's what you civilized folk on the continent do with rings).
    This is a 15 year old tree. 53 cm DBH:
    [​IMG]
    It would be interesting to know if they coppice or pollard paulownia trees... Or perhaps spending about 2 minutes searching the web would provide the answer? Yep: GUIDE_TO_ESTABLISHMENT_AND_CULTIVATION.
    There is a lot of information on that site about the trees, and this comment struck me as a good reminder for any forum on any topic especially since it was included in the context of claiming that fossil species found in one corner of a continent should be considered native to the whole continent:
    So, if you read a few seemingly authoritative sources along with this thread, the age of the tree (>15 years) is not addressed outside of the topic of producing 6 m long vertical grain knot free wood.

    belcofp.com/durability-by-design-rot-and-insect-resistance/ Depends on Eric Meir for durability. Eric does a heck of a job with most properties, but this one for this tree is asking a lot.

    The Influence of Age on the Wood Properties of Paulownia
    tomentosa
    less than 6 years, but age was the subject.

    https://www.fpl.fs.usda.gov General Technical Report FPL–GTR–224 Evaluating Naturally Durable Wood Species. These guys need an IT guy who knows better than to diddle with the url every 6 months! Search the report number after the url gets changed again.

    Termite Resistance At least they knew that they didn't know how old the wood was and thought it was important.

    Paulownia-sustainable-hardwood-lumber. But age was only a factor with respect to portability:
    "Sadie, age 5, carries a planed 8/4 Paulownia lumber board (14 BF)"
    [​IMG]
     
    montero likes this.
  12. skaraborgcraft
    Joined: Dec 2020
    Posts: 766
    Likes: 247, Points: 43
    Location: sweden

    skaraborgcraft Senior Member

    Yeah, from what i found, return in growth after 5 years is diminishing returns. Certainly i would have had enough timber to strip plank at least one 30ft yacht in 5 years. And probably an ongoing store of free firewood. It took 5 years just for my larch trees to really kick, and not even enough timber for a small bowsprit yet......
     
  13. Wrekin
    Joined: Nov 2023
    Posts: 9
    Likes: 3, Points: 3
    Location: France

    Wrekin Junior Member

    Thanks Dave, some great links!

    I've always been a "don't believe the hype" kind of guy. How often do we see the next big thing fall flat on its feet in this crazy upside down world we live in.....
     
  14. redreuben
    Joined: Jan 2009
    Posts: 2,081
    Likes: 279, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    I worked in a yard in Henderson WA that built 3 strip planked cedar hulls for the Farr 9.2. The last one was used to make a grp mould.
    This was 1988/9 so details are a bit vague but ......

    Being a round voluptuous hull the majority of the planks being square cut left a natural gap to be filled, on the flat sections the planks had a sawn bevel to provide a gap.
    The planks were fixed to the stations dry with 50mm double headed nails.
    As the planks began to twist a straight edge was laid on the mould to lay a fair line again, the planks were trimmed and planking then resumed.
    Strips of thin ply were stapled in between frames to keep planks aligned and fair if required.
    Some spiling was required at the ends.
    The glue was west system and micro balloons with absolutely minimal silica and was wiped into the gaps with rubber squeegees. Remember this glue only has to be as strong as the cedar so its pretty much an easy to sand fairing mix. Too much resin or silica makes the glue too hard and it wont fair well.
    There were some convex areas in the bow that were glued from inside.
    Next step was to remove the nails and fair the hull with a 24" jackplane followed by course grit on a 8" sanding pad.
    Fill any gaps and resin coat.
    Double bias on outside laid keel to sheer. Inside was uni laid keel to sheer. Extra layers in way of keel.
    Fairing was done with epoxy and micro mix using a tilers trowel with 10mm notches, keel to sheer
    Sand with torture board and 40 grit until you have minimum thickness then fill vertical gaps and re-fair.
    One resin coat then spray with epoxy hi build, sand and paint.
    Two experienced boat builders and a lacky (me) did one hull from planks to paint in about 10 days.
    I was only involved from the glassing onwards.

    Your mileage may vary.
     

  15. fallguy
    Joined: Dec 2016
    Posts: 8,218
    Likes: 1,881, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Boat Builder

    Great post from r/r.

    I’m gonna reiterate one thing I have experienced in various areas of building.

    If you use a very different hardness glue compared to the wood selection; when you go to sand the hull fair; the wood hogs in before the glue and very hard to ever get a fair surface.
     
    redreuben likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.