Norway Spruce for strip planking?

Discussion in 'Materials' started by Ranger1973, Oct 1, 2012.

  1. Ranger1973
    Joined: Oct 2012
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    Ranger1973 Junior Member

    The hull will be sheathed in glass fibre/epoxy anyway.When you say coat the end grain in 2 layers of epoxy are you running under the assumption that the hull wouldn't be glassed?Or is it just good practice to do this to the planking regardless?Your comments are appreciated.
     
  2. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,389
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    Most water absorption is at the end grain. It makes sense if you think about how tree trunks function in nature. People used to seal end grain with red lead paint before epoxy came along, and many traditional boat builders still do some form of this. Fiberglass can hide spots where water got in, and can trap it. If Aluthane, CrabCoat, or similar will seal sufficiently it'll save you the trouble of having to mix a two part product just to seal something quick prior to assembly.

    Curiosity makes me wonder if dipping the end grain in TightBond III would do the trick. I think even an inexpensive shellac or varnish would be better than nothing. Sealing the end grain somehow (after the wood has dried sufficiently) seems smart given that fir is less rot resistant than cedar.
     
  3. Ilan Voyager
    Joined: May 2004
    Posts: 1,268
    Likes: 194, Points: 63, Legacy Rep: 758
    Location: Cancun Mexico

    Ilan Voyager Senior Member

    I have an old experience in strip planks , my preferred method with one off boats. The version epoxy/glass is practically a sandwich where the wood plays the role of an active core with mainly longitudinal strength. So the wood has to be totally encasulapted. In fact it is a wood composite. Nothing to do with the classic strip-planck edge nailed with ribs and keel.
    Forget tightbond, gorilla and other stuff for boats there is marine epoxy and that have worked since 40 years...
    For the peculiar sandwich that is a composite strip plank, the core is simply a light wood with good qualities of gluing. Light because of weight, and most important the thickness...Rigidity and strength of a sandwich varies at the cubic ratio of the thickness.
    That eliminates all the heavy "strong" woods except for some local zones like gunwales, keel and other places.
    The Fir is pretty heavy (more than 600 kg/m2) and is not the best choice for a composite strip planck except in the "strong" zones. It's also a pain to sand because of the alternance of soft and hard grow rings. As you are in UK with good resin and glass, light pines would be a better choice at better price like the North Pine (480-520 kg/m3). As it will covered by layers of glass and epoxy, there won't be any problem of rot.
    It's also easier to make strip plank with a soft wood and the gluing surface of the edges is greater.

    The book by the Gougeon Brothers is now downloadable for free at the West System site. Read it. It's the bible and will answer to 99% of your questions.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 484, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    TiteBond III will soften considerably with immersion and epoxy doesn't like to stick to it. I'm not sure of it's moisture vapor penetration rate, but would suspect it's higher then epoxy. It does pass the type 1 WBP test, but just barely. The polyurethanes are starting to come a long way towards real waterproofness, though still are in the low 90% range, which will eventually permit moisture gain. Film thickness is the keys to the polyurethanes, which typically need quite a bit. On a trailered boat, this might not be a concern as immersion time isn't long enough to be significant. TiteBond III isn't especially good with bigger pieces and/or highly loaded elements (creep), but on stripper canoes and other small craft it'll work to glue the strips, assuming it's well prepped come sheathing time (removed from the surface). Lastly, it has a pretty short working time, though a slight water cut (less then 10%) can improve this a bit, it also dilutes the waterproofing properties. Personally, I wouldn't bother with two or three adhesives on a strip build. If it's sheathed, I'd just used epoxy. If the strips are glued with epoxy, you'll treat the end grain at the same time.

    As to Norway spruce strips, this species would be fine, but strip dimensions and/or sheathing schedule, should be scaled properly, especially with light weight softwoods.
     
  5. Ilan Voyager
    Joined: May 2004
    Posts: 1,268
    Likes: 194, Points: 63, Legacy Rep: 758
    Location: Cancun Mexico

    Ilan Voyager Senior Member

    You are very right. And I've seen many disasters with polyurethane. Furthemore there are a lot of marine epoxies at a decent price. It's better to work with only one resin and not to have to worry about compatiblity of different products.
     
  6. redreuben
    Joined: Jan 2009
    Posts: 1,813
    Likes: 137, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    The main vulnerability of wood prone to rot is the penetrations from screwing on deck hardware and fittings, the somewhat tedious solution is to drill oversize and fill with epoxy filler before re-drilling to final size.
     
  7. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,389
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    The stripping I've done was with PL Premium Polyurethane. I built outside, sometimes in wet and/or cold conditions. In places I tried Gorilla Glue. The result was a mess. I was yet another of the disasters with polyurethane that Ilan Voyager mentioned. I would NOT use those products, or build in those conditions, again. So those are the negative lessons I can offer.

    The reason TightBond III has been recommended (in these forums) over epoxy is that any excess epoxy squeezed from between the strips will be harder than the wood (especially if using a lightweight cedar). The question becomes how to sand it without sanding off too much wood thickness..? Even if you come up with a workable method for the convex outside of the hull, will it work on the inside? Some people do just fine mixing powders into their epoxy, but under the circumstances where I was working the handling of microballoons and fumed silica powder proved problematic. It seems to me a sandable epoxy fairing putty, such as http://www.epoxyproducts.com/datacream.pdf, http://www.star-distributing.com/smith/fillwhy.html, or SystemThree SculpWood or SilverTip products might work nicely. Perhaps there are also polyurethanes (other than the ones I used) with which one can get good results under more controlled circumstances.

    I'd be interested to know what people who've used resorcinol think of using that, or other waterproof glues not yet mentioned, for edge gluing the strips. A furniture maker repaired my broken wood daggerboard with a dark glue that may have been resorcinol, and the repair has performed well.

    An important difference between encapsulated planks and a balsa core is the direction of the grain. That's why I'm advocating sealing the end grain. Any moisture that gets in where there's exposed end-grain will get wicked along the plank, migrating longitudinally between the skins of the hull. You don't want that, and it makes redreuben's point about thru-hulls and deck fittings extremely important.

    I'll also note that if you're using enough fiberglass thickness to call this sandwich construction, over a fir core, that doesn't sound like a lightweight scantling. Of course it could be reduced to a decent degree if you use longitudinal stiffeners as well as transverse frames.
     
  8. redreuben
    Joined: Jan 2009
    Posts: 1,813
    Likes: 137, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Ian Johnstone, when building his 40' Crowther tri Baleena/Bullfrog/Australia's Child used balsa planking.
    He cut the planking into sections of about 4ft or so and re-glued them with epoxy to prevent/minimise the wicking as you described.
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 484, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Resorcinol and most other adhesives, other then epoxy, require quite good fits and high clamping pressures. This said resorcinol has been used and was the adhesive of choice before epoxy. Resorcinol can be difficult to work with, being temperamental about temperature and other environmental conditions. High clamping pressure and well fitted joints also are requirements.

    If proper procedures are followed, you should have a minimum or no cured ooze out to contend with. Simply put, if you wait to sand it off, you've missed the best opportunity to remove epoxy easily during the gel and green stage.

    I would not use micro balloons, spheres or Q-cells in an adhesive mixture. These have minimal surface area and are typically just bulking agents for a light weight fairing compound, not an adhesive mix. Good adhesive mixtures included fibrous materials, such as cotton flock, silica wood flour, milled fibers, etc. These materials have much more surface area on the individual particles, which offers more mechanical surface for the adhesive..
     
  10. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,389
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

  11. Ranger1973
    Joined: Oct 2012
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    Ranger1973 Junior Member

    Hi everyone.When i started this thread i was curious as to how fir/spruce would hold up as a material for strip planking.It seems that there are a lot of differing opinions as to the suitability of this wood for this method of boat construction-however,it also seems that the over riding opinion is that fir/spruce IS acceptable,if somewhat heavy,as a building material.The next question i'd like to throw out there to all is how THICK the said planking should be in either materials (fir/spruce) on,lets say,a 28-30 foot boat?I will also be questioning the suitability of different adhesive methods and different adhesives for strip planking.
    I must say i am very impressed so far with the wealth of knowledge that people are carrying on this site and also suitably impressed with the opinions given also.Remember i am absolutely and totally a layman and complete novice in these areas so am grateful for any and all assistance in these forums.
    Thanks...
    Just as an after note the hull after being planked will be glassed over and also epoxied inside,effectively encapsulating the entire hull.
     
  12. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 484, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That's a pretty self serving piece, listing all the products they carry as the methods to handle the seams on a carvel, just smacks of, well . . .

    Also several inconsistencies, which were common practice, but less so now, as more testing and durability trials come on line. For example, high build epoxy primers are not waterproof, as suggested. There are other discrepancies, but I don't know when this article was written, but it seems it is likely about 10 years old, where most acknowledged the non-waterproofing qualities of CPES, yet the definitive penetration tests had yet come in, so they're still on the "it can restore decayed wood's physical properties" bandwagon, which is does not. Some still buy into this marketing trick, but test have clearly proven that dead wood with highly diluted (about 70%) epoxy doesn't do anything, except make it dead wood with a thin, very porous plastic coating. Physical properties are slightly changed, but it's still dead wood, unable to support loads or in this case bear the strain of caulk being pounded into the seams.

    As to scaling the strips, well this is dependent on several factors and build methods. I can think of at least a dozen different strip build methods, each relying on a different percentage of longitudinal stiffness from the strips, which can be affected by the strip dimensions, sheathing schedule and other considerations. Simply put, you can have a pretty wide variance of strip dimensions based of several factors.

    What design are you building? What's it's build method? Are you attempting a conversion from one method to another? Is this a commonly employed strip method (there are about 6 common strip methods) or a bit of a one off?
     
  13. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,389
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    Dave Gerr's Elements of Boat Strength has several methods any of which could be applicable here. The lightest, attributed to Lindsay Lord, calls for using Vecra or Dynel (in epoxy) sheathing (in place of fiberglass) in order to make the hull deliberately flexible so impact loads are more distributed.

    To use the Gerr/Lord scantling method we'll need to know LOA (not counting sprits, pulpits, cutwaters without volume), Beam (not counting rubrails) and Hull Depth from sheer (top of deck at side) to top of keel inside the boat at midship. Shall we take LOA as 29 feet? What are the other two dimensions? Does the boat have long overhangs (LOA/DWL > 1.08) or pronounced flare (BOA/BWL > 1.12)? Is it's displacement/length ratio between 100 and 275? And remind us what the general description of the boat is. What sort of power? What's the intended top speed?
     
  14. Ranger1973
    Joined: Oct 2012
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    Ranger1973 Junior Member

    O.K.Lets say a multihull vessel of 29 foot L.O.A.,15 foot beam and hull depth from sheer to top of keel is 6 half foot:confused:.Under sail power.Not performance orientated.This is all an extremely steep learning curve for me-so please bare with!!:)
    As an after note do you have any opinions on expansion/movement of the hull when using strip planking?As the fibre orientation is all one way doesn't this compound any expansion??
     

  15. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 484, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I have a fair bit of experience with the Lord method. It is the lightest of all the strip planked methods, but I wouldn't recommend it arbitrarily applied, as the scantlings for this method can be quite dainty, compared to other methods, plus the goo factor which is considerably higher. The Geer scantlings for the Load method will make a heavier version of a Lord build, but this isn't an issue if properly spec'd out.

    I'd recommend one of the other strip methods, excluding traditional strip planking. Again, what design are you building? Strips are married to each other with adhesive, forming a homogenous structure, though fiber orientation is considered, they aren't separate strips and sheathing and fasteners can over come weaknesses in cross grain strength.
     
Loading...
Similar Threads
  1. CatBuilder
    Replies:
    40
    Views:
    11,817
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.