Norway Spruce for strip planking?

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

  1. Ilan Voyager
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    Ilan Voyager Senior Member

    I do agree with you. It's useless to have a over-strong glue and sanding is an important factor. Just enough strength than the joint breaks is the wood. Incidentally balsa in longitudinal planks is not the best of ideas, the strength is compression and shear is to low to make a suitable core (grain wood panel is another thing, but it's for sandwich). The price is not friendly even on the 165-200 kg/m3 quality.

    For easy finishing, the first requisite is a resin that sands well. Some resins have a very low point of softening and are sandpaper killers, a true pain, like the 106 of West System (plus the fish eye problem...) 30 years ago. Also, no resin will sand well if not fully cured...patience and heat pays.
    Cleaning when the resin is just gelled helps a lot; and making some special knives for cleaning is a good idea specially inside the hull.
    Besides, I maintain that thermoplastic fillers are not the best in any glue because they can be unpredictable specially in tension but also often in shear. The price of some, the good ones, is repulsive...

    My personal experience dictates first to make trials when yo do not know well the materials you're going to use...No manual will say; "our resin is a pain to sand, as it melts on the abrasive" or "our resin produces a lot of carbamate -blush- which clogs any abrasive even treated with zinc stearate".

    My experience says that hard wood flour is a bargain; cheap, strong, already thixotropic, pretty light and easy to sand. A mix of wood flour, glass microspheres (the good ones)and a bit of silica makes an excellent putty for strip planks, strong enough with a bit of flexibility. Silica is very hard to sand and must be kept at the strict minimum.

    Using a light wood that sands well helps a lot and the last but not the least a pneumatic belt sander outside the hull, and a pneumatic 7 inches circular sander with foam pads inside are a pleasure because first there are light and also they can be used for wet sanding of the final coatings, before the orbital sander...the dream, no dust, no heat, no clogging and very fast. A bit of skill is needed as you can make disasters with these tools.
     
  2. gonzo
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    gonzo Senior Member

    Stephen: we found out that there was enough resin seeping between the seams to be adequate adhesion. Also, the seams got scraped clean before the epoxy cured.
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    I do not see the need to switch to polyurethane when you have epoxy resins that do the job at decent prices.

    Also I do not see any true advantage with polyurethane but I have seen a lot problems with... I have tendency to take the advertisement claims a lot of grain salts, and make my own trials when planing to use unknown products.

    I'll believe the Oman claims when I read reports by serious independent laboratories like the CETIM in France or the Forest Labs (USDA) in the States, or at least scientific trials on a significant number of pieces. His own trials are ridiculous and a moisture cured urethane is not known to be the best sealer on a long time. Urethane is a simple ethyl carbamate, not a true POLY-urethane (=cross linked), as in the expensive paints. There is some confusion in his papers. For trailers I stay with a epoxy 95% zinc primary...
    .
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    You quoted Gonzo about the balsa core and it's allways, anyway in my knowledge, endgrain. Endgrain is very hard to sand..
    Concur pretty much what Ilan and Gonzo says above. Thou I have no difficulties using electric belt sander with one hand, and that doesn't mean I'm strong, just about having practiced enough...
     
  5. gonzo
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    gonzo Senior Member

    Duracore is end grain balsa with mahogany veneers on each side. It also has pre-made finger joints.
     
  6. TeddyDiver
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    TeddyDiver Gollywobbler

    Oops.. Didn't know that brand.. Stand corrected. :)
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    Duracore; Very good for race boats but the price for a home builder....
     
  8. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I'm seeing your fir strip planks being about 9/16" (14 or 15mm) thick. At this thickness we may find you need to throw in a couple additional ring frames and/or stiffeners. If you care about strength and ease of construction more than weight you could go a little thicker (5/8" perhaps). For bending both directions the strips would ideally be square, but you could go to 9/16" x 3/4"(19mm) or 5/8" x 7/8" without causing problems. Perhaps over the weekend I'll venture a candidate laminate thickness and take a look at what the maximum bulkhead/frame spacing would be.

    This is rough; just an initial guesstimate for preliminary consideration. I'd like to see if others in this thread concur or get something different. After laying out all your structural elements you should have your work checked by a structural engineer - a credential I don't have.
     
  9. PAR
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    PAR Yacht Designer/Builder

    If your sanding ooze out and drips on a strip build, you've wait way too long to address this issue. As Gonzo pointed out, you can scrape the ooze out and drip off the surface (both inside and out) after application, while the epoxy is still workable, in the gel stage or still "green". It's easy and part of the process if you want to save a lot of work. While still workable or in the gel stage, epoxy is easily removed with a plastic applicator or putty knife, even a sharpened piece of wood will do. The bulk of the goo is removed and you have minimal sanding when it's cured. An epoxy run typically takes 15 - 20 minutes, but then you spend the next few hours (depending on hardener), "chasing it" picking up the ooze out and drips.

    CPES isn't like epoxy primers, in fact most epoxy primers have more solids content than CPES!

    I don't have spec's on Progressive Polymer's aluminized polyurethane paint, but I can make a reasonable guess, based on it's description. It's likely a typical low cyanoacetate promoted cure polyurethane, but with a heavy content of aluminum oxide as suspended particulates. I use similar paints to lock down severe stains, as the aluminum particulates, which look like little tiny flakes under a microscope, tend to settle down and over lap each other when the vehicle flashes off. This forms a metal barrier that is quite effective at preventing stains from coming back to the surface. As to it's waterproofness, well, I'll side with the chemists in regard to polyurethane's durability immersed. The only time I've seen any polyurethane work in immersed situations is when it's applied and placed in considerable compression during it's full cure (a few weeks). This includes sealants and adhesives, as well as coatings. I've preformed some in field testing on the high cyanoacetate catalyst polyurethanes (two part spray only) and these do show considerable promise immersed, but the jury is still out.

    Again, speculation on scantlings with the information provided, is just folly at this point.
     
  10. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I think PAR is right that you (Ranger) need to settle on a design before going further with respect to scantlings. Have you purchased any study plans? Perhaps we're talking about a boat similar to one of these?
    http://www.tennantdesign.co.nz/index.php?page=shilo
    http://wharram.com/site/node/56
    http://wharram.com/site/node/61
    http://wharram.com/site/node/47
    http://wharram.com/site/node/48
    http://www.sailingcatamarans.com/windsong1.htm
    http://www.sailingcatamarans.com/sagitta.htm
    My opinion: I like the last of these, Sagitta, and you can download study plans online.
    Here are construction photos: http://www.midnight-rambler.co.uk/pictures.htm (This one's currently for sail used for 20,000 British pounds.)
     
  11. PAR
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    PAR Yacht Designer/Builder

    It's imposable to discuss scantlings, without a particular design in mind or considerable information about a proposed design, including a comprehensive weight study and a full loop on the design spiral. With these things in hand, the next step would be an evaluation of the various strip planking methods and an eventually selection, for the one best suited to your constraints.
     
  12. Ilan Voyager
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    Ilan Voyager Senior Member

    I agree totally with you, PAR.

    Stephen a part the last link, the Woods catamaran in English style -personally I prefer bigger mainsails and just a solent, plus gennakers-, the other cats are totally obsolete. I won't comment about the Wharrams, but deep vee hulls are been proved since 30 years to be non suitable for a good modern sail multi, whatever its use. The Tennant is a very old one: I've seen the plans when I was a young man and I'm now a grandfather with white beard (guess who makes Santa Claus every Christmas...)
    Ranger if you have not the formation nor the experience needed for designing a cruise catamaran, it will be better to buy plans for an architect of good reputation who designs modern boats, which are the result of the experience accumulated since 40 years. And you'll have the scantlings made by an experienced person...The cost of the NA is far less expensive than a full sized mistake...and I have seen a lot during the fashion of home boatbuilding in France.
    It's useless to build in 2012 a boat which was already a vintage in 1990 and unhappily you won't find any book with recent data about multihulls. 90% of the books on this theme are pure "%&?%%{{", totally outdated and often with assumptions proved dangerous. If you want to see true serious cruising and racing multis from 20 to 100 feet, the best place is La Trinité in France during the summer. There are at least 200 in the marina and 100 anchored outside. And after, go to Cowes in the Solent, you'll see a lot of beauties. You're in the UK...Take pics, by thousands, take notes, by hundreds. Detail everything, and keep that seems useful. Ask every owner or skipper about the rigging, behaviour etc.

    I feel you have not experience as you rely on a forum about a method of construction and scantlings. PAR and some of the members of this forum do not need to ask about scantlings and methods, and if they would have a doubt and need to ask in the forum, the formulation would be precise with all the data necessary to get a precise answer. NA is a profession with a long period of learning, with a knowledge acquired theorically and in the shipyards. A computer is just a tool, like a ruler, a rotring or the Copenhague series of crosses (I show my age, may add a planimeter?) and none software will correct the lack of knowledge. It will just make the primary calculations easier and throw some plans and worst some renderings on Rhino. The computer uses the data you give to it, and that is the true problem.
    I took the time to write all this bad literature (English is my 3rd language) not to be mean, nor to feel superior but just to warn you over the risks of too much confidence about boat design. It's far more complicated than you can believe. And more you know and more you become cautious. I hope you understood my good intentions even if the formulation is awkward.
     
  13. PAR
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    PAR Yacht Designer/Builder

    I still occasionally use my 40 year old planimeter, Ilan.
     
  14. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I'm editing what I posted here earlier because I see I misinterpreted something Ilan wrote, and reacted defensively. What I really want to say is that I don't think asking for suggestions is entirely misguided on Ranger's part. It makes sense to refine one's thinking a bit before taking one's project to a professional - especially if one's pockets are not deep. Anyway, now that I've written it, here's a summary of how I've responded to Ranger's inquiry:

    I've indicated my source, Elements of Boat Strength by Dave Gerr. I asked if anyone had a better source for multihull scantlings that we could readily access, and nobody put one forward. I noted that Gerr speaks of several methods of strip construction and calculating strip construction scantlings, and noted that Ranger said he has in mind substantial fiberglass sheathing on both sides (which says to me temporary station molds, temporary fasteners, and edge-glued strips). I noted that mine should not be the last word on the execution of strip construction, as my own first attempt didn't go well. I relied on the tables in Gerr and my general knowledge of boats to put forward a "guesstimate" as to where I thought we would likely to end up for a 29' sailing cruising catamaran strip planked in fir with substantial fiberglass sheathing. I stipulated that once the first turn of the design spiral had been completed, with preliminary locations of bulkheads and ring frames and enough information to calculate loads, Ranger should run the design past someone with more credentials in structure than I. I agreed that we shouldn't proceed further without design information, I identified several sources of available design information for which study plans are available at low cost, I identified one in particular that I believe to be a proven design by a multihull designer with a good track record, and I posted a link to photos of that design under construction in wood strip.

    The one thing I retract is saying I'm going to get into laminate schedule this weekend. I agree that that would be premature. We need a design, and the best way for Ranger to begin is to identify a similar existing design as a reference point.

    My favorite catamaran designs are Australian (The Schionning 9.30 is not a recent design, but it is one from this designer in the size range we're discussing). I've posted about that in other threads (http://www.boatdesign.net/forums/multihulls/lock-crowther-biography-30229-3.html#post421918) But study plans are not easily available for those at low cost, to my knowledge. I stand by my contention that Richard Woods is a designer of fast multihulls with a good track record, and the design I identified as the one I favor is a reasonably modern cruising cat. In fact I see he's working on an updated version, Stratus, with a rig like what Ilan suggests.

    Ilan says Ranger needs to have a preliminary weight estimate before deciding scantlings. In order to have a decent preliminary weight estimate he needs to have a preliminary hull weight per unit surface area. Assume Ranger's boat resembles Woods' Stratus design, or identify a better candidate. What weight per unit hull area should Ranger assume for the purpose developing a preliminary weight study?
     
    Last edited: Oct 7, 2012

  15. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I downloaded SCT last night and, without reading throughout the literature or being exact, popped in a few numbers close to what we're talking about. It came back spec'ing 24mm (nominal 1") plywood (were we building in plywood) for just about everything. I have come to think the thickness I gave before may have been skimpy, and a value around 20mm would not have surprised me. But 24mm seems heavy to me. Of course, if the strips are 20mm you'd be up to 24mm if you sheathed with 2mm glass either side. Any comment? Has anyone else used SCT or another ISO 12215-7 based routine?

    Before everyone objects again that we need a design first, let me note that the input required for SCT appears to be pretty basic.
     
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