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PrecisionMillwork
11-07-2016, 04:19 PM
I'm researching strip plank construction, in an attempt to formulate an "ideal" recipe for the liveaboard cruiser I'll soon begin building.

In every strip plank example I find, it's always the same usual species of cedars, fir, "mahogany" etc...
does anyone build in strip plank with species like Ipe, Afrormosia and similar?


Ive made a few test panels in various combinations, and so far, Im sold on dbl. diagonal + veneers + sheathed INSIDE and out (balanced)
With only 2x E-Glass on both sides, the samples seem to get MUCH stronger than simply 'glassing the outside, and I'd really like to understand the "why's" and find some quantification from an engineering standpoint???
my best extrapolation (guess) is that the structure is taking on characteristics of a Torsion Box, but Im also guessing there are a few on this forum who KNOW why, and I hope to hear from them, in regards to this.

upchurchmr
11-07-2016, 05:16 PM
You might research "The Gougeon Brothers on Boat Construction" which has lots of information on alternate building methods, with epoxy / glass sheathing.
This is the "bible" for wood epoxy. Although there are others now days.

Free down load here: http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Are you equating "strip planking" with "dbl. diagonal + veneers + sheathed INSIDE and out (balanced)"?

The next question that is always asked here is - what are you planning on building?

Glass sheathing inside and outside makes a sandwich structure.
If your wood thickness is large compared to the glass layers the "sandwich" benefits will be not as dramatic.

Toolate
11-07-2016, 05:29 PM
Here is an interesting read on cored fiberglass with plenty of engineering back up. http://boatdesign.net/articles/foam-core/

I have worked with Ipe on a number of projects and it is very stiff, heavy and probably the worst thing about it is that it is brittle and tends to crack if fasteners are not pre-drilled and driven very carefully. I would pass based on this then the weight personally but dont have enough experience to suggest an alternative.

I think attempting to glue anything to it would probably convince you otherwise as well.

Peerie Maa
11-07-2016, 05:36 PM
You might research "The Gougeon Brothers on Boat Construction" which has lots of information on alternate building methods, with epoxy / glass sheathing.
This is the "bible" for wood epoxy. Although there are others now days.

Free down load here: http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Are you equating "strip planking" with "dbl. diagonal + veneers + sheathed INSIDE and out (balanced)"?

The next question that is always asked here is - what are you planning on building?

Glass sheathing inside and outside makes a sandwich structure.
If your wood thickness is large compared to the glass layers the "sandwich" benefits will be not as dramatic.

It is a live aboard cruiser.
So the hull scantlings will need there to be enough wood in the skin to make any glass there for abrasion resistance rather than structural.
Unless it is like this live aboard http://forum.woodenboat.com/showthread.php?214608-Southern-Cross

ulav8r
11-07-2016, 06:05 PM
Glass inside and out performs much like the flanges of an I-beam or as a torsion box as mentioned by the OP because of it's tensile strength is so much greater than that of wood. Fiberglass only provides strength in tension, so the inside layer strengthens against outside pressures\forces and the outside layer provides strength against forces pressing out or trying to stretch. It also provides a slight amount of abrasion resistance, but not near as much as some other fibers such as Kevlar.

Peerie Maa
11-07-2016, 06:35 PM
So, as glass is crap in compression, you need substantial timber scantlings to handle the compression part of the hull girder bending. If you are building big enough to live on, you either use enough wood, or lots of GRP over a core providing shear strength. Fortunately unless you use flat panels, the convex shape of boats hulls helps you as they are naturally stable shapes, like a masonry arch or barrel.

upchurchmr
11-07-2016, 07:47 PM
Nick,

Where did you get that it is a live aboard cruiser?
I hate missing things but I didn't see that.

20', 30', 40'

Heavy keel?

Catamaran?

Funny how there are so many solid fiberglass boats out there if glass is crap in compression. Do all those boats just work in tension or shear?

PrecisionMillwork
11-07-2016, 08:24 PM
Gougeon Bros Bible is what inspired me to dig through 20+yrs worth of scrap-wood hording ( my Millwork/ cabinet shop is actually in its 26th year now, and I have a habit of saving anything Ithink I can use)
my test panels have been 5/16" - 3/8" double and triple diagonal strips of Ipe, Afrormosia and a few other hard, heavy and ridiculously strong tropical woods, veneers to follow have been "door skin thickness" (resawn thin then knocked down flat on the widebelt to about a heavy 1/8", and then simply 6oz E glass, (1 vs 2 layers. So far, only tried a few test panels compared against strip cedar "control group"

yep, The tropical woods are heavier, but holy-guacamole, are they ever tough!


I am still sitting on the fence over a couple designs.
-B&G (Roberto Barro, Luis & Luis) Cabo 40 (modified to my hybrid sheathed-strip-epoxy) and with a swing keel and a few other alterations)

Or:
-40-44ft version of B. Roberts Contemporary Cat 786 (with a mast and modified for wood/epoxy construction of course)

-a couple other cruising cat designs

We WANT a Cat, plain & simple, However, A solid Monohull like the Cabo 40 seems a more reachable goal,
+ the fact , -Her designer seems willing & interested at (what seems to me) basically redrawing the plans.

I've worked with quite a wide variety of species over the years, Ipe certainly has its nuances, But bonding isnt really one of them, "wiping with acetone/MEK/(solvent blend xyz)" and bonding is my least favorable method, as anything which seems to cut down the oils, is in fact adding residues and "oils" of its own, I've yet to have a glueup fail... but I can't say this doesn't worry me.

PL Premium (from a caulk gun) is very effective on Ipe and other tough to glue species, Resorcinol can be used with good results , as well as a few others, But my adhesive of choice is Smith's "Tropical Hardwood Epoxy".
Ive read quite a few discussions about PL being used in strip plank construction, & there seems to be quite a separation between the camps.
Smiths is an epoxy formulation, and they claim they're completely compatible with subsequent laminations of other epoxies (West, US, etc).

Mr. Upchurch, am I understanding correctly, that the "balanced" sheathing IS in fact acting as a "Torsion Box" structure?

I expect to ultimately use Aramid on outside, but only where it counts, Basically E-glass in & out, & Im also interested in incorporating Xynole/Dynel within the laminating schedule for ultimate puncture resistance .
Id love to learn how the various materials are CALCULATED, as opposed to building samples for destructive experimentation. How does an NA determine which layer goes where (for a given requirement) anyway?

upchurchmr
11-07-2016, 09:54 PM
A sandwich construction is similar in concept to a torsion box, but not exactly the same.

The comparison to an I beam is also typically used as a comparison.

Sandwich typically uses a stiffer or stronger inner and outer layer with an inner layer of a lighter material. The goal is usually to get a lighter structure with improved stiffness. Its possible to get improved strength, but at the cost of most of the weight savings.
Using Ipe or other heavy stiff hardwood reduces the benefit of a sandwich. As Nick says the heavy / strong interior construction means there is less benefit (to effectively none) for putting a strong but light weight covering of glass/ epoxy. The primary benefit becomes trying to eliminate water intrusion into the wood, and abrasion resistance. Sandwich does reduce the impact resistance, since you use thin skins and light weight (lower strength - like cedar) interior material.

If you have "sipped the kool-aid" from the Gougeons like I have, you will believe in the benefit of keeping the wood structure dry. Dry wood is significantly stiffer and stronger, and does not rot.
Water soaked wood will require much heavier scantlings to maintain the required strength.

The study of how to size a hull is begun with an engineering degree. If you want to start you need to try a "strength of materials" text. Along with a good bit of math you will have a start. Another requirement is a study of how loads are developed and reacted in a structure - the hull and rigging.
Good luck with that, because naval architects / engineers go well beyond the text.

My suggestion is that you learn as much as you can, then buy plans which meet your requirements, and accept the hull construction the designer has specified. There are no magic bullets, just a lot of hard work. Both designing and building. Remember that a hulls is 30-40% of the cost and time of the boat.

wizbang 13
11-07-2016, 10:09 PM
So much brainwork for a cruising boat!

Sailor
11-08-2016, 09:03 AM
I'm reminded of Raw Faith when he said, "accept the hull construction the designer has specified". Excellent advice. Though it would be nice to call myself an NA and design my own boat to build then go cruising in, I have to accept that I am not an NA, I never will be an NA and I'll get a much more suitable boat to the purpose if I let someone do the design work. If only George had listened and spend a bit of money on an NA, maybe his boat would still be around for him to take those kids sailing. I look forward to seeing where this thread goes. I too am curious about how the real NAs do this stuff and how they compile the info they complie to prove that their design is sound and will stand up to the tasks demanded of it over the years after launching. And it's not just the structural data, there's the stability calculations to be made as well. And what about taking a traditionally planked hull and building it using a sandwich or other glued structure? How does he redo all the figures given new weights, different materials (I might plank with cedar while you plank with Ipe making for two very different hulls even if they're the same shape). All very interesting stuff.

Peerie Maa
11-08-2016, 09:14 AM
Nick,

Where did you get that it is a live aboard cruiser?
I hate missing things but I didn't see that.

20', 30', 40'

Heavy keel?

Catamaran?

Funny how there are so many solid fiberglass boats out there if glass is crap in compression. Do all those boats just work in tension or shear?

Line 1 first post.
I'm researching strip plank construction, in an attempt to formulate an "ideal" recipe for the liveaboard cruiser I'll soon begin building.

You have to rely on the polyester resin for compression strength.

Peerie Maa
11-08-2016, 10:43 AM
I've worked with quite a wide variety of species over the years, Ipe certainly has its nuances, But bonding isnt really one of them, "wiping with acetone/MEK/(solvent blend xyz)" and bonding is my least favorable method, as anything which seems to cut down the oils, is in fact adding residues and "oils" of its own, I've yet to have a glueup fail... but I can't say this doesn't worry me.



Ipe is so hard and heavy that I would only use it for a keel shoe or for deadeyes,
I have not seen it in small scantlings, but I believe that it wont bend well. Boats are all bends and curves so I doubt that it has ever been used for boat building.

MN Dave
11-08-2016, 12:34 PM
So, as glass is crap in compression, you need substantial timber scantlings to handle the compression part of the hull girder bending. If you are building big enough to live on, you either use enough wood, or lots of GRP over a core providing shear strength. Fortunately unless you use flat panels, the convex shape of boats hulls helps you as they are naturally stable shapes, like a masonry arch or barrel.


Nick,
<<snip>>
Funny how there are so many solid fiberglass boats out there if glass is crap in compression. Do all those boats just work in tension or shear?


Line 1 first post.
You have to rely on the polyester resin for compression strength.
Nick has been chosen as the victim for this because the quote box is small, he is one of the more knowledgeable people who provide almost universally good advice here and he defended the statement. There are many others who repeat this same erroneous advice about fiber reinforcements while providing otherwise reliable advice. This makes the bad advice more convincing because it is coming from otherwise reliable sources.

We are used to looking at thin layers of hand layup fiberglass here that fail in buckling, not compression. Buckling is what happens when you compress a long pole. It will bow before it starts to break, and once it bows, it looses strength in the direction of the load rapidly. https://en.wikipedia.org/wiki/Buckling When you make a thick layer such as Mike mentioned in a solid FRP boat, the thicker skins resist buckling, especially curved surfaces. If the glass was not significantly affecting compressive strength and stiffness, FRP construction would not work. The correct statement is that unsupported thin layers of FRP do not provide much, if any compressive strength. The thin 6oz skins on a stripper are not unsupported. The FRP skins on a stripper only provide significant strength in the cross grain direction, and the compound curvature makes all of the properties hard to separate. This thread is about strip built, not strippers, I will get there.

The difference between compressive and tensile strength is more pronounced with carbon fiber, but even there, it is not low, just lower than tensile. The easiest way to look up reliable information about fiberglass laminates is to search for the readily available manufactured sheet material such as G-10 and FR-4 which are used for circuit boards and have to meet strict quality standards. They are made with many layers of light weight e-glass cloth with epoxy resin.

The tensile strength listed for G-10 in the 1990 Materials Engineering Material Selector Issue is 40 ksi lengthwise, 35 ksi crosswise and 35 ksi edge compression. The modulus of elasticity in bending (~2,500,000 psi) is close to the tensile modulus, which means that the compressive modulus is also close to the tensile modulus. The unreinforced resin would have a tensile strength of roughly 10 ksi and a modulus of 450,000 psi. The glass doubles the strength and increases stiffness by 5 times.

A hand layup will have a lower glass to resin ratio and some wrinkles, which will reduce the strength somewhat. The neat resin will have a tensile and compressive strength in the 9-10 ksi range.

What this means for strip construction is that the lengthwise stiffness of the wood will not change much, especially a very stiff wood like ipe, which is stiffer than a glass laminate skin. On the other hand, if I could find the cross grain properties, which are typically about 1/10 of the grain direction, the glass would add a lot of strength and stability. The tensile modulus of ipe is 3,200,000 psi. This is not a stripper, but thick strip construction where the edgewise strength is much greater. In this case the strength of the glass much less significant. The glass on a strip built hull is more effective as a barrier to abrasion, moisture and borers where the extra resin thickness needed to fill the cloth is a major factor. Having said that and recalling the threads on Dynel and abrasion, (http://forum.woodenboat.com/showthread.php?214420-Epoxy-adherence-on-top-of-previous-glass-mat) it follows that for this construction, Xynole or Dynel could be the better choice.

upchurchmr
11-08-2016, 01:19 PM
Nick is not a victim.

Nick just continues to make un-quantifiable statements that mislead.

In your own example, G-10 (glass) tension strength is 40 KSI and compression strength is 35 KSI. This is a very typical reduction in strength which yields useful structures all the time.
I understand that the OP mentioned IPE, but it is an extreme example which does not represent typical boat building.
I'm unable to find tension and compression strengths to compare for IPE - can you quote them?

Glass is not "crap" in compression. As you said, the latest wonder material (carbon fiber composite) is worse in relative compression.

I agree completely that unsupported thin layers of glass will fail easily in compression or actually buckling as you point out.
Please tell me what the comparison is to IPE in the same thickness and loading.

Peerie Maa
11-08-2016, 02:09 PM
http://www.wood-database.com/ipe/

You need to be careful in designing structures glued up of different materials. There have been some expensive failures, for example when engineers designed on tensile stress alone and did not allow for Young's Modulus.

Look at normal practice for cruising boats - all grp, or all wood with a thin external coat of cloth in epoxy.
If you want to pursue light weight racing craft, go for slightly less GRP with a light weight core strong in shear. But you need to be a Naval Architect with access to the appropriate analysis tools to get those right.

upchurchmr
11-08-2016, 02:50 PM
Amen brother.

100% agree.

Bob Cleek
11-08-2016, 07:00 PM
What follows is just my personal opinion, for what it's worth:

If you are planning a small boat to play with in the local bay, experimentation with non-traditional wood species, glues, and construction methods is fine. If, however, you are planning to take your loved ones and friends offshore and away from ready rescue, I would advise that you to purchase a proven design and build it exactly to specification, or to hire a seasoned navarch/yacht designer to create your design and build it exactly to specification. If any facet of the unusual design or materials used fails, you risk great expense or physical harm to you and your loved ones. Using tried-and-true methods and materials will reduce this risk significantly, which will allow you to sleep much more soundly. It will also help when you go to talk with your insurance agent.

As for using the exotic hardwoods you mention, you have to be aware of the weight that you are adding to the hull - maybe significantly more that the design calls for, which will impact stability, carrying capacity, and even seaworthiness. If you insist on doing this, I think that you would be well advised to do a detailed weight analysis to see what weight impact your ambitions have. If you build a cruising catamaran, I strongly suggest that you do not use hardwood for the hull core - the whole idea of cats is to have lightweight hulls. I would recommend that, in either hull choice, you save the exotic hardwoods for furniture and trim and use lighter, proven species for the hull.

Talk to a designer of wood composite boats about what you want. They will be able to guide you to good decisions, and help you clearly define what you want and need in your boat. Usually talk is cheap, and when you get serious, you can hire him or her to consult on your build method and materials. I might also point out that, in the grand scheme of things, the cost of a custom design is a mere fraction of the cost of the boat, and you will get exactly what you want if you take that path. There are many good designers "out there", and there are several whom are members of this Forum.

I will peek in here once in a while to see where this is going, and offer comments and advice once in a while. For several reasons I am a bit gun-shy about discussing detailed design & construction specifics on-line, but feel free to contact me privately, either through this Forum or directly to my e-mail at mmason1@bwr.eastlink.ca.

There's nothing wrong with "noodling" around with boats and wondering what would happen "if." That said, if you want to avoid a huge amount of wasted time, money, and even life... the advice above is as good as it gets. Think of it this way: "If you were building an airplane, would you design it yourself and build it unconventionally?" Small boats in shallow protected waters don't usually cause catastrophic losses when they turn turtle or fall apart because they are poorly designed and engineered. Big boats, big enough to live aboard, are another matter. Even if your "floating home" sinks at the dock and you're able to jump off without getting your feet wet, you've still lost your home and everything in it. Just because you've been saving Popsicle sticks for years doesn't mean that with enough epoxy you'll be able to build a decent boat out of them. Harsh advice, I understand, but we see so many folks posting in here which totally unrealistic dreams, often fostered by merchants trying to sell products on the promise of "quick and easy," the best advice to them is often, fuggedaboudit.

Jamesh
11-09-2016, 10:13 AM
Have you seen this design a proven strip planked design, modern and efficient yet live aboard friendly.
Why invent the wheel if its been done before?!
http://www.sailboat-cruising.com/cedar-strip-boat-building.html

Peerie Maa
11-09-2016, 10:45 AM
Harsh advice, I understand, but we see so many folks posting in here which totally unrealistic dreams.

Two of which broke up at sea, causing considerable trouble to the rescue services.

kbowen
11-25-2016, 09:38 AM
'can't really wade through all of this, but two thoughts come to mind: If the interior wood is quite strong and maybe not fully encapsulated, won't the expansion / contraction rip most any glass you put on it? Regarding the "I" beam structural analogy, my understanding is that the strength goes up as the 4th power of thickness, so the conventional wisdom has been to use a relatively lightweight inner wood that can be thicker for the same weight, separating the tension skins, and getting strength from the sandwich. ok a third thought, The Googe brothers have been known to advocate thicker glass on the interior than the exterior if impact resistance is desired.

upchurchmr
11-25-2016, 10:24 AM
The Gougeon brothers "advocate" various features based on extensive scientific testing with real materials/ sizing.

I would accept most anything they say, while looking closely at the way the test was run and what the assumptions were.

If you are not designing to Naval architect standards, you can succeed with other concepts.
That means if you are willing to go heavier you "can" use other methods.