: Would it be too much to ask for a truce, maybe an apology or two and then a
: to return what we all love - building and paddling?

Probably. My po' dead daddy used to say "There's no such thing as right or wrong, just smart and stupid."

Anywho, I'm a lawyer not an engineer. By training and experience I know bullcheet when I hear it. Frank Lloyd Wright said, "Engineers are a dime a dozen." Actually at the time he said it they were about ten bucks a week. Which is why daddy left Pratt and returned to the farm! I propose to set out some test results published some time ago by the Gougeon Bros. I have used these results and had no failures. As I say, I'm not an engineer, but my interpretation of the results does not support some conclusions posted here.

Strip Panel Test Results

The technical staff at Gougeon Brothers Inc. often encounters questions regarding the strip plank construction method of building canoes and other small boats. (this article is reproduced from their Nov./Dec. 1984 "The Boatbuiler") With this technique, thin strips of lightweight wood are bonded together and then covered on both sides with fiberglass cloth. Because very little information is available on the stiffness and ultimate strengths of the various combinations that can be used in this construction technique, it has been difficult for customers to decide what thickness of wood is necessary for their project, or what weight and how many layers of fiberglass cloth are needed. We have done preliminary testing in an effort to develop data which will enable us to provide useful information to builders.

The strip plank samples used in the tests were constructed of Western Red Cedar. They were cut into 12" squares, machined to specified thicknesses, and weighed on a digital gram scale. The specimens were covered with varying weights and layers of fiberglass cloth which were applied using WEST SYSTEM Epoxy, mixed at the specified five to one ratio. The samples were again weighed and measured. A platen was designed and constructed to hold each test sample securely in our MTS test machine* throughout the testing procedure without yielding to the testing stresses. *See:
http://albums.photopoint.com/j/ViewPhoto?u=1502758&a=11341576&p=44949237&f=0

All of the test samples were placed in the platen so that the loads exerted would be parallel to the grain, thus loading them in their weakest direction. The test machine was setup to gradually increase the load on the sample until failure occured. The machine also accurately measured the amount of deflection at failure.

The chart below shows strength as "pounds to failure", and stiffness as "inches of deflection" at failure. Marine plywood of standard sizes used in small boat construction without fiberglass cloth is listed on the bottom of the chart as the known quantity for comparison. As expected, the samples became heavier with the addition of fiberglass cloth and epoxy. However, surprisingly little weight was gained relative to the increase in strength and stiffness. Because only one sample in each category was tested, data may not in all cases follow expected patterns. A more extensive testing program will likely result in averages that would follow expectations. Nevertheless, the infor mation gathered does allow us to make some general conclusions that will prove helpful to builders uncertain about the thickness and glass cloth variables.

Sample--Thick-----Glass------#'s to---Panel
#---------ness-----Schedule----Failure--Weight--Deflection

CEDARSTRIP PANELS
1D-----3/16"-----1 Layer 4oz.-----162------6.5oz.--.85"
2D-----3/16"-----2 Layer 4oz.-----309------8.8-----.82
3D-----3/16"-----1 Layer 6oz.-----214------8.0-----.73
4D-----3/16"-----2 Layer 6oz.-----500-----10.6-----.90

1A-----1/4"------1 Layer 4oz.-----150------9.0-----.45
2A-----1/4"------2 Layer 4oz.-----375-----10.3-----.70
3A-----1/4"------1 Layer 6oz.-----221------9.8-----.49
4A-----1/4"------2 Layer 6oz.-----450-----12.3-----.58

1B-----5/16"-----1 Layer 4oz.-----188-----10.6-----.43
2B-----5/16"-----2 Layer 4oz.-----499-----12.6-----.66
3B-----5/16"-----1 Layer 6oz.-----300-----11.6-----.48
4B-----5/16"-----2 Layer 6oz.-----500-----14.1-----.44

1C-----3/8"------1 Layer 4oz.-----250-----12.7-----.42
2C-----3/8"------2 Layer 4oz.-----675-----14.1-----.66
3C-----3/8"------1 Layer 6oz.-----298-----13.1-----.32
4C-----3/8"------2 Layer 6oz.-----823-----15.4-----.51

OKOUME MAHOGANY PLYWOOD
1F-----5/32"-----1 Layer 4oz.----211-------8.5----1.47
2F-----7/32"-----1 Layer 4oz.----325------10.9----1.01
3F-----1/4"------1 Layer 4oz.----429------12.8-----.79

1E-----5/32"-----NO GLASS---------45-------6.9----1.60
2E-----7/32"-----NO GLASS--------149-------9.1----1.20
3E-----1/4"------NO GLASS--------225------10.7-----.63

BIRCH 5 PLY
4E-----1/4"------NO GLASS--------400------14.4-----.73
END OF ARTICLE

Tests of Laminated Panels

Gougeon Brothers recently conducted impact tests on four types of wood composite panels that were furnished by Walter Greene of Greene Marine in Yarmouth, Maine. (this article is reproduced from their July/August 1985 "The Boatbuilder")

Walter designs and builds custom sailboats and is currently building a 45' hull, designed by Art Paine. This hull is being built out of southern white cedar veneers over spruce and mahogany stringers using WEST SYSTEM Epoxy.

The owner of the boat is Dick Cross and he plans to sail it in the 1985-86 BOC challenge. This race is a singlehanded, around-the-world race.

We were pleased to do this testing because it gave us an opportunity to compare the relative effectiveness of various synthetic fiber fabrics in toughening laminated wood hulls against impact damage from such things as rocks and floating debris.

The four panels, all about 12" X 15" and 3/4" thick, were constructed from four layers of 3/16" cedar, laminated with WEST SYSTEM Epoxy. Different fabrics were laminated with the wood in various locations, as shown in Figure 1*. Wood layers layers 1 and 4 were oriented with the grain running at right angles to the grain of layers 2 and 3. *See:
http://albums.photopoint.com/j/ViewPhoto?u=1502758&a=11341576&p=44947739&f=0

Our test fixture allows us to drop a 70 lb. steel projectile from various heights onto the center of a test panel that is supported around all four edges. The projectile has a rounded nose (1-1/2" radius). For this series of tests, we dropped the projectile three times on each panel, first from 5", then from 7" and finally from 12".

Since impact energy equals weight times the height dropped, the successive energy levels were 350 in-lb., 525 in-lb., and 875 in-lb.

After the first drop on each panel, examination showed a shallow dent on the top face (outside of hull) that was about 1" In diameter. In examining the back face of each panel (inside of hull) we found either no damage, or very slight cracks. However, as the drop heights were increased, we found considerable differences in damage on the back faces of the panels. The following table compares back face damage (inside hull) for each panel after the last drop.

PANEL #l Minor cracks within a circular area about 2-1/2" in diameter. (Probable negligible loss of strength).

PANEL #2 Moderate cracks within a circular area about 5" in diameter. (Moderate loss of strength).

PANEL #3 Extensive cracks, some raised up to 1/16" within an area approximately 10" in diameter. (Substantial loss of strength)

PANEL #4 Extensive crack development in an area about 8" X 10" with crack edges lifted up about 3/32".(Substantial loss of strength).

The results of these tests can only be used to rank the various wood composites tested in order of their resistance to impact damage and cannot be used to predict whether the materials will be satisfactory when used in a boat hull. However, several lessons can be learned:

1. Laminating synthetic fiber fabric, such as E-Glass and Kevlar with wood veneers increases the strength of the composite hull under impact loads.

2. While adding fabric reinforcing layers to the outside of the hull can increase the strength, the most effective materials use comes from using cloth reinforcement both at the outside and near the inside layers at the hull.

Panels 1 and 2 which had Kevlar or E-Glass located near the panel back sides were substantially better in resisting impact loads than panels 3 and 4 which had cloth only in the top layer.

3. By laminating a high modulus fiber cloth on both surfaces of a laminated wood panel, we are creating a "sandwich" structure which provides high strength at a modest increase in weight and cost. END OF ARTICLE

FATIGUE
Fatigue is an accumulation of damage that is caused by repeated loading of a structure. Since 1978, the engineering staff of Gougeon Bros. (this article reproduced from their March/April 1985 "The Boatbuilder") has been involved with long term fatigue tests of various structural materials. At the opening day of the National Boat Show in New York's Coliseum, Meade Gougeon spoke of the results of these ongoing tests in his presentation "The Fatigue Aspects of Boatbuilding Materials".

In Meade's presentation, he said that in recent years an embarrassingly high percentage of the boats racing in top caliber competition have suffered from breakdowns due to material failures. Results have ranged from a minor inconvenience to the extreme of losing entire boats with loss of life. He feels that some reasons for this poor performance might be as follows:

1. Lack of money, time and facilities by the pleasure boat-oriented marine industry to fully test material combinations and evaluate their application.

2. Lack of good knowledge of the long term fatigue behavior of a chosen composite laminate.

3. Lack of understanding of the limitations of unidirectional composite materials, especially the secondary properties such as interlaminar shear.

4. Lack of understanding of the long-term effects of environments on materials.

5. Lack of well developed (properly implemented) quality control programs.

He explained that published strength values usually indicate the capability of a material to resist a one-time load without failing. However, the same material may fail at a much lower load if the load is repeatedly applied and then removed over a period of time. In order to describe the strength of a material under repeated (or cyclic) loading, test information can be presented in graphical form.

The graph on the back of this page* describes how the strengths of various materials used in boat construction are reduced as we increase the number of cycles that the load is applied and released. In this case, each cycle involves applying a maximum tension load to the material, then reducing the load to a level 1/10 of the maximum level. The vertical scale on the left side of the graph shows the maximum load during each cycle as a percentage of the one-time load capacity. The horizontal scale at the bottom shows the number of cycles. (10^2 equals 100 cycles, 10^3 equals 1000 cycles, 10^4 equals 10,000 cycles, etc.) *See:
http://albums.photopoint.com/j/ViewPhoto?u=1502758&a=11341576&p=44949230&f=0

To illustrate the use of the graph, we can use several examples. If we know the maximum one-time (or ultimate) load that laminated wood can withstand, then we can use the graph to figure what maximum load can be applied a million times without failure. Moving along the horizontal scale to 10^6 cycles, we then move up to the curve labeled "Laminated Wood". Then we draw a horozontal line back to the left margin, where we see that the largest load that can be applied on million times to laminated wood is approximately 65% (or 2/3) of the maximum one-time load. Similarly, if we follow the same procedure for a typical glass composite, we see that the largest load which can be withstood for one million cycles is approximately 21% of the maximum one-time load. For most of us, it's far more important to understand what a material is capable of after experiencing one million (10^6) cycles, than in a one-time load situation.

How does fatigue loading affect boat design? Wave frequency has been monitored on a hull, and associated water pressure loads on a hull have been shown to increase and then decrease once every three seconds. At this rate, one million cycles of repeated loading would be reached after only 833 hours, or approximately 35 days of continuous sailing under wave conditions. Commercial craft might log this number of hours over a relatively short time span. Most racing and pleasure boats might require several seasons of operation to achieve one million load cycles.

In any case, as designers and builders enter into the use of new composite materials, they must consider not only the maximum onetime strength of these materials, but also the reduced strength available to resist fatigue loads extending over millions of cycles.

END OF ARTICLES
Hope this is helpful. For anyone who may be concerned no copyright was claimed on this material when published by the Gougeon Bros.