Main Beam Load Test
The purpose of the test was to demonstrate that the hull platform was sound and could support the loads it was designed for. The demonstration of this would eliminate any question of the hull platform’s integrity and hence seaworthiness.
John Koon’s report stated that Dragonfly was a “marginally maintained hull platform.” He questioned the integrity of the hull platform when stating “the mast could have been over-active, moving excessively out of column, as a result of the platform/main beam yielding to compression.” States that “the condition of the platform /main beam / compression path-post could have caused the failure as described by Mr. Wigginton.” These outrageous assertions with no foundational evidence explicitly imply that the vessel was unseaworthy. However, to a individual unfamiliar with construction or structural loading of a catamaran and looking for a reason to deny the claim, Mr. Koon’s observations was easily accepted.
John Koon asserted that the beam yielded to compression even though there was zero evidence of any stress cracks along the beam. Bill Trenkle a SAMS surveyor and Larry Montgomery, the Lloyd’s agent and NAMS surveyor, attested to this fact. In fact, Bill Trenkle noted that the cracks John Koon identified were in non-structural areas. Larry Montgomery also revealed that John Koon did not go into the anchor lockers or other appropriate areas to actually inspect the main beam for cracks.
Fortunately we don’t have to rely on opinions when we can test that the structure is in fact sound. We knew we could conclusively prove John Koon’s beam yielding assertion incorrect by testing the deflection. Tightening the rigging places a measurable load on the beam. The deflection (the degree to which a structural element flexes) as a result of the compression is measured. This would demonstrate whether the deflections met the specifications of the vessel designer, Kurt Hughes
However, without a mast, it was difficult and quite expensive to accurately simulate the load on the beam. However, once we installed a temporary mast used to return to California, it was now possible to conduct a repeatable and industry standard load test.
We loaded the beam with over 22000 lbs. by tightening the wires that hold the mast in place and determined that the deflection was less than 1/16” (0.066”), which was the deflection that Kurt Hughes had specified in his 1/29/17 report (Kurt Hughes – Beam Strength.pdf).
This conclusively proves that the integrity of the beam today is exactly the same as it was when launched in 1998 and could not be a cause of the dismasting.
John Koon, the damage surveyor for ProSight made several misleading and false statements in his report. These statements were proven false in other portions of our complaint. This test provides one more piece of evidence that puts into serious question the credibility of any opinions presented in John Koon’s report. The shear number of proven false assertions or assertions with no real supporting evidence, should completely discredit the report or anything offered by John Koon.
The remaining information of this document explain the specific details of the load test and pictorially demonstrate the process and results. The load test is a repeatable industry standard test. If requested we will conduct this test in the presence of a ProSight or Lloyds representative.
Concepts behind the testing
Mr. Wigginton graduated as a mechanical engineer from Imperial College London. Mr. Wigginton worked as an engineer in equipment design for heavy equipment and processing. This experience provided him the basis to analyze the structural forces at play on an ocean going vessel.
Kurt Hughes reviewed and validated the load testing technique. Kurt is the designer of many sailing vessels and masts including Dragonfly.
Dragonfly’s rigging is called a “tripod”. It consists of two shrouds, (port and starboard) and a “headstay”. This picture shows the starboard shroud (the line from the mast to just above the 6) and the headstay (the line from the mast forward).
Our headstay is a roller furler with the headsail on it. It attaches to the cross beam on the front of the boat. The shrouds attach to the oversized chain plates. These three wires put a downward load on the beam thru the mast to hold it in place on the mast step.
This also shows where the mast is located on the boat.
This schema from Kurt Hughes shows that the mast sits directly on the main beam. We have drawn a line between the A and R to represent where the main beam is. The main beam goes from one side to the other and is approximately 5” thick.
The shrouds and headstay are held in place and tightened by turnbuckles (left).
A turnbuckle consists of two threaded eyebolts, one screwed into each end of a small metal frame, one with a left-hand thread and the other with a right-hand thread. The picture to the right shows the inner workings.
The tension can be adjusted by rotating the frame, which causes both eye bolts to be screwed in or out simultaneously
To determine the amount of load put on the beam by tightening the shrouds the “The Folding Rule Method” is used. Per the specifications, a 2-meter portion of stainless steel 316L wire will stretch 1mm for each 5% of its strength. This is true regardless of the wire diameter. Therefore, it is possible to determine the load based on the stretch of the wire with a 2-meter pole attached to the wire.
Per the specifications the strength of the 9/16″ 316L stainless shroud wire is 37,000 lbs. The goal is to put over 20,000 lbs. of load on the mast to see the deflection of the beam. We will need to stretch the wire 4mm to achieve the load we desire. The reason for that load will be clearer later in the results.
We also need to be able to measure the deflection in the beam. The mast surround sits directly on the beam behind the mast and is available to us inside the salon. We can use a horizontal laser level beam to measure the deflection as we change the loads on it by tightening the shrouds.
In a nutshell we will use 2-meter PVC poles attached to the shrouds, tighten the wires with the turnbuckle, measure the stretch in the wire with a caliper to demonstrate the load. We will then utilize engineering and geometric equations to determine the approximate loads. Using a laser level beam recorded before and after the load is applied will identify the deflection.
The test process
- Loosen the starboard and port shrouds at the turnbuckles to reduce the current load.
- Horizontal lines are drawn 1/16th –inch apart on a piece of paper.
- Tape the paper on the mast surround at the beam.
- Focus the laser beam directly across from the paper.
- Align the laser beam with the bottom line on the paper.
- Clamp a 2-meter piece of PVC pole to both shrouds (316L stainless wire) so the bottom is at the top of the turnbuckle fitting.
- Turn the turnbuckles to tighten the shrouds.
- As the wire stretches the two-meter PVC pole moves up as the stainless stretches. The movement is measurable based on the distance between the bottom of the PVC pole and the top of the turnbuckle.
- Continue to turn until there is a 4mm change by using a digital caliper (a very precise measuring tool) is used.
- Record the change in the laser beam.
Calculating the Load
Using the folding rule test, the shrouds can be tensioned to 20% of yield strength by extending 4mm on the 2-meter length. Therefore 4mm is equivalent to 7400lbs of tension for each shroud
To calculate the total load on the main beam by the mast, the two shrouds and the headstay loads need to calculated and added together.
The downward force on the mast is calculated as follows.
Length of ST = 68.5
Length of SHF = 18
Length of SPF = 11
Length of SFx = 65
ST = (37,000 *.20) = 7,400
SFx = 7,400 * (65/68.5) * 2 (shrouds)
Sfx = 14044
SHF = 14044 * (18/68.5) = 3689
SPF = 3689 * (11/18)
SPF = 2254 lbs.
There are three wires (2 shrouds and headstay) pulling the mast to hold it in place. The forces of these three wires must be balanced. Therefore, the pulling forces from the mast to the shrouds and the mast to the headstay have to be equal.
We don’t know what the tension of the headstay is, but we can calculate it because we have the pulling force of the shrouds. So we can use simple geometric equations to determine the tension and thus the vertical force of the headstay.
HPF = SPF = 2254
Length HT = 70
Length HFx = 65
Length HPF = 18
HT = 2254 / (18/70)
HT = 8767
HFx = 8767 * (65/70)
HFx = 8140
Total Load on Beam by Mast
The total load would be to total of the force of the shrouds (Sfx) plus headstay force (Hfx)
14043 + 8140 = 22,183 lbs.
Conducting the Test
|Attached a 2-meter PVC pole to the starboard and port shroud wires.
Al shows that the pole is 2 meters with the tape measure. Al is 6’3.
Note that he is measuring from the clamp that holds the PVC pole to the shroud wire.
Below is the measurement at the turnbuckle fitting
|The PVC pole sits at the top of the turnbuckle fitting before the turnbuckles have been tightened.|
|The starboard and port turnbuckles before they are tightened.
Note the number of threads visible.
|The paper is taped to the mast surround so the laser beam is at the main beam.
This is the laser beam prior to the tightening of the turnbuckles.
The laser beam is parallel to the top of the main beam
Note that the bottom of the laser beam is on the bottom line.
|The turnbuckles are tightened.
Note the change in the threads visible from the earlier pictures.
|The digital caliper is used to show the distance between the bottom of the PVC pole and the top of the fitting on both sides
Starboard shows 4.10mm
Port shows 4.11mm
Per the load calculations this causes each wire to put an approximate of 7400 lbs. on main beam via the mast.
The laser beam after the tightening.
Note the bottom line has moved down below the laser beam less than 1/16”. This is consistent with Kurt Hughe’s original design specifications.
This load test utilized industry standard techniques and standard engineering equations to demonstrate thru pictures that John Koon’s assertion that the beam yielding to compression was ludicrous. Kurt Hughes, the vessel designer, states that under full main sail the load on the beam would be on the order of 25,000 lbs. and yield 1/16”.
This demonstrates that the deflection is consistent with Kurt Hugh’s design and would yield only a small fraction of an inch. In fact Kurt Hughe’s designed the main beam to handle 21 times the anticipated full load. Therefore, even a higher load would be only a fraction more. This amount of main beam yield compression could not possibly lead to the mast buckling as suggested by John Koon. This proves his assertion false and should put in question ALL other baseless assertions by him.