Fender Washers--Basically Useless?

Drew has been at it again...  Here he is testing fender washers as might be used instead of proper backing plates for items thru-bolted on deck.  Drew made two posts; I have included both of them here. 

In the process or researching an article on backing plates, it seemed worthwhile to actually test some washers. After all, it was the failure of fender washers that led to cracking of my deck and the need to remount the winches.

Not really very flat anymore.... The deck paid the price.

I used a 3/4" pine board as a surrogate for a cored deck and tightened a collection of 1/4" washers untill the first damage to the wood, and until failure. To no surprise, common washers, fender washers, and HDPE were glaring failures, and FRP and thicker metal washers were fine.

This looked fine to start, but within hours it started to bend and within 24 hours is was bent worse than the SS fender washer. This could lead to a hidden failure if not monitored (1/2" HDPE)

(click to enlarge table)

And then there is always the matter of what happens in wet places. Though I like aluminum for ease of fabrication, I also know its limitations.

This bow cleat is a little shaky.

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As ramp-up for some Practical Sailor testing, I thought I would share a preview.

First, unable to secure scraps of deck material for which I could be sure of the pedigree, I laid up some of my own. The testing will based upon 1/2-inch balsa core with (1) 6-ounce cloth and (1) 17-ounce biaxial layers on the deck side and (1) 17-ounce biaxial layers on the under side.

I drill a 1/4-inch hole (no epoxy plug, block of wood on the back side) and tightened down a fender washer against it. At 10 in-pounds (about 675# load) the washer had distorted and the laminate was failing. for comparison, the bolt working load of a Lewmar 40 winch (1/4-inch bolts) with a strong grinder is about 500 pounds each. In other words, without an epoxy plug the bolt will fail under working load and standard ASME bolting load, with no safety factor for aging and fatigue. It is about 5x weaker than good design suggests. It also explains why I had a PO installed winch rip out.

By 18-in-pounds the fender washer was buckled and the nut was well into the core. For comparison, this is about 50% better than a plain pine board in each case.

I repeated the test with only lock washer. The same result! The fender washer resulted in no increase in strength. The point being, that the bolting washer provided better support in close, the end result being the same.

Testing for the actual project will involve proper epoxy plugs. However, since under the load the bolt will NOT be supported on the other side (the winch or cleat will be lifting) in the real world, the top side support will be supplied by a 4-inch diameter ring spacer, allowing the washer to pull through, if that is what it wants to do. I've tested this without the epoxy plug; not surprisingly, it lowers the failure load and creates top side damage much like I saw on my failed winches.

We'll see. But for now, the moral of the story is that fender washers are basically useless; they fail as soon as they are actually needed.

Nano-tech Experiment #3 (and reports on #1 and #2)

This post originally appeared on Windborne in Puget Sound

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This is the third experiment with the Rustoleum nano-tech product called "NeverWet" - a super hydrophobic coating that can be applied from a spray can.  (Experiments #1 and #2 are here and here.)

For this experiment, we will be seeing how long the retained air film persists, and if the nano-coating has any anti-biological properties in sea water.  I think it might, since the retained air film could make barnacles and such uncomfortable, or might even prevent them from touching and attaching to the actual surface.  We'll see. 

 

Here's what I did:

• I took a scrap of fiber-reinforced ABS plastic (left over from the refrigerator refurbishment) and masked off one side of it.  The other side got the NeverWet treatment.  I suspended it (from the hole you can see, partially covered with blue tape) in the water off our finger pier at Anacortes on December 21, 2014.  The finger pier is a floating one, so the coupon will never be exposed to air, except when I lift it up for inspection.

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Report on Experiment #1

Experiment #1, as of Dec 2014

Experiment #1 began more than a year ago, in October, 2013.  For this test, I applied the NeverWet to our canvas sea hood. All was well until Nature's own nano-tech (pine pollen) arrived on the scene.  It coated and buried the NeverWet, and allowed water to once again wet the surface.  In an attempt to remove the pollen, I gently wiped part of the surface with a sponge damped in soapy water.  As you can see, that portion of the surface never recovered its hydrophobic properties.  Whether it was the mechanical action of the sponge or the surface tension-destroying property of the soap, I will never know.  But the portion of the sea hood that did not suffer from pollen accumulation or the soapy sponge is still every bit as water-repellent as ever.  From this I can propose that the coating is not strongly affected by UV.

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Report on Experiment #2

Experiment #2 began in April of 2014, when I applied NeverWet to our dinghy propeller. It was amazing to see that the submerged prop looked like it was made of polished silver due to the thin layer of air it retained while submerged.

We used the dinghy normally for the entire 2014 season, giving no further thought or special attention to the prop.

By the end of the season, the nano-tech coating had ablated off the outer 1/2 of the propeller blades, but was still active on the inner half.

From this I conclude that NeverWet is not suitable as an anti-barnacle coating for boat props (guess we're still stuck with Barnacle Ban), but it could likely serve well on things that do not suffer from the abrasion of high-speed turbulent water contact.

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The Future

It is the results of Experiment #2 that led to Experiment #3. Experiment #2 showed that the air film persisted while submerged over periods of days, and even in the presence of extreme turbulence. Will it be retained for months on end? And if indeed the retained air film is effective at retarding or preventing biological growth, NeverWet could serve for difficult-to-protect items such as depth sounder or speedo transducers.  And if the price could be gotten down low enough, perhaps NeverWet could even serve as a bottom paint alternative (for sailboats at least).