The Yard Guys

[forsailbyowner]

Some time ago I read a book on building boats with fiberglass. The author recommended placing a wedge of foam between the bulkhead and hull then tabbing over that on both sides. It was said that this prevented hard spots that would show stress cracks after severe use in big seas situations. This would kind of go against the filet and tab idea... no?

[neilpride]

Originally Posted by forsailbyowner

Some time ago I read a book on building boats with fiberglass. The author recommended placing a wedge of foam between the bulkhead and hull then tabbing over that on both sides. It was said that this prevented hard spots that would show stress cracks after severe use in big seas situations. This would kind of go against the filet and tab idea... no?

Not really because the fillet and the tabbing itself have some flexural properties and the pillow or soft material is thin , few mm...

[smackdaddy]

Okay, just getting back online to address your post more thoroughly.

Originally Posted by jimbunyard

No attempts were made to calculate manufacturing prices, but it is expected
that the execution time will be shortened in the case of adhesives fillet. The
perspective of automatisation will make the joining process cheaper.

In this case 'cheaper' means weaker. See the following statements on strength.

No ageing effects or fatigue and creep effects have been taken into consideration during the testing program. For a full characterization of the adhesive adherend T-joint system these effects have to be studied.

So two of the main concerns we as consumers, and more specifically consumers who trust their lives (at least in part) to a product, are not even being considered.

I definitely think you're stretching here. The study is very clear as to exactly what it is, by its title: "Analysis of bonded joints for small craft and marine applications" and its Abstract:

This Thesis investigates the possibility of replacing, in small craft and recreative boats, some of the more traditionally made joints (using tabbing) with ones made using structural adhesives (adhesive used where the load applied may cause the separation of the adherends [2]), which have the potential to be quicker to produce and have good fatigue resistance.

It also focuses on methods that are available to a small and medium size boatbuilding or boat design company in order to design and produce a general safe, light weight adhesive joint.

And you want to discount it because it's not testing joints for fatigue or creep over many years? Isn't that quite a different study?

Originally Posted by jimbunyard

In the case of a T-joint with tabbing and QCel microballoons fillet R12mm...

This tabbed joint required about 7N/10mm more force than the Plexus joint before what they considered failure.

In the case of a T-joint with vinyl ester/Epiglass HT120 fillet...

This tabbed joint required about 20N/10mm more force than the Plexus joint before what they considered failure

In the case of a T-joint with Plexus MA550 fillet R20mm...

This Plexus joint apparently caused the failure of the panels by application of force either 7n/10mm or 20/N/mm earlier than the two tabbed joints. So the tabbed joints were roughly 25 and 75 percent stronger (That's what I get in my head, you figure it out) Not only that, the Plexus joint deflected further than either of the others, under substantially less load.

So to sum up, if I use the Plexus joint as described in the above thesis, what I get is a joint that deflects more, under less load, and is prone to inducing (potentially catastrophic) panel fracture, as compared to traditional fillet and tabbed joints.

This bolded part is what I meant by my previous post that failure of the joint and failure of the bond are two very different things. For example, why did the Plexus joint fail? Simple, it was because the bond was so strong. Again, from the thesis:

The joint using a R20mm Plexus MA550 fillet has benefited from the stiffness and the good adhesion characteristics of the adhesive but in all the tests the panels joined ware damaged earlier than for the benchmark samples.

In all three samples, the fracture mode was flange core shear failure. In addition, sample T15 showed interlaminar failure of the inside skin of the flange when the test was stopped. On average, samples built using Plexus MA550 are weaker in strength and are stiffer than the first two groups. Being rigid and having good adhesion to the substrates, MA550 adhesive transmitted most of the load into the panels being joined, and the core of the flange was the first to fail.

So the question here is what happens when the panels are not weak test panels as described:

The scantlings of the bulkheads and the hulls panels were kept the same during the testing, a PVC core and epoxy laminated E-glass skins were used.

If the panels are built to handle high loads (e.g. - a glass hull, etc.), doesn't it mean, precisely due to the MA550's property of transferring the load into the panels, that the joint itself is far stronger?

Remember, purely in looking at the joint, the thesis also reported this:

The joint using a Sikaflex 252 fillet has shown the most interesting results such that none of the materials forming the joint suffered any visible damage after deformation.

It was the "give" in Sikaflex, and in traditional tabbing, that allowed more force before failure - because the force was NOT transferred to the underlying materials prior to breaking.

So is Sikaflex a better material for bonding a bulkhead or stringer because it didn't break the panels like even traditional tabbing did?

So, yeah, you've got to be careful how you read the report. For example, I remember someone above complaining about the radius of the tabbing in relation to the adhesives...but there is perfect justification listed for that in the thesis.

In any case, I certainly don't find anything in there that says Plexus bonding is inherently inferior to the bond created by traditional tabbing. Quite the opposite.

But I also certainly wouldn't call it...

Originally Posted by jimbunyard

sophomoric, unclear and in-concise

You just have to understand what's being presented. It's not simplistic. It's a thesis.

Originally Posted by jimbunyard

So that leads us back to your assertions.

It could be construed that you have some hidden, unfathomable agenda.

It could be that you're a crypto-engineer, i.e. you have to believe the results to see them. (Or in this case misrepresent them)

Or you could (somewhat perversely) enjoy making other people use their brains.

Or any number of other postulates.

But in this, as shown by the thesis you cherry-picked....

Heh-heh. "Cherry picked"? Dude, you're welcome to find all the other non-industry marine joint studies between traditional tabbing and adhesives that are out there and post them here to refute anything and everything I've said.

Good luck with that.

As for this part...

Originally Posted by jimbunyard

But in this, as shown by the thesis you cherry-picked, and the real world experience of many people (for me not against the Plexus but for the bonded, filleted and tabbed), the evidence is overwhelmingly against the idea that Plexus is better in these applications.

But hey, chose for yourself. That's part of the reason I entered this discussion with an example of failed tabbed joints.

See, that's why you need to read it more judiciously. That's not the case at all. It's the opposite.

As to strength and other features of Plexus, I'll leave you with these from the same thesis...

The joint using a R20mm Plexus MA550 fillet has benefited from the stiffness and the good adhesion characteristics of the adhesive but in all the tests the panels joined ware damaged earlier than for the benchmark samples.

Plexus MA550, Sikaflex 252 and a vinyl ester mixed with filler were assessed as adhesives in T and single-lap joints. Sikaflex and Plexus are two of the most commonly used adhesives in boatbuilding. The first one is classified as flexible and the second one (MA550) as intermediate ([32]). The vinyl ester and fillermixture is expected to behave as a rigid adhesive.

Isn't this the opposite of what people have been saying?

The adhesive Plexus MA550 (supplied by ITW Plexus) is a two component methacrylate, mixed with 10:1 ratio, working time 40-45min., with 75% of ultimate strength in 70-75min. It is primerless, requires no sanding or grinding and virtually no surface preparation. The adhesive has received from the main classification societies, Lloyds of London, DNV (Det Norske Veritas) and ABS (American Bureau of Shipping) approval for the use in marine structure.

This is why Neil's pics of the failed bond in the Bene is so compelling. What exactly happened to cause that? It certainly doesn't line up with what everyone in the actual industry is saying.

Figure 3.27: ASTM D1002 - Single lap joint test of composite adherends and vinyl ester/Epiglass HT120 mix adhesive. Using only composite adherends, in average, Plexus MA550 is the strongest adhesive but very closely followed by the mixture and with Plexus MA550 being more flexible than the mix.

Plexus is the strongest adhesive but more flexible than the mix? Hmm.

Using both aluminium and composite adherends (a hybrid joint), in average, Plexus MA550 is by far the strongest and most flexible adhesive.

Again, my only agenda is to cross-check claims that are made. That's how you learn. So far, the claims and "real world experience of many people" don't hold water with the actual data that's out there.

So someone is not quite right here.

[neilpride]

Quote:
The adhesive Plexus MA550 (supplied by ITW Plexus) is a two component methacrylate, mixed with 10:1 ratio, working time 40-45min., with 75% of ultimate strength in 70-75min. It is primerless, requires no sanding or grinding and virtually no surface preparation. The adhesive has received from the main classification societies, Lloyds of London, DNV (Det Norske Veritas) and ABS (American Bureau of Shipping) approval for the use in marine structure. This is why Neil's pics of the failed bond in the Bene is so compelling. What exactly happened to cause that? It certainly doesn't line up with what everyone in the actual industry is saying.



Still on the Plexus thing? What exactly happened to cause that? honestly i put my 2 cents in flexing cycles, thats it,since xxx number of cycles x years .... Make a test Smack, next time you sail your Hunter, go in a hard tack , tight the sheets, set the boat hard in the wind, found a day with a litle chop in the bay , run inside of the boat and found a gap between the grid liner and the real hull, or better a gap between a bulkhead and the hull, place your fingers there and feel the flexing.... Boats need to flex by nature, if not , they break, some flexing is normal, some abnormal flexing not, thats why maybe why in the bene the bond fail......

[colemj]

You don't think it has anything at all to do with bonding it to a varnished piece of plywood?

Our boat has several things glued to it solely with Plexus and we are a catamaran - we flex and twist in ways that would give you mono guys apoplexy. The parts glued with Plexus are some of the most flexed parts on the boat. The boat is over 16yrs old and the Plexus is still holding fine.

My bets on those Bene's with failed bonds is poor application of Plexus.

Mark

[smackdaddy]

That's exactly why this failure in this Bene is so interesting. First, to your point cole - it certainly seems that gluing to a varnished piece of plywood would be the culprit. BUT, the thesis states that Plexus will form a strong bond to common marine substrates WITHOUT prep. Second, the bond didn't fail at the plywood on that Bene...it failed at the glass where you'd think it would be the strongest.





Neil, I completely understand flex, cycles, fatigue, etc. in boats. And, as stated in that thesis, Plexus is both strong and flexible. So, was it over-flexing in really rough seas that caused that failure? Was it an impact? Or, more troublesome, was it simply X number of flex cycles over X number of years?

If the latter, we should start seeing a lot of this exact problem across the fleet. And that's a huge problem. If the former, what's the big deal with this single failure on this Bene?

If anything, what I see in these photos is a pretty crappy application (poor radius, thin application, etc.) Of course, I still don't know exactly what we're looking at here. But it definitely failed whatever it is.

[colemj]

I was referring to another set of Bene photos showing rudder posts, etc - I forgot about the above ones. I get so confused here…

As for the above ones, I don't see the Plexus failing. It looks like the laminate failed, because there still appears to be resin and fibers stuck to the Plexus. That is why I asked if there was previous tabbing ground away from it (there is a suspicious straight and even-width bond line running parallel to it that is the usual width of tabbing). It also appears to have been set in some type of recess. And then there is that strange discoloration and buildup on the wood itself.

All in all, everything EXCEPT the Plexus looks strange to me in those pictures.

Mark

[smackdaddy]

Originally Posted by colemj

I was referring to another set of Bene photos showing rudder posts, etc - I forgot about the above ones. I get so confused here…

I know what you mean. The other Bene that sunk was Blue Pearl. But that one really shouldn't even be part of the discussion due to its history. Then I think Neil put up some photos of yet another Bene that had no failures - but was pointing out areas he thought might have been suspect in the Blue Pearl thing.

[Exile]

Originally Posted by smackdaddy

That's exactly why this failure in this Bene is so interesting. First, to your point cole - it certainly seems that gluing to a varnished piece of plywood would be the culprit. BUT, the thesis states that Plexus will form a strong bond to common marine substrates WITHOUT prep. Second, the bond didn't fail at the plywood on that Bene...it failed at the glass where you'd think it would be the strongest.





Neil, I completely understand flex, cycles, fatigue, etc. in boats. And, as stated in that thesis, Plexus is both strong and flexible. So, was it over-flexing in really rough seas that caused that failure? Was it an impact? Or, more troublesome, was it simply X number of flex cycles over X number of years?

If the latter, we should start seeing a lot of this exact problem across the fleet. And that's a huge problem. If the former, what's the big deal with this single failure on this Bene?

If anything, what I see in these photos is a pretty crappy application (poor radius, thin application, etc.) Of course, I still don't know exactly what we're looking at here. But it definitely failed whatever it is.

I've seen a number of products in the marine world claim they can be applied w/o prep. May be true, but every technician in the field I've talked to say that it's better to prepare mating surfaces, usually through mechanical abrasion. Plexus apparently also claims no prep is needed which presumably makes this part of the construction process less expensive. But does your thesis merely assume this based on the mfg.'s claim, or did it actually test it in a manner which simulates real world conditions? (No, didn't read all 90-something-plus pages -- you'll just have to tell me).

Your response also implies that the manner in which the Plexus was applied on this particular Bene was an isolated incident. Could be. The whole cost-cutting process in mass-produced boats, however, is dependent on creating consistent & uniform processes that can be applied to the largest number of units. A more logical explanation may be that over 90% of this model & mfg. -- like most sailboats as has been pointed out -- spend their lives sitting at the dock. Perhaps Neil knows more about this particular boat's history.

Not sure if it was on this thread or on "Rudder Failures," but Polux mentioned that his boat was both glued and tabbed. Might be helpful to know why, right?

It's an old clichè, but especially given the complexity of boat design & construction, it definitely holds true that a little bit of knowledge can be (literally) dangerous.

[neilpride]

I dont know guys how many times i need to repeat the same thing about the pics, there is no Fg before , the yellow spots in the bulkhead and in the White part of the gelcoat could be rest of glue from a previous headliner , no idea, the boat dont have any damaged from outside or inside, the owner words, this boat have 2 Atlantic croosings under the keel,thats all...

[smackdaddy]

Originally Posted by Exile

It's an old clichè, but especially given the complexity of boat design & construction, it definitely holds true that a little bit of knowledge can be (literally) dangerous.

Same thing can be said for assumptions.

[smackdaddy]

Originally Posted by neilpride

I dont know guys how many times i need to repeat the same thing about the pics, there is no Fg before , the yellow spots in the bulkhead and in the White part of the gelcoat could be rest of glue from a previous headliner , no idea, the boat dont have any damaged from outside or inside, the owner words, this boat have 2 Atlantic croosings under the keel,thats all...

Okay, then let's try to clear this up. Do you think the greenish substance is Plexus? That's what I thought you were saying earlier.

Then, if that yellow stuff was glue from a headliner, and not the same adhesive that pulled away from the hull - then the question is: Was the Plexus bonding correctly done in the first place (e.g. - was enough applied, was the fillet sufficient, etc.)?

Again, back to the various issues being discussed here...if the green stuff is indeed Plexus and the yellow stuff is a different adhesive for the headliner, you have to be impressed that the Plexus stuck to that varnished wood with a tiny fillet. On the other hand, you have to be concerned that it instead pulled away to the top coat of the FG hull.

It goes back to what was being talked about in the thesis. Because Plexus transfers the load to the substrates, more so than traditional tabbing, the strength of the substrates is critical. The fact that the FG failed in this case (not the plywood) definitely says something about the FG.

[colemj]

Was this a bulkhead/deck bond? I didn't catch that. Where on the boat? Then yes, maybe the yellow on the wood is glue from a headliner.

Is there a recess of some type the whole thing is sitting in? What is that?

Mark

[Exile]

Originally Posted by smackdaddy

The other Bene that sunk was Blue Pearl. But that one really shouldn't even be part of the discussion due to its history.

Not part of the discussion? That's convenient but unfortunately illogical, unless you don't wish to be objective but instead have some other agenda.

Prior damage to Blue Pearl? Yes, but passed survey by the new owners as I recall (fwiw). So direct correlation b'twn. the prior damage and the aft bulkheads coming apart in rough seas? Calls for speculation, i.e. maybe. Same deal with Cheeki Rafiki, i.e. lots of variables, much of it anecdotal even if could be confirmed. But then there's Dockhead's story of smacking an uncharted submerged rock on his Moody with such force that it caused the bow to lift out of the water to the point of exposing the thrusters. Result of ensuing survey? No structural damage. And of course plenty of older, "saltier" boats with keel bolts that have been sailed extensively but don't suffer their rudders falling off.

As I've said, there's a definite upside to the profusion of cheaper, mass-produced boats in the past decade or two. The relevant question for boat buyers is whether (a) the less expensive construction methods & materials result in making them less seaworthy due to cutting corners in building the hull, keel, rudder, and other basic structural components; (b) if so, is this an acceptable trade-off if the boats will not be sailed in regions which would subject them to high stresses; and (c) is even the assumption of a "trade-off" reasonable given the conditions the ocean is capable of producing in any region and at any time.

[Exile]

Originally Posted by smackdaddy

It goes back to what was being talked about in the thesis. Because Plexus transfers the load to the substrates, more so than traditional tabbing, the strength of the substrates is critical. The fact that the FG failed in this case (not the plywood) definitely says something about the FG.

Don't need a thesis to come to this conclusion.