The Yard Guys

[Terra Nova]

Costs associated with custom titanium parts can be expected to be much more than stainless. The material, itself, costs many times that of stainless, though it weighs 1/2 as much. And welding it requires even more care than stainless.

Here is a drop-down desk I built into the aft cabin of a Beneteau First 435. The hinged struts are machined from titanium.

[smackdaddy]

Back to the Plexus thing. Here's a video showing marine applications. It's awesome for the drunken Dino tunage if nothing else.

ITW Plexus Structural Adhesive - YouTube

One thing I saw was that in the first application they ground down the top coat. Would that avoid the issue we see in Neil's photos above?

[smackdaddy]

And one last resource. Here is an interesting thesis study that tests traditional tabbing of a "T" joint (like a bulkhead) against Plexus and Sikaflex:

Analysis of bonded joints for small craft and marine applications

What they did was create a simple "T" joint with the various methods, then they pushed a leg of the "T" down to test the joint. The tabbing was the weakest overall join.

Sikaflex was the most flexible - and therefore the least destructive overall (they considered it a "strong" joint since it didn't break the panels). Plexus was the strongest and stiffest - and broke the actual panels before the join let go (they considered it a "weak" joint since it broke the panels).

From the report:

Tabbing:
In all three samples, the failure was initiated in point A (at the end of the gap - see Fig. 4.10). It continued with delamination of the tabbing along the inside skin of the flange. By the time the experiment was stopped (atChapter 4 - T joints 99 around 50mm deflection), sample T9 had a crack developed across the core of the T-leg (a failure in shear) and samples T10 and T11 had a crack developed across the fillet in compression. It is important to observe that no damage was recorded in the flange panel, meaning that the joint would fail before the panels.

Plexus:
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.

The joint using R20mm Plexus MA550 radiused fillet have proved the rigid nature and the good adhesion characteristics of the adhesive. In all the tests the flange was damaged (core shear) earlier than the benchmark samples. Again, it would be interesting to know the results of tests using a smaller fillet radius.

So, at the end of the day, Plexus was clearly the strongest method of adhesion - the the point that the flange materials (bulkhead and hull) break before the joint lets go.

Despite the delam shown in Neil's photo, I'm just not seeing much evidence out there that traditional tabbing is better overall than an adhesive fillet like Plexus.

[minaret]

Originally Posted by smackdaddy

And one last resource. Here is an interesting thesis study that tests traditional tabbing of a "T" joint (like a bulkhead) against Plexus and Sikaflex:

Analysis of bonded joints for small craft and marine applications

What they did was create a simple "T" joint with the various methods, then they pushed a leg of the "T" down to test the joint. The tabbing was the weakest overall join.

Sikaflex was the most flexible - and therefore the least destructive overall (they considered it a "strong" joint since it didn't break the panels). Plexus was the strongest and stiffest - and broke the actual panels before the join let go (they considered it a "weak" joint since it broke the panels).

From the report:



So, at the end of the day, Plexus was clearly the strongest method of adhesion - the the point that the flange materials (bulkhead and hull) break before the joint lets go.

Despite the delam shown in Neil's photo, I'm just not seeing much evidence out there that traditional tabbing is better overall than an adhesive fillet like Plexus.

You don't seem to have paid any attention at all to the discussion in the other thread about flanged bulkheads. Do you see a flange on the bulkhead in Neil's pics? I don't, just a fillet. Which failed. And yes, you can clearly see they ground off the coatings first on that failed joint. I see it fairly often.

[Reefmagnet]

Originally Posted by Terra Nova

Costs associated with custom titanium parts can be expected to be much more than stainless. The material, itself, costs many times that of stainless, though it weighs 1/2 as much. And welding it requires even more care than stainless.

Here is a drop-down desk I built into the aft cabin of a Beneteau First 435. The hinged struts are machined from titanium.

Hmm, what happens to all the old turbine blades from jet engines, I wonder? I reckon these could be re-purposed and machined into chainplates and similar if the costs weren't prohibitive. Anyone know the value and sources of scrap turbine blades?

[smackdaddy]

Originally Posted by minaret

You don't seem to have paid any attention at all to the discussion in the other thread about flanged bulkheads. Do you see a flange on the bulkhead in Neil's pics? I don't, just a fillet. Which failed. And yes, you can clearly see they ground off the coatings first on that failed joint. I see it fairly often.

I'm paying attention. That's why I'm researching it a bit more. If you take the time to look at the report I just linked to, you'll see that they were testing an "unflanged" T-joint as well (like what we see in Neil's pic).

What I see in Neil's pics is definitely a failure of the bond. But what does that say about the use of Plexus filleting in general? Are you saying these reports/tests are all bunk because of Neil's pics?

[a64pilot]

Originally Posted by Reefmagnet

Hmm, what happens to all the old turbine blades from jet engines, I wonder? I reckon these could be re-purposed and machined into chainplates and similar if the costs weren't prohibitive. Anyone know the value and sources of scrap turbine blades?

I've got about a 20 LB AH-64 main rotor blade grip, I think it 6/4 titanium, but
I doubt you could do much with it, machining ti is a real bear, since the fall of
the USSR, Ti isn't that expensive, it the machining cost that are high.
In a perfect world I'm replacing my chain plates with TI ones
In a perfect world I'm replacing my glassed in chain plates with TI
I think to weld TI, it has to be both submerged and in a noble gas? Never welded it myself though just what I got from reading

[minaret]

Originally Posted by smackdaddy

I'm paying attention. That's why I'm researching it a bit more. If you take the time to look at the report I just linked to, you'll see that they were testing an "unflanged" T-joint as well (like what we see in Neil's pic).

What I see in Neil's pics is definitely a failure of the bond. But what does that say about the use of Plexus filleting in general? Are you saying these reports/tests are all bunk because of Neil's pics?

Good lord man, a T joint is, by definition, flanged. Take the T flip it upside down, and bond it down in your mind. They even mention it right there in your post.

[onestepcsy37]

Originally Posted by Cheechako

Yeah.... I think it probably falls under the heading "Never, ever, ever, ever leave your boat to have work done without being around...."

Friend of mine just got back to florida from virginia. Bought a tartan 34 up there cheaply that had a small interior fire and was sold to him by the insurance company. Before he came back he hired a cleaning company to get the mold and smokey smell out of the interior. The boat had new foam cushions and upholstery. Now he finds out, long distance, that the cleaning company threw out all the cushions. Probably will cost him thousands to replace new cushions that just needed to be washed.

[smackdaddy]

Originally Posted by minaret

Good lord man, a T joint is, by definition, flanged. Take the T flip it upside down, and bond it down in your mind. They even mention it right there in your post.

Oh, now, let's not get carried away with the terminology. When I said "unflanged" I was referring to this drawing that you complained about in the other thread:



The top vertical piece on the left has an actual, integral flange. The top vertical piece on the right is butt-joined to the horizontal piece. It's has no integral flange....just like in the report.

Now, stick with me here, when joined together, then the lower piece of this combo is called a "flange" - like this...



...but it's still 2 pieces butt-joined together (no integral flange on the web like in the top image).

This is what the report and its photos refer to. The "flange" piece breaks in that report. The "web" piece stays intact.

In the tabbed version, the tabbing fails and the joint separates. In the plexus version, the "flange" breaks and the joint remains intact.

Cool?

[EngNate]

304SS is not for below waterline, 316 is. If it doesn't say 316, it most likely isn't. 304 and 18-8 are the same. I work with a couple of Chinese guys who were engineers over there. They say that the traditional philosophy of manufacturing there is to make products with limited life spans so your company stays in business!

[Terra Nova]

Bulkheads should be tabbed on both sides, not just one, the way the example shows.

[smackdaddy]

Originally Posted by Terra Nova

Bulkheads should be tabbed on both sides, not just one, the way the example shows.

The example in the report and photos was tabbed on both sides.

[jimbunyard]

Man, that ITW video was disheartening. I guess those glue dispensers feel they're lucky just to have a job (or maybe they're Deltas and Epsilons). I imagine their days are numbered though, the corprocats will soon give those jobs to robots...

The most interesting thing about this picture;



in comparison with this picture;


is the difference in the size of the radii in the fillets. The fillet in the Plexus joint is easily twice that of the fillet in the tabbed one. Does this indicate a testers' bias, or inconsistent experimental controls, or designed joint criteria? It makes a huge difference.

Additionally, from what I know of Plexus's almost crystalline hardness (I'm aware that ITW makes at least dozens of products and that some of them should include flexibility), the use of a deformable core panel in the test leaves me with more questions than answers, as regards this particular application.

I prefer bonding, filleting and tabbing. Hope I'll be forgiven, the pictures below are from a 21 ft., 85 mile an hour bass boat, but the idea is the same, When does use become abuse?, and seems in line with the general question about what makes a boat seaworthy (dare I say bluewatery?)

The boat was rated for 200 hp, the owner put a 225 on it, which is not uncommon. He also added a 6 inch jack plate, which resulted in what you see in the pictures. The buttresses (for lack of a better word, knees maybe) were tabbed but not bonded and were still securely attached at the floor. The boat itself when getting on plane pulled severely to port and once on plane listed about four inches down to port while running, indicating an induced hull twist under power.

The first picture is just an overview showing what is to me a basic design flaw, an unsupported transom.

2 and 3 are closeups of delaminated tabbing.

Picture 4 shows what is to me the correct way of installing bulkheads (although in this case they're actually stringers), that is; bonding the panel to the hull, filleting as generously as possible and practical, and tabbing, in this case with a layer of 18 oz roving 5" wide, followed by a layer 8" wide followed by a layer of .5 oz mat 10" wide, all laid wet one after the other.

Picture 5 shows the overall substructure, the different fillet radii where the stringer meets the transom on the outboard versus the inboard is the key point.

Picture 6 is just a vanity picture after gelcoating.

pictures 7 and 8 show the reason for the different radii of the fillets where the stringer meets the bulkhead. While I felt pretty sure the new reinforcements would be more than adequate, I also knew why the owner brought the boat in and therefore recommended the addition of the aluminum plate, just to CMA.

Pictures 9 and 10 are also vanity pictures, but I always like to see the end result. It's interesting though, in picture 10, the "hand laid hull" logo doesn't say anything about how strong the boat was, or wasn't. Often times the owner, or the conditions, have more to say about that. (The manufacturer is no longer in business)

And by the way, the white putty shown in the fillets is just glass beads mixed a little wet, with a little silica added to control runny-ness. My seat of the pants tests show that this putty is stronger than PVC foam or wood and is much easier to sand than milled fibers or anything else. This yields the smoothest fillet, which allows the best tab layup, which yields the most strength. It's the system, not the individual components, that give strength.

Which of course leads back to '(mass) production' boats. Many production boats cannot be assembled in any other way than using the glue in liner or modular approach, indeed, it appears that many boats are designed around the solution (a glue gun) rather than the other way around.

For a status symbol, no problem. To trust these boats in the Northern North Atlantic or South Polar Seas, I'd try to make damn sure the glue spreader was fat and happy....

[Island Time O25]

How much of the weight difference would be between 200HP and 225? One would think not even 10% as that extra HPs are probably squeezed out by some electronic/injection means and not from a larger set up.