>The XPS I used is what was readily available. It was the type usually used for insulation.

So, if you don't mean bead foam, which might explain your water obsession, as you probably read in my prior posts, that has a 0.1MPa shear. Which is a quarter of what you were expecting.

That probably explains the delamination you were not expecting. So it was a core shear problem, not a skin core interface problem

>The primary difference between a boat and plane is that a plane usually contacts the ground with rubber wheels specifically designed for that.

Did you read my post? I mentioned airplanes in the context of you suggesting water kills the XPS skin interface. Which, history suggests, it does not.

>Any thermal expansion of infiltrated water can cause very high stresses on bonds when confined.

Is this a big problem in foam core boats? You mention it repeatedly, as if it is a giant concern. Am I missing something insightful here? Is there a history of entrapped water destroying laminates that otherwise would be fine with water exposure? Can the water not get out the same way it got in?

Not that i am advocating for injecting water under the skins of boats. I wanna be very clear on that!

>I know from experience that H80 with thin skins is durable.

So does Rob, and everyone else. Which is why it is on the BOM. But that was never the question, was it?

>I would not use materials commonly used in the aircraft industry for a durable boat without thorough testing.

Not that I ever suggested you should. But do you mean like carbon, glass, and epoxy? Or aerodynamics.

>I would not use any open cell core on a normally immersed portion.

Are you saying XPS is an open cell core? Or is this speaking to other materials more generally? Like the hexagonal products? I can agree with that.

>I would not use a core material that degrades in sunlight.

I could not find any UV data on H80. Even in the technical manual. Do you have any? As I know it, PVC does not do well in UV environments, but coatings can make it great. I don't know how you coat a foam. But I am not a great chemist.

Also, you agree that aircraft get closer to the sun? Ah, I see you do later on.

>There are typically signs plastered in many spots on an aircraft “no step”. A shoe is mild loading compared with a rock or a log that the hull will surely strike.

Remember, I mentioned aircraft only in the context of you suggesting there was some sort of problem with water in the XPS interface. Which the thousands of hours of aircraft suggest this is not a problem. They also do not put a ladder on aircraft so you can climb back in after you jump off! Yes, boats and planes are different!

>If XPS was used as the initial former to get a shape and then covered with a heavy skin that was structurally sound without the core then that would likely be durable. XPS is suitable in block form as a bulkhead or solid buoyancy.

I think you are saying, in your experience, XPS can be used as filler. And you mean cheap building insulation XPS. Which makes sense. Cause that's what you know.

Do you have any experience with higher grades of XPS? How about lower grades of Divinicell H? How about Finfoam?

>Water will find a way in. It may be possible to start with a watertight skin but there are many ways it can deteriorate and allow water in eg hull fittings, grazes from collisions and so on.

Can you explain why you are obsessed with water infiltration?

>If you had skin that could take a good blow from a 2kg hammer (maybe more than 1000gsm) then it is likely the skin would remain water tight for a long time and it would not matter much how it was stiffened.

I just don't understand the point here.

>The two test I have described should give good relative comparisons for boat skins. Even if you could get XPS with the same tensile strength as PVC H80 and the same initial bond strength I expect the XPS would still not perform as well in the fatigue situation. I expect this is related to fatigue strength. There is some data here for PVC foam:
>https://engagedscholarship.csuohio.edu/cgi/viewcontent.cgi?article=1113&context=enme_facpub
><https://engagedscholarship.csuohio.edu/cgi/viewcontent.cgi?article=1113&context=enme_facpub>
>XPS does not seem to have the rebound or toughness of PVC core.

You mean of some grades of PVC core. Like you are not suggesting H35 is always better than Highload 1000?

>I cannot find any fracture toughness data on XPS. If you can then compare it with the data in the paper or perform your own comparative tests.

You have set the bar at what H80 can do. But H80 is chosen due to factors that are not really engineering based, right?

>The other factor that comes into play with lightly skinned core is UV deterioration. I have seen polypropylene honeycomb turn to dust in as little as 5 years sun exposure. A light glass skin with only a coating or two of paint will let sun in. You would also need to check the resistance to UV radiation of the materials being compared. PVC marine core darkens when exposed to UV but its mechanical performance does not seem to deteriorate. UV performance of a core material on an aircraft should be one aspect relevant to a boat.

It seems that H80 is awesome. Its tough and great and never fails. Sail the boat into a wall, and the H80 will be fine.

Does that not suggest it is over engineered? Like if you dropped to H60, would you expect failure?

If half the cost of the boat is H80, is that not worth looking at?

Now, in the context of how cheap the boat is, perhaps it is kinda tilting at windmills.

Still, I think it is an interesting discussion.

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