Just one thing that a lifetime (50 years) of sailing has thought me well. You never go in to storm intentionally. Or other challenging situation. You get to them unintentionally. But you better survive them. And those are the moments when I want to be able to trust my boat can take what I can. So if your boat is designed for good conditions only then you better stay close enough to shelter that you can reach it before the s**t hits the fan.

But since you seem to have decided that you want to build the boat with cheaper core please do so and if you survive tell us how it went.

Arto

On ‎Friday‎, ‎October‎ ‎26‎, ‎2018‎ ‎03‎:‎16‎:‎57‎ ‎AM‎ ‎EEST, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

| <<Planning what happens beyond that is less interesting to me, Although it would be good to know what approaching failure and failure look like.>>
|
|   You might want to plan on a failure where the foam goes first, which might give you some warning when that boat is stressed way past its design goals.
|
|   For reinforced concrete, you want the steel to fail, because it will stretch in tension and the structure will deform.  If you put in so much steel that the concrete matrix fails in compression, the failure is instantaneous and explosive.
|
|   The key is a "safe" failure that gives you time to react.
|
|   So it might make sense to do a 3D FEI analysis based upon the materials being used.

I agree. It would be great to know what a failure looks like. But I am not sure it's important. Ya, a FMA can tell us what it takes to fail a part, but I have no Idea how you do it on a boat, nor its value. Like, is there a hurricane simulator one can sail in, to see what breaks? Are they at all accurate?

In aviation, there are known high stress maneuvers. +9g to -9 g type stuff. Plenty of simulators in aviation.

But, given a FEA can tell you you want a H97 and a 666gsm biax, the answer is kinda impractical. Given there are a small number of options for cores and fibers, you kinda are forced into light, medium, or strong kinda thing spec, right? And that's gonna force, I think, failures when sailing in a force stupid into weird places, because, generally, you don't sail in a force stupid. Apparently, in a HP, you are supposed to grab a bottle and go below.

So I am not sure the value of a FEA. But I could be sold on it. If you don't have very tightly defined goals, it can get expensive fast.

|   You'd want a failure that's close to the glass, so you're not wasting material, but goes before the glass, so there's at least a tiny warning envelope.

I am not sure that's a priority. Ya, if it's cheap and fast. But I think most sailors are never gonna max out the safety margin. So, I think, remembering what a near fail is gonna look or sound like, that's gonna give said sailor an edge to react while sailing in a force stupid near the edge of failure, I just don't see it as a likely event.

And all that analysis goes out the window when, as Rob describes, he adds a little more tow. And a builder takes Robs spec, and adds a little more. And a builder that wants to sail in a force stupid will add a lot of tow, perhaps.

|   It wouldn't be as dramatic and clear-cut as with concrete, give nature of the skinned composite, but the goal would be to be able to back off when you hear a sickening noise, look at a deformed component, and then limp home. 
|
|         - Mike

Its quite possible a failed part would look and work fine. It may just deform in unexpected ways sooner when reloaded.