Foam core hull compression damage

[bunnins3]

Originally Posted by OneBoatman

I agree with Captain Bill, it is true that that under high point loads the core will try to flow away from the stress and the skins act more brittle by comparison. The good news is you don't need to be an engineer or materials expert to address "cradle waves" because they are not a specific sign of anything amiss. Most of everything else that has been offered here is great to know but the takeaway should be that if you like the boat, the deformation you see is more than likely not a result of moisture penetration and not a dealbreaker per se. Most all boat hulls will locally deform at the stess points if left on stands or in a cradle for a long time, and certain constructions are more sensitive than others. It is also generally true that assuming uniform construction, the deformed areas are likely not now nor were they any weaker than the rest of the hull when the vessel was put to rest. What to do. Assure yourself there is not also local weakness present or moisture in the core for any other reason is prudence. I like Boatpoker's suggestion of using Saran Wrap. Doing this extra bit of investigation will either result in a deal or could push you to keep looking. Building the area back to profile is done for aesthetic reasons not just because sailors like their bottoms smooth but because you need permission to drill holes in a boat that isn't yours yet.

Thanks OneBoatman! Yeah I think we’ll go along with your first comment. Investigate possibility of moisture further if the owners willing. Then if it’s purely just the compression without moisture or anything else going on we can go about bringing it back to profile with the rest of the hull!

[boatpoker]

Originally Posted by bunnins3

Thanks for the information and the links! Since you’ve surveyed that many corbins you’re a good man to know. How’d you determine the one Corbin had core separation? Through percussion testing or other ways?
Would you be worried about the structural integrity of the one we’ve shown in the pictures or putting it as more cosmetic? Thanks.

Yes, percussive sounding to determine core separation.

Without checking it myself, i can only guess ... it's probably serviceable IF there is no core separation in that particular boat. The catch is, if you ever try to sell it, you'll be on the wrong side of a tough sell.

[rslifkin]

If the core is delaminated, but the skins are intact, wouldn't it be possible to inject epoxy into the area to fill any voids and re-bond things provided the core isn't so squished that it would be a structural concern? The core is foam, not wood, so it's not like the core will have rotted and turned to mush.

[boatpoker]

Originally Posted by rslifkin

If the core is delaminated, but the skins are intact, wouldn't it be possible to inject epoxy into the area to fill any voids and re-bond things provided the core isn't so squished that it would be a structural concern? The core is foam, not wood, so it's not like the core will have rotted and turned to mush.

If the core is separated there may be a small amount of moisture even if only from condensation. If it has been separated for some time there is likely loose foam "dust" from working. Epoxy does not do well bonding moist, dirty surfaces.

[rslifkin]

Originally Posted by boatpoker

If the core is separated there may be a small amount of moisture even if only from condensation. If it has been separated for some time there is likely loose foam "dust" from working. Epoxy does not do well bonding moist, dirty surfaces.

If the boat were sailed like that, absolutely. But I'd think foam dust, etc. would be a much smaller concern if it delaminated from stuff being flexed too far while sitting on land.

[boatpoker]

Originally Posted by rslifkin

If the boat were sailed like that, absolutely. But I'd think foam dust, etc. would be a much smaller concern if it delaminated from stuff being flexed too far while sitting on land.

Perhaps but no way to know other than opening it up to see.

It would still be an issue if selling the boat. I'd sure want to know what was going on if I found an area of the hull that gave different moisture readings and/or different soundings than the rest of it.

It's pretty easy to find areas of a hull that have been repaired with different methods than original construction ... somewhat more difficult to determine the validity of those types of repairs.

[Tetepare]

Great thread.

If the hull had delaminated from the core, why would it not recover to original shape?

To rather answer my own question, I know of a Catalina 30 that suffered cradle compression, and the hull did not fully return to original shape. The c30 of course is a solid hull.

[boatpoker]

Originally Posted by Tetepare

Great thread.

If the hull had delaminated from the core, why would it not recover to original shape?

To rather answer my own question, I know of a Catalina 30 that suffered cradle compression, and the hull did not fully return to original shape. The c30 of course is a solid hull.

I think Captain Bill explained point loading and cold flow in post #11 pretty well. Sitting in water, there is no such point loading to force it back.

I've seen lots of hull deformations in single skin boats caused by cradling too. Most times they return to original shape eventually, sometimes they don't.

[ardenlester00]

Friends,


I had a trihull (40' houseboat) fiberglass foam center partially collapse (under the straps on two sides) when tamilift straps crunched them during lifting.


My only option was to layup several layers of resin/fiberglass over the crunch.


I felt good about my work, it floated (and was floating years later). The patch is underwater so "pride" isn't a factor. Practicality is!


Dennis

[Cadence]

No experience with it but I had read, years ago, that Airex foam will deteriorate with age.
It may be worth researching?

[Cheechako]

If no water saturation, I would just fill and level the dents and move on.
It IS disconcerting that such a large area is caved in. But unless the boat is "warped" it's not going to effect much. A dent wont make it leak. But I doubt, looking at the core sample, that the dent is going to pop back out. If it does the core will be delaminated in spots. Is that huge? Not necessarily..... until you sell. If you do get the dents out somehow, you can inject epoxy slurry into the voids if handy enough to identify them.
Not a fan of cored hulls but whether the total project is worth all the work is up to you.

[foufou]

Airex foam is such a different product than klegecell or divinycell. I had a piece some years ago that I bit into (shark bite test) and to my surprise some minutes later it had completely recovered its original shape! Those other two structural foams are much more brittle and have other significantly different characteristics. Airex has a low deformation temperature so may not do well on a deck in the tropics. But its ability to return to original shape can be a serious asset. You probably need to assess whether it has de laminated and if hasn't the deformation is likely of little consequence.

[Captain Bill]

Originally Posted by foufou

Airex foam is such a different product than klegecell or divinycell. I had a piece some years ago that I bit into (shark bite test) and to my surprise some minutes later it had completely recovered its original shape! Those other two structural foams are much more brittle and have other significantly different characteristics. Airex has a low deformation temperature so may not do well on a deck in the tropics. But its ability to return to original shape can be a serious asset. You probably need to assess whether it has de laminated and if hasn't the deformation is likely of little consequence.

While I agree that Airex foam is a different material than the Klegecell or Divinycell it is still a thermoplastic. Depending on which version they used in the construction it will still cold flow. The only difference is the amount of pressure it takes to do it and the speed at which it deforms. Temperature of course affects the speed. A boat sitting on the hard in the sun can get pretty hot, especially when painted a dark color. I had my boat on the hard for a couple of weels one summer and the foam in the black rudder on the south side of the boat deformed dramatically. Supposedly the foam core was Airex, though I haven't taken it apart to be sure. After visiting the website of the company that made the rudders in the aftermath, they had a warning to not paint the rudders a dark color or cover them when on the hard as sunlight on a dark surface is enough cause issues with the foam in the rudder. It would have been nice if the manufacturer of the boat would have passed along that little tidbit of information. Since the OPs boat was sitting on the hard and the hull color was on the dark side it might have increased the temperature enough to increase the speed of the cold flow. The fact that it can return to its shape after a dynamic impact really doesn't tell you much about what it will do under static point loads for a long period of time.

[nofacey]

IF THE PRICE IS RIGHT…..buy it & sail for a season before fairing. There is no reason for it to have become water saturated while in the pit……..the constant pressure & extreme heat deformed the hull.
Go Sail!

Corbin’s are beautiful boats.

[merrydolphin]

I have had this happen. My boat was on the hard in desert Sea of Cortez for about a year. I put the boat in the water and crossed oceans with it. And it did mostly flatten out with time. There is one photo that looks like a little sharper angle that the rest. I think it is a combination of heat and pressure. My Hulll was solid FG. Indents were caused by jack stands. After that, I always sound for bulkheads. And put stands there. Again, the hull was solid, not cored. Maybe after a while, sound for any delam.