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Old 28-02-2024, 10:45   #1
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Hull damage from Jackstands

im viewing a boat to purchase which had previous damage from sitting on the jack stands all winter. it is a foam cored hull which apparently compressed at each jack stand. The owner says the yard injected epoxy resin into each location so all is well. I have my doubts; it seems to me a properly constructed hull should not react that way. Any comment or opinions appreciated.
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Old 28-02-2024, 10:56   #2
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Re: Hull damage from Jackstands

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I have my doubts; it seems to me a properly constructed hull should not react that way.
I think it is less about the hull construction and more about the yard using an adequate number of stands given the hull construction, and placing those stands where there is internal structural support.

How did you learn about the core compression? Is the hull still visibly deformed?
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Old 28-02-2024, 11:00   #3
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Re: Hull damage from Jackstands

My boat has a foam cored hull (Airex), and we use jackstands. There has never been any compression. For hull compression to happen there would have to be substantive force on the pads, which should not happen. Either that, or the hull is very thin...
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Old 28-02-2024, 11:46   #4
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Re: Hull damage from Jackstands

Any boat with a cored hull will be damaged if the weight of the boat is carried by the jackstands. This is the yard’s fault.

A yard who knows what they are doing will always sound the hull looking for bulkheads so the jackstands have rigid structure behind them. This won’t stop compression of the foam in the core it enough weight is applied.

Far more important, jackstands should carry no significant weight. The boat’s weight is supported by the keel, the stands are just there for balance. Any yard that doesn’t know this should not be lifting boats.

This can happen in unpaved yards after heavy rains, the keel blocks sink or get undercut, and the boat is left hanging on the stands.
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Old 28-02-2024, 12:07   #5
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Re: Hull damage from Jackstands

"Injecting Epoxy" is not a solution: if the hull oil-canned in the area of the jackstands, it's likely there's "core sheer," where the core has separated from the surface skins and is damaged as well as not adhered to the surfaces.
The cure is to cut off a section of outer skin, remove all damaged/delaminated core, and glass over after replacing the damaged core.
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Old 28-02-2024, 12:27   #6
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Re: Hull damage from Jackstands

Walk away and find a boat without a compromised hull unless there are compelling reasons to buy this boat and you are willing to repair the damage properly.
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Old 28-02-2024, 13:28   #7
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Re: Hull damage from Jackstands

Bendriver it's really not a big deal. The yard mucked up by not supporting the hull weight on the keel. Once properly repaired it should be fine. Injecting epoxy resin into the hull is BS. The hull structure has been compressed so there should be no voids to fill. Unless the fiberglass skin popped of the core when the pressure was released. Injecting epoxy is not going to fix that so the hull skin needs to be removed. I have surveyed a solid fibreglass yacht that had concave sections from jackstands. She had been abandoned for years and obviously been badly supported.
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Old 28-02-2024, 14:06   #8
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Re: Hull damage from Jackstands

A related issue sometimes appears as in inadequately supported jack stand legs. Some yard guys in a rush to leave or too lazy to look for flat wood blocks to put under the stand legs. I've seen those legs sink in into asphalt. Must've been either a fresh asphalt or from hot temps.

Anyway, the flat blocks go not just between the hull and the stand but also under the stand legs. I usually stop by a few times per winter to check on the ground underneath. Out of 15+ years may be 3-5 times there was a need to readjust the stands to compensate for the softening ground. This was both over the gravel as well as on regular asphalt.

My first boat, a 27 footer, was winter stored annually at friend's backyard - just regular grassy somewhat sloping ground. But the haulers were pros and made sure the blocks under the keel did their job, even with the rains, snow melt and whatnot.
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Old 28-02-2024, 17:50   #9
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Re: Hull damage from Jackstands

I may be going blind but have we been told what sort of hull it is? I presume it is a yacht and not a powerboat?

Have you told is what core material has been used? Is it balsa, klegecell, divinycell. airex.....? Different core materials have very different properties.

If it is a yacht there should be no foam core on the keel and as has been said the weight of the yacht(?) should be supported by the keel.

"Far more important, jackstands should carry no significant weight. The boat’s weight is supported by the keel, the stands are just there for balance"(SailingHarmonie)

You might be interested in this Dec 22 thread?
Foam core hull compression damage
https://www.cruisersforum.com/forums/f55/foam-core-hull-compression-damage-259618.html
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Old 28-02-2024, 20:22   #10
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Re: Hull damage from Jackstands

Thanks all for the reply’s. The boat broker told me about the compression so I would not be surprised upon viewing the boat. The hull is still deformed with dents where stands sat. From what I hear on the forum, injecting epoxy is not a solution. And if delaminating occurred, it will require a surgical repair.
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Old 28-02-2024, 20:33   #11
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Re: Hull damage from Jackstands

I should have mentioned the boat is a 55 foot sailing yacht, not a power boat. The coring is divinycell and goes below the water line.
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Old 28-02-2024, 23:19   #12
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Re: Hull damage from Jackstands

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I should have mentioned the boat is a 55 foot sailing yacht, not a power boat. The coring is divinycell and goes below the water line.
Well Diviniyell will never rot as it doesn't absorb water. It is quite a hard core and once compressed would not return to its original state.

I would not have filled it with epoxy but would have laid epoxy/glass over the dent. If it was a big issue you wouldn't want to hit any sokid flotsam in the water would you?

Airex will not absorb water but while it is hard it has a "memory" and if crushed (as in hitting a floating object) it will return (or attempt to) to it's original state.

What do you do if you hit an object in a steel or aluminum boat and dent it?
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Old 28-02-2024, 23:54   #13
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Re: Hull damage from Jackstands

Sounds like the boat was stored on the dry with the keel not supported or only partially supported, ie the boat (and partial keel) weight taken up entirely by the jackstands. I would be careful buying a boat which had that kind of treatment.
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Old 29-02-2024, 00:57   #14
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Re: Hull damage from Jackstands

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Originally Posted by Fore and Aft View Post
Bendriver it's really not a big deal. The yard mucked up by not supporting the hull weight on the keel. Once properly repaired it should be fine. Injecting epoxy resin into the hull is BS. The hull structure has been compressed so there should be no voids to fill. Unless the fiberglass skin popped of the core when the pressure was released. Injecting epoxy is not going to fix that so the hull skin needs to be removed. I have surveyed a solid fibreglass yacht that had concave sections from jackstands. She had been abandoned for years and obviously been badly supported.
Cheers

I have just read your post and I agree with you 100% (And you are a Marine Surveyor!)

I would be outraged if the boat yard did that to my yacht but it's not the end of the world. Lots of boats get dented but they can be repaired.

As I said in a previous post I'd epoxy glass cloth over the dent until the dent was filled, use some "body filler" to finish it off and then paint it. END OF STORY
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Old 04-03-2024, 11:55   #15
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Re: Hull damage from Jackstands

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Walk away and find a boat without a compromised hull unless there are compelling reasons to buy this boat and you are willing to repair the damage properly.
Totally agree
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