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Old 23-02-2013, 10:06   #91
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Re: Opinions about Cored Hulls ...

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Originally Posted by s/v Jedi View Post
That's the thing: cored hulls have no core where things like thru-hull fittings are. What you write above is a myth afaik.

When Contest built solid glass boats they boasted about it as much better too, until they finally managed to built a cored hull. Here, now I kick a Dutch product too


I've seen many cored hulls with no solid block out around skin fittings, it's very common. It's only become standard practice to do solid blocks for fittings in the last decade or so. Most powerboat builders still don't do it, and that means a majority of boats are like this. Seen lots of saturated core result from stress fractures from an impact that were invisible in bottom paint, can't see them until you start grinding and chase them out. This means you could have a problem from that bump in the night you thought was no big deal, but actually left invisible stress fractures in your outer skin, leading to eventual core saturation.
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Old 23-02-2013, 10:11   #92
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Re: Opinions about Cored Hulls ...

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I've seen many cored hulls with no solid block out around skin fittings, it's very common. It's only become standard practice to do solid blocks for fittings in the last decade or so. Most powerboat builders still don't do it, and that means a majority of boats are like this. Seen lots of saturated core result from stress fractures from an impact that were invisible in bottom paint, can't see them until you start grinding and chase them out. This means you could have a problem from that bump in the night you thought was no big deal, but actually left invisible stress fractures in your outer skin, leading to eventual core saturation.

Agreed, many powerboat builders don't even relieve the core in below the waterline fittings Many sailboat builders did relieve the core in areas where deck fittings were to go ..... then they installed fittings elsewhere, directly through the core.
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Old 23-02-2013, 10:14   #93
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Re: Opinions about Cored Hulls ...

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..... then they installed fittings elsewhere, directly through the core.


Lol, yep, seen that a whole lot, straight from the factory.
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Old 23-02-2013, 10:35   #94
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Re: Opinions about Cored Hulls ...

I bet that if one were to go back to page 1/2 on this thread we will find that the same things are being said over and over.
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Old 23-02-2013, 10:48   #95
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Re: Opinions about Cored Hulls ...

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Lol, yep, seen that a whole lot, straight from the factory.
Oops... forgot about powerboats and other clueless builders
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Old 23-02-2013, 10:54   #96
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Re: Opinions about Cored Hulls ...

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Oops... forgot about powerboats and other clueless builders


That means you forgot about 80% of the boats on the planet. Some of them are cruisers too you know....
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Old 23-02-2013, 11:07   #97
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Re: Opinions about Cored Hulls ...

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Was lookin at a 40 foot sailboat. One of my reservations about the boat was that it was balsa cored above the waterline. am i over reacting?? the boat is a steal.... I mean arent there plenty of boats out there 35 to 42 foot that dont have cored hulls? that wood just seems like one more thing to worry about.. i cudnt imagine recoring the sides... So i guess im looking for something full keel solid glass. All advice greatly appreciated!!
There is a great book on the subject..........

"Fiberglass Boats" by Hugo Du Plessis.

Its the best straight up unbiased text that I have read on the subject. Might help to check it out before taking the plunge. Personally I would be wary of any older boat that was cored and is considered a "steal".............
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Old 23-02-2013, 14:34   #98
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Re: Opinions about Cored Hulls ...

!!! No stress relief (epoxy or hard insert) around holes !!

No,no, cardinal sin with cores. You just cant do that except on the lightest fittings internally!.

As Ive said we have a Kelsall PVC foam/glass cored catamaran. Ive tried occassinally to fit something non critical by just drill and through bolt (eg VHF mount etc). As soon as you tighten the bolt down it crushes the foam, and deforms the glass. If you just leave it moderately tight with big penny washers its ok till the fitting gets pushed about (kids!), which then levers the bolt, crushing the foam. A nuisance on the VHF, but disaster for a balsa cored hull fitting.

The proper process is simple, for a 6mm bolt, drill a 10mm hole through one skin, stopping when you reach the other. Depending on the expected load, clean out a recess of foam inside the hole. Fill it flush with epoxy, drill the 6mm hole trough, and bolt up tight. Even a minimal plug will hold immense load, we have high load fittings mounted this way, and they all survived 6000+ ocean miles without problems or leaks.

Its not that different from my glass/ply boat, all holes had to be drilled and epoxy soaked to stop eventual water ingress and rot.

If its common practice on fizz boats to just bolt through the core, then no wonder you have such horror stories about cored hulls. Thats just basic cheap construction/cost reduction manufacturing.

Like everything marine, you have to do it properly if its going to last.

Rob
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Old 04-07-2013, 06:22   #99
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Re: Opinions about Cored Hulls ...

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I've worked on plenty of HRs and Swans with core problems. Most of the rest you list have not been around long enough to see many examples. Obviously newer methods like SCRIMP make all the difference, but the vast majority of boats out there were not built in the last ten years.
Just looking thru this subject thread when I came across your posting.

Wondered if you ever had any experiences with polypropylene honeycomb cored vessels??
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Old 04-07-2013, 06:32   #100
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Re: Opinions about Cored Hulls ...

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I respectfully disagree, I think ? I'm not sure what you mean by "major" builders but I have seen dozens of boats with wet or rotten core including, Niagaras, Nonsuch's, C&C's, J-boats, Farr, Regal, Sea Ray, Doral, Cruisers and I'm sure I could list more if I took the time to dig out my files.

I have a little article on my website titled Balsa Core = Compost. I must admit that I wrote it after doing a re-core job so it may be a little biased
Any files on polypropylene cored vessels? nidacore etc,
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Old 04-07-2013, 06:43   #101
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Bonding to PVC foam

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Not having any direct experience with foam cores makes me bow out of this part of the discussion but as far as FRP resin, I would think it would have a hard time adhering to the PVC with out some sort of "teeth" to grip and even then, how tough is this bond? I guess maybe there's a binder??? I know epoxy and resin "pop" right off of my plastic palates.
I might suggest you visit Derek Kelsall's website and review the MANY vessels he has built with PVC foam cores....with GREAT success.
( I just took half a day and read thru a lot of his site)
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Old 04-07-2013, 06:56   #102
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Re: Opinions about Cored Hulls ...

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I completed my 2,804th survey yesterday. My records show you have it backwards.
That's quite a record !
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Old 04-07-2013, 07:55   #103
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Re: Opinions about Cored Hulls ...

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That's quite a record !



Lol, we quit keeping track some years back at over 35,000 haul outs!
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Old 04-07-2013, 08:00   #104
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Re: Opinions about Cored Hulls ...

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Just looking thru this subject thread when I came across your posting.

Wondered if you ever had any experiences with polypropylene honeycomb cored vessels??


Sure. My experience is that once water ingress begins on a honeycomb core, it's very bad. The honeycomb can contain a whole lot of water! I remember one big swim step I opened up must have had at least a hundred gallons of water trapped inside. Owner couldn't figure out why his boat didn't want to trim any more! I wouldn't use it myself for this reason. Building boats out of air is bad, it does not displace water.
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Old 04-07-2013, 22:20   #105
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Re: Opinions about Cored Hulls ...

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Just looking thru this subject thread when I came across your posting.

Wondered if you ever had any experiences with polypropylene honeycomb cored vessels??
In 48 years of concentrating on foam core structures as designer and builder, the materials have proved to exceptionally easy to use, totally reliable/durable, economical and exceedingly versatile. Nothing else compares. No, I do not sell foam. My choice is based on my own direct experience. Obviously I see and have used alternatives. The materials spec has changed little over the years. The technique to handling the materials has changed totally. All of my standard catamarans start as a kit of flat panels, infused on a mold table, from which it gets a smooth finish and ensured fair lines.

It is unfortunate that sandwich structures as a whole have suffered from a fair amount of poor choice of materials, poor choice of technique and some strange beliefs on behalf of a few professionals. For example, in US a lot of surveyors condemn any core below wl. All my boats have foam below wl. Most designers still specify balsa for decks. Experience tells us that they will almost certainly rot at some time. Some very simple rules will ensure that decks of foam sandwich are totally reliable. Claims are made by suppliers of different cores point to a list of failings of PVC and Corecell foam. I can say positively, that none of these apply if done correctly.

Mention was made of the bond between skin and foam. The surface of the foam is cut cells. When done correctly, each cell is filled with resin, providing a 100% contact between the foam and the skin.

Honeycomb does not have the track record of foam and it is no where near as versatile. Remember we are dealing with v. thin skins. Skins too thin to guarantee that water will not penetrate. A fissure in the skin reaching the foam is of no consequence. A fissure in a honeycomb or balsa core is not good news.

I can point to many boats I built in the 60's and 70's which are passing survey today. I know of none which have been scrapped. A few wrecked. A few tris capsized but no sandwich failures.

The topic is covered in Catamarans - Kelsall Catamarans - Boat Designs

Happy boating,

Derek.
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