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daletournier · 01-01-2017, 18:37

Another point is the concern of being cored below the waterline. My current boat is solid grp below the waterline while my last as mentioned was balsa. I wasn't concerned with having a below the waterline composite, generally the only holes are through hulls ,in my case were flush, very unlikely for water to get into the hull. Above the waterline is a different story, lots of holes where things are bolted on etc......maybe it should be composite under the water and solid above?..lol. ( im joking)

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Polux · 02-01-2017, 05:01

Quote:

Originally Posted by daletournier

Another point is the concern of being cored below the waterline. My current boat is solid grp below the waterline while my last as mentioned was balsa. I wasn't concerned with having a below the waterline composite, generally the only holes are through hulls ,in my case were flush, very unlikely for water to get into the hull. Above the waterline is a different story, lots of holes where things are bolted on etc......maybe it should be composite under the water and solid above?..lol. ( im joking)

Normally on the boats that have a full cored hull they have solid GRP on the places that have through the hull passages.

rourkeh · 02-01-2017, 05:24

There is no way I would own a hull that is manufactured with core below the waterline. It is a disaster waiting to happen, and because you cannot see it does not mean water ingress has not occurred.
This is an excellent summary of why not to use coring below the waterline.
Cored Hull Bottoms
it is the end to any argument in favor of this idea.

Bleemus · 02-01-2017, 07:03

Wow, I guess I am lucky to be alive. Sailed across the Pacific three times on a boat with a balsa cored hull. Also saw a few Tartan 37s doing the same thing. Surely they are dead by now.

Polux · 02-01-2017, 07:41

Quote:

Originally Posted by rourkeh

There is no way I would own a hull that is manufactured with core below the waterline. It is a disaster waiting to happen, and because you cannot see it does not mean water ingress has not occurred.
This is an excellent summary of why not to use coring below the waterline.
Cored Hull Bottoms
it is the end to any argument in favor of this idea.

All performance cruisers, almost all the cats, all the race boats have a sandwich core. The old ones, and there are a lot of very old racing boats around, should have been scrapped a long time ago, if what you say was true with the catastrophic results you mention.

Yes, water ingress possibility is something one should be aware of and periodically checks should be nade but even if that is the case on a foam core boat the treatment is not difficult if one has the right equipment and not many work hours are needed, providing the state of the core is not on an advanced state of decay.

Maybe you don't understand fully the advantages of a cored hull? it is not only about weight but about stifness.

To give you a comprehensible example: Imagine a typical massive fiberglass long batten from a mainsail (the bigger one). if you hold it by the middle you will have a huge flexion on both sides. Now do the same with one of those sandwich battens with the same size that are used mostly on race boats and you will see that the bend is very small compared with the fiberglass one.

In fact when you double the thickness of the core you will have a 12 times increase in stiffness. With massive fiberglass you have to use a huge a big thickness of fiberglass to have a fraction of a stiffness of a cored hull with an huge increase in weight.

Bendy boats are not good neither for the performance neither by many other reasons and that's why cored hulls are a better solution than massive hulls.

Of course if they are well built or not is a completely different matter, being the building process a more complex and technological one, also more expensive and that is way few mass production boats use cored hulls.

That is why Jeanneau, Beneteau and Dufour come up with a different (but in my opinion, a inferior solution) to give stiffness to their hulls, using what they call contre moule, that is a kind of interior skin separated from the outside one. Off course, with industrial means it is cheaper than to built than a cored hull

rourkeh · 02-01-2017, 08:02

"To defy the authority of empirical evidence is to disqualify oneself as someone worthy of critical engagement in a dialogue."

Dalai Lama

smj · 02-01-2017, 08:47

Quote:

Originally Posted by rourkeh

"To defy the authority of empirical evidence is to disqualify oneself as someone worthy of critical engagement in a dialogue."

Dalai Lama

To quote David Pascoe as being the only authority on cored construction is ridicules. Many good boats out there with core below the waterline, just has to be done correctly.

UNCIVILIZED · 02-01-2017, 09:22

Pound for pound, cored boats are stiffer, tougher, lighter (not pound for pound, but length for length), & have a few other perks. And on the impact resistance thing, I've seen (& repaired) enough collision damage to say this without much question. Plus my 2-tonner was foam cored, & you could be comfortable inside of her in shirt sleeves on a 40 deg. PNW day, with no heater running. I'd not hesitate to buy another, given a good survey.

To put foam core vs. solid into perspective for everyone, even non boat owners, consider this. Which would be more comfortable to live in, a refrigerator, or a filing cabinet of the same size? The amount of steel per sqft is relatively equal, so that their panel weights are on par with each other. Yet one is ice cold to the touch, while the "cold" on is comfortable to rest against. This at room temps, with the "cold" one (fridge) being seriously colder than the filing cabinet, yet it's warmer to the touch. And it's probably a good bit more damage resistant as well. Especially if you were to construct both to the same weight per sqft of structure. As it's easy to perforate the metal that's the thickness of a filing cabinet, not so much a cored structure.
Then there's the question, which one floats?

Cheechako · 02-01-2017, 09:39

Solid hull better in my book. The one cored hull I had cost me about $30K... You just have to roll the dice I guess. Have a great surveyor. Don't buy anything with the core not eliminated around any penetrations. (solid glass at penetrations) Most decks have some wet core somewhere and they aren't even in the water. Why would that be...?

Bleemus · 02-01-2017, 10:00

Quote:

Originally Posted by Cheechako

Solid hull better in my book. The one cored hull I had cost me about $30K... You just have to roll the dice I guess. Have a great surveyor. Don't buy anything with the core not eliminated around any penetrations. (solid glass at penetrations) Most decks have some wet core somewhere and they aren't even in the water. Why would that be...?

Because people dont rebed deck fittings like they should.

captainstubbie · 02-01-2017, 10:02

Great discussion, thank you? I'm curious, are repairs fairly simple for the average do-it-yourself person when damage does occur?

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UNCIVILIZED · 02-01-2017, 10:09

Quote:

Originally Posted by captainstubbie

Great discussion, thank you? I'm curious, are repairs fairly simple for the average do-it-yourself person when damage does occur?

Repairs generally aren't too complex, unless you're dealing with exotic materials, or boats built to fairly close design tolerances. Though there's definitely some technique involved, & a few "little tricks" to things. But if you're handy with tools, are willing to do a bit of research first, along with some testing & practice on non-critical bits/side projects, then you'll likely be fine. And it rarely hurts to have a good mentor, & or, a helper who's quick on the uptake.

captainstubbie · 02-01-2017, 10:23

I am assuming that a cored hill below the waterline still has a gel coat interior and exterior on the surface of the laid up fiberglass?

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UNCIVILIZED · 02-01-2017, 10:30

Quote:

Originally Posted by captainstubbie

I am assuming that a cored hill below the waterline still has a gel coat interior and exterior on the surface of the laid up fiberglass?

I'd say most of the time, yes. Though there are plenty of boats that use paint, or epoxy. Well, primarily boats built with epoxy. Regardless it's a non-issue.