Cored or un-cored hull?

[coopec43]

Originally Posted by Amnesia II

Quite right, it was in your quoted section that “the general public” along with me thought solid fibreglass was stronger and generally better, an I still feel that way.

Despite what the experts say?

[Dockhead]

Originally Posted by Amnesia II

Quite right, it was in your quoted section that “the general public” along with me thought solid fibreglass was stronger and generally better, an I still feel that way.

Well, you should define the terms.


Solid fiberglass OF THE SAME THICKNESS is stronger than a cored panel of the same thickness. But it will be 5x to 8x heavier. Is that "better"? Depends on the boat, I guess. For a barge that might be ok.


Solid fiberglass of the same WEIGHT as a cored panel, will be many times weaker. Is that "better"?


The most expensive boats -- Swan, Hallberg Rassy, Contest, Discovery -- all have fully cored hulls, all the way to the keel stub. A very few exceptions -- some Nauticats, some Oysters -- are fully cored down to the waterline.


Solid core hulls, with no coring at all, are common only on cheap mass produced boats, at least in the last 20 years. In the last 20 years or so, such hulls are made quite thin, for weight and cost reasons. I don't think anyway would ever say they are "better". Expensive boats have thicker, fully cored hulls which are much stronger. And much more expensive than the thin solid hulls you find on some Beneteaus and other mass produced boats.


A cheap cored hull made without protection against water intrusion is not a good thing. The owners of Groupe Beneteau are no fools -- quality cored construction involves resin encapsulation, vacuum bagging, and other techniques, and is expensive and time consuming. But quality cored construction is definitely better -- if you want the hull to be strong, rigid, and at the same time reasonably light.

[Benz]

^^^ Dockhead is right, and I will only add that coring has gotten a bad name because many boats were cored with balsa (which is about the best material IF you can keep it dry, a difficult thing on a boat), and even with plywood. Sooner or later moisture gets in, usually around a careless screw hole or skin fitting.
But any of the many types of non-water-absorbent foam, properly done (of course, properly done is a must for any construction method-they're all bad if done wrong), and properly engineered, will give a construction huge advantages over an uncored layup.

[daletournier]

Originally Posted by Davidhoy

Sorry to hear about your damages. Not sure about your specific model, but I read that, at least with the Catalina 470, the hull is solid below the waterline, and is cored from about 6" above the waterline and up. Your model may, of course, be different. One of the replies above suggested contacting Catalina, and from what I hear their support is second-to-none, even for older boats.

I know your pain, as I'm dealing with major damage to my Morgan 462, which was t-boned at her dock by a 100ft motor yacht. Sadly, in my case, even though the hull is solid glass, it could not withstand the impact without significant damage to the hull (down to the waterline), deck, cabin-top, and mizzen mast. Hope your insurance company is cooperative - I'm dealing with the other guy's insurance company now, and it's not fun...

-David

I have a 470. Yes solid glass below the waterline and engrain Balsa cored above.

[clockwork orange]

Dockhead and Benz have it right on all counts. Balsa is an excellent core that has gotten a bad rap because of being used by low quality builders and/or low quality owners.
When the term "stronger" is thrown around you need to qualify what that means. A heavily built solid fiberglass hull may well stand up better to being pounded on a reef for a little longer than a cored hull so if you are in the habit of running into things or running aground I can see how the brute force and ignorance engineering approach may be comforting. However for those who place more importance on sailing performance the superior panel stiffness afforded by coring is more important. Panel stiffness with low weight is one of the most important design considerations if sailing performance matters to you and this can only be achieved with coring from a practical standpoint.


Steve.

[coopec43]

Agree Steve

In regard to pounding on reefs solid glass is better on the keel : I most certainly wouldn't use core material there. Of course a bit of extra weight of solid glass down there is not a problem anyway.

My hull and deck are cored and the yacht is quite cool even on a hot day so that is an extra bonus.

Clive

[jewt]

Having owner and operated a 1969 Morgan 41 K/CB for 34 years, that had a solid glass layup, at least a inch thick at the turn of the bilge, I vote for solid glass. She was bulletproof.

Cored hulls are lighter and possible faster on some points of sail but not as rugged and able to bounce off docks or other boats, not that ever happens.


jewt

New Bern,

[Dockhead]

Originally Posted by jewt

Having owner and operated a 1969 Morgan 41 K/CB for 34 years, that had a solid glass layup, at least a inch thick at the turn of the bilge, I vote for solid glass. She was bulletproof.

Cored hulls are lighter and possible faster on some points of sail but not as rugged and able to bounce off docks or other boats, not that ever happens.


jewt

New Bern,

To each his own!


But I think you would be hard pressed to find a boat built like that these days. I think that method of construction was abandoned by virtually the entire industry, at least 20 years ago. Maybe Nauticat as the sole exception?


Why are Beneteaus referred to as "Bendy Toys"? Because the hulls are not cored. They are solid glass and are engineered thin enough to be reasonably light. Once you do that, solid hulls are far more flexible than cored ones.



Cored hulls are like I-beams -- you move the load-bearing parts of the structure away from each other in order to improve the geometry of how the loads are carried:

"The principle is similar to that of an I-beam girder. Two sections oriented in one direction are separated by a third lighter section oriented at a right angle to the first two. In theory, this is the ideal way to dramatically increase thickness and stiffness while not increasing weight."

http://www.wavetrain.net/boats-a-gea...ored-laminates

It depends on the choices of the designer, but it is easy to make a cored hull far stronger than a realistic solid one. Balsa has extremely high compressive strength (and altogether has higher specific strength than titanium) and makes a really strong sandwich panel. For impact resistance, some builders will add a layer of Kevlar -- my boat has this.

[FPNC]

Having been involved in production fiberglass boat manufacturing for about 30 years. I have been intimately involved with manufacture of cored hulls from 18' to 45' in length. This involved sport, commercial and even high speed military vessels.

I would not purchase a hand laid cored hull vessel regardless of the core that was used in the construction. I would consider a CPVC cored hull that was infused using a proper vacuum bagging technique and if I was involved in the actual bedding of the core, I would accept CPVC core hand laid in the hull.

The skill required to bed core properly and limit unbonded and void areas in the core is seldom seen in marine manufacturing.

[Davidhoy]

Originally Posted by jewt

Having owner and operated a 1969 Morgan 41 K/CB for 34 years, that had a solid glass layup, at least a inch thick at the turn of the bilge, I vote for solid glass. She was bulletproof.

I agree that Morgans are strong boats, but they are not indestructible. My 462 was hit by a 100ft motor yacht 3 weeks ago, and the damage was catastrophic. Not that a cored hull would have fared any better, mind you...

[Dockhead]

Originally Posted by FPNC

. . . The skill required to bed core properly and limit unbonded and void areas in the core is seldom seen in marine manufacturing.

I'm sure you have tremendous skills, but do you really think that Swan, HR, and Discovery are incapable of "bedding core properly"? I don't believe I've ever heard of a core problem with any of those boats, even if there were some structural problems with some HR's, some years ago.



I think even keels falling off is more common, than core problems, on high quality European boats.

[JPA Cate]

Originally Posted by Davidhoy

I agree that Morgans are strong boats, but they are not indestructible. My 462 was hit by a 100ft motor yacht 3 weeks ago, and the damage was catastrophic. Not that a cored hull would have fared any better, mind you...

A long time ago, a Tayana 55 was T-boned in the Sea of Cortez by a shrimp boat, and that wound was reminiscent of yours. Yours is worse. I am sorry the damage was "catastrophic". That sounds like "exceeds value of vessel to repair." What a sad blow! I hope it is all made right in the fullness of time.

Ann

[Davidhoy]

Originally Posted by JPA Cate

A long time ago, a Tayana 55 was T-boned in the Sea of Cortez by a shrimp boat, and that wound was reminiscent of yours. Yours is worse. I am sorry the damage was "catastrophic". That sounds like "exceeds value of vessel to repair." What a sad blow! I hope it is all made right in the fullness of time.

Ann

Thanks Ann! It’s a bit of a roller coaster ride right now, trying to deal with the other guy’s insurance company. Fortunately there’s no question of fault, as my boat was docked at the time. The damage in the photo I posted is only the most obvious “wound”, there’s much more. I hope you’re right, and that things will be made right, but right now it’s looking like we will end up with the short straw. Why does the law seem to protect the insurance companies more than us?!?

-David

[deluxe68]

Originally Posted by Dockhead

Well, you should define the terms.


Solid fiberglass OF THE SAME THICKNESS is stronger than a cored panel of the same thickness. But it will be 5x to 8x heavier. Is that "better"? Depends on the boat, I guess. For a barge that might be ok.


Solid fiberglass of the same WEIGHT as a cored panel, will be many times weaker. Is that "better"?


The most expensive boats -- Swan, Hallberg Rassy, Contest, Discovery -- all have fully cored hulls, all the way to the keel stub. A very few exceptions -- some Nauticats, some Oysters -- are fully cored down to the waterline.


Solid core hulls, with no coring at all, are common only on cheap mass produced boats, at least in the last 20 years. In the last 20 years or so, such hulls are made quite thin, for weight and cost reasons. I don't think anyway would ever say they are "better". Expensive boats have thicker, fully cored hulls which are much stronger. And much more expensive than the thin solid hulls you find on some Beneteaus and other mass produced boats.


A cheap cored hull made without protection against water intrusion is not a good thing. The owners of Groupe Beneteau are no fools -- quality cored construction involves resin encapsulation, vacuum bagging, and other techniques, and is expensive and time consuming. But quality cored construction is definitely better -- if you want the hull to be strong, rigid, and at the same time reasonably light.

Pretty sure the older Swans do not have cored hulls. The Swan broker listings show them to be solid. The newer boats are cored but not sure what year they started that.

[model 10]

Met a guy with a Corbin who ran onto a reef in Belize. He got off and didn't sink or get caught. The hole in the hull looked horrible from the outside but it was just a bulge on the inside.