Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 03-11-2015, 06:12   #76
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,752
Re: Most boats have liners; which ones do it best?

[QUOTE=Azul;1952727]
Quote:
Originally Posted by Dockhead View Post
Well, the sources you quote do not say that uncored hulls are stronger. And they could not since it is not true. Ask an engineer.

From Fiberglassics (if you had googled Fiberglassics and core)

Stiffness vs. Strength

As you can see, adding a core between two fiberglass skins is a great benefit to stiffness. But stiffness and strength aren't the same thing. Confusing the two can be disastrous at sea.
In the previous example, 1” of core material was sandwiched between two ¼” fiberglass skins, resulting in stiffness 37 times greater than just ½” of fiberglass alone. But how much was the strength improved? The answer may shock you.
The increase in strength was hardly even noticeable. The overall increase was limited to the strength of ½” fiberglass plus the strength of the core material itself. It still takes a roughly equivalent amount of force to break through solid fiberglass as it does to break through cored fiberglass, the difference is that solid fiberglass is going to deflect, (bend), long before it fractures.
Now here's where it gets tricky.
When you hang a 250 lb outboard from your transom, any flexing will amplify the amount of force caused by motor.
Let me use another example here. If you get on your bathroom scale it may say you weigh 175 lbs. But if you hop up and down on the balls of your feet while standing on the scale, you'll see the needle jump all over the place. You may only weigh 175 lbs, but on the downward motion, the needle might register 300 lbs. In this analogy, you are the outboard and the scale is the transom. When you're hopping up and down, that's the amount of force amplified by the deflection.
So, while a cored transom may not increase the overall strength, it does mute the amount of deflection and thus, the amplified force put on the transom. The result is a transom that isn't stronger, but instead, a transom that, because of its stiffness, lessens the force against it.

Apology accepted.
Care to provide some engineering calculations behind that? This is a mere anecdote, not engineering, and it is completely false.

If you compare a cored structure with two 1/2" pieces of GRP with a 1" piece of core between them, to a solid 1" piece of the same type of GRP, that structure will be 7 times stiffer and 3.5 times stronger, and that is if you are using foam or some core without much strength of its own. If you use balsa, the difference will be still greater, because balsa is quite strong in its own right.
__________________

__________________
"Parce que je suis heureux en mer, et peut-être pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 03-11-2015, 06:40   #77
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,752
Re: Most boats have liners; which ones do it best?

Here's another source for you, which explains WHY cored structures are stronger:


"Sandwich structures consist of 1) a pair of thin stiff strong skins (faces, facings or covers); 2) a thick lightweight core to separate the skins and carry loads from one skin to the other; and 3) an adhesive attachment which is capable of transmitting shear and axial loads to and from the core (Fig 1.1).

"The separation of the skins by the core increases the moment of inertia of the panel with little increase in weight producing an efficient structure for resisting bending and buckling loads. Table 1.1 shows illustratively the flexural stiffness and strength advantage of sandwich panels compared to solid panels using typical beam theory with typical values for skin and core density. By splitting a solid laminate down the middle and separating the two halves with a core material, the result is a sandwich panel. The new panel weighs little more than the laminate but its flexural stiffness and strength is much greater. By doubling the thickness of the core material, the difference is even more striking. Thus sandwich panels are popular in high performance applications where weight must be kept to a minimum, for example aeronautical structures, high speed marine craft, and racing cars. In the most weight-critical applications, composite materials are used for the skins; cheaper alternatives such as aluminium alloy steel or plywood are also commonly used. Materials used for cores include polymers, aluminium, wood and composites. To minimise weight, these are used in the form of foams, honeycombs or with a corrugated construction (Fig 1.2).


Click image for larger version

Name:	Capture.PNG
Views:	78
Size:	31.4 KB
ID:	112150

"
Design of Sandwich Structures, Achilles Petras, Cambridge University


https://www.repository.cam.ac.uk/bit...78E?sequence=1




The reason why cored structures are stronger (and not just stiffer), is geometry -- they act like a BEAM. The calculations in the tables provided (which are widely used by engineers) are made using beam theory. In reality, a cored structure can be stronger or less strong than beam theory indicates, depending on the properties of the core, particularly shear strength, and quality of the bonding between the core and the skins. As I mentioned in a previous post -- balsa cored structures may be MUCH stronger than beam theory predicts because of the high strength of the core in its own right. Provided of course that the bond strength to the skins is up to the (not easy) task.
__________________

__________________
"Parce que je suis heureux en mer, et peut-être pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 03-11-2015, 06:43   #78
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by Azul View Post
You keep saying liners aren't structural, but almost by definition they are structural. Nautical architects bond liners and furniture and bulkheads to the inside of a hull to increase its strength, not just to hide stuff like wallpaper or to provide a cheap floorpan to a boat. It is not an airplane.
No, what I am saying is there are "liners" that exist primarily to make the interior, example a head / shower or galley etc. can be completely built outside of the boat, then lowered in and glassed in to the hull prior to the deck being joined to the hull. Now they may add structure, but the hull doesn't rely on this structure, the hull is strong / stiff enough without this liner, and since that is the case, you can have different shaped and sizes of liners that compose different components for different models of the boat with the same hull.

Then there are girds or a matrix whichever you prefer, which has one function, to increase strength and or stiffness of the hull, the hull is not stiff enough without this matrix, it's required, seems you see these around the keel for obvious reasons.

The difference is a bond failure of one is a nuisance, needs to be fixed, but the hull won't fail because of a dis-bond.
A dis-bond of the other since it is primary structure, could lead to hull failure.
__________________
a64pilot is offline   Reply With Quote
Old 03-11-2015, 06:45   #79
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

Since nobody is actually addressing the initial question (I guess there are fewer bazillionaires on here than I thought that can actually afford a new sailboat that is full of high tech wizardry,) here are some players that are playing with resin infusion which does require a big investment and enough common sense to do a liner well:

From Reinforced Plastics:

Other builders of fast cruising yachts, both sail and power, have sought similar benefits by adopting vacuum resin infusion. Germany’s Hanse Yachts, which has a reputation for employing efficient modern production methods, infuses the sandwich glass/epoxy skinned Corecell foam cored sandwich structure of its 630e fast sail cruiser, for example. Significantly, Hanse now owns Dehler Yachts and the Dehler 41 is similarly infused, though the resin used in this case is vinyl ester.

Infused foam cored sandwich is also the basis for X-Yachts’ Xp 38 sailboat (the ‘p’ signifies performance) in which the resin is epoxy, although an earlier infused model, the Xp 33 has vinyl ester as the resin. The roll call of infused performance cruisers also includes the latest C72CS sailboat from Dutch builder Contest Yachts, the Solaris One-60 from e-Yachts, the J-111 from J-Boats and the Tartan 4700 from Tartan Yachts in the USA (the last-named also has carbon composite mast and boom). Croatia-based AD Yachts offers infusion as an option for its ‘performance optimised’ Salona 38. Oyster Yachts, known for its quality sail craft, made a foray into the infusion of superyachts at its RMK subsidiary in Turkey where three vessels up to 125 ft long were built before recession struck.

When I get my inheritance I will opt for an Oyster, solid decks too. I have an aversion to rotten core.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 06:46   #80
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Most boats have liners; which ones do it best?

Stronger is not a good descriptive term, it sort of like saying pretty.
How about us saying resists bending, crushing or shearing or puncture, whichever your talking about as opposed to stronger.
__________________
a64pilot is offline   Reply With Quote
Old 03-11-2015, 06:48   #81
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

[QUOTE=a64pilot;1952761]No, what I am saying is there are "liners" that exist primarily to make the interior, example a head / shower or galley etc. can be completely built outside of the boat, then lowered in and glassed in to the hull prior to the deck being joined to the hull. Now they may add structure, but the hull doesn't rely on this structure, the hull is strong / stiff enough without this liner, and since that is the case, you can have different shaped and sizes of liners that compose different components for different models of the boat with the same hull.

This is not the case. A hull needs bulkheads and furniture and liners to meet its designed strength. You obviously have little exposure to boats. Anyone that has done a tiny amount of work around them knows that a fiberglass hull can even be deformed by a jack stand if it is not placed under a bulkhead, stringer or the keel.

An airframe is usually designed to stand alone to meet its designed strength not taking into account the interior, such as seats and headliners as these are often replaced during the course of its use.

Sheesh, you guys need to read more. I'm just an average guy and don't have the time to keep correcting all of this stuff. It's like trying to drink from a firehose.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 06:52   #82
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by a64pilot View Post
Stronger is not a good descriptive term, it sort of like saying pretty.
How about us saying resists bending, crushing or shearing or puncture, whichever your talking about as opposed to stronger.
Now you are getting it, a little- I am not the one imprecisely using the word stronger. Cored hulls have more resistance to shear, compression and are stiffer. They do not have more resistance to puncture.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 06:53   #83
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Most boats have liners; which ones do it best?

Bulkheads yes, but not all dividers are bulkheads and not all liners are structural, or furniture inside of a boat is either, some of it can safely be removed.

On edit, none of the grids can be safely removed
__________________
a64pilot is offline   Reply With Quote
Old 03-11-2015, 07:02   #84
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by Azul View Post
They do not have more resistance to puncture.

I sound argumentative but I'm not, but they can have as much or higher resistance to puncture, their exterior skin can be just as thick or a better layup than a "solid" hull. I've seen solid hulls built with chop guns that weren't really that stiff or resistant to puncture, just heavy.
From a pure "strength" perspective a core beats a monolithic layup.
I don't know squat about race boats, but I'd bet there aren't any solid hulled America's Cup boats?

But cores scare me, I fear water intrusion, how many wet decks are there, and they aren't under water. When I was boat shopping I looked for a solid hull and a deck if cored, the core was impervious to water intrusion. So I dislike cores from a financial perspective I guess, but admit that is the way to light weight and stiff.
__________________
a64pilot is offline   Reply With Quote
Old 03-11-2015, 07:06   #85
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by a64pilot View Post
Bulkheads yes, but not all dividers are bulkheads and not all liners are structural, or furniture inside of a boat is either, some of it can safely be removed.

On edit, none of the grids can be safely removed
You are quoted as saying there are two types of liners, one structural and one not. Now you are modifying your position as your understanding changes which is the point of this thread drift I suppose. Even the bookshelves in most boats are structural.

You are right in that things like cushions and tea pots are not structural.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 07:08   #86
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by a64pilot View Post
I sound argumentative but I'm not, but they can have as much or higher resistance to puncture, their exterior skin can be just as thick or a better layup than a "solid" hull. I've seen solid hulls built with chop guns that weren't really that stiff or resistant to puncture, just heavy.
From a pure "strength" perspective a core beats a monolithic layup.
I don't know squat about race boats, but I'd bet there aren't any solid hulled America's Cup boats?

But cores scare me, I fear water intrusion, how many wet decks are there, and they aren't under water. When I was boat shopping I looked for a solid hull and a deck if cored, the core was impervious to water intrusion. So I dislike cores from a financial perspective I guess, but admit that is the way to light weight and stiff.
The point is, if you would read the citations, that a core does not add any strength to the hull (for example for puncture) other than the strength of the core itself, it is additive and not a multiplier such as it is for shear and stiffness.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 07:17   #87
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

[QUOTE=a64pilot;1952772]I sound argumentative but I'm not, but they can have as much or higher resistance to puncture, their exterior skin can be just as thick or a better layup than a "solid" hull. I've seen solid hulls built with chop guns that weren't really that stiff or resistant to puncture, just heavy.
From a pure "strength" perspective a core beats a monolithic layup.
I don't know squat about race boats, but I'd bet there aren't any solid hulled America's Cup boats?

You might want to review the demise of the Hugo Boss VOR boat. It was a victim of fancy new high tech boatbuilding.

Race boats are designed without regard to practicality with immense amounts of money spent to decrease weight but retain strength. They fail and crack and sink a lot as the envelope is stretched.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 07:22   #88
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Most boats have liners; which ones do it best?

Cores function as the I in an I beam, the I is considered to add no structure at all, zero.
It has one function, to separate the two webs and to keep them separate, and that does make an I beam much more resistant to bending than two flat bars laid on top of each other.
__________________
a64pilot is offline   Reply With Quote
Old 03-11-2015, 07:31   #89
Marine Service Provider
 
Azul's Avatar

Join Date: Jun 2012
Location: Beaufort, NC
Boat: 1968 Cal 34, 1984 Catalina 22, 1987 Sanibel 18, 1968 Tanzer 16, 1989 BW Outrage 19, BW SS 15
Posts: 525
Images: 2
Re: Most boats have liners; which ones do it best?

Quote:
Originally Posted by a64pilot View Post
Cores function as the I in an I beam, the I is considered to add no structure at all, zero.
It has one function, to separate the two webs and to keep them separate, and that does make an I beam much more resistant to bending than two flat bars laid on top of each other.
Ironically, I beams are used as an example in at least two of the three citations I offered. Again, an I beam is designed to be stiff. A core is used to be stiff and light. To get the same amount of stiffness as a cored hull, it would take a lot more thickness of fiberglass. Take for example a coachroof, where coring is common in order for it to be stiffer ie not like a trampoline when you walk on it. Weight for weight, the cored roof won't resist a sledgehammer more than the uncored solid roof. Also note that coachroofs are above the waterline and also weight placed higher in a sailboat is a bad thing so coring a coachroof often makes sense. Until a knucklehead starts drilling hundreds of holes into the core without proper technique allowing water infiltration, which is then hidden from view until it is extensive by a liner. Fortunately for most cored hull boat owners, poking holes in a boat with tools below the waterline is intuitively dangerous.
__________________
Azul is offline   Reply With Quote
Old 03-11-2015, 07:32   #90
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,752
Re: Most boats have liners; which ones do it best?

[QUOTE=Azul;1952758]
Quote:
Originally Posted by Dockhead View Post

Duh. You don't get it. Stiffer is different than stronger. Now you are arguing with Minaret as well.

.
If you will read the tables and articles I posted, or any serious engineering source, or talk to any engineer, you will see that cored structures are both stiffer AND stronger. I posted separate figures for both stiffness AND strength.

If you choose to form opinions about engineering questions (like strength) on the basis of anecdotes from non-engineers, and to ignore actual calculations, that's your business, of course.
__________________

__________________
"Parce que je suis heureux en mer, et peut-être pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What Boats Have the Most Headroom? adell50 Monohull Sailboats 23 11-02-2015 12:01
What was the most important or most interesting ... Rakuflames General Sailing Forum 25 24-09-2012 20:52
Eliminating Boats with Liners - Advice avb3 Monohull Sailboats 57 11-02-2012 13:55
Windvanes: Which Ones and Where !? bdurham Auxiliary Equipment & Dinghy 8 25-04-2011 07:21
What Do You Miss the Most? What Do You Like the Most? sww914 Liveaboard's Forum 21 22-12-2009 10:43



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 06:09.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.