# Why use Mat?



## MooreMiller (Sep 10, 2016)

I believe it usually is sandwiched between two layers of cloth or woven roven to provide a solid bond between the two when using a polyester resin.
Mat is also used to lessen print through of cloth or woven roven into gelcoat in a female mold.

I believe a laminate made up of mat is generally weaker and heavier than a laminate made entirely of cloth. 

Some boats are made up entirely of mat, like most Gheenoes. 

I believe that is correct as I'm still learning, so please correct me if I'm wrong!


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## firecat1981 (Nov 27, 2007)

You got most of it right.

Matt is used mostly with ester resins to prevent pattern bleed through from the various woven or stitched cloths. Polyester resin shrinks about 3% when curing and that is why the pattern can show through. Epoxy only shrinks about 0.5% so it's not a huge issue. Matt can help binding between fabrics because it takes up the spaces left in between, but only really beneficial in between heavy weight cloths. Many boats are built with it, but it's not nearly as strong as other types of glass. It's used a lot as a way to build up bulk, remember heavier weight in some boats means a better ride. I may have left some stuff out.


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## YnR (Feb 16, 2015)

You can apply it quickly with a single person so for those cheaper builds that only use mat, you can significantly cut down, not only on material costs, but labor as well.


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## firecat1981 (Nov 27, 2007)

Why would you need more then one person to wet out any other glass? I've always felt Matt was harder to work with. Plus don't forget Matt uses more resin then cloth so the cost savings might be debatable. If you were talking about chopper guns then I'd probably agree with you.


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## predacious (Sep 1, 2016)

firecat1981 said:


> You got most of it right.
> 
> Matt is used mostly with ester resins to prevent pattern bleed through from the various woven or stitched cloths. Polyester resin shrinks about 3% when curing and that is why the pattern can show through. Epoxy only shrinks about 0.5% so it's not a huge issue. Matt can help binding between fabrics because it takes up the spaces left in between, but only really beneficial in between heavy weight cloths. Many boats are built with it, but it's not nearly as strong as other types of glass. It's used a lot as a way to build up bulk, remember heavier weight in some boats means a better ride. I may have left some stuff out.



close enough...however,matt can not be used with epoxy...



firecat1981 said:


> Why would you need more then one person to wet out any other glass? I've always felt Matt was harder to work with. Plus don't forget Matt uses more resin then cloth so the cost savings might be debatable. If you were talking about chopper guns then I'd probably agree with you.


when "skin coating" a hull - a real build,build a hull in a mold,it's quite helpful when there's 2 people laying it up


matt use WAY LESS resin than cloth - think you may have got that backwards...


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## firecat1981 (Nov 27, 2007)

Um no Sir, you are quite wrong. Matt has a 70:30 resin to glass ratio, cloth uses a 50:50. So given equal weights Matt uses a lot more resin. Here's a chart in case you don't believe me

http://fgci.com/pdf/common material thicknesses and weights.pdf

It's always helpful having an extra set of hands on any build, but just cause it's not popped from a mould dosent mean it's not a real build. Cloth is easier to lay out and because it retains it's pattern it's easier to get your target thickness and wet out.

Also many types of Matt are now designed to be used with epoxy, you are thinking old school.


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## D. C. Ward (Oct 26, 2015)

Why does cloth show through more than mat? I would figure it'd be the other way around since mat is a lot more coarse


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## firecat1981 (Nov 27, 2007)

I guess in simple terms as I understand it you can think of it like camo. You go out to the woods, do you hide behind a stack of branches or a blind made of cement blocks? Your eyes easily pick up straight lines, 90 degree angles, and repeating patterns. So even though you can get some bleed through even with Matt if your gelcoat isn't done right, your eyes may never really see it, but they would recognize a woven pattern quickly.


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## predacious (Sep 1, 2016)

most mfg's use a chopped strand matt,for "skin coating" a hull
mostly using 1.5oz and 2oz - chopped strand isn't compatable with epoxies....

normally,when a product is built,the resin is the same throughout the entire process

with the exception of core matt,chopped strand matt will use far less resin than laying up 1708


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## Sublime (Oct 9, 2015)

I wouldn't say it doesn't add strength and you wouldn't have to use 1.50 oz. , .75 oz is readily available. You guys don't think cloth is heavy? With chopped strand most guys can easily get 60% resin 40% glass.

I don't see why you couldn't use a nexus veil to hide pattern, but nexus adds no strength.


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## YnR (Feb 16, 2015)

firecat1981 said:


> Why would you need more then one person to wet out any other glass? I've always felt Matt was harder to work with. Plus don't forget Matt uses more resin then cloth so the cost savings might be debatable. If you were talking about chopper guns then I'd probably agree with you.



One guy on a chopper gun vs multiple laying cloth. Faster and cheaper. Obviously not necessarily better but if you want to pump out cheap hulls, quickly, it would be the preferred method.


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## Sublime (Oct 9, 2015)

Some confusion going on here.

1.50 oz is cloth. Some builders use a chopper gun without roving (the part that gets chopped by razors in the gun) to spray and catalyze the resin at the same time. A skilled guy can do that without getting too much resin. 

Kevin with ECC at one time would build you a totally hand laid hull if you wanted it. Infusion is great but it doesn't cut the labor in half I don't think. There is a lot of work in cutting and placing the cores and mats in place up front.


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## predacious (Sep 1, 2016)

Sublime said:


> Some confusion going on here.
> 
> 1.50 oz is cloth. Some builders use a chopper gun without roving (the part that gets chopped by razors in the gun) to spray and catalyze the resin at the same time. A skilled guy can do that without getting too much resin.
> 
> Kevin with ECC at one time would build you a totally hand laid hull if you wanted it. Infusion is great but it doesn't cut the labor in half I don't think. There is a lot of work in cutting and placing the cores and mats in place up front.





there's many different cloths and matts - there's no confusion on my part....


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## WhiteDog70810 (May 6, 2008)

Chopped strand is cheap and fast. Let's not worry about chopper guns any more.

My initially query was more targeted towards why guy working on a build in his garage would use mat, specifically something like 1708. If you are covering a core of some type, why is the 17 oz fabric so commonly used is conjunction with 8 oz mat if the mat adds weight but not strength? Does the mat provide cushion to allow the stiff fabric to smoothly span high points along edges?

Nate


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## predacious (Sep 1, 2016)

WhiteDog70810 said:


> Chopped strand is cheap and fast. Let's not worry about chopper guns any more.
> 
> My initially query was more targeted towards why guy working on a build in his garage would use mat, specifically something like 1708. If you are covering a core of some type, why is the 17 oz fabric so commonly used is conjunction with 8 oz mat if the mat adds weight but not strength? Does the mat provide cushion to allow the stiff fabric to smoothly span high points along edges?
> 
> Nate



1708 adds stiffness / strength

laying a layer of chop strand over it - it "smooths" it out - avoids shards and looks "pro"

using a chop strand before matt,it allows the heavy matt to conform better to the surface - example:
if there's a heavy radius/bend - this avoids "voids"


"build" - I get confused over the term "build"

"build",to me means "build" as in lay up a hull and build it
anything else,that's "modifying"
I read that term a lot -"I built my boat" - then I see someone who added a forward casting deck ?? car people use that term too - "i built my car" - then I see that person put wheels and tires along with shocks on the vehicle...

it's a little confusing

"garage build" - I expect to see someone laying up a hull,or building a stitch and glue boat.often times,what I see is a guy restoring an old hull and adding a few things to it,along with replacing decks/transom


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## weldandglass (Sep 29, 2009)

Chapter1:

Important note: If you don't like seeing and interpreting words (i.e., reading for comprehension) just skip to "*Bottom line*" and the end of Chapter 3.


Let’s start from the beginning just so we can set straight some of the basic facts.


Mat or Chopped-strand mat (CSM) is a type of fiberglass fabric consisting of short, randomly oriented fibers held together by a binder. CSM that is “Powder Bound” is compatible with epoxy but “emulsion bound” mat is not. The emulsion bound mat requires the presence of styrene (only present in ester resin systems and not epoxy) to property dissolve the binder and as such, emulsion bound mat will not wet out properly with epoxy resin. Mat/CSM does, in fact, utilize more resin than any other fabric type per capita. Mat is typically sold in ¾ oz, 1 oz and 1.5 weights. This refers to ounces per square foot and this oz/sq ft designation is different from the way most other fiberglass fabrics are classified, as explained below. Mat has the lowest mechanical properties of any fiberglass fabric type but is a component of most polyester/vinylester layups, for interlaminar bonding purposes. Mat typically requires around 2 oz of resin per 1 oz of glass regardless of lamination skill, which equates to a roughly 33% glass/66% resin ratio. This is a general, widely accepted rule of thumb and of course varies somewhat based on laminator skill, proper wet out, type of resin etc. Exact percentages could be argued but what is not very arguable is that mat requires more resin for proper wet-out than other woven or directional fabrics, given equal fabric weight.


While we’re on fiberglass fabric types, let’s clear up some more confusion.


Woven roving is a heavy fiberglass fabric consisting of relatively loosely but continuous bundled fiberglass strands woven together in a 0/90 orientation. Woven Roving (WR) is most commonly available in 18 oz or 24 oz weights and this refers to ounces per square yard, unlike the mat-weight designation. As such, a square yard of 18 oz WR weighs approximately 18 oz while a square yard of 1.5 oz mat weighs 13.5 ounces (9 sq ft/yd * 1.5 oz/ yd). Most production hulls these days are built with polysester resin and alternating layers of CSM and WR. WR has much higher mechanical properties than CSM but is still on the low end of the fiberglass fabric strength/stiffness to weight ratio spectrum.


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## weldandglass (Sep 29, 2009)

Chapter 2:

Cloth is a finely woven fiberglass fabric with fine, continuous bundles of tightly packed fiberglass woven together. It looks like, well, a finely woven cloth. The fiberglass bundles are woven in a 0/90 orientation. It has much higher mechanical properties than both WR and CSM. Cloth, however, is typically only available in weights ranging from 4 oz to 10 oz per square yard and is very seldom used in production hulls because it takes many, many layers of cloth to build sufficient thickness or bulk due to the fabric being relatively very thin. As such, cloth is typically only used by home builders as a finish layer or for light-sheathing of wood built hulls where the wood provides the stiffness and strength and the cloth is only present as a water proof, abrasion resistant barrier.


Uni-directional, Bi-axial, Triaxial, etc. fabrics are the highest modulus E-glass fabrics available. They consist of one or more layers of very tightly packed continuous fiberglass bundles, all running in one direction. These continuous glass fiber bundles are stitched together rather than woven and as such the fiberglass bundles are not bent or kinked, which results in much greater mechanical properties than other e-glass fabric types. The bending that occurs when weaving WR and cloth actually reduces the mechanical properties of the fiberglass fabric and in the case of WR, the bundles are not as tightly packed and are much coarser, which also reduces mechanical properties. There are many types of fiber orientations for these fabrics including 0/90, 45/45 and 0/90/45. Commonly available biaxial fabric weights range from 9oz/sq yd to 24 oz/sq yd.


Many people use “cloth” to describe biaxials and other directional fabrics but this isn’t correct.


Stich-mat style fabrics have also become popular and there are many types of this kind of fabric 1708 is a 17 oz layer of biaxial e-glass with a .75oz CSM layer stitched to it. 1208 is a 12 oz biaxial with a .75oz layer of matt stitched to it. This gets confusing for most because the directional component of the fabric is oz/sq yd while the CSM component is .75 ounces/sq ft rounded to an “08”. Geez...... These types of fabrics allow for builders to layup three layers at once with the CSM in tow for increased interlaminar bonding. 

So why use mat?


Prior to the advent of epoxy resins, polyester and vinyl ester resins were the only resin systems available to boat builders. Vinyl esters offered significantly improved mechanical properties relative to polyester resins, but neither polyester nor vinyl ester resins are gap filling. As such, it was and still is common practice to put a layer of mat (chopped-strand mat, CSM) between laminate layers to ensure a good interlaminar bond. CSM retains more resin than any other kind of fiberglass fabric. As such, it provides a more absorbent, squishy and resin-rich layer between layers of fiberglass (cloth, woven roving, biaxial or something else). However, you pay for this better interlaminar bond with increased weight and not much increase in mechanical properties. As stated before, any CSM/mat layer will require approximately 2 oz of resin per 1 oz of glass, if utilizing hand lamination. When hand laminating WR, good builders can achieve something like 60%/40% resin to glass ration and 50%/50% resin/glass is achievable for cloth and directional fabrics (unidirectional, biaxial, etc.). Again, these are relatively widely accepted rule of thumb rations that you can research using a simple google search and reading from reputable sources.



Epoxy has somewhat changed the game for hand laminating because it is gap filling. It is possible to laminate with no mat utilizing only WR, cloth or directional fabric layers utilizing polyster or vinylester resins but it is not common practice as the laminations require much more attention to detail to ensure good interlaminar bonding and even then the interlaminar bond or “peel strength” within the laminate often suffers. With epoxy however, use of mat is not necessary and very good, all directional fabric layups are achieved utilizing epoxy resins. These types of laminates offer the highest mechanical properties for e-glass hand layups and are typically only utilized with core laminates where the core is used to increase the stiffness of the panel and skin thickness of the laminate can be significantly reduced due to significantly higher mechanical properties of the laminate. However, the collective history and knowledge of production boat manufacturing has revolved around the use of ester resin systems. While epoxy resins have become relatively common place in aerospace industries, they are still not utilized as frequently in the marine industries due to lack of knowledge within the available pool of laminator employees, differing cure cycles, cost and lack of compatibility with other polyester and vinyl ester resin systems (gel coats, etc.) which have been the industry standard for decades.


So… interlaminar bonding is one reason for using mat when using ester based resin systems. Another is skin-coating the mold, as mentioned in a previous post. Most builders will lay one or two layers of CSM behind the gelcoat in a mold to prevent print-through of successive fabric layers due to the exotherm/shrinkage that occurs during ester-based resin curing.


Back to fabric styles and weights. Stating that mat uses less resin than cloth or directional fabrics is certainly not correct, but we have to compare apples to apples. A square yard of 1.5 oz mat, once properly saturated, will contain approximately 13.5 oz of fiberglass and 27 oz of resin for a total weight of 40.5 oz. I’ve never seen a 13.5 oz directional fabric but 12 oz 0/90 or 45/45 biaxial is common and one square yard of this fabric once properly saturated will contain approximately 12 oz of fiberglass and 12 oz of resin for a total weight of 24 oz. As such, the biaxial fabric will weigh much less and provide greater stiffness/strength than the mat/CSM layup.


Lastly, mat is relatively cheap. Mat allows builders to achieve bulk quickly and cheaply. Cloth and directional fabrics (biaxials being the most common) are much costlier. WR is somewhere in between. Stiffness is a function of thickness. A boat of a given size must have a given hull thickness to be sufficiently stiff, and this is a basic engineering principle. You could build an all biaxial fabric and epoxy hull out of solid fiberglass that would last a lifetime but the laminate would be significantly more robust than necessary and unnecessarily costly. Most laminate structures built entirely of fiberglass rely on the cheap bulk that mat provides to achieve sufficient thickness without significantly increasing cost. This is where cores come in. By adding light weight, foam cores such corecell or divinycell, builders can achieve necessary thickness/stiffness of hull and frame panels with a modest price increase. These cored structures, particularly when combined with high modulus fabrics and resin systems (vinylester or epoxy resins and directional fabrics) offer the highest mechanical properties and lowest weights for e-glass laminates. This was the spirit or the driving concept behind some of the of the initial poling skiffs and this is why I became interested in cutting edge composites technologies.


As more manufacturers of boats and particuarly skiffs come into being the diversity of options will increase. You can buy a hull built with minimal material and build-process compromises and pay an absolute premium or you can buy a hull utilizing less modern techniques and materials and pay significantly less. There will always be a place for both extremes and everything in between in the market but I do wish there was a way for average consumer to really understand what they were buying and properly evaluate the trade- offs between fit/finish, cost, weight and longevity of the hull. Probably no way to make this happen but a girl can dream....


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## weldandglass (Sep 29, 2009)

Chapter 3:

I haven’t addressed more exotic fabrics like Kevlar, carbon and S-glass but feel like I should briefly. For purposes of this discussion it is hopefully sufficient to say that these fabrics are very high modulus materials and really only have a place in cored composite structures utilizing very quality hand lay ups, resin infusion or prepreg and mat should be used minimally or not at all in these types of layups. However, the mere presence of these high modulus fabrics doesn’t mean the build is quality or “high tech”. In fact, carbon and Kevlar are the most misused materials in boat building and are often only used for marketing purposes (i.e., the method of use of the materials doesn’t improve stiffness or reduce weight; it only makes the buyer feel like they’re getting something special). I also haven’t addressed the use vacuum bagging or vacuum infusion, although I’ve seen lots of misinformation on this board on this subject as well. Even if vacuum bagging or resin infusion are utilized the above still applies. CFM (continuous filament mat, an infusion compatible mat) is utilized frequently in infusion but again, the infused mat layer is resin rich and doesn’t provide much stiffness relative to the added weight. The highest modulus bagged or infused laminates will be comprised entirely or mostly of directional fabrics with minimal CFM. When bagging or resin infusing the interlaminar bonding problem that mat solves in conventional hand layups doesn’t occur because the laminate layers are so tightly packed together. As such, any CFM present in an infused laminate is only there to facilitate resin flow or provide bulk. 


*Bottom line*: mat sux but it's in almost every single fiberglass boat hull in existence because you probably can't afford the hull that has no mat.


Hopefully this clears up some things for anyone interested. 

I’ll probably regret posting this as I regret virtually all of the few posts I make.


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## yobata (Jul 14, 2015)

This is probably my favorite thread of the entire board. Thanks to all contributors!


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## DuckNut (Apr 3, 2009)

WhiteDog70810 said:


> Chopped strand is cheap and fast. Let's not worry about chopper guns any more.
> 
> My initially query was more targeted towards why guy working on a build in his garage would use mat, specifically something like 1708. If you are covering a core of some type, why is the 17 oz fabric so commonly used is conjunction with 8 oz mat if the mat adds weight but not strength? Does the mat provide cushion to allow the stiff fabric to smoothly span high points along edges?
> 
> Nate


The 08 in the 1708 is NOT 8oz, it is .8oz. The reason it is there is because without it it would just be 17oz cloth. The mat is used to enhance bond between two layers of cloth in the layup schedule.

No, the mat does not smooth out the high points, but it would aid in that with enough mat as the resin would eventually fill the valleys. 

A simple layup would be gelcoat, mat, cloth, mat, cloth. The mat/cloth could be one piece or seperate and achieve the same objective.


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## firecat1981 (Nov 27, 2007)

Weld, you have way more motivation and patience then I do to sit and type all that out. I agree with every thing you said, and I'm sure we all appreciate the posts. But why do you regret posting here?


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## weldandglass (Sep 29, 2009)

I'm a shy lurker and it's inherently against my personality to post on public forums. It's a painful process for me. I don't necessarily regret posting but I always feel like I will.


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## firecat1981 (Nov 27, 2007)

Well your post was informative, well read, and not at all displayed in a demeaning or arrogant way as far as I saw, so I thank you for that.

A little disappointed you didn't address the mechanical comparisons between foam core and wood...I'm just kidding. I'm a wood fan ;-)


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## WhiteDog70810 (May 6, 2008)

weldandglass said:


> I'm a shy lurker and it's inherently against my personality to post on public forums. It's a painful process for me. I don't necessarily regret posting but I always feel like I will.


Don't worry. The rest of us make fools of ourselves so frequently that you'll blend in with the wallpaper. Additionally, your posts are long enough to scare off the trolls.

Nate


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## c_ronius (Mar 16, 2010)

Weldandglass, From one lurker to another... thanks for making these posts. I found it informative and appreciate you (and others) sharing in detail. Not too much else I find interesting around here nowadays, so please blab away.


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## tomahawk (Mar 9, 2012)

Good stuff here. Informative and enjoyable reading.


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## CurtisWright (May 9, 2012)

Multiple reasons
1. It is impossible to air roll a thicker weave fabric, like woven roving without it. You end up with millions of air bubbles and a poor bond.
2. Fabrics are used for tensile loads. resin and matt is the only valuable componet for compressive loads. Adding a woven fabric to a compressive member is a waste of money. Compressive loads = The outer skins of the hull and the top of the cap/ decks. Tensile loads = the bottom of decks/cap and the inner most skin on the hull. (this is my beef with HB, they put the kevlar on the wrong side of the core so you are paying for 0% benefit. I equate it to having gold teeth. Worthless for the application, but tons of people still pay for it)
3. When glassing in bulkheads, transoms and such, woven fabric sandwiched between torn pieces of matt provides the best bond. the under matt allows for the air bubbles to be easily rolled out and the top piece hides the woven fabric and makes for a cleaner look. It also gives some meat for grinding/ fairing the tab into the hull for an even cleaner look.


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## predacious (Sep 1, 2016)

this ^^^^^


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## weldandglass (Sep 29, 2009)

As noted by Curtis, when a load is imparted on a foam-laminate panel, the panel deforms or attempts to deform in a "C" shape and the laminate skin on the load-side is put in compression and the laminate skin on the opposite side is put in tension. In tension, the fibers of the laminate skin are pulled apart and in compression the fibers of the laminate skin are pushed together.

There's no question that aramid fibers have very high tensile strength and relatively low compressive strength and as such, in order to gain the full benefit of kevlar, it should be placed as far away from the anticipated load (on the side opposite the load). Dave Gerr and many other engineers/naval architects suggest that S-glass outer skins and kevlar inner skins in a foam sandwich panel will offer some of the the highest stiffness to weight ratios available (see attached stress/strain graph for aramid (kevlar) fibers put into tension and compression, pulled from "Structural Composite Materials) and this has some real implications in the microskiff world.

However, high modulus fabrics are not useless in a deck layup or another scenario where the skin is most frequently put in compression and CSM/mat does not provide similar structural properties as high modulus fabrics. If you fall while fishing and the full weight of your knee lands on a cap panel, your knee would impart a compressive load on the outer laminate surface . High modulus fabrics do offer better compressive strengths and these fabrics would provide better localized impact resistance and stiffness (withstand more load before the individual fibers within the laminate buckled or failed) than matt/CSM (see attached table of properties for common csm and woven fabrics, also pulled from "Structural Composite Materials").

This type of compressive load is contrasted with puncture or piercing. If you drop something sharp onto the cap or your boat (such as needle nose pliers falling tip down) the force of the of the impact is highly localized. In this scenario, the stiffness and strength of the panel is relatively useless and laminate thickness is pretty much the only factor that applies (I tried to find a technical reference for this as I've seen it many times and will edit later if I find it). In this scenario, the compressive strength of the exterior laminate matters very little and the thicker laminate will resist puncture while the thinner laminate will not (i.e., a thicker, low modulus laminate will mostly likely perform better than a low modulus thin laminate in this scenario). Puncture resistance is the real downside of small, foam-composite boats. In boats over 25-30 ft or so in length, the hull and other structural panels of the boat have to have a certain core and laminate skin thickness to provide a threshhold level of stiffness/strength and by default, these laminate skins are thick enough to provide sufficient puncture resistance. However, once you move into the realm of "microskiffs" the "scantlings" (core and laminate skin thickness for individual hull panel members that provide sufficient stiffness/strength) are such that you can build a boat with very thin laminate skins that are sufficiently stiff and strong but do not offer the proper threshold level of puncture resistance. As I think I mentioned in my previous post, this is where CSM can be added to provide "bulk" (i.e., thickness) for increased puncture resistance without adding significant cost.

Lastly, although this is moving into the theoretical and would have to be confirmed by someone with a higher pay-grade than myself, I can imagine how wave-slamming loads would put the exterior laminate of a cap or other structural member into tension rather than compression. If the cap is structural (i.e., a stiffening member of the hull structure) then having a "balanced laminate" (high modulus fabrics both on the exterior and interior skins) would benefit the overall hull "performance" and longevity. If you read much marine engineering text the concept of the "balanced laminate" is very common.


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