4oz. VS 6oz. ?

[beekeeper]

Wooden boat + 10yds. of 6oz. fiberglass and epoxy = ?lbs.

How much less would the same boat finished with 4oz. cloth and epoxy weigh?
I know you would loose 20oz. from the cloth, but is there a savings from maybe needing less epoxy?
Anybody know a guestimate, or range of weight for how much a yard of glass and epoxy adds?

beekeeper

 

[beekeeper]

Nobody knows? Any thoughts?

Has anybody used any other weight glass cloth besides 6oz. to build their boat?
Why? How well did it work? Is 4oz. strong enough for a strip build?

beekeeper

 

[tx river rat]

Bee
The question about the weight of 6 ounce and 4 ounce glass is hard to answer. The way you apply the epoxy and the amount of coats will effect the weight more than the glass will.
I want use anything less than 6 ounce and I double that in places of high wear.
Ron

 

[beekeeper]

Ron
I knew there might not be an absolute answer. Also figured the epoxy would be applied to each weight glass with the same care and skill, so there should be some comparison. Just wondering how much weight might be saved, because the 4oz. should take less epoxy. Stress areas may need 6oz. doubled but other areas may not need that much. Just sort of a "Whats good enough?" question, not a "This is the best way." statement. I was looking for the added benefits of glass and epoxy, but trying to reduce the extra weight it adds.
Do you think in practicle terms it takes about the same amount of epoxy to wet out 6 as it does 4?
4oz. is 2/3 of 6oz. so would it take only 2/3 as much resin?

beekeeper

 

[FlaMike]

I think Larry at Rika could most likely answer the question about the weight difference. I'd call whoever I bought my epoxy from if you ordered it from a manufacturer.

As for making a choice between the two cloth weights, I'd consider other factors as well in the decision.

What is the main purpose of the glass in the first place? Is it mainly to seal the wood? To do that and provide abrasion resistance? Or is it figured in as a main component of the structural integrity?

Also, if building from a design, what does the designer specify?

Beekeeper, I know you are more likely to be building you own design, so that last point wouldn't apply.

If the glass is there for strength, as in a true wood/glass,epoxy composite boat, I'd still ask myself "Just how strong do I need?" Maybe the 4oz is enough.

Just rambling a bit here. Not telling you anything you don't already know.

Mike S.
Spring Hill, FL

 

[makenmend]

Can't speak to the weight, but I use both, 6oz for hull, 4oz for deck & bulkheads. 4oz weave requires less epoxy to get good fill for sure.

MM

 

[tx river rat]

Bee
I think you are missing my point, I can make the weight of 6 ounce glass with the right application to weigh very close to 4 ounce with a normal application and it will be much stronger .
On a 12 ft boat from 3 to five lbs difference
The glass has nothing to do with sealing the wood , it is for strength stifness and wear
Ask Maken Mends about putting 4 ounce inside a strip built.
How much strength you need is up to the individual and how they use and maintain the boat.
Ron

 

[Kayak Jack]

Hitch hiking on Mike's statement about the glass/epoxy being a main component of structural strength, I'd consider:
1. How much strength is needed at any specific location?
2. How much strength is contributed by the wood there? Some woods will contribute more than others.
3. How much strength needs to be contributed by glass/epoxy? Some glass/epoxy layups will contribute more than others.
4. How badly do I not want to hear my boat say, "CRACK!"?

 

[beekeeper]

Bee
I think you are missing my point, I can make the weight of 6 ounce glass with the right application to weigh very close to 4 ounce with a normal application and it will be much stronger .
On a 12 ft boat from 3 to five lbs difference
...............................
Ask Maken Mends about putting 4 ounce inside a strip built.
.....................
Ron

Ron
I thought I understood and was agreeing with your post. :? I only added coments to say I was not disagreeing with your choice of 6oz. cloth. and to say the 4oz. may not be enough in all places, but enough in others. I don't think you stated anything about a differance in applying epoxy to each until now. I know 4oz. cloth overloaded with epoxy could be heavier than properly wetted out 6oz.
Could you not use the "right application" with the 4oz. and it be lighter than the 6oz.? Not as strong but maybe strong enough for use in some places.
What is the right application? I thought anything less than filling the weave would not be as strong, more coats than that would only add weight. That is what I would call a normal application. I assumed each weight cloth would be done normal. The 4oz. would require less epoxy to be filled and should weigh less.
Sorry if I did not state my questions clearlly.

mkenmends
What about putting 4oz. insde a strip build? Bad experance? For narrow panels(sides) would it work if 6oz. was used the outsides?

beekeeper

 

[tx river rat]

Bee
I was just trying to make the point that depending on how you apply it there really isnt much difference in weight.
Is three to 5 lbs on a completed boat worth the extra toughness you get? The way your pics show your usage of your boats I think you would be happy with both applications
The only thing I would add is in my experience and usage the heavier glass ( 6 ounce) will be on the inside and the lighter glass on the outside.
Ron

 

[jdupre']

I found this while poking around.



"The ideal ratio of epoxy to glass is 1 to 1. So, each ounce of cloth will require one ounce of epoxy to saturate and fill. The 4 oz cloth including epoxy will therefore weigh 8 ounces per square yard and the 6 oz cloth including epoxy will weigh 12 ounces per square yard.

The surface area of the boat, 10.5 sq. yds. with 4 oz cloth and epoxy will weigh 84 ounces or 5.25 pounds. With 6 oz cloth and epoxy it will weigh 126 ounces or 7.875 pounds.

These weights are just for the cloth and epoxy, they do not include the wood and hardware used to build the boat nor the varnish for finishing."

Glen Smith Site Admin. Bear Mountain Boats.

 

[tx river rat]

I wasnt to far off on the weight.
I really dont think there is an answer to your question Bee( "Just how strong do I need?) If there is one you are the best qualified to answer it.
Ron

 

[jdupre']

Bee, I would say if you have any doubt whatsoever on strength of a particular joint, use 6 oz. cloth. 2-3 lbs of extra weight for peace of mind is a great trade-off in my book.

No one knows the lower limit of what will be "enough" but the person willing to skirt that limit ......and occasionally going over it ( or under it, in this case ). That's an endeavor that is not for the faint of heart.

I'm curious as to any one on this forum having a boat that simply failed structurally because they used cloth that was too light.

 

[tx river rat]

On another forum I am on there is a gentleman that is into super light boats. His advice cost at least three folks to have to go back and redo a boat because they wouldnt stand up to the abuse.These were first or second time builders.
Now you take Chuck he builds super light and has no problems but he is an experienced builder and paddler.
Personally I hit a rock in some rapids flying with light cloth on the inside,blew a hole in the side of my boat. after that went to 6 ounce ,I have hit hard enough to fracture the outside of the hull but never had it penetrate thru like I did with 4 ounce.
Ron

 

[Kayak Jack]

Hitch hiking on both Ron & Joey, I would reserve light cloth for the sides of a boat, and use heavier cloth on the bottom. I use boats fairly roughly, and have never feared a hull failure. Seemed to me that zealous use of a sqeegee was more influential than cloth thickness.

 

[seedtick]

optimum resin content is typically about 33%

Less than that and you're not supporting the fibers, more than that and you're depending more on resin strength, which is less than glass

So a lighter cloth will require less resin to achieve maximum performance (strength). But maximum performance of a lighter weight system is less than a heavier weight system .

You always end up with the same question, "How strong is strong enough?"

 

[beekeeper]

1st. question was about weight differances. That has evovled into one about strength. How strong is 4oz. compared to 6oz. and is it strong enough for a strip build.
Anybody like to look at this and simplify?
http://www.guillemot-kayaks.com/Buildin ... index.html

beekeeper

 

[oldsparkey]

I used 3 oz ( tight weave ) one one strip build and it is still together. Naturally the whole boat was covered in glass.
I also used 2 oz on a stitch and glue boat and it worked really well.

I also found that the heaver the glass the more epoxy it required to get the job done. I used 10 oz glass on the bottom of one boat and thought I would never get the weave filled with epoxy. Never , ever , again.

Chuck.

 

[seedtick]

"1st. question was about weight differences" - A 4 oz cloth filled with 35% resin will weigh about 2/3 of what a 6 oz cloth filled with 35% resin


"Anybody like to look at this and simplify?" - If you're looking at a comparison of 4 and 6 oz , then you need to only look at sample a and sample d. Note that he did not use cloth but unidirectional fibers laid at 90 degree orientation. His final conclusion is that the strength to weight ratio is pretty much the same. Not surprising, if you use enough 4 oz composite to equal the weight of a 6 oz composite, then the strength should be similar.


"and is it strong enough for a strip build." Back to the original question of how strong is strong enough. I don't think that paper tries to answer that question so much as to show the increased strength you get by adding a high performance fiber (like aerofab or Kevlar) to the composite.

 

[Kayak Jack]

How strong is strong enough? Just about 1 or 2ounces stronger than needed. Use is situational, obviously. Rocks are one of the major ingredients that ramp up any definition of "situational". And, not all rocks are created equal.

One of the most important questions about force applied to a structure, like a boat hull, is PSI, pounds per square inch. 144 pounds of force applied across a square foot of wood produces 1 psi. It would shove a boat around, but probably wouldn't deflect the wood much nor penetrate it. However, that same 144 pounds applied to only 1 square inch yields 144 psi. Applied to 1/2 square inch yields 288 psi. That would deflect wood moch more, and could well penetrate and break it?

Sharp rocks will produce much higher psi than would a gently rounded, smooth rock. Igneous rocks would likely be the sharpest, metamorphic rocks too, and sedimentary rocks likely to be least sharp edged. (Generalization)

Mud, sand, and sediment will actually cushion a boat pretty well, and not offer much stress to strain a hull.

All this being said, a builder has to figure where and how he will use the boat (situation), and what is most important - weight/cost or strength. Then, proceed with his own best interests in mind.