epoxy and glass over wood

[smokinone8]

fiberglass boats are not very thick yet are very seaworthy . i'm a journeyman carpenter and have just started building the woods design flica . i have built other designs in the past . i've always used glass over ply . as per the plans .

i would like to know why i have to use glass in the mix .

the ply is very strong on its own . then saturated with epoxy . 4 or 5 coats outside and 2 or 3 in side . this in my opinion is very strong . much stronger than just glass .

except for resistance to minor scratches what does the glass do ?

can i get away with not using glass in the mix ? or below the water lines?

sorry , just think it's a bit of a waste .

using marine ply and west system

thanks ahead of time

[apex1]

i would like to know why i have to use glass in the mix .


Welcome on board.

The glass´s main function is to provide abrasion and impact resistance due to it´s hardness compared to saturated ply.
Thats it....basically
Do not omit applying it! It is a proven addition.
And you might be interested to read this thread too:
http://www.boatdesign.net/forums/classification/fiberglass-over-cold-molded-26270.html

Regards
Richard

[rasorinc]

Glass assures waterproofing and stops wood from checking. Doug Fir marine ply is known to check which paint cannot stop and epoxy only cannot stop.
You do not need heavy cloth so 6-8 oz. is fine. You have gone to a lot of work and I would not leave out this final step. Think of screws working loose allowing water entry. Stan PS regular glass offers almost zero abrasion resistance products like Dynel do and it is good to put an 8" tape over glass along the stem and keel for that. Xynole is even better than dynel.

[PAR]

I'm reasonable to assume you meant to say 6 to 8 OUNCE fabric is fine. Personally I've never seen 6 pound cloth before, but I suppose you could order some if you really wanted it.

Douglas fir can check, even under thin layers of cloth, so given a choice between no sheathing and a light weight cloth, go with the cloth. If you can avoid Douglas fir, do so. Finishing Douglas fir can test you skills and persistence.

Regular cloth DOES offer considerable abrasion resistance compare to just painted wood, though there are other fabrics that are better, such as Dynel and Xynole. If the boat is small, light weight and will receive good care, I wouldn't use either of these "fancy" fabrics on it. They can add a good bit of weight. On the other hand if the boat will be beached, dragged up shore lines and other rough handling, then consider one of these other materials instead of regular cloth sheathing.

A light weight sheathing DOES NOT offer much by way of penetration or puncture resistance. You need a fairly thick laminate or high tech fabric to get appreciable puncture resistance gains.

[ThomD]

Since you do not state you are using Fir, it is always possible you are using a marine grade plywood of some other species. Some of these do rather well with paint alone. Over the years, though, I have noticed that my boats were lower maintenance the more parts I sheathed. I used to only sheath the outsides, then outside and the floor, then the outside and the insides, and finally the whole boat including wrapping the shears. The more I wrapped the less problems I had. About the only thing I wouldn't sheath these days would be dispossable boats. Like if you drift down a river where hauling the boat out is not worth the cost, or some kind of prototype.

Some people claim that just coating with epoxy is worse than just coating with paint, because the paint, say latex, is easily repaired, and doesn't trap moisture. A boat with a heavy epoxy coat will have some breaks that let water in, but will make it difficult for the water to migrate out. No personal experience on that though.

[rasorinc]

YES PAR, I changed lbs. to oz. Please forgive my advancing C.R.S. Also I am very upset about the 3 missing boaters and just made a post on that.
I received my pilots licence in 4/4/60 and it seems this loss is just pilot error.
and maybe some macho thrown in. What a waste. Stan

[smokinone8]

the plans call for 6oz. and 3oz . now i'm not talking painted wood . i'm talking about several layers of epoxy on the outside of both hulls . this would be a good layup . the glass would not be the thing that makes it waterproof . it would be the epoxy covering that seals . i only see the glass as added weight and money .

if i'm wrong . i will certainly cover with glass . i just can't in my mind descide .

have read and viewed , even known a few who didn't use glass and their boats have been fine .

we want to cruise blue water with this boat . but this day and age money matters .

will it provide that much more protection

[rasorinc]

Go with what the plans call for. There are reasons it is specified. I mentioned 2. best to you, Stan

[PAR]

Epoxy alone is a fine waterproofer, but it's fragile without reinforcement. Fillers are reinforcement, some much stiffer and stronger then others of course. Fabrics also are reinforcements, again some with differing physical properties added to the epoxy.

Even a thick epoxy coating is very vulnerable to impact, abrasion and flexing. Adding fabrics can dramatically improve the physical properties of the coating.

On epoxy coated surfaces, it just makes good sense to use a fabric to reinforce the matrix.

[apex1]

Although I did not describe the characteristics of the resin and fabrics, nor the values for abrasion and impact resistance (its all not as easy as it looks to be), I think, as a conclusion, we are at my first statement again.
Apply the glass / Epoxy as your design postulates! Especially with cruising in mind. It is NOT just adding weight and cost!

Thanks PAR for brightening my very broad statement.

Regards
Richard

[smokinone8]

i want to thank you all for answering my question . i have alot more investigating to do on the subject . when it comes to the wood i'm very knowledgeable . just not that informed on fiberglass and its properties .

i have covered the other boats i've built with glass because the plans call for it . without thinking .

this time i'm asking alot of questions that i'm unsure of the answers . hoping to get clear answers that make sense . it's still aways away from being complete . so , i'm going to have more questions for everybody here .


remeber that life begins where land ends ...

[PAR]

Most designers of plywood boats are asking for 'glass sheathings. Plywood quality has dropped substantially in recent years so it's a good bet. On small, simple boats, the costs and effort of a sheathing can add up to be a large portion of the build. On boats over say 12', there's usually enough investment to warrant the additional effort and expense of a sheathing.

[Fanie]

remeber that life begins where land ends ...
Damn ! I saw this and got a sudden urge to go floating...

[apex1]

Most designers of plywood boats are asking for 'glass sheathings. Plywood quality has dropped substantially in recent years so it's a good bet. On small, simple boats, the costs and effort of a sheathing can add up to be a large portion of the build. On boats over say 12', there's usually enough investment to warrant the additional effort and expense of a sheathing.

And let me add please (you do´nt mind Paul), even if you use highest quality of hardwood, as I do, it is a substantial addition to the skins strength. Look at my Gallery, you´ll notice the material used.
And do´nt hesitate to ask the audience... all of us are learning here! I have the impression that the more experienced learn even more than the laymen.

Regards
Richard
and I like your last statement

[smokinone8]

it's tattooed across my back . with a picture of my boat . sorry i don't know how to put it next to my name or up load to conversation

[teakcell]

I slice teak veneer and other species + manufacture epoxy cold molded products for a few years. When it comes to making a hull, I would never imagine saving on glass cloth but I would rather save on buying a cheaper epoxy (eg: good quality unknown brand one but not west system), and cheaper wood specie...again, this is if I had no other option as dropping down the costs...

[smokinone8]

that's sounds like a better idea . i will look into that aption .

thanks


life begins where land ends

[apex1]

that's sounds like a better idea . i will look into that aption . thanks


Do so, teakcell knows, what he talks about, they do´nt have too many choices in Myanmar.

[ancient kayaker]

Glass is said to increase the cantilever strength of ply by 2x or 3x, and the designer will have taken that into account when specifying the ply thickness.

It may be OK to leave off the glass if you use thicker ply, but as Paul says it's probably false economy except in very small boats. However, I don't think it should be used for sealing, the boat should be watertight to start with.

I admit I didn't use it myself, but only because my boat is light enough that I can carefully carry it and put it into the water, and it is not fast so it doesn't hit rocks hard.

Remember that epoxy deteriorates in sunlight and must be protected by UV resistant paint or varnish.