Thread: Attn MIK and PAR: Lightweight 'glass vs. heavier glass

It's simple. I have to suggest you go with Mik's advice ... because PAR's in the US where he can't get at me whereas Mik lives locally where he can get at me anytime he likes

Richard

Go with the light weight cloth. Remember that one of GIS's outstanding features is it's light - it's easy to handle on shore and it handles well on the water. Putting heavy cloth on just adds weight - not only do you lose the advantages of light weight, you make the vessel more likely to damage itself. All you are doing with the cloth on GIS is making the bottom less likely to be punctured - if you hit something so hard that the difference in puncture resistance between 2 and 6 oz cloth is telling, you have mishandled the boat dramatically and the extra weight will probably mean that something else will break in that bump. You don't need the cloth for structural reasons - the wooden structure will handle all the normal forces of handling and sailing.

Rick,

For abrasion resistance anything less than 4oz cloth will give far less protection.Better you go with 6-8oz.For a boat that is not going to be raced the small weight difference will not matter.

Even if you were building to race,2oz cloth is probably too light.I'ts used mainly by model builders,whereas 4oz & occasionaly 6oz is used by surfboard manufacturers (I've got one next door) for strength,as well as boat builders looking for bottom protection against normal bumps & scrapes.Bigger boats may benefit from heavier cloths or different fabrics like like "Dynel".

I've just finished the 3rd of 3 hollow wooden surfboards & covered these with 4oz cloth for abrasion resistance....it's very lightweight.

If you are still worried about the weight of 6-8oz cloth,just do the bottom only & paint the sides.

You say you are only going to cruise & camp with your Goat Boat so I don't see a small increase in weight will ever be noticeable....about the same as a few extra stubbies of your favourite amber lunatic soup! It has a powerful rig & anyway,the extra weight,little that it would be,is down low giving extra stability.

imho.

Al.

The weight difference between a 2 ounce fabric, resin filled and a 6 ounce fabric, resin filled on a GIS, will be about a single pound in total weight. If a single pound is this much of a concern, then you probably shouldn't use a sheathing and go "really" light weight.

4 ounce fabric and less is what I use, when I want to see the wood and have at least something between it and whatever it rubs against, without the fabric being visible. Neither offers very much abrasion protection, but they are better then nothing. 6 ounce is just barely visible, but acceptable to many folks, as a clear covering that offers some abrasion protection. Once you get into 8 ounce or heavier fabrics, there's no disguising it and the weave is plainly seen, except in a dark room. The amount of abrasion resistance is considerably higher with these heavier fabrics.

On the other hand, if you intend good abrasion protection and will be painting the surface, regular 'glass cloth isn't the best choice. Polyester (Dynel, etc.) or one of the modified acrylics (Xynole, etc.) are far and away better. The polyesters are 3 times better then the same weight 'glass fabrics and Xynole is 6 times better. These materials will not finish clear, use a lot more resin (2 to 3 times as much for the same weight 'glass), tend to float if you apply too much resin and are generally more difficult for the novice to handle. This said, they also conform to curves, corners and odd shapes much better then 'glass cloth. It's this feature, plus is high abrasion resistance that makes these fabrics a common choice for deck sheathings or work boat hulls, where abuse will be the norm, not the exception.

Polyester fabrics cost about the same as a good quality S 'glass. Xynole is costly, but nothing like Kevlar or carbon, which require you to sacrifice small children and family pets.

In the end, you need to decide how you'll use the boat, based on several factors. Be honest with yourself about how you'll care for the boat, if it'll be dragged over rocks, up onto beaches, etc. If you're like most, you initially take fine care of the boat, but within a few years it'll start losing it's luster and care will drop off. This is normal. A light sheathing will require you be easier on her, then with a heavy sheathing. The best way to make this decision is to look at your current boat or the last one you owned. Was it clean, dry, freshly waxed, buffed and under cover? Where repairs to dings, nicks and scratches made promptly or do you have to rebuild the carb each spring, because you left last season's gas in it and it fouled everything up. If still having difficulty with this decision, ask your wife or best friend how you take care of things. If they're anything like my friends or my other half (the one that must be obeyed), then you'll get a prompt, unabashed and concise answer. If it was me asking, probably followed by a swat in the back of the head and the weird sound of demented lauphter.

Thanks for your replies. It's good to hear the pros and cons of each position. I thought the weight difference between 2 and 6 oz. glass would be greater than that, but it just shows what I don't know. I plan on doing the bottom panel only, not the entire outer hull. Outside will be painted, with only the interior left bright.

Howdy,

The Jarcat uses 4mm ply with 2oz glass. And it is much bigger than the Goat.

I agree that a knowledgeable builder adds very little weight when they glass a boat, but have noticed very substantial weight gains on amateur built boats.

Stitch and glue canoes seem to be going up and up and up in both the amount of glassing and the amount of weight as an example.

I would suggest the lighter glass if it is available.

If it does the job ... why not!

MIK

Go with the 6-8oz mate,for peace of mind....better to err (which you would not be doing) on the safe side....your bottom's not going to get any thicker from wear & tear!...(nothing personal intended).

Al.

Thanks guys for your thoughts. One last question: How much weight might I expect to gain with a 2 oz, 4 oz, and a 6 oz. bottom covering only on a GIS? Bear in mind that I am a rank amateur

Rick

The real weight here is the resin - you need enough to "wet out" the glass fibre cloth.

ISTR that the figures for this (using WEST System epoxy at the recommended coverage) is set out in the Gougeon Bros book

It takes approximately the same amount of resin as the cloth weight to get it applied. This assumes it's well applied. The novice usually has a lot more resin then they need involved, so double your figures. In other words if you need 3 yards of fabric and it's 4 ounce stuff you'll need about this much resin to apply it. 6 ounces would be reasonable and 8 quite wasteful, per yard. Total layup (3 yards), 12 ounces of fabric and 12 to 24 ounces of goo. As you can see we're not talking about a lot of weight, even if you slather it on with a wire brush (not recommended).

Thanks PAR and JMK. Yes, I was aware of the resin being the heavier of the components. It sounds like, realistically I could expect 5-7 lbs total for glassing with 4 oz.. That isn't much, and in real terms the difference between handling a 130 lb. boat on shore and one 140 lbs. wouldn't really be noticeable, at least for me.

I'll fluctuate that much depending on the how recently I've visited the bathroom.

I come to boats from model aeroplanes and I suppose that I just rebel at putting any weight on that is just a passenger (except if it is a human passenger!). I find it hard enough to build light as it is and to just add weight to 'protect' against bumps which should be avoided seems unnecessary. But then I take the same view of cars - I prefer to see a light, well designed car that drives well to a monster with steel panels that would suit a tank.

Sure it is only 10lbs (or 4.7kgs) but that is about 7% of the total weight for something that you don't need - as Mik said

I would suggest the lighter glass if it is available.

A lot of builders put nothing on the bottom.

If you knew what sort of bumps & scratches you were going to get you could choose your cloth accordingly.

Only you will know what weight of cloth will give you peace of mind.

There's probably no correct answer.

Al.