Hi Andy. I am a retired structural engineer. The large deflection test you did (thin laminate over long span) causes the test specimens to deflect so much they go into membrane tension (think tension in the plane of the laminate like a suspension cable). Therefore, putting them rough side up or rough side down will make a difference (in theory, rough side down will create more friction at supports and permit a greater degree of stiffness during membrane tension and thus reduce the deflection). And as Todd Dunn commented, epoxy can take 4-5 days (my experience is 7 days) before you get the full stiffness. I think you should review the technical data and find which resin has the higher flexural modulus. The higher the modulus the greater stiffness it will add to the laminate. I did the homework for you and found 5:1 Total Boat Epoxy has a Flexural modulus of 450,000 to 460,000 psi. 2:1 Total Boat Epoxy comes in at 330,000 to 360,000 psi. Total Boat Polyester Resin is only 17,205 psi. So the Epoxy is your best choice for higher stiffness, with the 5:1 being the stiffer of the two. However when it comes to laminates, even though epoxy resin is much stiffer than polyester resin, the glass fibers provide most of the stiffness. 1708 fabric has 17 ounces of fibers running in +/- 45 degrees with 3/4 of an ounce of matt backing. Fiberglass fibers have a modulus of 10,500,000 psi. With 50% of this stiffness running one direction in 1708 fabric and 50% in the opposite direction, you still have an approximate modulus of 5,250,000 psi. Glass to Resin volume should be at about 60% to 40%. However, I find hand lay-ups are wetter and end up being about 50/50. So the glass in your laminate is going to provide 50% x 5,250,000 psi or an effective modulus of 2,610,000 psi. 5:1 epoxy will only contribute an additional 50% x 450,000 psi = 225,000 psi modulus to the laminate. 2:1 epoxy will contribute 50% x 330,000 psi = 165,000 psi additional modulus. Polyester will only contribute 50% x 17,205 psi = 8,602 psi additional modulus to the laminate. Summing up, 5:1 epoxy and 1708 at a 50/50 volume ratio will give a total modulus of 2,835,000 psi. 2:1 epoxy will be 2,775,000 psi and Polyester will be 2,618,600 psi. Therefore, in conclusion, the 5:1 epoxy laminate will be 8% stiffer than the polyester laminate; the 2:1 epoxy laminate will be 6% stiffer than the polyester. You will have to decide if this small increase in stiffness is worth the extra cost of epoxy or just use 10% more glass with your polyester lay-ups. Hope this helps.

Andy I know you probably don't get told this enough but I for one really appreciate what you do here

I wonder if you realise Andy just how useful these comparison tests are to us all? It's not only tremendously helpful to note the differences in the products, but also to watch a well-practiced and skilled hand operating a resin-spreading paintbrush. Then there are the little notes like how long a shelf life we have with vinylester. More power to you mate. Dave, Hampshire, UK.

As someone new to boats and boat work I would like to thank you for your channel. I am learning so much

Andy, just want to say thank you, I just finished the transom on my bass boat, full over haul of boat, I have watched just about everyone of your videos, my wife is hooked also, if it wasn’t for your videos I would have never been able to do it..thank you from South Carolina..

I like the testing of your various availible materials before applying them to your project. Thanks for taking us along, we all benift this way.

I would be very curious to see the same test with a two layer laminate. I think that would be much more telling.

loved this video! ty for taking the time to bring us in your questioning

Hey Andy, doesn't matter how many of your videos I watch, I still smile wide when I hear your kid do the closeout.

About to do some major projects on the boat. This has been very informative at the perfect time!

I have been manufacturing and repairing fiberglass aircraft parts and are FAA Approved. You need to check your facts, on vinyl ester, because it is a more flexible and chemical resistance than Polyester and Polyester is a stiffer resin. There are different epoxies, some are stronger depending on application and fuel resistance. Vinyl Esters have more than a 3 month shelf-life, Polyesters have a shorter shelf-life than Vinyl Esters. I been doing this for over 30 years and had some of the best, Lockheed Martin Composite Engineers I know advise me of what the best on the market. Fiberglass Cloth 7500 around a 10 Oz cloth or a 12 Oz cloth would have given a much better test and results. Also be advised on Resin Manufacturers some have much better resins and epoxies than others. I have vinyl ester that 7 months old and still has the same viscosity as when purchased; and also, you need to follow the Manufacturers Directions on Storage, the higher the heat the shorter the shelf-life of Polyester and Vinyl Ester resins are.

That was what i was looking for, thank you very much.

A break test would have also been interesting. Thanks for posting.

I recognize that theme music from Cabela's Deer Hunt for PS2, that was almost 15 years ago. I spent hours playing that game. Wish I had come across your channel before tackling my turbine blades.

wonderful job! thank you!

perhaps the best video of any kind on all of youtube

You might want to add impact testing (to assess brittleness) as well. Standard impact testers use a 1/2" diameter ball (matched to a 1/2" diameter die) and a 4 lb weight dropped from up to 40 inches to generate up to160 in-lb of deflection. I don't know a lot about fiberglass, but an exterior grade coating should take 160 in-lb of force without cracking. In your application, you'll get an indication of which system will be more forgiving when the owner drops a lunch hook on deck.

Very interesting video! Thanks!

Interesting to say the least. I'm in the midst of deciding to glass a camper build I'm doing. You're providing a lot of information as I head towards this stage of my project. Decisions - based on information gained.

I'm about to replace a deck on a 27. I've been going back and forth on deciding whether to laminate with epoxy or polyester. This info really helps!

Thanks again 💪

Nice test

Nice little test. I would suggest retesting the pieces after 4-5 days to get the epoxy to its full cure. Of course if you were being serious about this you would have weighed the strips before and after adding resin to determine the glass to resin ratios. That will have an effect on stiffness. I don't think bond strength will be an issue for adding a layer of glass to the top, but when you finally decide to put some glass on the bottom of the deck do use epoxy to get the best bond. A couple of layers on the underside of the deck crating a cored structure will give many times the additional stiffness of adding glass to the top of the deck as I am sure you know.

Good stuff. I applaud you for trying to get a handle on this. I would suggest a few enhancements: 1) Create a 2-3 layer lamination. 2) Use a longer 2 x 4 and line them all up together. 3) Add one weight to each strip, check the deflection, repeat. 4) Do a quick estimate of how much you spent on glass and resin for each strip. You obviously can't do vinyl ester again, but you could publish a cost estimate for an equivalent amount of resin used for VE vs. the others.

It looks like something else can transfer over from the Rutan/Melville "Moldless Composite Construction" process. FIberglass doesn't have any significant bending resistance by itself. Fibers are only strong in tension. In the sandwich construction world, we put a skin on top, then foam (or other core), then a skin on the bottom. As long as the edges are brought together (the core is 'closed out'), the top skin will resist upward deflection, and the bottom skin will resist downward deflection. The glass is the strength - the epoxy is only there to keep the glass fibers where they belong. One of the first couple of exercises we make when learning this construction method is to make a 'confidence layup' using foam and plain fiberglass cloth (no mat). We make a 16 inch long piece of 1/2 inch thick foam about 1.5 inches wide, then carve a bevel in the long sides to the top is about 1 inch wide. It gets 4 layers of fiberglass cloth on top, and 4 plies on the bottom - both 2 plies of unidirectional and 2 plies of bidirectional. When it's placed over the two 2x4 pieces as you did, it'll hold a 200 pound person without significant deflection. To finally break it takes jumping on it so the bottom glass fails. The TL:DR here is that if you want to stiffen the deck, you'll get much better results glassing a 1/2 inch thick 'stringer' under the deck than adding a layer of glass on top. For a copy of the handbook google MCHSAC composite construction pdf. The confidence layup is on page 3-15. Cheers...another Andy

At the sailing school I used to work at, we used polyester resin for our hull repairs. But, our boats also had fairly flexible hulls. I suspect your layering choices will make as much or more difference than the resin itself (between epoxy and polyester) as far as net hull strength. But there are other considerations as well, UV resistance, yield strength and if you want it harder to snap or harder to flex. I will have to check out what you ended up with and how it went.

Thanks man I'm working with 1984 larson delta sports 8500 and I have to do some body work and by seeing you I'm going with polyester .

Nice video, I've used all resins alot and have not experienced strenth differences between the two but nice to see a test. For small jobs at cool temps cyanoacrylate is definitely stronger but in the heat can cure before wet out

NICE TUNES

Very cool. I was wondering if the difference comes from the bonding strength, and that epoxy is superior when bonding to other materials. I think you once said, if making a whole part, you use poly or vinyl for the cost savings, but if bonding to a other part or surface, use epoxy. I'm excited to see more. Great vid.

This is not a strength test, its is an elastic modulus test. Polyester generally exhibits higher stiffness (Modulus of elasticity )but considerably lower strength (Ultimate tensile Strength UTS, as well as impact strength), particularly before post cure. Interestingly stiffer resins are usually lower impact strength. Amine adduct epoxy (the yellowy smelly one with mix ratios in the 4 or 5 -1 ratio as opposed to the 2-1 west system type chemistry) exhibit much more defined curing as well as less viscoelastic creep (sagging while still young) , in other words ready for service sooner, and the reason they are used for more production cycle applications where they need to be man-handled out of moulds promptly to make way for the next layup. Its also worth noting curing temps play a major role in the performance properties of final cure with epoxy not just on cure times, whereas polyester/vinylester resins temp has very little effect on final properties, it generally only effects cure times.

Its an interesting topic. So many people just pick epoxy because "its the best". However many times regular polyester is just fine. Most people would be absolutely shocked at the number of IRMA and MARIA boats that I have watched being repaired with just regular no name polyester resins (Trinidad makes tons of no name resins). In fact I know of one Lagoon that was repaired under the supervision of the Lagoon factory and polyester was used almost exclusively. Anyway. I enjoy the channel. If I was a betting man, I would say that adding 2 or 3 layers of glass to the Bertram will correct the issue.

How many layers of fiberglass can you do? And will adding layers of fiberglass to a existing deck strengthening it??

Neat test, I was hoping you would say the 2:1 but as you mention, wet out, cure time and cost. Looking forward to see the winner being installed and the final result. Thanks.

I think you should consider the results of the vinylester because most of us would just use it anyway if it was on their shelf at home regardless of the expiration window.

thanks

Great Video. When I worked in the boat factory we would get different formulas of Polyresin depending on the season. Do the West and TB resins come in winter and summer formula??

I think one sheet test is as important as each added sheet to a laminate. Good show. I want to see two layers at 45°. You could try 7sing a motorcycle belt tester, maybe? I looked up 5:1 fiberglass, and got meaningless stuff. Is that 5 oz fiberglass? Looked thin. But, what is 5:1? If you don't mind? Thanks Giovanni

Doesn't matter we all know that you don't like to sand and will use the poly , I can't remember when you last used 5to1 epoxy for a big project??? Love your videos watch Boat Works every week I've learned so much from You Thanks

Great test Andy, AND your camera work is great in this video. My compliments sir. Even with the air crease in the poly, it showed great ridgedness. I think it did show that the epoxy both 2:1 and 5:1 were easier evenly absobed by the fibremat then the poly, making the resin easier to work with. I got the advise that since my boat is made of polyester I should not use epoxy anywhere on the boat as it is not compatible, strength and flexibility wise. What are your thoughts on that? Cheers.

Wish you would have tested the West System! But great video! Thank you

I suggest you get in touch with This Old Tony, Keith Fenner or our favorite Canadian gearhead AvE and try to develop some sort of stress strain test.

How would you go about repairing a fiberglass corner?? boat slid of the trailer rubbed on aspalt and made a 1 inch hole, would it be good to make a mold and pour thicken epoxy?

Can you make a video on how to flow coat the inside of a boat as a finish coat? 🤙🏽 I’ve just built a 3.8m fibreglass runabout from a majority of your videos. rebuilt the transom, deck and all interior compartments. I just need to see a flow coat video to finish it off. Thanks for your videos mate

B.O.A.T = bang out another thousand....

I would suggest "while you have the test strips" clamping each test strip between a couple peaces of wood with an equal amount of strip protruding on each. That way you can stack weights until each fails and determine what would crack first under stress. Just an idea. 😎

Would you ever consider using west system epoxy? Love your show too! I'm a fan.

Great video... my dilemma is which one to use and when, or is it a matter of preference?

Thank you, ya seriously help me out! Just wanted to quickly mention I'm partly a backyard scientist (and probably an additional three parts mad scientist), and that gives me a special love for data. Now I know beggars can't be choosers but with just a few more little nuggets I could really, really sink my teeth in. A few things that would be game changers would be stuff like a fixed ruler standing on end then setting your camera up so roughly centered (bonus points if snap a mesurment from the lens to ruler), use a known weight (don't gotta be scientific, just known. Anything from a 9" Mastercraft tin snips to a fresh can of wd40 would work), and collecting what I call "ratio data" (instead of just a 2" do mesurment after 5s, 10s, and 15s). Even with just that I could roughly work out things like elasticity, plasticity, rigidity, and sorta get a feel for how it will fatigue and possibly how it will fail... wouldn't take me 2 minutes to tell you which would make the best flooring, which for the skirting, which to use on your steps rises and which for the runs, and have a fairly reasonable idea which would work best for a hypothetical hot tub too! The calculations can be tricky, but if you want I'm always game to teach (and by that I mean spare you the bs and make you a little calculator app... or rather send you the one I made to spare me the bs 😂. Lmk if you're interested). In any case, awesome video and thanks for getting me one step closer to completing this guitar! Cheers!

I guess you could do a test with different # of layers of laminate too I would be interested Not sure about everyone else

I put a little wax around the inside of the lid, never gets stuck and seals great

Hi Andy, Could I request a vid on the subject of consumables and cleanup? Brushes/applicators, stirrers, cups, masking and spray gear.. What/how do you clean, what do you bin.. etc. And with the various resins today, what do you consider to be the quickest, least messy option with the minimum of cleanup?

What do you use the John Deere loader for? Moving boats around? would love a quick run down on it!

need your advice, for a coffee table or a bench which is better to last longer or be useful Epoxy or Polyester ?

Try Orca 511. It's by far the best structural resin I've tested. 24oz woven roving (with no csm between layers) 12 layers yielded 92Ksi. 32 layers of 3.6 oz carbon fiber yielded 120ksi at 24% the mass of the roving sample. Both samples were vacuum infused with a 75% glass/carbon content and used a very controlled post cure.

Is it possible to use a wooden form and apply fiberglass to create a usable waterproof bath tub for van conversion. Looks as though many layers are necessary for firmness. Anyway just looking for light weight options.

What this experiment said to me was that you can use polyester, in a pinch, without sacrificing too much. I always considered polyester to be a generic but inferior resin to epoxy. It's just so much easier and cheaper to work with. Thanks.

I think the best way to add stiffness is to change the shape of the structure. So you can either make the whole deck thicker or glue beams underneath for support. Making it thicker with glass and resin is one way and maybe the easiest way to do this is with poly resin and glass mat. It will be thick and therefore stiff. 1x1 glass square beams glued to the ceiling would be lighter and stiffer, but a lot more work. I prefer epoxy over polyester when I want the best adhesion. I really have not seen poly fail where epoxy would have worked. I also prefer the lower odor of epoxy. More and more I'm using poly for the quick set and the low cost. Thanks for sharing your experiment!

I would like to see some tests of how strong epoxy\fiberglass over thin plywood like 1/4 or 1/8

You should maybe address the bonding issue as well. I think that comes into play more often than the strength issue.

Question Andy. A few years ago I was repairing a surfboard for a friend. I used polyester resin to fix the hole and t just would not buff out and shine like the rest of the board. When I gave it back to him he looked confused. I told him how I tried to buff it and use a polishing compound etc but it would not take the shine. He said well, usually you dont need to polish the Epoxy boards... Doh. Questions is, how do you know what material you are working with if you do not know what the original construction of the boat is.

Another informative video! Isn't 1708 a laminate by itself? Have you considered Coremat to bulk up your deck?

interesting and an effective way to get a good guesstimate with a simple test. My gut says that the stiffness has much more to do with the geometry of the laminate (as you implied) and that other factors would be much more important. Toughness and resistance to impact would be two characteristics that I would be interested in . I think that most of the stiffness would come from the thickness of the laminate (the thicker the laminate the more tensile strength can increase stiffness) and the stiffness of the core itself.

water can seep into the fiber glass mat from the edges . Makes a deference what resins you use .

hi great video, thank you. on the other hand I think you should use millimeters it's much more precise

I recently bought 5gal of vinylester resin with a 9 month warranty from the date of sale. I think the issue is the vinyl wasnt catalyzed enough. In my experience, on average vinyl ester needs to be catalyzed a little hotter than poly.

Was there any weight difference between the samples? That should be a factor as well..

Just a thought but you should of measured not only how much the piece sags down but also how much memory does it have when you remove the weight does it come all the way back straight where it started

this is like comparing a sheet of plywood, instead of the box beam that you are supposed to build with it for a structural load.

A suggestion. You might test your samples in more defined configuration, as the sample materials are in both tension and compression, and the glass is near or in what is called the "neutral axis" where the structural properties are not well defined. I would put the samples in tension or in some cases, in compression, structurally stabilized. I would suggest making a small beam with a layup on each side of a sheet of foam, for comparison purposes. See examples at channels (sevtec) or ( sevtecsev) on you tube. An included one half inch thickness sheet of foam carefully bonded to the underside of your foredeck before your layup will help in your stiffness problem. The sevtec 14 foot long boat hulls referenced are nothing but single and double fiberglass layers over each side of one-half inch, 4 lb/cubic foot foam.

So. 2:1 in my experience is formulated to have similar stress tolerances as polyester because it is designed to be used with polyester boats.

Did you use 2% hardener on Vinylester? Important or it will be sticky most of the time.

What is PVA used for? (@ 7:10) Obviously Ive never worked with polyester resin but I want to fiberglass the top of a plywood camper shell and I have epoxy but it MIGHT be easier with polyester resin.

I watched this yrs ago and im back with a thought. I have 43 year old teak hand hold on deck of sailboat. They are in good shape nothing compared to their matching holds in the boat. They are far from breaking. Im thinking of a fiberglass tape wrap then epoxy the glass and repeating say 2 times. Then a compund and sand and paint. Do you think that would protect and keep stiff over the years. Another suggestion was to just use epoxy over the teak. Your thoughts on either of these two . Thank you

How do you identify the difference between resins in an old boat? What it’s made of originally, mine is amber in color.

From your commentary, I think you know that technically strength and stiffness are different things. But, you titled your video "strength" and then only tested stiffness. I think this may mislead people that don't have a good understanding of the difference between the two. So, here are my highly simplified engineering definitions (yes, I know these definitions leave a lot out -- if you want to discuss more strict definitions, I can do that): Strength - How much force it takes to break something Stiffness - How flexible something is (this is what was tested in this video) These two are often related - compare rubber and steel. Steel is strong and stiff. Rubber is not so strong and not so stiff. I think examples like this sometimes lead people to think strength and stiffness are always related. They are not. A couple of examples: 6061-T6 aluminum has about the same yield strength as cold rolled steel. But the steel is almost 3 times stiffer. Chrome moly steel can be about twice as strong as cold rolled steel, but the two have the same stiffness. In fact, most steels have the about the same stiffness, regardless of strength.

I can see you were careful when you made the parts. But the stiffness in bending is so highly influenced by the thickness of the part that even a few thousands of an inch difference in thickness will outweigh the differences in the resin. The deflection the part decreases with the cube of the thickness. So, lets toss in a few numbers and see how much difference in thickness alone would give the results you saw. First, the numbers you gave for the 3 good parts were 2-7/8, 2-3/4, and 2-3/4. Assuming the supports are standard 2X4's, then the deflections are 5/8 (.0625), 3/4 (.75), and 3/4 inches. To go any further, I need an thickness for your test parts, so I'll guess that those parts are around 1/16 inch thick. Lets assume the part that deflected 5/8" is exactly .060 thick. Now, how thick would the 3/4" deflection parts need to be (if the resin, and everything else, were the same). Well, here's the ratio -- (x^3) / (.060^3) = .625 / .75 or rearranging x = [(.625/.75) * (.060)^3]^1/3 = .0564. Note: ^3 is cubed and ^1/3 is the cube root. So the more flexible part would be .0564" thick -- 3-1/2 thousandths of an inch thinner than the stiffer part. I suspect you will agree that the thickness of your parts was not accurate to 3-1/2 thousandths. I'm not a statistician, but my gut feeling is you need to test maybe 10 of each part to have any confidence in which is really stiffer.

When I buy glasfiber i always get filler. What is resin good for?

Andy question on laying your glass on deck are you going to smaller square pieces or one big piece also if you use 1208 biaxel glass do rotate 90* per layer for strength build up thanks JT Ps if I send u my fishing team decal would you put it on your bandsaw billboard it's about 6x6inches again Thanks JT

Many comments here are comparing flexibility with strength in a way that ignores the inflexibility of the gelcoat. The fact that no one has fallen through the deck let’s us know it is plenty strong. Andy is trying to take the deflection out that is cracking the gelcoat.

Good fun, Andy! Other comments have referred to elastic modulus and adhesion vs linear deflection properties, both of which are important components of resin performance. What's critical is what happens at the molecular level during the chain polymerization reactions. All the resins you tested (when within shelf life) tend to polymerize in linear chains, but epoxy in general exhibits more cross-linking between polymers than does polyester. Here's a cute video (with a scientist in a white coat!) showing another strength measurement. ( kzfaq.info/get/bejne/qN1jiMlnx7a0lKc.html ) As a scientist, I like this because it includes replicates and tests to failure in terms of comparable force metrics. Plus, he uses a cool measuring tool!

Hi, what is the roll of plastic sheet called

Why do you prefer PVA vs. using wax?

I have a polyester resin question. Have you used polymer planet polyester resin? Apparently, it’s a DCPD resin that requires no wax or sealants to cure. It shrinks less and can be used for laminating. I wonder if you know enough if it compares to the standard laminating resins with strength, flexibility, and overall performance. Thanks!

you were using a knydex style glass product often the chopped strand is not recommended to be used with epoxy as it has a binder on it that is designed to be dissolved with poly resin. You got better strength with the poly resin because it is the right tool for that particular kind of fiberglass. a fair test would have been 2 layers of normal weave wetted out and stuck together.

I think a better test is which one will bond to the old deck the best. West marine according to their research says epoxy he will have the more permanent bond

I want to build a square drop trailer foam boards pink ones and ( s fiberglass )do you thank the floor could be made without using any wood and be strong enough may have to sleep on ( wife kicks me out for snoring )

Hi sir I hv a question Wht do i use with the foam Polyster resin or epoxy resin ?

I kinda wonder if these strengths are linear. A 2ft piece is strong as 4ft. Or does one lose its strength comparatively over length. In any event interesting video.

Really old video, not sure if you look at comments here anymore, but maybe someone else knows. I am wondering what the weight of say a 4mm plywood strengthened with fiberglass would weigh compared to using say 12mm plywood. My bed in my campervan is built using 12mm plywood across 3 ikea skorva metal beams. But the beams are held up using 2x4 lumber. I'm thinking fiberglass must be a lot lighter than wood.. ?

No matter how many time you tried to experiment with the Epoxy or Polyester resin and you will always get different result due to different home town climate such as in Oklahoma we have vary up and down humidy compare to Florida heavy humidy so it really depends on where you live and weather according to my experience work with fiberglass. Polyester resin is cheaper than Epoxy and short shelve life compare to Epoxy has long shelve live so both resin will work on any fiberglass and yet still will make the boat float!! Smile!!!

Hi Andy, hoping you'll read and respond to this. I decided to make a swim platform for my bowrider. The total length of the platform is 80" and 24" deep. I bought a 3/4" sheet of Coosa Bluewater 20 (probably should have gone with 26) cut it in half with the intent of bonding the two pieces together for a total thickness of 1.5". I'm concerned it's not going to be stiff enough. How would you bond the two pieces together? I have a gallon of polyester resin already so I'd like to use what I already have. Should I just poly the two pieces and clamp them together or use something like cloth or mat in between? If so, which (cloth or mat) would you suggest. I plan on using something over the exterior of of the Coosa as well (mat or cloth) and finally gel coating it. The platform isn't completely rectangular with rounded corners and a slight V in the center to match the boat contour as well as a slight taper from where it will attach to the boat toward the rear. Is chopped mat my best choice for everything or should I use cloth and mat together. I can envision having two or more people standing on this from time to time so I need it to be stiff and strong. How would you go about bonding the two pieces together and then what would you do to cover both? Suggestions would be greatly appreciated. Thanks

👍

Almost thought that cap sad AvE at first glance...

you mention that strength and stiffness comes from multiple layers bonded together... how many layers though? I’m assuming a foredeck needs less layers than lets say the hull, obviously, but by how many layers? what’s a good rule of thumb for determining what parts of the boat have x number of layers???

Poly , tested and true for decades. I’m assuming because of the color you tested with Isophthalic polyester ?.

The deflection is a function of geometry and modulus of elasticity. Tensile yield or ultimate strength has no effect on deflection. Interesting test though.

Curious why you would use vinyl ester when it does have such a short shelf life. Some people rave about it of course.... As a fiberglass repair craftsman I wonder if you feel it necessary to try to use the same base of resin that the original piece or boat you are working on was made with. My glass experience has been limited to gliders (sailplanes) and only helping the licensed repair person to fix various damaged areas. Each glider manufacturer allows only their recommended resin for any repairs.

I always use resin, What I'd like to see is the same test but by Cost. like $10.00 worth of resin compared to $10.00 worth of epoxy. Around $100.00 for 5 gallons of resin to about one gallon of epoxy!

I don't think that this tells very much- and let me preface this with saying that I am just someone with passing interest in this, not an expert. First, there is a big difference between elastic modulus, and strength. One thing that is sometimes wanted in a resin is lower elastic modulus, (or more flexibility), so that the forces in the composite are transferred to the glass. What was tested here was flexibility, or elastic modulus, not strength. To test strength, you have to break the parts.