Sam, can you elaborate on the vinylester vs epoxy details that you mentioned? I am not an engineer but have read and worked with... I would say more than the average sailor regarding composites and materials science.
Beside cost, I have never really heard of any benefit of vinylester resin over epoxy resin in virtually any application. My understanding has always been that epoxy resins have greater adhesive properties, greater strength and stiffness properties, greater fatigue resistance over time due to the nature of the cure (vinylester cure seeing ~5-10% 'shrinkage'), greater resistance to water incursion, greater chemical and UV stability, etc. Of course, this all in addition to epoxy being easier to work with, having a longer shelf life, less volatility, less harmful to human life, etc.
Not trying to pick a fight over technical details insomuch as trying to learn more about a subject that maybe I didn't have as good of a grasp on as I thought I did.
Madman,
I come from an aerospace background where we use epoxy almost exclusively for many of the reasons you mention. For home builders and DIY composites guys, or frankly for most boat yards, I wouldn't use anything else but epoxy because of the shelf life concerns and nastiness in using vinylester. For many years I was also led to believe that vinylesters have lower strength and stiffness properties than epoxies and that is why we are using epoxy in the aerospace world. I went and checked this out and the data doesn't really support this:
Interplastic Vinylester: Flexural Strength 128 Mpa, Tensile Strength 75 Mpa, Elongation at Break 7.9%
Norester 680TPA Vinylester (at least one major F18 builder is using this): Flexural Strength 149.6 Mpa, Tensile Strength 87.5 Mpa, Elongation at break 4.2%
Pro Set 125/229 (AFTER post cure at 140 deg F for 8 hours): Flexural Strength 134 Mpa, Tensile Strength 72 Mpa, Elongation at break 4.7%
MGS 285/287 (the only aviation certified room temperature cure resin system): Flexural Strength 115 Mpa, Tensile Strength 75 Mpa, Elongation at break 5-6.5%
I also have test data comparing Vinylester with Epoxy in composite coupons, including fatigue (driven by elongation at break to a great extent) and the report concluded that you can use either as long as they are properly mixed and cured. One should also keep in mind that epoxy molecules form the backbone of most vinylesters.
The bottom line is reach the same conclusion as this gentleman:
http://www.multihulldesigns.com/pdf...%20are%20Preferable%20to%20Polyester.htm"In conclusion, both epoxy and vinylester are much preferred to polyester. Structurally, epoxy and vinylester are close in properties. Epoxy however is much easier to work with, and is much more forgiving."So, in a production environment with controlled temperature and controlled mixing of vinylester, plus you are using it at a pace that is well under the shelf life, their is no reason a vinylester part should be any different than an epoxy part.
I didn't go looking at vinylester vs. epoxy in terms of shrinkage during cure or moisture resistance, but I believe both are relatively similar with the nod going to epoxy. The biggest area that epoxy wins in is secondary bonding, with some epoxies having shear strengths exceeding 4000 psi and Vinylester more like 500-1000 psi. So it is now class legal to use epoxy to do the hull seam which is a good thing, though there may have been a loophole in the rule allowing this for a long time and exactly how that seam is done in my experience is going to make a much larger difference to the stiffness of the boat than what glue the actual panels are made from (well, as long as polyester isn't the backbone of said panels). The other driving factor in stiffness is how well the beams fit the sockets and how stiff the beams are. A bonded beam F18 would be a nice improvement over the bolted connections but it isn't enough of an improvement to warrant a change in the class rules or make it vastly more expensive to ship the boats to cool regattas like St. Barths.
