I don't have that particular book, but if you need...

Posted By: Kristen, Sanderling, TX-LA-OR
Date: 6/27/08 10:24a.m.

Report: outside forum guidelines

In Response To: The boat building thing really has my attention (Carl, Horizon Cat/Picnic Cat, Central Texas)

an explanation of some term or another, I'm sure we can explain. There are a few different moduli (obviously modulus in plural) running around when discussing the strength of materials... A few off the top of my head... Modulus of Elasticity (also known as Young's Modulus). Frequently represented by the letter "E". It's the ratio of stress to strain. You can find tables of E for various materials all over the internet. This is prior to a material being stressed past it's elastic point and into deformation. Modulus of Resilience and Modulus of Toughness, rigidity, rupture, volume expansion, aren't really mentioned anymore as terms, so I doubt it was that. Section Modulus. Consider a beam, like a piece of wood, maybe a 2 x 4. Consider it sitting on top of two blocks, spread out some distance, and in between those two blocks, you've hung your lunch hook off the beam. The lunch hook as well as the weight of the beam induce a bending moment. Will your beam break? The appropriate equation is S = M/Z, where S = stress (allowable stress, which is usually the actual allowable stress divided by some safety factor), M is the bending moment caused by your anchor, and Z is the section modulus, which is a special property based off of the shape of your wee beam. (It's usually in inches^3 or some similar unit that's been metricized.) For a beam of rectangular cross section, Z = (b*(h^2))/6, b = base, and h = height. So now you know why it's better to have the beam sit tall instead of sitting flat to oppose the anchor, as opposed to flat. Even if your common sense didn't tell you. I used to look at people who built their own boats (like Russell) with awe. Now I've buit a few chined ones with him. I still look at him with awe, but I realized that it's not that hard to do yourself (hard to do perfectly and with the craftsmanship that perhaps CJ does, but that's why you'd hire someone if aesthetic perfection really mattered). Graham and Carla (if I recall her name correctly) are extremely helpful, even when I've called up not even asking for assistance with one of their designs. Using epoxy is much MUCH easier and more foolproof than polys, isos, and vinyls. Try to watch the humidity and heat requirements, be uber prepared every time you start hotwork, have a second person to help you, and you'll be fine. We've found that I'm far less likely to get ill from the epoxy as well. Graham can get you a good deal on his epoxy; Russ is a big fan of MAS, which is the only kind I've ever used. We're building the Cascades out of epoxy from here on out, because we believe it has much better qualities from a working standpoint, as well as being better suited to the marine environment. Work in small quantities till you get the hang of it. I betcha CJ could give you a weekend tutorial if you asked nice. It would be a fantastic experience to share with your son. Give it a whirl. Do it soon though--the price of a barrel of epoxy, delivered, just about doubled in the last few months.