*THE HULL TRUTH is the world's largest FREE network for the discussion of Boating & Fishing. Whether you're researching a new boat, or are a seasoned Captain, you'll find The Hull Truth Boating & Fishing Message Forum contains a wealth of information from Boaters and Sportfishermen around the world.
Questions for OReely on Lamination,Materials and Strength
Notices
Welcome to the updated THT!
If you are having trouble signing in, please email feedback@thehulltruth.com with your username and we will help you. We thank you for your patience as we help you access the new site!
What have we answered in the real world of production 20ft to 40 ft boats?
As far as using premade stringer grids dont you have to have an ample ammount of sales to justify production runs of premade stringers? Isnt a custom built stringer glassed to the hull as one unit the strongest? Are you concerned with weight bringing carbon fiber into the equation? If you want to use carbon fiber then the use of any other resin then epoxy is a weak link and wasting carbon tensile strength? If you are bonding premade carbon stringers to a hull with methacrylite isnt this a weak link in using carbon? As far as the people that posted that they feel stupid reading this thread? Dont !!! The modern world would not be here today if we waited for so called engineers to tell us its safe to cross the atlantic ocean in a boat or airplane? No pioneers are the people that move the world forward and engineers tell us why we cant do that? Dont feel stupid by the use of a lot of $10 dollar words.
I’ve been out of the office for a couple of days and a lot of good info has been presented.
I think that having a 1/2" bond line between the hull and stringers wouldn’t adversely affect the performance of the grid. Since any loads high enough to cause a failure would likely be via impact, there probably wouldn’t be time for the bond line to deflect a great deal if using a low elongation adhesive. Also, the adhesive in the bond line is basically acting as a drag strut and transfers force from the hull into the stringers so, even if it does deflect, it is still transmitting force into the stringers. I would be more concerned about long term performance of the bond if it was subject to static loading. Maybe if the boat sat misaligned on a trailer for an extended period of time in a way that there was a static shear applied to the joint.
The problem with using different materials to resist a force is more of an issue when the two materials are acting in tandem. To expand on Darbi’s plywood example, sometimes we use both wood (OSB) and gyp (Sheetrock) shearwalls to resist lateral loads in a building. Gyp is weak and brittle when compared to OSB and typically exhibits very little yielding before failure. If you have both materials resisting load in a particular direction, the gyp panels can load up to failure long before the OSB panels. When the gyp fails, all of the load it was resisting is instantly transferred to the wood panel, which is then overloaded, and fails. By using the two materials, the capacity you actually achieve is much less than the sum of the parts. This can be the case with steel and concrete, steel and masonry, wood and CF, CF and E-glass, and many others.
With production boatbuilding (of which I have no experience) I would think that the additional analysis and increased material cost would outweigh any benefit you would see in using the higher strength materials. The way I see it, the biggest problem posed at this point is where to find the money to stay in business. If stringer and joint failures were causing boats to fall apart, then you would see companies looking into innovative ways to fix the problem. Like OReely pointed out, most have a system that uses materials that are strong enough for the application and a process that lends itself to economical production so it’s not worth going out on a limb with something radically new, even if it may lead to a better product down the road.
OReely, I looked at the website referenced in your sig and it looks like you’re primarily into retro work. Do you use MMA adhesives in doing repairs? It’s my understanding that they are less sensitive to surface contamination than epoxies, but I’ve not their use in other than production settings. Also, are MMA adhesives cross linked?
It’s true that engineers are typically a pretty conservative bunch.
Anyone can design and build a boat, airplane, balloon, etc then hop in and try to cross the Gulf, Atlantic, or go around the world. If they succeed, they’re a genius, if they fail, they were just a fool with a crazy idea. Either way the risk is usually confined to the individual or party involved.
An engineer will look at a problem and be able to state that if you apply this solution, the part won’t fail, no one will become stranded, no one will die, etc. In commercial engineering (R&D is a whole different ball of wax), failures rarely occur because, in today’s litigation happy world, the personal, professional, and financial repercussions of failure are severe.
I’m thankful for the pioneers that are willing to stick their neck out in order to prove that something will work. They are the innovators that have improved our lives in so many ways. But if I’m designing a boat, building, bridge, or plane for the use of some family I’ll never know, be sure that the design will be based on proven and reliable methods and that I’m willing to bet everything I’ll ever have that it’ll be safe.
All other things being equal, using CF instead of e-glass may or may not result in increased performance.
If the main loading in a particular application is shear or tension, the CF reinforced piece will likely be stronger, lighter, or both. If the piece is in compression, you may not gain anything and the reduced area of reinforcement may actually make the section weaker. Once the load in the system reaches the point of failure of the weakest link in the chain, it will fail.
Often the option of CF is chosen so that the part can use less of a stronger reinforcement in order to achieve the same strength with lighter weight. This benefit typically comes at an increase in cost that may only be justified in a high performance setting. Regardless of which component becomes the weak link in the system, it’s fine as long as each component has enough strength to prevent a failure. It’s possible to get the weight savings from using CF in the stringers, have the bond to the hull be the weak link, but still come out ahead because the bond is still strong and rigid enough to perform.
What got your hackles up? Did an engineer kick sand in your face at the beach when you were a kid? It's just a friendly conversation. I believe the discussion was more of a theoretical exercise with some real world experience thrown in for balance. Most of the questions you raised were covered in the posts prior to yours. I'm pretty sure there isn't a modern boat that didn't have an engineer involved at some point. I can just about guaranty there has never been a plane that crossed the Atlantic that wasn't engineered. And I believe the guys who were saying they felt dumb were saying it a little tongue-in-cheek.
Trey,
I'm involved in two businesses in the marine industry. A repair/custom job shop and a semi custom, low volume boat mfg. I don't see much call for MMA in the repair shop. Along the lines of what Bly pointed out about amortization of molds, one-off construction doesn't seem to lend itself to adhesive bonding very often, at least economically. It's easier to build a net shape and tab it in place than build additional flanges for bonding surfaces. One negative thing Plexus does that I found out the hard way, it inhibits the proper cure of gelcoat. We put some parts together and let it cure for a couple of days. After fairing, we tried to spray gel over the surface to cover the bond line and it wouldn't cure.
In the boat mfg business we use a limited amount of Plexus in a couple of high stress areas. We are currently evaluating some retooling to take better advantage of the material.
As far as the Plexus being less sensitive to contaminates, part of the sales pitch is labor savings by cutting out surface prep due to it's aggressive nature.. It is supposed to offset the high cost of the material. I've looked at the literature and done some down and dirty shop testing and I can report that they're not lying. Plexus will bond through chemical mold release as well as paste wax mold release. It will bond aged DCPD resin based laminates and pretty much everything else we tried. I don't know the answer to the cross linking question.
I have enjoyed this conversation thoroughly. As I stated earlier, I'm not an engineer however, I have built numorous production boats...I use these conversations to continue the learning process.
Besides the obvious stringer & bulkhead bonding, I've used Plexus to bond & seal livewells...if you've ever attempted to tie a livewell in with fiberglass tape into a euro transome, its quite difficult. We actually modified our livewell tools to provide a better flange for this process change, Plexus works well bonding aluminum backing plates too. Another point about MMA...you would be surprised by the gelcoat companies who are beginning to blend MMA into their gel as a way to become MACT compliant. We have run multiple tests with this gel against our mold release & it's been interesting (in a good way) to say the least.
What a great thread. I would love to see more of this type of discussion by the experts in the various areas--engineering, laminate production, and adhesive technology, as well as "yacht design". Perhaps even a series of tutorial discussions.
My my limited experience in boat building/sailing; often mast or spar failure is due to a rigging failure. The carbon fiber mast has to be kept in a very close column--as noted in previous posting. As soon as it is out of column--even in light air, down the rig comes. The older keel stepped aluminum spars, were somewhat self supporting--and they just bent, and often recovered. I had a racing boat in partnership--my partner stressed a mast to the point where the 5/16" rigging had stretched about 4"--well beyond its yield strength of about 11,000 lbs (as tested). Yet there was no damage to the aluminum mast despite a delfection of about 12"--a carbon fiber spar would have broken with a similar deflection of only a few inches.
I also find it interesting the use of MMA/Plexus adhesives in boat building, for grid adhesion.
In the pipefitting and commercial plumbing trade of which I have recently retired
Along with developing and building my own 1/4million dollar sport fish boats{I sucessfully built 12 boats before returning to what put the most bread$ on my table} in the late 80s. I have overseen work crews in nuclear powerplant piping. refinery piping and large casinos and power houses. I have had buildings fall down around me that made national news and piping systems that I had to almost get in fist fights with the engineers so that my men would not get killed doing what an engineer said should work? An engieer can design a perfect Arse Hole on the computer screen and I am the one that is responsible for making it shiet!! 99% of the time any use of carbon fiber with out the use of epoxy resin is just plain stupid. Its like building a 10 billion dollar suspension bridge and using a 2x6 to to link the middle 10 ft of the bridge?? Both my children growing up became national ranked crew rowers. I ended up repairing quite a few 56 ft long carbon fiber and kevlar 8 man crew shells that weighed less then 200 pounds. I know the difference between e glass S glass and all the different forms of carbon glass. I have worked with prepreg. post curing . you guys are pounding sand. I remember years ago in the early 80s some nut engineerd a fiberglass hull from the chine down and an aluminum hull sides and superstructure.He used some earlly version of plexus to bond it. You have probably never heard about this ? Well the only way I found out about it was a vacation trip to Ocean Reef club and someone dragged my rear over to see this engineers missguided work floating in a dock there. My humble uneducated and untitled opinion is that, Any production boat hull should be built with solid fiberglass 1708 or heavier biaxial stitched type glass and vinylester resin. No coring below the water, especialy balsa crap. as far as stringers and out board transoms, I am a strong proponent now of coosa penske {very dense fiber foam board} where ever plywood in boats was fomerly used. Its cheaper and keeps its dimension better then marine plywood. from the water line up any core that you trust. Why are you guys trying to reinvent the wheel? You want a boat that wont last, engineer a core into the hull. Can you engineers tell me why I should not be impressed with the coosa type panel and who ever engineered it? can you tell me why 50 year old 233 formulas with solid fiberglass bottoms and plywood stringers that lasted 40 years should not be rebuilt with penske board stringers and transom and last 100 more years and still be known as one of the finest riding 23 ft boats ever made?
Well, I guess this thread has run it's course. We went from a civil discussion about the merits of different materials to something else. I could make comments about certain posts that have disrupted the flow of information, but why bother? It would just lead to further swirling around the drain.
Thanks to all who participated in a constructive manner.
What have we answered in the real world of production 20ft to 40 ft boats?
