Guogeon Brothers on Boat Construction

[John D]

Stan@FourWheel posted a picture of one of his aluminum frames next to an image of a buildup of a prototype composite camper. He asked about the cantilever structure. I wondered if a few hundred pounds of static load on the overhang was an adequate test. Let me submit another point of inquiry in connection with composite resin construction, namely “fastening”.

“Gougeon Brothers on Boat Construction” is a treatise on building boats. Gougeon Brothers produces and sells West System Epoxy, premium composite fillers, glass cloth of many types and weights, and other products used in boat construction. Their products are recognized as some of the finest available. Gougeon Brothers has worked out many of the techniques for construction and handling of epoxy resin composites through years of testing and practical application. For years, they published a journal on the subject of building many different composite structures and are one of the most respected sources of information on the subject that is known.

Following are 3 illustrations from their book, just to whet appetites for the quality of their published work. A copy of their book on boat building would be useful to camper builders, especially those using composite resins exclusively. Maybe the builders of the composite campers have already studied this material. I hope so.

 

[ntsqd]

Really, really rough RoT for dynamic loads "simulated" as static loads is 3X the mass. Then add in a basic Factor of Safety for such a thing; I'd start at 2:1. I.e. say a 150lbs person was going to ride in the cab-over portion while going down the highway (highly unlikely example, but it's what popped into my head right now). For a quick estimate of if the structure was up to that I'd look to see if it could support a 900 lbs. (150 * 3 *2) rectangularly distributed load (both width-ways and longitudinal orientations)without needing to consider fatigue life issues because if fatigue life considerations enter the picture the structure isn't up to doing this job.

When you consider that geometry plays a bigger role in stiffness than does mass I would be more inclined to do these calcs for a metal structure as those cause me more concern. Those likely to try to execute in any sort of composite method will likely be in one of two camps, well researched and educated on the topic or clueless and my observation is that the latter are extremely rare. Unfortunately, everyone with welding machine thinks that they can weld.....

 

[pods8]

John is this going to be another random spattering of statements or are we going to discuss something? I'll join the conversation unless it turns into something in which I can't tell what you're trying to communicate.

I've read the entire book you're talking about as one of the resources for my composite home build you are referencing (by the way it's not a prototype, it's my personal camper I'm building). Yes there is a large fillet under where the cantilever connects to the front wall. Also when I jointed all the flat panels together there is an interior fillet and the exterior corners are radiused to eliminate stress concentrations (and also the glass lays easier). Is there a question here? Are you just pointing out the book for others not familiar?

Loading: I was loading the cantilever to get more of a feel for the deflection as opposed to failure strength (theoretically the cantilever should hold over 1T static at the very front based on how I designed it but that is just what the paper says). Deflection will be come a issue to me well before failure. Off the top of my head: It was a 320lb loaded out at the end of the cantilever and based on the size of the bags would have been about 4.5' out to center of mass, I believe there was 1/4" or so of deflection at the front of the top of my head? Considering I'm 200lb and would be sleeping about 15" out in terms of center of mass and the wife is 130lb and would be about 45" out I think we're doing just fine there with some room to spare for "dynamic motion". Also I'm building a compartment under the bed which will have 3.5" tall ribs running front to back to hold up the bed platform which will stiffen things some more (even though the magnitude of the load is carried in the side rails).

You seem to have a bit of negative fixation on composite campers, what's up?

P.S. Got other questions in working with epoxy & various fillers let me know, I'm not an expert but I've log'd some hours with it on my project so far.

 

[John D]

pods8, I am wishing you the best of luck in your project. John D

 

[pods8]

Thanks. Here's a couple more filleting photos per the thread subject:

I glassed all my panels flat in the horizontal, then joined them with thickened epoxy, then the inside corners got a thickened epoxy fillet (I used a west system #804 spreader for this which will give ~3/8" radius). Over that a couple plies of fiber glass oriented perpendicular to the joint and +/-45deg. (Same one the outside which were rounded instead of getting a fillet).

Under the cabover I installed a triangular wedge of foam to create a large fillet, this also got thickened epoxy along the seams and then fiberglass plys.

Note there is peel ply over the fiberglass in both those photos in case it's looking odd to folks.

Feel free to chat/question/inquire if you want, just have the courtesy if you're actually talking about my build to ask me a question and not beat around the bush.

 

[Mark W. Ingalls]

Holy crap, that looks hard...

 

[pods8]

Holy crap, that looks hard...

Mainly time consuming. Little finesse here and there but pretty straight forward, just takes up time.

 

[Mark W. Ingalls]

Mainly time consuming. Little finesse here and there but pretty straight forward, just takes up time.


I can imagine hearing that from the Emperor who requisitioned the Great Wall...

 

[turbothrush]

Note there is peel ply over the fiberglass in both those photos in case it's looking odd to folks.

Feel free to chat/question/inquire if you want, just have the courtesy if you're actually talking about my build to ask me a question and not beat around the bush.


Just registered to ask about the peelply
pods8 , What is the reason for the peelply ? Does it make it less likely to pull the cloth out of the filleted corners while wetting out the glass or does it improve the surface finish of the epoxy before filling/priming .I haven't been using it in my hardside build and am thinking maybe giving it a try. Thanks

 

[pods8]

I can imagine hearing that from the Emperor who requisitioned the Great Wall...

You have a point...

Just registered to ask about the peelply
pods8 , What is the reason for the peelply ? Does it make it less likely to pull the cloth out of the filleted corners while wetting out the glass or does it improve the surface finish of the epoxy before filling/priming .I haven't been using it in my hardside build and am thinking maybe giving it a try. Thanks


I put the peel ply on over the last layer, it causes the epoxy to fill in the weave of the glass underneath, smooths out fiberglass edges by holding them down and forming a little epoxy transition between the thickness variation, keeps the surface clean until you're ready to use it, causes any excess resin (or blush) to form on the outside of it which will be peeled off. Then when it comes to finishing the part or bonding something else to it you just peel it off and give it a light sanding (it's supposed to be bond ready after just peeling but a little sanding to be on the safe side doesn't hurt) which is fairly easy to do because you don't have all the low spots in the fiberglass weave that you can't really get to w/o sand blasting or sanding away actual fiberglass to get to them. Also I don't have to worry about getting epoxy and stuff on the top of it as I'm working on adjoining areas since it just gets peeled off.

It adds cost in terms of the peel ply and extra resin used but I figured the other benefits were worth while. If every ounces matter in a build (like it does with composite airplane builds) then it's not the best route because it's better to fill the outer weave with micro slurry rather than resin but as mentioned above that requires different preparation in the end. I'm not worried about the small weight increase.