I finished the battery boxes, which include non-metallic hold-downs for each battery that are independent of the lid, which will be secured with simple latches. The boxes are stbd of the engine, under the future quarter berth platform.
The boxes are fiber glassed (polyester resin), cored with coosa board (1/2" for the big box, 1/4" for the small box). Laminate schedule was one layer of 1.5 oz CSM against the coosa board, then one layer of 1708 (1708. CSM, coosaboard, CSM, 1708). I did not vacuum bag the panels for the boxes because the additional strength/compactness was not worth the effort and expenditures of vacuum bagging consumables.
The hold-down mechanism for the big box consist of molded fiberglass brackets (2 per battery) that hold the battery in all three axes. They are individually removable by unscrewing the cap screws that are tapped into epoxy/glass blocks. I made cardboard model, made a plug, then the mold. From that mold I pulled 8 brackets. For the hold-downs for the small battery, I just laid up fiberglass directly on the battery, then popped that part off and ground them smooth.
All of these individual brackets are attached with the same cap screws to an angle "iron" that I made out of fiberglass. Use used an existing 2" 90 degree angle as the form and vacuum-bagged the 4 layers of 1708 with polyester resin.
All box panel penetrations are back-filled with epoxy because, although strong, i didn't want to crush the coosa board. I use a 1 1/4" hole saw to drill out an ample hole at each penetration, then carved out additional core beyond that. I didn't push the hole saw all the way through, just through the outer layer and the core. I left the inner layers of fiberglass alone, then back filled with epoxy.
The big box lid is cored with 1/4" coosa board, same layup schedule as the panels, except the underside of the lis is one layer of CSM and one layer of 10oz cloth. The small box lid is an experiment with Airex foam board (AIREX T92). Is substantially lighter and is likely what i'll use for the hard dodger.
I made the lid by first cutting the core to the exact perimeter of the box top, when while holding it in place, wrapped fiberglass round the lid and the box, essentially glassing the lid core to the top of the box. To ensure separation, I wrapped the box top with clear packing tape.
It was interesting to observer that packing tape cause the resin that is right up against it to not cure while in contact with the tape. Once the part is removed form the tape, the resin will cure. This delayed-cure later is very thin and the majority of the resin cures, just not that paper-thin layer that is in direct contact with the packing tape. Epoxy will cure against packing tape, but poly- and vinylester resins will not. it's too bad because packing tape is a very cheap release material for quick, rough molds. I often tape up some cardboard, ten lay up whatever. Tape and cardboard make a quick-n-dirty mold.
The big box sits on a bed (coosa-cored panel) that is through bolted to plywood/glassed boards that are glassed to the hull. The small box is through bolted to a coosa-cored panel that is glassed to the hull on one side. the other side (against the big box) is bolted to the big box with 3/8" cap screws that are tapped into epoxy back fill in the side of the big box.
The big box is held to the beds with stainless steel brackets I made: through bolted to bed and through bolted to box with flat head machine screws.
interior of both boxes is gelcoated. Actually, It's coated with tinted epoxy. I had to use epoxy because, although the panels are poly, I reinforced inside and outside corners with epoxy/1708. The presence of epoxy precluded the use of poly-based gelcoat. I wanted a white, smooth interior surface for easy cleaning.
The over current protection will be immediately outside of the boxes for both positive cables. The cable pass-through holes are just below the lid, so the lid does not interfere with the cables.
Items left to finish:
1. Find and install latches for both lids.
2. Install drains in each battery box (probably epoxy/cloth block threaded for 3/8" or 1/2 pipe threads. That way , I can flush out the boxes and drain, then screw in the male plug to close the drain.
3. Design, make, install the brackets for over current protection just outside of each box for the positive cables.
4. Figure out box ventilation.
Note: Wiring in pictures is temporary. I'm not really going to have lower-gauge twisted pair when I redo the wiring.
More pictures
http://bodylens.com/Gallery/thumbnails.php?album=56
Wow! We are in the process of searching for our first (small) fiberglass project and were thinking of battery boxes. I feel like I underestimated it. What was the benefit of using the Coosa? Just weight? Or would you have had to layer CSM and 1708 even if you used something else? For some reason I got the sense that the coosa board provided very little structural support that needed the slack picked up by the glass.
Oh, they look really good!!
This is the new gold standard for battery boxes on a P365! It's one of my winter projects coming up-I will have to step up my game!
The battery boxes are straight forward. Thank you for the compliments. The hardest part is the design. Once the plan is on paper (well, just laid out in my head or modeled with cardboard, not really on paper), the building went pretty quickly. They turned out nice. it was really important to make them strong enough to contain the batteries during a knock-down and that the hold-down mechanism can handle the inverted mass of the batteries. I considered using a lighter foam, but was concerned that the epoxy 'grommets' (the backfill ) at the bolt penetrations might tear out. Coosa board is a bit heavier, but much stronger and very porous (I think it's closed-cell foam), thereby giving much surface area for the epoxy to grip when I back filled. With the layer of heavy cloth embedded into the outer surfaces of the coosa board, I think there low risk of tear out. Hold-downs needed to not obstruct battery caps or terminals and wanted as little metal inside the box as possible so I don't accidentally touch + and - terminals.
Jordan, I use Coosa board because that is what I had and I eschew wood whenever I can. I see very few uses for wood (great for cabinetry cabinetry, cleats for some shelves and temporary structures). I wanted a sandwich design because fiberglass by itself is too flexible and heavy. The Coosa board is actually really strong. its made of resin impregnated foam sandwiched between layers of what looks like woven roving. It's easy to cut with an angle grinder that has a 1/16" abrasive wheel (same wheel I use to cut stainless steel). In order to get the stiffness I wanted, I had to have a core and balsa is not flat (it's actually warps a bit and will not lie flat) and I had coosa already because am using that for glassed-in cleat and core for the round cockpit hatches I made. Coosa is pretty strong. Scroll to 23 minutes, 50 seconds, https://www.youtube.com/watch?v=sOJLYIr_Anc
Yes, regardless of core I would use one layser of CSM, then 1708 on each side, polyester resin only). If using epoxy, i would have used just 1708, then maybe a couple of layers of 17 oz biaxial, not mat, but there is no reason to make the panels with epoxy. It actually might be worse. The CSM in poly wets out and softens to fill in the roughness of the substrate, then the stiffer, stronger 1708 layers on top of the still-wet CSM. Without the CSM, the 1708 would bridge small gaps, leaving air pockets.
The stiffness comes from the separation of the interior and exterior skins of fiberglass and how far they are separated by the core. I made the panels, then used wire to stitch the panels together. Inside of each corner, I ran a bead of thick epoxy and, once that cured, I removed the wires and glassed over the corners inside and out) with fiberglass.
To answer your questions/statement more directly:
- What was the benefit of using the Coosa? To separate inner and outer fiberglass skins to create stiff panel that is lighter than same thickness of just fiberglass
- Just weight? Combination of stiffness and weight. Also, Coosa board is flat and doesn't warp, rot, or delaminate
- Or would you have had to layer CSM and 1708 even if you used something else? Regardless of core, CSM and 1708 would be used.
- For some reason I got the sense that the coosa board provided very little structural support that needed the slack picked up by the glass. Coosa board is strong, inflexible, does not absorb water, relatively light, and easy to cut/file/shape.
The only small fiberglass project is laying up a flat panel. Everything else needs a mold or design. Polyester resin shrinks when it cures (epoxy does not) so it will constrict whatever you've put it around. If used on a female mold, it will pop off readily. When used on a male mold, it's a little tougher to pop off.
FYI, although I refer to this as Coosa, it's not. It is a similar material I picked up local for about $120/ half-inch 4'x 8' sheet (maybe it was $160/ sheet?). There are apparently several competitors to Coosa board.
One thing to keep in mind about core material is that the fiberglass (really, the resin) has to stick to the core and the core material can't be easily be separated or torn off. When a cored panel is bent (will not bend much), the outer layer of fiberglass is stretching and attempting to pull away from the core and laterally tear from the core. If the core is weak (i.e. white styrofoam, or poly-iso), that fiberglass layer would easily tear away. A core that is made out of plastic (pvc, polyethlene, etc..., must be very rough for polyester resin go 'bite' into (mechanical bond). If epoxy is used, the surface can be smoother because epoxy sticks to almost anything. The smoother the material, the harder it is for the resin to stick. No resin can stick to a piece of glass. I probably could have used polyester (or vinylester, stonger bond) for glassing the corners of the box, but I know epoxy has stronger bond and wanted to ensure that the box will not break apart.
Somehow, I missed this response when it was made. Thanks a bunch! Gives me quite a bit to think about.