ply-balsa sandwich

Rick,
as long as you understand what you are committing to and enjoy the build a beach cruiser is a great project and product. It's wonderful to be creating something that can take you places you would never see otherwise on just your own power and what the environment gives you.

I just recommend marine ply stitch and glue to every first time builder so that the hull is done before anyone can change their mind about how enjoyable building a boat is. The other thing about cold mold vs stitch ply is that the result is so pretty it's like sailing fine furniture -you don't want to paint, you want to show off your handiwork -and not bang it up or drag it over rocks. Stitch and glue is painted over, banged around and quickly repaired after it dries out.

I have graphite/epoxy on the bottom of my PAX 20 kayak, I thought it was for speed. It is holding up well but I have certainly not dragged it over concrete, just slid over river rocks in shallows and even that makes me cringe. On the jet we ran a bronze half round rub strip along the keel. graphite-epoxy sounds like a great candidate for systematic testing!

 

Mind you, I don't recommend the concrete test on a regular basis. But it's been done a few times to my boats with some amazing results. Eventually it'll wear off if you keep pulling those stunts so you may need to reapply it.

Also note that the graphite will prevent patches from adhering well to the boat. I rode plywood/epoxy dories down the Grand Canyon one year (magical experience) and asked the guides why they didn't use the graphite trick. They told me that they used to, but if they experienced hull damage during the trip they would be unable to patch it with their emergency epoxy kits without a sander to remove the graphite.

 

I would think the ratios are important. The graphite is just microscopic ball bearings -great dry lube, terrible aggregate. In higher fill ratios graphite would just make weak plastic. If I was applying it (I didn't build my PAX 20) I think I would thicken epoxy with microfibers, lay it on flat, and then blow the graphite on the surface until all I could see was dry. After cure I would dust off the excess and maybe seal it with something so it wouldn't leave shiny grey marks on everything it touches.

 

depends on the weapon the .50 is fired from...
handgun - loose fabric of several layers of kevlar is sufficient... it still will brake your rips.
rifle - now way. sniper rifles with .50 caliber have such a high impact energy that you cannot stop the bullets with something you are wearing like a vest...
the strongest bulletproof vests can withstand rifle calibers up to 7.92 mm and they have ceramic plates in the outer layers to fragment the bullet and distribute the force over a greater area...
the -loose- kevlar-layers are on the inside of course... always first the hard shell and then the soft shell...

if we are talking vehicles, the hard shell is still on the outside with a kevlar fabric encapsulating the passengers to catch all fragments still penetrating the inside or from bits and pieces coming loose...

now helmets is a different thing...
these fabrics are hard compounds but their design relies very much on deflecting the bullet or shrapnel while vests are constructed to absorb the whole energy...

so much for military safety equipment...