Bracket theory

[Bushwacker]

Originally Posted by thehermit

That’s a pretty cool analysis you got going here.

Like Bushwacker said...the stress points on the 2 piece glass bracket seem to be slightly different. On mine it is here:



I have a lot of glass there but i do get cracks in the paint. This bracket has a plywood core...and over time I expect more flex there. I would like to see what Hermco is thinking for a gusset.

The hairline cracks in my bracket are exactly where you drew that circle, in the center of the radius, running vertically up and over into the horizontal radius between the top surface of swim platform and forward face of the engine mount area. The cracks have been there for a long time and haven't grown, so I don't expect any problems from them.

I believe the gusset Don is thinking about would extend the swim platform to fill in the area in the circle. He would add material that runs from the aft face of the engine mount surface to the aft face of the swim platform, intersecting it a 45 degree angle instead of the current 90 degree angle. I believe this would spread out the load and eliminate the stress concentration that typically occurs in a 90 degree corner.

On a related note, when we wanted to know where to put strain gages on an experimental part at Pratt & Whitney 20 years ago, we often didn't have the fancy 3D models because they were very expensive back then. Our lab guys would spray the part with something called "Stress Coat", which was nothing but a very brittle lacquer. We would then apply a load to the part, and where the stress coat cracked is where we would lay the strain gages! That stuff was so sensitive that you couldn't even take a coated part out of the air conditioned lab because just a small temperature change would crack it!

I view gel coat as simply a slightly less sensitive version of "Stress Coat"!