Vincentc
Legendary Member
- Joined
- Jun 3, 2008
- Messages
- 1,514
- Status
- OWNER - I own a Hatteras Yacht
- Hatteras Model
- 43' DOUBLE CABIN (1970 - 1984)
This may be of some value to you.
Before re-attaching the swim platform brackets, I ran a test yesterday. See photos below.
7 of the attachmet bolts had pulled out. The transom is has two layers of <.6 cm fiberglass with an 1.8 cm foam core between them. There are 6 ss brackets each secured by (4( 3/8 ss bolts. (8) of the fasteners are not accessible inside the boat and terminate inside the core. I decided to add some backing plates epoxied inside the core, inserted from holes on the outside the transom for those blind fasteners.
Initial fastener plan
I had 2.5 cm x 5 cm backing plates fabricated out of 1/8" ss flat bar. Each has a tapped 3/8" hole. Each plate is to be secured inside the core and the foam core in the immediately surrounding area removed and replaced with fg cloth and filled epoxy.
The test
The stresses are significant and I decided to perform a test of the backing plate and filled epoxy. I drilled several 7cm holes in a piece of 1.8 cm plywood, put a piece of 1.2 cm plywood behind it and filled each hole with a different filler/epoxy mixture. They are: colloidal silica, milled fiberglass, colloidal silica and milled fg, and one with wood flour and c/s.
I drilled 3/8 holes through the center of the filled areas and used a forstner bit to remove the 1.2 cm plywood backing from the area around that hole. I inserted a 3/8 ss bolt, with a nut and washer then used a 90 cm wrecking bar set-up with a 2 to 3 cm base to try and pull the nut through the epoxy. I also tested the strength of the threaded hole in the 1/8" ss plate.
Results:
I first attempted to pry the bolt held by the 1/8" plate. The wrecking bar is a 90 cm lever against a base that is roughly 2 or 3 cm long. I assume that is a mechanical advantage of 30 or 45 to 1. Standing on the test board and pushing against the wrecking bar I believe I can generate at least 50 and more like 80 lbs of force which would yield 1500 to 3000 lbs or so.
With close to my maximum force I was able to pull the bolt through the ss plate. Note that the plate was set above a 1" dia hole which allowed the plate to deform into the hole and when the surrounding plywood compressed.
I then tried to pull a standard nut with washer through 1.8 cm thick epoxy filled with colloidal silica. With all the force I could generate, I could not do it. That force did deform the washed and compress the nut/washer into the epoxy about .4 cm.
I then reduced the thickness of the epoxy with a forstner bit the thickness of a 3/8" ss nut and repeated the test. At about 1/2 force against the wrecking bar, it pulled through.
Conclusion,
I am going to put a ss compression nut behind the 1/8" plate to give more strength to the fastener and will use a few layers of fg cloth and biaxial fg to reinforce the epoxy.
http://s1123.photobucket.com/albums/l554/vjcast/Epoxy bedding and fastener test/
Before re-attaching the swim platform brackets, I ran a test yesterday. See photos below.
7 of the attachmet bolts had pulled out. The transom is has two layers of <.6 cm fiberglass with an 1.8 cm foam core between them. There are 6 ss brackets each secured by (4( 3/8 ss bolts. (8) of the fasteners are not accessible inside the boat and terminate inside the core. I decided to add some backing plates epoxied inside the core, inserted from holes on the outside the transom for those blind fasteners.
Initial fastener plan
I had 2.5 cm x 5 cm backing plates fabricated out of 1/8" ss flat bar. Each has a tapped 3/8" hole. Each plate is to be secured inside the core and the foam core in the immediately surrounding area removed and replaced with fg cloth and filled epoxy.
The test
The stresses are significant and I decided to perform a test of the backing plate and filled epoxy. I drilled several 7cm holes in a piece of 1.8 cm plywood, put a piece of 1.2 cm plywood behind it and filled each hole with a different filler/epoxy mixture. They are: colloidal silica, milled fiberglass, colloidal silica and milled fg, and one with wood flour and c/s.
I drilled 3/8 holes through the center of the filled areas and used a forstner bit to remove the 1.2 cm plywood backing from the area around that hole. I inserted a 3/8 ss bolt, with a nut and washer then used a 90 cm wrecking bar set-up with a 2 to 3 cm base to try and pull the nut through the epoxy. I also tested the strength of the threaded hole in the 1/8" ss plate.
Results:
I first attempted to pry the bolt held by the 1/8" plate. The wrecking bar is a 90 cm lever against a base that is roughly 2 or 3 cm long. I assume that is a mechanical advantage of 30 or 45 to 1. Standing on the test board and pushing against the wrecking bar I believe I can generate at least 50 and more like 80 lbs of force which would yield 1500 to 3000 lbs or so.
With close to my maximum force I was able to pull the bolt through the ss plate. Note that the plate was set above a 1" dia hole which allowed the plate to deform into the hole and when the surrounding plywood compressed.
I then tried to pull a standard nut with washer through 1.8 cm thick epoxy filled with colloidal silica. With all the force I could generate, I could not do it. That force did deform the washed and compress the nut/washer into the epoxy about .4 cm.
I then reduced the thickness of the epoxy with a forstner bit the thickness of a 3/8" ss nut and repeated the test. At about 1/2 force against the wrecking bar, it pulled through.
Conclusion,
I am going to put a ss compression nut behind the 1/8" plate to give more strength to the fastener and will use a few layers of fg cloth and biaxial fg to reinforce the epoxy.
http://s1123.photobucket.com/albums/l554/vjcast/Epoxy bedding and fastener test/
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