2205 Duplex Stainless Steel chainplate fabrication

[Pauls]

A slight radius at the corners of square holes does NOT eliminate the stress riser. It reduces it slightly. By all means use round holes. As Jim said, they are cheaper, easier and eliminate the stress raiser issue.

I'm a mechanical engineer. I calculate stresses. I promise you that you do not want square holes.

Duplex bolts are a great idea. Do not be concerned about the diameter of the head on different size bolts. All bolts have head designs adequate to take the ultimate ie breaking strength of the bolt.

When you install your new chainplates be sure to torque the bolts fully tight. Definition of fully tight technically is about 85% of the ultimate breaking strength of the bolt. For you that probably means make them really tight. The chainplates when loaded want to slide up the side of the hull. High clamping force is what makes them secure. This is why you want a solid metal backing plate on the inside of the hull, to spread out the clamping force exerted by the bolts.

[Wind River]

I really appreciate the input from all of you.

Allan and Chris - Thanks for the links. I have been searching for someone with an online store that had some pricing for the 2205 bolts and didn't find any. Yes, there were many sources that could quote me on what I needed. I guess I phrased it wrong when I said there were not may options for these bolts. Plenty of options, just not online stores. I will submit quote requests to some of these businesses and see what they come back with.

Jim - No offense taken about my misguided reasons for using the carriage bolts. When I started this whole chainplate ordeal I was simply removing them to paint the hull and re-installing them with new bolts. I tried to duplicate what was there and liked the original look so I proceeded in that direction. I asked a few other about the square holes and the general consensus was that with the thickness of the material, it would be fine. These were all opinions, but none where from engineers. Regardless, I felt comfortable enough with the idea at the time. Not so much anymore.

When I discovered the cracks, I started looking at other options for materials. I researched here on this forum about titanium chainplates. I saw your reference to your 2205 duplex stainless ones and that is why I started looking into that material as well as titanium. So thank you for that.

Paul - Thank you for your input also. I will opt for the round hole and source the correct fasteners.

As far as the redesign goes I think I will do as Chris suggests and just make sure I get a good solid connection through the "Channel or Chain wale" and not over complicate this even more. The rig has stood for 35 years to date. With the stronger material and tighter attachment higher up, I believe it will be good.

I'm still waiting for a second quote from another source for titanium chainplates. I was turned on to this company from another Cruiserforum member. I will report back with what I find.

Interesting that two places that advertise they carry 2205 stainless plate have told me they do not carry it when I inquired about. United Titanium and United Performance metals.

I will continue my search.

Thanks again,
John