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Old 04-11-2020, 14:08   #1
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Drill Hole in Stainless Steel Pipe

I have a a 2" Stainless Steel upright pipe 16 gauge that holds up my davit system. I drilled a 1 1/8" hole in the pipe to allow wires to run down the pipe and into the boat.

My after thought concern is the possibility of weakening the pipe. I have attached an image to help illustrate.

The hole is under a cross member that would likely keep the pipe from being about to collapse in the direction of the hole but I hope to get some other opinions.
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Old 04-11-2020, 14:22   #2
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Re: Drill Hole in Stainless Steel Pipe

Hard to say. It depends upon how the pipe is loaded. If the force is straight down that is probably the strongest direction for the pipe. If there is a bending moment then it has been weakened. But how over built your system is I have no clue. You could add a second pipe welded from below the hole to the horizontal pipe above it. OR you could weld a larger pipe over 2” pipe so that the metal is doubled around the hole, like a sleeve that also has a 1-1/8” hole in it.

Why not contact the initial fabricator and get his advice? He should have some idea of the strength and how the system was designed to handle the loads.
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Old 04-11-2020, 14:26   #3
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Re: Drill Hole in Stainless Steel Pipe

Unfortunately I did not have this fabricated and I have no means to contact the person who did. Good point about the support member welded below.

This pipe is straight up with no bend at all.

If it were to collapse wouldnt it have to collapse inward in the direction if the hole? If that is the case then I would be hard to to since the cross member above the hole goes to another upright pipe on the other side of the boat. To collapse inward it would have to bend that cross member.
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Old 04-11-2020, 14:57   #4
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Re: Drill Hole in Stainless Steel Pipe

My gut says it's fine. Certainly fine in compression/weight, if there were davits angling up from right above the hole, then there would be some leverage stresses there that could ovalize the hole and shape around it. How thick is the metal? witout an overall picture and idea of loading it's hard to say. But if that hole is 1-1/8 then the tubing must be 2" or so? Pretty stout.
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Old 04-11-2020, 15:00   #5
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Re: Drill Hole in Stainless Steel Pipe

That looks like a pretty big hole relative to total pipe diameter. To be safe, I would have a diagonal piece welded below that hole and then across to the piece perpendicular and above.
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Old 04-11-2020, 15:05   #6
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Re: Drill Hole in Stainless Steel Pipe

He said 2” diameter 16AWG.

We have no idea of the loads. His dink could be anything including a center console with a 20hp ob.
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Old 04-11-2020, 16:20   #7
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Re: Drill Hole in Stainless Steel Pipe

The dingy is about 200 lbs with everything in it. The structure also holds up 3 solar panels at 38lbs each for a total weight of about 314 lbs being supported. The solar panel end (right in the images attached) is the back of the boat and where the dingy hangs.

All of the pipe is 16 gauge and the uprights are 2" diameter. They are pretty beefy pipe. The cross member is 1.5". There are 1" pipes running from the davit system to the SS arch that came originally with the boat.

I have attached a couple mockups of what the whole davit system looks like for reference. The red circle on image 2 and 3 is where the hole is.

The opposite side has a 1" hole in the same location and has been that way since before we purchased the boat over 2 years ago. This has never created an issue.

The new hole ended up being 1 1/8" only because that was the hole saw size I had available.
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Old 04-11-2020, 16:59   #8
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Re: Drill Hole in Stainless Steel Pipe

I would weld a short piece of pipe into that hole, about 3/4" long, and push fit half way in, then weld all round.
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Old 04-11-2020, 17:06   #9
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Re: Drill Hole in Stainless Steel Pipe

That's a pretty good idea. That should have the benefit of supporting the pipe pretty well.
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Old 04-11-2020, 18:57   #10
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Re: Drill Hole in Stainless Steel Pipe

Quote:
Originally Posted by sy_gilana View Post
I would weld a short piece of pipe into that hole, about 3/4" long, and push fit half way in, then weld all round.
1+

To the OP, just remember you are looking at static loads on a nice day. Add some weather, dink fills with water, wind load on the panels, the boat is beating. That is what you have to imagine and design for.

Good luck.
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Old 04-11-2020, 19:22   #11
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Re: Drill Hole in Stainless Steel Pipe

You can lift the boat from the davit, the 2" is a big tube. even if you reduced the strength by 50% you have enough.
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Old 04-11-2020, 21:27   #12
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Re: Drill Hole in Stainless Steel Pipe

I don't understand where your tender hangs from. If it hangs from the 2" cross member I don't think it is much problem, if it hangs from under the solar panels then it might be a problem.

You have said the cross member is 1.5in and the upright is 2in but in the pic in post #1 they look the same size.
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Old 05-11-2020, 07:58   #13
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Re: Drill Hole in Stainless Steel Pipe

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Originally Posted by Dave_S View Post
I don't understand where your tender hangs from. If it hangs from the 2" cross member I don't think it is much problem, if it hangs from under the solar panels then it might be a problem.

You have said the cross member is 1.5in and the upright is 2in but in the pic in post #1 they look the same size.
I was mistaken, the cross member is 2in.

Attached are 2 more pictures showing how the dinghy sits.
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Old 05-11-2020, 09:34   #14
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Re: Drill Hole in Stainless Steel Pipe

Looks pretty Skookum (Canadian for sturdy or strongly built). To be safe maybe it should be beefed up as suggested by others. That said here is a link to an interesting article regarding carrying a dingy on davits while offshore.
https://www.riggingdoctor.com/life-a...vits#:~:text=A dangling dinghy in davits,drain plug in the stern.&text=The weight of the dinghy,much closer to the waves.
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Old 05-11-2020, 09:42   #15
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Re: Drill Hole in Stainless Steel Pipe

At least from the picture your tube wall thickness seems rather skinny, the hole large. I'd weld on the outside of the tubes 2 SS triangles, 2mm thick, long side bend inward 2 or 3 times, forming a triangle or square tube, allowing access to your hole
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