Drilling Through C Channel

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Soundevice
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Drilling Through C Channel

Post by Soundevice »

Morning!

I've just about finished up with my trailer repairs and had a few questions re putting penetrations through the C channel frame of the trailer. I've switched to rubber brake lines and purchased SS clips to attach them to the frame with self tapping screws (#12 is what I had in my shop but may purchase a smaller size depending on replies to this post!)
I've also replaced the lights and wiring and may want to put a through hole in the frame to run wire from the fender lights to catch the main line. My questions:
-Because the trailer capacity is so closely rated to the actual weight of the boat, is it ok to drill any holes into the frame? I've had difficulty finding out how much strength is lost doing this.
-If so, what hole size is acceptable and does placement on the C channel matter (middle, top, bottom?)
-When using self tapping screws, does the fact the holes are filled with the screw help in strengthening the hole?

I may be over thinking things a bit here but figured there was no better place to reach out for some thoughts!! I will have to pull my boat in the next few weeks so trying to get the overhaul completed this weekend. I've not attempted to drive the boat onto the trailer yet so that will be an adventure in itself!!

Thanks for any thoughts-
Ben
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Tomfoolery
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Re: Drilling Through C Channel

Post by Tomfoolery »

Soundevice wrote: Wed Sep 22, 2021 4:20 am-Because the trailer capacity is so closely rated to the actual weight of the boat, is it ok to drill any holes into the frame? I've had difficulty finding out how much strength is lost doing this.
For practical purposes, no strength is lost if you drill through the middle of the web (the vertical part). For common beam shapes in bending, the middle is the neutral axis, and there is no bending stress along that line; max bending stress is at the top and bottom surfaces. Shear stress is maximum there (and zero at the top and bottom), but it's low and won't matter.
-If so, what hole size is acceptable and does placement on the C channel matter (middle, top, bottom?)
See above for placement. Drill a hole and deburr it just large enough for what you need to do. There is no advantage to going oversized.
-When using self tapping screws, does the fact the holes are filled with the screw help in strengthening the hole?
No. They just sit there taking up otherwise vacant space, but they neither help nor hurt. But I wouldn't use self-tapping on structural steel; better (IMO) to use stainless machine screws with stainless self-locking (aka 'aircraft') nuts, or simple stainless hex nuts with lock washers; the star type can help with grounding the ring terminal on the end of that wire. The mounting bolt can double as the location for a ground wire, though I run ground wires to all the lights since frame grounds tend to deteriorate over time.
Last edited by Tomfoolery on Wed Sep 22, 2021 9:50 am, edited 1 time in total.
Tom
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Dougiestyle
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Re: Drilling Through C Channel

Post by Dougiestyle »

What I am using to hold down trailer wiring is liquid electrical tape. I run the wire next to the frame and use a temporary clip or weight it down with whatever is handy, then paint this stuff on in maybe 3 to 5" (Kind of like a stitch weld), let it dry well, remove your clips and weights. It seems to work well and can be pulled off if need be. It also works well to prevent abrasion and being black it is less visible.

Good luck with your first attempt at landing the boat on the trailer.
Dougiestyle
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C Buchs
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Re: Drilling Through C Channel

Post by C Buchs »

OverEasy
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Re: Drilling Through C Channel

Post by OverEasy »

Tomfoolery is right about the neutral axis aspect as long as the hole doesn’t get more than 2X the material thickness as a general use of thumb ( the real calculations take into account web height, thickness, concentrated load locations, flange size, flange thickness and sharp edge factors but you really don’t want or need to go down that rabbit hole :D ).

I’d avoid the self-tapping screws and go with a smaller smooth debarred through hole and SST screws/washers/self-locking nuts instead.
Your talking a really minor cost difference vs. a real longevity benefit.

I’d also go with Tomfoolery on ground wires to each electric assembly. Frame grounds corrode and develop progressively higher resistances over time. Running the real ground wires now will save you multiple headaches later.

Not a great fan of the liquid electrical tape stuff as I’ve seen it crack and dry out over time releasing what it was supposed to hold.

Better to use the clamps and bolt them on place.If that doesn’t work for you then there is always the tie wrap approach….
I’ve taken a tie wrap around the C-Channel with the wire captured in the empty part of the C. Then taken a second tie wrap and secured the wires to the first tie wrap to minimize the movement. Use the Heavy Duty black UV resistant tie wraps. (The white ones deteriorate in sunlight over time …Been there..done that…have the Tee shirt :P )

Hope this helps. Post pics of your trailer. Great project!

Best Regards,
Over Easy 😎😎🐩🐈
Soundevice
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Re: Drilling Through C Channel

Post by Soundevice »

Excellent info!!
Putting a hole in the center does make sense as I can see the flex on the channel being mostly on the corners and bottom. I came to the right place (admittedly, I figured some of you guys have engineering experience judged from the posts I've read!) I absolutely will use SS nylon nuts and washers.

As a side, any issues with electrolysis with mixing mild steel and SS? Once again, the oracle is all over the place on this. I'm in construction and am aware to not use stainless fasteners with zinc coated hangers for decks and framing as they will potentially fail. This has come up a few times so perhaps y'all could field this? I had to use dissimilar metal (or coating) on the brake assemblies as the posts for the brakes were galvanized and the nuts and washers I used were zinc plated (7/16" is apparently an odd size and couldn't get nuts in SS or galvanized.) I imagine the effect is minimal with rain/fresh water but curious if I end up dipping in salt water, could this end up corroding the steel? Would a bit of silicone be helpful?

Re the liquid tape and the 3M product, I'm more of a fan of mechanical attachments. Though adhesives can be insanely strong, there always seems to be cases where everything seems prepped properly but things won't stick right! (or stick waaaay to much!)

And thanks for the sentiment re my first attempt to land her! My first attempt to sail (last year) ended up with me on the front page of the Butler Eagle!!! The instructor didn't cue me onto the fact there is a drain plug on the cat he sent me out on the FIRST DAY (!) and after an AMAZING start the bow started plunging into the water and capsized, partially sinking. Had to get a tow back from the safety boat and there happened to be a reporter from the local paper there, got me all humiliated in the water trying to lift the boat out, haha! So this is why I just don't want to end up on youtube at the launch, ha!!
Still bought a boat so must be an idiot or addicted...or both!
Soundevice
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Re: Drilling Through C Channel

Post by Soundevice »

And re grounds. I ended up getting a white ground wire to run all grounds directly back to the truck connection. Minimizes penetrations and can be a poor connection with painted/rusted metal...
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Tomfoolery
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Re: Drilling Through C Channel

Post by Tomfoolery »

Little SS screws, which are more noble than the carbon steel they're clamping against, won't be eaten through galvanic action. The frame will. But the area is so small under the head or nut, and the electrolyte so infrequently present (it doesn't live under the sea), that the worst you'd see (maybe) is a little loosening over a long period of time. I'd guess the trailer will rust apart and the connections for wiring and lights will still be solid.

You could always use nylon hardware, but that's unnecessary IMO.
Tom
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OverEasy
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Re: Drilling Through C Channel

Post by OverEasy »

Here is a table from the American Galvanizers Association.
These guys are the “go-to” guys for everything galvanized …..

Image

So, it would be best to use HDG (hot dip galvanized) hardware on a galvanized trailer rather than SST if dunking in Salt Water or Fresh Water to prolong the corrosion resistance of the galvanized frame members.
I don’t mind relearning stuff when one least expects it! :o :o . I’m glad you piqued the old brain cells! :D :D
(One aspect with the SST hardware that is something of an advantage is that for repetitive use aspects where one is consistently taking apart and putting back together an assembly the SST hardware doesn’t rust or corrode like galvanized hardware can. In those situations I use a dab of silicone or Teflon grease on the threads to avoid galling and use regular lock washers with plain nuts instead of nylock nuts.)

Hope this helps in understand a little bit more about the materials we all come into contact with in using, repairing and modifying our vessels, securement and their transit devices.
(Learning, Understanding and Sharing valid accurate information is some of the fun part of messing about in boats! :) :) )

Image

Image

The nylon attachment hardware is also a good idea too! But if you get the non-black (Not UV resistant) type I’m not sure how long they would last before becoming embrittlement.

Best Regards,
Over Easy 😎😎🐩🐈
Soundevice
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Re: Drilling Through C Channel

Post by Soundevice »

Interesting!
The above pretty much confirms that in this particular case I may be over thinking the potential for damage. Kind of a half academic and half practical concern! My plan is to shoot a little rustoleum on the torqued nuts and lockwashers on the brake assembly plate to minimize exposure to water. I don't really intend to drive in the snow so really the only bad electrolyte I will (hopefully!) be exposed to will be dipping the boat in the ocean at some point. I imagine a good rinse off after doing so would help. The fasteners of concern are also easily accessible and so I can keep an eye on them. Again, these are just some unconnected thoughts in my mind that now seem pertinent now that I've got a boat! Thanks for the insight, I'll be sending some pics along here when I get it all together...
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