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Old 18-09-2015, 14:18   #1
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Stanchion backing plates - how thick?

We have a Bristol 29.9 and this weekend we're going to start rebedding everything, beginning with the stanchions.

We're planning to use G10 for the backing plates, but I'm not sure how thick it should be. Is there a general rule of thumb? 1/4"? 3/8"? 1/2"?

Thanks.
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Old 18-09-2015, 14:42   #2
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Re: Stanchion backing plates - how thick?

1/4" was used on my boat, about 1.5 times the size of the stanchion bases. I strongly suspect the stanchion tubing will bend or break now before the backing rips out.

FWIW, I also used 1/8" G10 and made little cutouts the same dimensions as the stanchion bases. I epoxied them to the deck to elevate the stanchion bases slightly above the deck level and mitigate any chance of water ingress. Probably overkill but figured what the hell..
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Old 18-09-2015, 14:55   #3
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Re: Stanchion backing plates - how thick?

We used 1/4". The previous plates were 1/4" of regular fiberglass layup, including the gel coat, so the G10 is quite an upgrade. Further, it was the general recommendation I came up with upon searching here and other forums.
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Old 18-09-2015, 16:42   #4
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Re: Stanchion backing plates - how thick?

Mmmm . . . . If you are going to all that work . . . . A better solution is to get g10 rod that is a snug fit inside the stanchion tube. Drill one hole thru the deck the dia of the rod. Run a piece of rod straight down until it hits the hull. Epoxy it in the hole thru the deck and glass it to the hull and under the deck. Leave about 3" sticking up above deck. Slide the stanchion on top and fix with a set screw.This will never ever leak nor ever need to be redone.
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Old 18-09-2015, 17:00   #5
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Re: Stanchion backing plates - how thick?

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Originally Posted by estarzinger View Post
Mmmm . . . . If you are going to all that work . . . . A better solution is to get g10 rod that is a snug fit inside the stanchion tube. Drill one hole thru the deck the dia of the rod. Run a piece of rod straight down until it hits the hull. Epoxy it in the hole thru the deck and glass it to the hull and under the deck. Leave about 3" sticking up above deck. Slide the stanchion on top and fix with a set screw.This will never ever leak nor ever need to be redone.
So no through bolts on the stanchion base in this case? All the strength comes from the epoxied rod? Definitely sounds like it won't leak. Do you think it as strong as the original through bolts?
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Old 18-09-2015, 17:43   #6
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Re: Stanchion backing plates - how thick?

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So no through bolts on the stanchion base in this case? All the strength comes from the epoxied rod? Definitely sounds like it won't leak. Do you think it as strong as the original through bolts?
yea . 3/4" G10 rod very strong - the stanchion will bend first

this is how its done on some custom boats - pretty much all thru deck bolts replaced with integral pieces
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Old 19-09-2015, 09:58   #7
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Re: Stanchion backing plates - how thick?

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Originally Posted by laika View Post
1/4" was used on my boat, about 1.5 times the size of the stanchion bases. I strongly suspect the stanchion tubing will bend or break now before the backing rips out.

FWIW, I also used 1/8" G10 and made little cutouts the same dimensions as the stanchion bases. I epoxied them to the deck to elevate the stanchion bases slightly above the deck level and mitigate any chance of water ingress. Probably overkill but figured what the hell..
Good practices, if labour-intensive with the G10. I don't know if the Bristol's deck is cored, but just remember to epoxy the bolt holes to isolate the core, and to put a little bedding halfway up the bolt threads so that it forms a seal when dogged down. Bedding on the topside of the backing plate is insurance, as well.
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Old 19-09-2015, 11:29   #8
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Re: Stanchion backing plates - how thick?

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Originally Posted by laika View Post
1/4" was used on my boat, about 1.5 times the size of the stanchion bases. I strongly suspect the stanchion tubing will bend or break now before the backing rips out.

FWIW, I also used 1/8" G10 and made little cutouts the same dimensions as the stanchion bases. I epoxied them to the deck to elevate the stanchion bases slightly above the deck level and mitigate any chance of water ingress. Probably overkill but figured what the hell..
I made topping plates using 1/2" fiberglass sheet. 1/4" backing plates.
Guy
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Old 19-09-2015, 11:46   #9
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Re: Stanchion backing plates - how thick?

ES--interesting concept.

For backing plates, again, marine plywood and aluminum sheet can be fabricated easily and are inexpensive.
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Old 19-09-2015, 11:49   #10
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Re: Stanchion backing plates - how thick?

I fabricated all new backing plates throughout. I constructed mine out of 1/8 inch Stainless steel. for any of the hardware that is hard to reach I drilled and tapped the holes for 1/4-20 bolts. I did this so I could tighten the hardware from above deck. I know that this sound like over kill but when it comes to safety I don't skimp. I used 1/4-20 stainless Steel bolts. I used Bed-it butyl tape for beding. I purchased scrap fall-off stainless from a "Water-Jet" cutting company. I cut the stainless with cut-off wheels in an angle grinder. I drilled the stainless in stages starting with 1/8 inch dia. and drilled my final hole one drill size larger than required. be sure to drill at low speed and I used vasaline intencive care to lubricate the drill. If you don't want to cut the plates yourself the "Water-Jet" company can doo it for you. Some of the places will be able to weld parts as well. Some of their scrap will be almost fabricated. I used some scrap that was 1 inch wide for backing for my sail tracks and various hooks etc.
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Old 19-09-2015, 17:46   #11
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Re: Stanchion backing plates - how thick?

It depends... Just for the backing plate 1/8 G10 is fine. But if you switch to 1/4" you can tap it and don't need anything but the bolts.
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Old 19-09-2015, 17:57   #12
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Re: Stanchion backing plates - how thick?

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...if you switch to 1/4" you can tap it and don't need anything but the bolts.
No way!
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Old 19-09-2015, 18:59   #13
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Re: Stanchion backing plates - how thick?

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It depends... Just for the backing plate 1/8 G10 is fine. But if you switch to 1/4" you can tap it and don't need anything but the bolts.
G10 is that strong with bolts? What kind of thread is best?

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No way!

I just did some googling and it says that the g10 should be at least as thick as the bolt. So, 1/4" bolt = 1/4"+ of g10. Not sure if fine thread or course thread would be better. It says to epoxy or loctite the bolt.
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Old 19-09-2015, 19:54   #14
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Re: Stanchion backing plates - how thick?

My objection is to tapping the G10 in lieu of using self-locking stainless nuts and fender washers.
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Old 19-09-2015, 22:50   #15
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Re: Stanchion backing plates - how thick?

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My objection is to tapping the G10 in lieu of using self-locking stainless nuts and fender washers.
Object all you like tapping G10 for deck hardware is very common on large ocean going race boats.

Use coarse thread not fine. Unlike metal the matrix needs the extra thickness

We always used loctite not epoxy, in case we wanted to remove whatever we were attaching.
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