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Old 28-11-2012, 16:00   #1
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What Backing Plate Size?

I am making backing plates for my Beneteau 423's mooring cleats. Factory supplies SS fender washers.

I am planning on 316 SS to keep them thin and compatible with the bolts.

How thick should the material be?

Because of clearance I can't make them a lot wider than the washers, but how far should I extend them beyond the bolt? I am sure the longer the better but what would be a reasonable amount to make it worth the effort to change out the washers?

Thanks,
Harry
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Old 28-11-2012, 16:10   #2
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Re: What backing plate size?

Quote:
Originally Posted by hlev00 View Post
I am making backing plates for my Beneteau 423's mooring cleats. Factory supplies SS fender washers.

I am planning on 316 SS to keep them thin and compatible with the bolts.

How thick should the material be?

Because of clearance I can't make them a lot wider than the washers, but how far should I extend them beyond the bolt? I am sure the longer the better but what would be a reasonable amount to make it worth the effort to change out the washers?

Thanks,
Harry
For 5/16" bolts I'd recommend 1/4" thick SS as large as you can go. A normal size would be 1-1/2 to 2 times the footprint of a deck fitting.

Personally I like to use 3/8" and 1/2" G10 material. Which can be epoxied the the undersize if one likes, making it even stronger. For my anchor windlass, I epoxied 4 sheets of 1/4" G10 to fit the radius of the deck.
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Old 28-11-2012, 16:26   #3
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Re: What backing plate size?

2 bolt cleats or 4 bolt? as Delmarray mentioned, thick plates are good because they will distribute the load well. thin plates bend allowing the fiberglass to take point loading. If the deck is cored there, this is especially important.....
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Old 28-11-2012, 16:44   #4
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Re: What backing plate size?

I second using G10 over metal. It's easier to work with, and can be epoxied in place, then drilled. Which makes installation a snap.

As for size, as big as you can? Ideally at least double the size of the fitting. But it is more important for it to spread the load in the direction of the expected force than perpendicularl to it.
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Old 28-11-2012, 16:53   #5
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Re: What backing plate size?

I might add, if it's epoxied/fillered in place it spreads the load evenly around the bolts. Where as, if it's just a flat plate, the load is on the high spots until it's been crushed to shape of the mating surface, which may loosen the bolts.
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Old 28-11-2012, 17:16   #6
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Re: What backing plate size?

You guys have a good source on G10? I did some quick googling... Looks expensive.
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Old 28-11-2012, 17:30   #7
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Re: What backing plate size?

A backing plate on the typical mooring cleat may do nothing at all. The force is pulling the bolts sideways thru the deck.
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Old 28-11-2012, 17:37   #8
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Re: What backing plate size?

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You guys have a good source on G10? I did some quick googling... Looks expensive.
No more then SS. I use to buy it locally until the guy retired. But most plastic distributors carry it or can get it.
e.g. GRADE G10 FR4
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Old 28-11-2012, 18:13   #9
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Re: What Backing Plate Size?

daddle, if you have ever seen a cleat tear a piece of deck right off you wouldn't say that.

By the way if the deck is cored there, even with (especially with) plywood, you will need to build up an epoxy canulus or you will just crush the deck. If it is solid FG then you are okay.
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Old 29-11-2012, 06:12   #10
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Re: What Backing Plate Size?

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... By the way if the deck is cored there, even with (especially with) plywood, you will need to build up an epoxy canulus ANNULUS or you will just crush the deck. If it is solid FG then you are okay.
The Annulus*, or annular space, is the space between concentric circles.
The inner circle is the fastening diameter. The out circle represents the removed core material, filled with epoxy.
* Latin for "little ring"
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Old 29-11-2012, 07:52   #11
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Re: What Backing Plate Size?

I wish I still had the photo, but after Fabian, gusting to 177 mph, we found 8 ft of the foredeck of a Cheoy Lee Midshipman still attached soundly to the mooring cleats, rest of the boat, vacumn cleaner job.
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Old 29-11-2012, 08:35   #12
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Re: What Backing Plate Size?

Canulus, annulus...I have three years of highschool Latin in my noggin, but I just call it a "doughnut"!
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Old 29-11-2012, 18:57   #13
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Re: What backing plate size?

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Originally Posted by delmarrey View Post
For 5/16" bolts I'd recommend 1/4" thick SS as large as you can go. A normal size would be 1-1/2 to 2 times the footprint of a deck fitting.

Personally I like to use 3/8" and 1/2" G10 material. Which can be epoxied the the undersize if one likes, making it even stronger. For my anchor windlass, I epoxied 4 sheets of 1/4" G10 to fit the radius of the deck.
The two bolts are 1/2", 3-1/2" apart. Unfortunately the bolts are a bit short so there is only 1/4" or so showing below the nuts. I was hoping to change to nylock nuts, but will go with Loctite with as think a plate as I can manage. I am hoping to also use a thin layer of epoxy and compression resistant filler to help spread the load.

I wil definitely check out the G10 to for my windlass as those have about 6" below the nuts.

Thanks to all!
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Old 29-11-2012, 20:23   #14
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Re: What backing plate size?

Quote:
Originally Posted by hlev00 View Post
The two bolts are 1/2", 3-1/2" apart. Unfortunately the bolts are a bit short so there is only 1/4" or so showing below the nuts. I was hoping to change to nylock nuts, but will go with Loctite with as think a plate as I can manage. I am hoping to also use a thin layer of epoxy and compression resistant filler to help spread the load.

I wil definitely check out the G10 to for my windlass as those have about 6" below the nuts.

Thanks to all!
Why not just buy new longer bolts?
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