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Old 09-10-2014, 11:28   #16
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Re: Re-installing Stanchions

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Originally Posted by Ann T. Cate View Post
Skipmac,

If the backing plate underneath the stanchion is large enough, you won't get gelcoat cracks from levering on the stanchions. Maybe I'm wrong, but it seems to me to be a deal of spreading out the load.

For background, we have never had a boat that had (or required?) rubber pads under the stanchion bases. However, if you're convinced they need them, why not go get some thin hard rubber pads? from a rubber products seller? As long as you did good with the backing plates and your choice of sealant, you ought to be okay.

Ann
Hi Ann,

I have made large, heavy backing plates but I don't think that will relieve all the stress on the top skin of the deck.

Did a force calculation, assuming someone hoisting themselves up from a dinghy grasping the stanchion about 24" from the deck and pulling with a force of 50 lbs, both reasonable estimates I think. That would put a force of about 800 lbs where the edge of the stanchion base meets the deck.

Been many years since I spent a lot of time on OP's boats but from my yacht broker days I seem to recall it was very common to see surface cracks in the gelcoat around the stanchion bases. Even a well made boat that's a lot of pressure on a small point.

Maybe a question, how many forum members with older fiberglass boats have small cracks around the stanchion bases, especially the ones by the lifeline gates?
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Old 09-10-2014, 11:51   #17
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Re-installing Stanchions

Our 1989 Tayana 42 has no cracks around stanchion bases. There are raised pads built into the deck for the stanchion bases. I believe the deck is solid glass under these pads.


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Old 09-10-2014, 12:48   #18
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Re: Re-installing Stanchions

Here's a recipe for reinforcing your deck around the stanchion bases, should you so choose.

First you need to make sure that the holes for the fasteners are drilled oversized, & properly filled with epoxy. An easy trick for this is once you drill the holes oversized, is to take an allen wrench & put the long leg into the chuck of the drill. Then stick it into the hole, & use it to remove a bit more core. The diameter's up to you.
- Use a shop vac to suck the core dust out of the holes.

After which, of course, you tape over the holes on the underside of the deck, & do your epoxy fill.
- If you like, you can mix the epoxy with milled or chopped fibers to strengthen & toughen it. (see the West System guides, or System Three "Epoxy Book").

DON'T add more than about 1/4" at a time, 1cm MAX (depth/thickness wise). Or the epoxy will go exothermic on you, which may cause bad things to happen ;-) But make sure to keep adding epoxy incrementally while it's still "green", (until the holes are full) so that all of the epoxy pour(s) bond together as one piece.

Once that's done, for a load spreader plate on deck, pick up some G10. It's a high pressure epoxy laminate, which, depending on what fibers are used & in what percentage by weight, can be stronger than aluminum. MatWeb - The Online Materials Information Resource Get some that's say 1cm - 1/2" or so thick.

Ease/bullnose all of the corners, and (preferably) bevel the edges of the plates to some degree, so as not to create stress risers where the edges meet the deck. Though if you're not worried about such, you can just bullnose (round over) the edges. But that would defeat the purpose of beefing up the area under the stanchion bases to prevent stress cracks.

From there, drill holes in it to match the ones in the deck (which you put in after filling your oversized holes) & the stanchion bases. Then epoxy (use epoxy & milled fibers again) the pads in place where the stanchions are going to go, using bolts to hold it in place while your epoxy milled fiber blend cures.
- Remember to pre-coat the bolts with release agent. That & to sand off the gel coat or paint where the plates will go, & wipe said areas down with acetone or MEK).

And Viola, you have heavily reinforced the deck around your stanchion bases. After which you mount them as before, with sealant, backing plates, etc.


PS: To some degree, the milled fibers blended into the epoxy, in between the load spreader plates & the deck, is also to level them (or set them at whatever angle you desire). And to fill any gaps & such. There's a great explanation in the section on hardware bonding, (hardware) base casting in the book "On boat construction". Which is available for free download via Pdf on the West System site.

Also, if you want to get fancy, & you have say, foam cored decks. You can use G10 to replace the core in any area where you're adding a high load fitting. Albeit, after swapping out G10 for the light weight core, you have to re-laminate fiberglass skin over top of it.
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Old 09-10-2014, 14:12   #19
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Re: Re-installing Stanchions

skip- Grainger and McMaster should have this stuff too, but Amazon sells it as well. They bought out Small Parts Co. about two years ago, great suppliers for all sorts of "exotic" materials and bits.

EPDM Sheet, White, 0.062" Thick, 12" Width, 24" Length, 40A Durometer, FDA Compliant: Epdm Rubber Raw Materials: Amazon.com: Industrial & Scientific

This is white "EDPM" silicone rubber sheeting, and it is available in many thicknesses and sheet sizes. Should stay flexible for a very long time. There may be other more suitable materials, but I think this is one of the right ones to use. No other sealant should be necessary.
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Old 12-10-2014, 19:32   #20
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Re: Re-installing Stanchions

This is a most fortunate coincidence, this discussion. I have removed ALL of my deck hardware in the last couple weeks, in preparation for a complete deck repaint and non-skid application. Here's what I've observed after the last twelve years: I removed my securing bolts using a Milwaukee 28 volt impact driver socket, with someone inside the boat holding a wrench on the nylock nuts. Zip! Off the nuts came, and zip, out came the 3M 5200-sealed fasteners. The 1/4 inch aluminum plate backup pads (double the surface area of the stanchion base) remained in place due to the 5200 I used to keep it there. The backup pads were underneath a 3/4 inch epoxied plywood backup pad that spanned a couple deck stringers. No apparent issues with these. Between the stanchion base and the deck, I used a 1/8 inch reinforced black neoprene gasket, seated in 5200, on both sides of the gasket. The stanchion, without its fasteners, broke free of the stanchion with a mild application of bend. The gasket came free with the use of a sharp wide chisel. Underneath the gasket there were NO signs of fracturing of the epoxy/fiberglass over plywood, caused by the torquing of the stanchion under full application of my massive body. Now that the deck is clear, I have drilled out all the holes, recoated the walls with epoxy resin, then redrilled for the future fasteners. I'm in the process of repriming with epoxy primer, to be followed by three coats of Sterling Cloud White LPU. Then, new neoprene gaskets will be set into fresh 5200, the now-polished stanchions, pedestals, windlass and other hardware will be set atop the neoprene gaskets, receiving a dab of 5200 at the bolt holes, then everything will be wound down with a wrench and socket wrench. Two days later, I will torque everything down a couple more turns for good measure. While the neoprene does exhibit some degradation on the extreme edges from UV light, everything else is effectively brand new, but I still change it out. I do this every 12, or so years. This is the third (and probably last) time I will have done this routine. I have used butyl tape on customers' boats, but I prefer my system for my own. There have been ZERO leaks or degradation of the plywood/epoxy core, in this time. I am sticking to this formula.
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Old 12-10-2014, 20:55   #21
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Re: Re-installing Stanchions

I think putting any sort of padding underneath a stanchion is a bad idea. Here's why.

If the base of the stanchion is strong, and the backing plates are solid enough to not flex, then when you tighten them down they provide even, continual contact across a broad section of the deck. If you add padding, you're introducing, by definition, the opportunity for the stanchion to tilt, even just fractionally, when lateral force is applied. You're then applying concentrated force against the edge of the stanchion base plate in the direction of the force. The padding will bottom out, and you'll have a line of pressure much greater than if the base was flat and monolithic against the deck, and so greater possibility of fracturing the gel coat.

This is also a reason why I think the suggested practice of sealing a fitting, screwing it down hand tight, letting the sealant set, then torquing it down to make a sealant gasket is not a good idea with fixtures subject to load.

If the deck is not going to flex, then the gelcoat is not going to crack, unless you do something (like padding) to create the opportunity for pressure points to develop.

I do in fact put rubber (1/16" hard neoprene sheeting) under some fixtures, but only things like flag pole sockets, thru-deck fittings, etc. that are not subject to any appreciable load.
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Old 13-10-2014, 10:02   #22
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Re: Re-installing Stanchions

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Originally Posted by Roy M View Post
This is a most fortunate coincidence, this discussion. I have removed ALL of my deck hardware in the last couple weeks, in preparation for a complete deck repaint and non-skid application. Here's what I've observed after the last twelve years: I removed my securing bolts using a Milwaukee 28 volt impact driver socket, with someone inside the boat holding a wrench on the nylock nuts. Zip! Off the nuts came, and zip, out came the 3M 5200-sealed fasteners. The 1/4 inch aluminum plate backup pads (double the surface area of the stanchion base) remained in place due to the 5200 I used to keep it there. The backup pads were underneath a 3/4 inch epoxied plywood backup pad that spanned a couple deck stringers. No apparent issues with these. Between the stanchion base and the deck, I used a 1/8 inch reinforced black neoprene gasket, seated in 5200, on both sides of the gasket. The stanchion, without its fasteners, broke free of the stanchion with a mild application of bend. The gasket came free with the use of a sharp wide chisel. Underneath the gasket there were NO signs of fracturing of the epoxy/fiberglass over plywood, caused by the torquing of the stanchion under full application of my massive body. Now that the deck is clear, I have drilled out all the holes, recoated the walls with epoxy resin, then redrilled for the future fasteners. I'm in the process of repriming with epoxy primer, to be followed by three coats of Sterling Cloud White LPU. Then, new neoprene gaskets will be set into fresh 5200, the now-polished stanchions, pedestals, windlass and other hardware will be set atop the neoprene gaskets, receiving a dab of 5200 at the bolt holes, then everything will be wound down with a wrench and socket wrench. Two days later, I will torque everything down a couple more turns for good measure. While the neoprene does exhibit some degradation on the extreme edges from UV light, everything else is effectively brand new, but I still change it out. I do this every 12, or so years. This is the third (and probably last) time I will have done this routine. I have used butyl tape on customers' boats, but I prefer my system for my own. There have been ZERO leaks or degradation of the plywood/epoxy core, in this time. I am sticking to this formula.
Sounds great Roy! Yes, 5200's holding ability on metal is grossly overstated often on this forum.
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Old 13-10-2014, 10:17   #23
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Re: Re-installing Stanchions

Suijin, not all boats are exactly the same. I've been working on them for, approaching, forty years. Physics hasn't changed, though. A stanchion, a pulpit, or anything that is subject to leverage loads means that a profound amount of pressure, far beyond the mere weight of a large man, gets exerted on the fulcrum of the item. In this case, the relatively sharp edge of metal plate. Someone suggested rounding this edge off. That's not a bad idea, but the issue remains the same: the edge becomes the fulcrum and the lever arm (the stanchion, or whatever) generates huge forces to crush what lies beneath it. Maybe you don't see it immediately, but when you work on older boats you begin to notice those little, radiating (and often rust-stained) cracks that develop. On a solid glass boat it's not as critical as with a cored deck (foam, balsa, plywood, whatever). I abuse my boat because I think that's normal and expected of it. I then take measures to reduce the consequences of this intentional abuse. It has paid off over the years.
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Old 13-10-2014, 10:25   #24
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Re: Re-installing Stanchions

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If you are concerned about the stanchion bases torquing the deck, put reinforcing glass under the pads. Buy laminated sheet glass in 1/8"-1/4" thickness from McMaster-Carr, cut it into pads an 1" or more larger than the stanchion base, epoxy them to the deck and reinstall the stanchions on them. This is probably over kill but would give you stanchion bragging rights in the marina.

I would not use anything but caulk under the bases. A compressible pad will allow the stanchions to rock ever so slightly and probably cause leaks around the fasteners.
Skip,

I wouldn't put anything under 'em except for your butyl... If you're really concerned... break the edge of the base with a barely imperceptible bevel that will fill in with butyl....

If you're so inclined to still want something... I say Peter has it going on with the glass board, or even 1/16" G10...

Clamping anything flexible under there is asking for trouble...

PS take a pic, so we know what yer bases look like... 4 hole rectangle?
Or crappy 2" round with a center bolt like my crappy crappidy crap crap crap... (I think I'm switching bases)
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