Mounting Stanchions

[Bowdrie]

Must all four of fasteners for each of the bases be within the 4" wide, (horizontal measuring,) of the deck edge?
Can the inboard fasteners for the bases be inboard of that 4" wide structure at the deck edge?
Can you post a simple cross-section sketch of what you're up against?
I've successfully used a couple of different methods to accomplish what "I think" you're trying to do, but a clearer presentation would help.
One thing is for certain; using raised pads to mount the bases on goes a very long way to prevent water intrusion issues in the future.

[coopec43]

Originally Posted by Bowdrie

Must all four of fasteners for each of the bases be within the 4" wide, (horizontal measuring,) of the deck edge?
Can the inboard fasteners for the bases be inboard of that 4" wide structure at the deck edge?
Can you post a simple cross-section sketch of what you're up against?
I've successfully used a couple of different methods to accomplish what "I think" you're trying to do, but a clearer presentation would help.
One thing is for certain; using raised pads to mount the bases on goes a very long way to prevent water intrusion issues in the future.

Bowdrie


Who are you addressing your query to?

[Bowdrie]

Originally Posted by coopec43

Bowdrie
Who are you addressing your query to?

Post #15, the last one on the previous page.

[whmiles]

I know it is tempting to think that at least two bolts might be able to go through the deck on the inboard side. I have seriously looked at this option but I would not be happy to have only two bolts through fitted because it would create rotatory forces between the two sets of bolts with unsatisfactory compression forces being applied to the deck.
But, much more importantly, I’m afraid that it is just not possible. That 4” is probably a bit understated as the width varies along the deckline. -No, it is not possible to do that. I need another answer. If I were to place the stanchion so that two bolts could go through it would be a long way inboard, not quite in the middle of the available deck but operationally unworkable.
Do you have any other ideas?

[whmiles]

A cross section sketch will take a bit longer.

[s/v Jedi]

Originally Posted by whmiles

A cross section sketch will take a bit longer.

I think I know the best option, but you will need some specialty tools and materials.

In short: you make G10 fiberglass inserts the size of the stanchion bases plus a little. Then you make a pattern (piece of plywood) for a router so that you can route a slot for that insert for an exact fit. For depth it’s best to stay just proud of the deck, for example a 1” thick insert and a 7/8” deep slot.

Next is drilling and tapping the insert for the four stanchion fasteners. With 1” thick G10 you want to drill and tap short of going through, i.e. 7/8”. The most important reason for this is that no epoxy can enter from below when mounting these into the deck slots.
Also, two countersink holes under the stanchion base for screws into the wood below.

Mounting is done with thickened epoxy and the two screws. After the epoxy is fully cured, some sanding and priming and paint with the rest of the deck.

The stanchions simply mount with bolts using medium strength threadlocker.

[rslifkin]

Originally Posted by s/v Jedi

I think I know the best option, but you will need some specialty tools and materials.

In short: you make G10 fiberglass inserts the size of the stanchion bases plus a little. Then you make a pattern (piece of plywood) for a router so that you can route a slot for that insert for an exact fit. For depth it’s best to stay just proud of the deck, for example a 1” thick insert and a 7/8” deep slot.

Next is drilling and tapping the insert for the four stanchion fasteners. With 1” thick G10 you want to drill and tap short of going through, i.e. 7/8”. The most important reason for this is that no epoxy can enter from below when mounting these into the deck slots.
Also, two countersink holes under the stanchion base for screws into the wood below.

Mounting is done with thickened epoxy and the two screws. After the epoxy is fully cured, some sanding and priming and paint with the rest of the deck.

The stanchions simply mount with bolts using medium strength threadlocker.

That's a good way to do it. Otherwise a well mounted set of studs in the deck would work as well. Stanchion goes over the studs and gets held down with acorn nuts and washers.

[s/v Jedi]

Originally Posted by rslifkin

That's a good way to do it. Otherwise a well mounted set of studs in the deck would work as well. Stanchion goes over the studs and gets held down with acorn nuts and washers.

The problem is the wood underneath, as it reintroduces the high risk of getting wet again, which is the problem the OP is fixing.

So for mounting studs, you need to drill bigger holes, then cast epoxy and drill correct size holes after it is cured. Cast epoxy doesn’t hold threads as good as G10 fiberglass but it is done regularly and I haven’t observed a failure yet (it is often done for genoa track fasteners). The advantage is that it doesn’t require a router and it’s cheaper

[Bowdrie]

Originally Posted by s/v Jedi

Cast epoxy doesn’t hold threads as good as G10 fiberglass but it is done regularly and I haven’t observed a failure yet

I've done similar on a deck without core and lots of wood thickness underneath.
Using a spade bit, (~3/4",) to drill thru deck and then "wobble" the bit a little as it goes deeper.
This makes a hole that's wider at the bottom than at the deck.
Made-up a little plywood jig to hold 4 lengths of 5/16ths all-thread in the same pattern/orientation as the base, and longer than necessary.
Coated the all-thread parts with a couple coats of Boeshield T9 that was allowed to dry.
With suitable masking, the holes were almost filled with epoxy with the high-density filler.
Threads of all-thread also coated and the jig with the all-thread parts lowered into the holes with the plywood jig propped up above deck level to allow preliminary clean-up of flow-out epoxy.
when all was hard the nuts were removed from the all-thread parts, the plywood jig lifted off of the all-thread parts and then the all-thread parts were simply unscrewed from the epoxy castings.
Bases went on with machine screws, and with ~ 2-1/2" of thread length those bases were not going anywhere.

[coopec43]

Eventually I made up fiberglass pads, wedged them where necessary (say 15mm-10mm), epoxied the pads to the deck then through bolted/Sikaflex the stanchions to to the deck pads.

How will they ever leak?

[rslifkin]

Originally Posted by s/v Jedi

The problem is the wood underneath, as it reintroduces the high risk of getting wet again, which is the problem the OP is fixing.

So for mounting studs, you need to drill bigger holes, then cast epoxy and drill correct size holes after it is cured. Cast epoxy doesn’t hold threads as good as G10 fiberglass but it is done regularly and I haven’t observed a failure yet (it is often done for genoa track fasteners). The advantage is that it doesn’t require a router and it’s cheaper

Definitely. Whether it's through bolted, studs, or threaded holes for bolts, the core needs to be kept isolated and dry and the load needs to be spread into the deck enough that someone falling on a stanchion won't tear it out of the deck.

[coopec43]

Originally Posted by rslifkin

Definitely. Whether it's through bolted, studs, or threaded holes for bolts, the core needs to be kept isolated and dry and the load needs to be spread into the deck enough that someone falling on a stanchion won't tear it out of the deck.

I assume the "lifelines"(?) must be kept quite taut to prevent the stanchion being torn out of the deck?

[rslifkin]

Originally Posted by coopec43

I assume the "lifelines"(?) must be kept quite taut to prevent the stanchion being torn out of the deck?

I'm personally a fan of lifelines being just snug. That's enough that they don't give too much with pressure applied and will spread some of the load vs putting it all on one or 2 stanchions. Having any significant tension applied isn't necessary. I do see a lot of sailors with noticeably slack lifelines and I've never been a fan of that (especially because slack lifelines make a poor hand hold).

As far as not tearing out of the deck, if they're mounted decently, I think a lot of common stanchions will bend before the mounting fails. It's only when they're mounted poorly that breaking free would be a concern.

[Bowdrie]

Many years ago, the engineering dept. of the Naval Acadamy did a project on such an issue.
They found that the most obvious cause of stanchion failure was the lifelines going slack due to the bow/stern pulpits flexing when a load was placed against the lifelines.
The up-shot?
1, Don't let the pulpits flex, have secure triangulation in the structures.
2, Keep the lifelines tight.

[rslifkin]

Originally Posted by Bowdrie

Many years ago, the engineering dept. of the Naval Acadamy did a project on such an issue.
They found that the most obvious cause of stanchion failure was the lifelines going slack due to the bow/stern pulpits flexing when a load was placed against the lifelines.
The up-shot?
1, Don't let the pulpits flex, have secure triangulation in the structures.
2, Keep the lifelines tight.

And in general, when it comes to something that's intended as a safety device like lifelines and stanchions, just build it stronger than it should ever need to be. A solid top rail instead of traditional lifelines is also a nice upgrade.