Blind bolts to Fix Stanchions to Deck.

[Richard10002]

In a search, sbc mentions alloy expander bolts, but I'm not certain whether they are what I need, or where I can get to have a look at a picture on the web. Something which expands in the hole may not be right, as it doesnt seem too deep. thing it needs something which opens up at the back of the hole, to spread the load a bit.

The problem is that my stanchions are bolted with 2 bolts to the toe rail, which is fine. But there is also a bolt which goes through the deck into a part of the hull you just cannot get to... maybe I could if I got the jigsaw to the top side of the nicely fitted internal cupboards.

The bolts through the deck are loose and just spin without undoing, so I've hacksawed them off a couple of bases.

something like this looks like it might work, but can you get them in stainless, and am I on the right track?

Cheers

Richard

 

[steve_cronin]

Stanchion Bases are always a looser...

...in a GRP boat.

Just look at the mechanical advantage of the leverage.

Even before you attach any guardwires and impose the weight of a human or several humans thrown against them or even the weight of two yachts being pressed together (along with the down-pull of three to five heavy fenders trapped in the diminishing angle between the hulls at a regular frequency over very long time periods) you must know that the basic force of the ratio of a lever with at least 24" on one side of the fulcrum and 1/2" on the other, is enormous. Those are only the sideways forces. The fore and aft aren't inconsiderable either.

Most of those who have had to chisel away woven rovings and resin from the undersides of stanchion sockets after first destroying the inner cabin lining to get at the glassed over nuts and/or studs will know what I am talking about.

Luckyly, on my current boat, a Bavaria, provision is made for access to the stump bolt on every stanchion base by removing a series of small plywood panels by the removal of a few self tappers on each.

Even so, IMO, they are only anywhere near to being 100% reliable on a welded steel boat with steel decks unless they are butressed.

Steve Cronin

 

[cliff]

[ QUOTE ]
The problem is that my stanchions are bolted with 2 bolts to the toe rail, which is fine. But there is also a bolt which goes through the deck into a part of the hull you just cannot get to... maybe I could if I got the jigsaw to the top side of the nicely fitted internal cupboards.

[/ QUOTE ]If it was me I'd want a good load spreader below the deck. Why not use a hole saw and cut a nice circular hole in the top side of the nicely fitted internal cupboards. This would give access and would be easy to fit a cover over the hole or even screw in some soffit vents.
--------------------

"Artificial intelligence is no match for natural stupidity"
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[FAITIRA]

When I built my last boat, I used a hole saw as you describe Cliff and used the blanks/plugs used in kitchen units etc, about 2"dia, they were available in white or brown and made a neat access point to all the track/ deck fitting fixings.

 

[bigwow]

Would rivit nuts do the job?

 

[Richard10002]

[ QUOTE ]
Would rivit nuts do the job?

[/ QUOTE ]

Not sure how they work? the top of the bolt is at the bottom of the stanchion tube, so no way of getting a rivet gun down there, (I dont think so anyway).

Are there any web pics or references?

Cheers

 

[jwdorst]

Although I would agree with other posters that stanchions are rarely really reliable, certainly without some form of reinforcement under the deck, I think this is what you are looking for: blind rivet nuts ( http://www.gesipa.com/com/04/01/index.asp ). The come in a variety of materials and sizes and are offered by a variety of suppliers. Gesipa are however one of the leading brands. These rivet nuts require a special tool which Gesipa also supply ( I got mine on E-bay). All very pricey of course.... but it does work.

Mine is an aluminium yacht. I don't think you want to be riveting in GRP as the laminate would probably be destroyed around the edges of the rivetting hole.

However, perhaps you have enough room under the deck to slide a prefabricated reinforcement plate, with pre-installed blind rivet nuts, into the required postion under the stanchion base. You could then insert and tighten the bolts from the top and would not require additional room under the deck to accomodate a spanner.

 

[jwdorst]

Here is a useful animation of how rivet nuts work. This shows the use of a powered rivetting gun, however manual tools also exist and the principle remains the same. http://www.enfasco.com/frame4.htm

 

[bigwow]

They are like a threaded top hat that expands behind the panel like a rivit and leaves a tube with a thread. Sounds like you would not be able to get the puller in anyway, it was just a thought.

 

[owen]

unfortunately richard you are up against the perennial moody stanchion base problem.
There is no alternative other than accessing the under deck if you want to make a good job of it
a metal expander bolt will be relying on pressure exerted on the thickness of the deck which at say less than 1 inch thick is not enough.
Rivets would not have enough area under deck to provide the resistance to pulling out( bear in mind the original bolts use 1 inch washers)
As you may know some people rather than disturb the cabin woodwork dispense with the central bolt and just fill the hole with silicone.
another thought is to fill the central hole with epoxy and then screw in the largest self tapper that will go in.
An enterprising manufacturer might produce some stainless butterfly fixing that spring out into the void after being pushed through the deck but i have never seen any which would fit.
good luck

 

[Richard10002]

[ QUOTE ]
There is no alternative other than accessing the under deck if you want to make a good job of it

As you may know some people rather than disturb the cabin woodwork dispense with the central bolt and just fill the hole with silicone.


[/ QUOTE ]

You've got the picture exactly. At the moment I'm dispensing with the central bolt where they have had to be removed, but will consider the underdeck access over time.

I'll be keeping an eye open for S/S butterflies.

Cheers

Richard

 

[dickh]

I've just replaced ALL the bases and stanchions on my boat which are like yours - 2 bolts through the toe rail and one bolt through the deck. You MUST replace this deck bolt otherwise the stanchion will not be strong enough. On my boat, two bases had been replaced but the centre screws were not - one hole had been filled with silicon and the oyther had a selftapping screw fitted which was useless. All the stanchions had corroded into the bases. I had to cut holes in the plywood lining to get at the nuts, use either a jigsaw and a small padsaw or as suggested a hole saw as long as you can get the drill in position and don't drill through the deck with the pilot drill!(I wish I'd thought about a hole saw!) I covered up the jagged hole with a varnished thin plywood cover secured with 4 small SS selftappers. Advantage is that you will be able to access the nut in the future and your stanchions will be as firm as possible. Allow 3 to 4 hours per stanchion base. Drill out the countersunk screws holding the base to the toerail first with a ¼" centre drill followed by a 6mm drill. Allow one centre drill per screw - they blunt and break easily.
Make sure when fitting the bases to coat the SS screws with DURALAC to prevent corrosion in the future.
Good Luck!

 

[Richard10002]

[ QUOTE ]
I've just replaced ALL the bases and stanchions on my boat which are like yours - 2 bolts through the toe rail and one bolt through the deck. You MUST replace this deck bolt otherwise the stanchion will not be strong enough.

Make sure when fitting the bases to coat the SS screws with DURALAC to prevent corrosion in the future.
Good Luck!

[/ QUOTE ]

Dick,

Thanks for that. I'll be replacing the deck bolts at some time in the near future, but need to think my way around where, and how, to make the holes internally.... also how big to make them.

On Duralac..... I dont think they had invented this when the boat was built, or when anything S/S + Al was fitted. I now coat every differing metal with it, and plan to undo and redo on a 6 monthly/yearly basis.

Cheers

 

[Guest]

Can't exactly picture your problem but maybe this (it's the solution I'm coming to on my stanchions .....)

My boat has L shaped inverted stanchion bases. 2 bolts vertically down through a raised GRP toe-rail. There are then 2 horizontal short bolts from inner side into toe-rail.
From cabin / underdeck - it is too narrow to get fingers or tools up in there and when I've pulled out the bolts - no nut has appeared or seemed to be in place !
So my original solution and works ! Is a long stud threaded bar of same thread size as old bolts ... push down through stanchiopn base and toe-rail till you can get to end under deck to place washer and nut. Wind these on till 2 - 3 threads are proud. Pull stud bar up so that washer / nut is up under toe-rail and nut on top wound down and tightened. Snap of stud bar. Clean up top and fixed. That was solution #1.
Now I ma having solution #2 made locally here ... extra long stainless steel bolts and special nuts that are actually a rectangular plate with centre threaded hole. The bolts are long enough that end is just out of sight under deck - but accessible to put the "SBC" plate nut on. Being rectangular - it will a) have good backing area to take the weight, b) stop itself turning when tightening by virtue of the "wings" touching sides of toe-rail inner. It will look better as the visible top will be a bolt head again instead of a nut and bar thread.

The above is probably no use to you ... but thought I'd post !