How to mount stanchions?

The reason why I don't want to use SS backing plates is weight.

As the stanchions are 900mm against the 600mm "normal" height stanchions I'm already 50% overweight. If I use SS plate it will be heavier and not as strong as f/g. As I would need X20 plates the weight would be considerable.

I'm going for structural channel

Pound to pound, FRP is actually a stronger material than steel, making it a much stronger system

Screenshot 2021-09-28 at 18-35-32 fiberglass channel beam - Google Search.png
 
Forget the grp channel. What you are trying to do primarily is prevent pull through of the nut and washer through the substrate. A thick piece of grp or some very large metal washers will do the trick. Similarly, forget the o-ring. It adds nothing if you use an appropriate sealant such as butyl.
 
geem said:
The difficulty with both of these materials is they are hard or very hard to drill insitu. It is possible to pre-drill them but then getting them in the correct place can be tricky. I would go the grp route for this reason. Having had to re-drill the aluminium backing pads that I are glassed in to my deck to reinforce the Genoa tracks, I can confirm that drilling through grp then in to aluminium is a complete nightmare. The grp blunts the drill bit. We had to sharpen drill bits a hundred times.
Click to expand...
One would pre drill the aluminium, using the stanchion as a pattern. Put the bolts through the deck, Put epoxy ( with suitable filler) on back of plate such that it beds evenly. Offer up the plate ( having first checked it fits OK.) Then bolt up. What is hard about that?
As for GRP blunting drill bits !!! Yet you suggest using even more GRP ??? seems an odd decision.
Trying to get under a side deck to roll on GRP with resin etc is time consuming & MAY well result in air pockets etc. Rough edges & a finish that is NOT neat. Using a pre made GRP channel just makes it harder to access the ends of the bolts & tighten the nuts. It still has to be pre drilled, like the aluminium. Unless stuck in place first, which can be a faff. It has to be supported whilst the glue goes off.
Like I said the GRP expert is limited in his range of opinion & should be ignored - apart from advice on which resins & fillers for bedding etc.
 
coopec said:
The reason why I don't want to use SS backing plates is weight.

As the stanchions are 900mm against the 600mm "normal" height stanchions I'm already 50% overweight. If I use SS plate it will be heavier and not as strong as f/g. As I would need X20 plates the weight would be considerable.

I'm going for structural channel

Pound to pound, FRP is actually a stronger material than steel, making it a much stronger system

View attachment 123302
Click to expand...

I have an inner forestay deck mount to improve and was going to use stainless as the backing pad. I was advised that GRP is stronger than steel and could use a GRP backing pad as it is stronger, based on your lb/lb comparison.

Steel density is about 0.3lb / cubic inch, GRP is about 0.055 lb / cubic inch. So for the same strength you need a lot of GRP compared to steel.

UTS of 316 Stainless is 580 MPa, UTS of GRP 250 - 450 MPa. Stainless is stronger than GRP.

In the end I settled for a stainless backing pad, at 5mm, about 120mm x 70 mm (to fit the space) for under the deck pad eye and will take a strap down into the hull to tie the inner forestay to.

My advice is to think carefully about this. The base of your stanchion is very narrow, my experience of stanchion bending is that it is a longitudinal force from berthing movement into or out off, that bends the stanchions and you have a larger lever than most with the extra stanchion height. I am not sure that a GRP backing pad will resist the force and it could crush if too thin, pulling the bolts up into the deck core.
 
BlowingOldBoots said:
It would be worth downloading their free guides. They show how mounting hardware through cored decks can be done securely, and many other relevant topics. The advise given on here concurs with what West claim is good practise. As someone who has done a lot of DIY on boats, the West Guides are good sources of information on GRP work. I am surprised that you don’t know about them as they usually pop up when googling for advice.

That’s what they have to do with your plans.
Click to expand...

I am of course aware of the West System

I'm not interested in West System as they use epoxy and I use polyester/vinylester.
AND they are double the price of other suppliers for the same product.
 
geem said:
I don't know what you are using but common sense when laying up flat glass sheets to make backing pads is you would use heavy cloth. Probably the heaviest cloth you are likely to use when boat building. From experience, the heaviest cloth most supplier carry. It's quicker to do than say using 7 oz cloth that will take 20 layers or so to get to something substantial enough for the job in hand. Good luck
Click to expand...

I made up a mold today for channel section. It is 5ft long so I should be able to get around six backing pads per lay-up.

I'm going to use CSM and WR which should be strong and quick to layup.

Thanks for your help(y)
 
[/QUOTE]
coopec said:
I am of course aware of the West System

I'm not interested in West System as they use epoxy and I use polyester/vinylester.
AND they are double the price of other suppliers for the same product.
Click to expand...

I think you are being deliberately obtuse, it demeans you. I never said use West, I stated that the advice given corresponds with West’s Guides, which are considered good guides for GRP work, irrespective of the Epoxy, Polyester glue type. I was hoping that you could be assured that the advice was sound, which was the objective.
 
  • Like
Reactions: pvb


I think you are being deliberately obtuse, it demeans you. I never said use West, I stated that the advice given corresponds with West’s Guides, which are considered good guides for GRP work, irrespective of the Epoxy, Polyester glue type. I was hoping that you could be assured that the advice was sound, which was the objective.
[/QUOTE]

OK I get your point.

I don't think they are the authority on fiber-glassing. I don't agree with their advice regarding building of drinking water tanks which would/did not have approval of WHO(?)

I think they may have updated their literature. (I'll see if I can find it.)(y)

PS I THINK THIS IS IT. I may have stumbled on the article straight away. Here it is here. (I haven't had time to read it to see if they have updated their advice to comply with U. S. Coast Guard (USCG) regulations, Food and Drug Administration (FDA) regulations, American Boat & Yacht Council (ABYC) standards)

Epoxy Composite Tank Guidelines
 
Last edited:
Daydream believer said:
One would pre drill the aluminium, using the stanchion as a pattern. Put the bolts through the deck, Put epoxy ( with suitable filler) on back of plate such that it beds evenly. Offer up the plate ( having first checked it fits OK.) Then bolt up. What is hard about that?
As for GRP blunting drill bits !!! Yet you suggest using even more GRP ??? seems an odd decision.
Trying to get under a side deck to roll on GRP with resin etc is time consuming & MAY well result in air pockets etc. Rough edges & a finish that is NOT neat. Using a pre made GRP channel just makes it harder to access the ends of the bolts & tighten the nuts. It still has to be pre drilled, like the aluminium. Unless stuck in place first, which can be a faff. It has to be supported whilst the glue goes off.
Like I said the GRP expert is limited in his range of opinion & should be ignored - apart from advice on which resins & fillers for bedding etc.
Click to expand...
So you don't think grp blunts drill bits? It does. The problem isn't that they blunt them, it the fact that you cannot then drill through steel or aluminium once blunted. A blunt drill bit will drill grp but not steel. That was my point. You obviously misunderstood.
Their are many ways to reinforce for fittings. Bonding grp pads on to the underside of the deck with epoxy putty is easy. I have done it.
Once your pads are in place you may have something like 3/4" of solid grp. You can then position your stanchion bases and drill through the lots.
I have never suggested using channel. I wouldn't as I see no benefit.
I good friend of mine is an excellent boat builder and he uses grp sheet for reinforcement out of choice. It keeps the boat as a single material. You get less sweating where bolts come through due to condensation. Metal backing plates sweat due to the cold bridging of the through bolts.
There will also be some condensation from bolts but not as bad with grp as metal
 
geem said:
So you don't think grp blunts drill bits? It does. The problem isn't that they blunt them, it the fact that you cannot then drill through steel or aluminium once blunted. A blunt drill bit will drill grp but not steel. That was my point. You obviously misunderstood.
Their are many ways to reinforce for fittings. Bonding grp pads on to the underside of the deck with epoxy putty is easy. I have done it.
Once your pads are in place you may have something like 3/4" of solid grp. You can then position your stanchion bases and drill through the lots.
I have never suggested using channel. I wouldn't as I see no benefit.
I good friend of mine is an excellent boat builder and he uses grp sheet for reinforcement out of choice. It keeps the boat as a single material. You get less sweating where bolts come through due to condensation. Metal backing plates sweat due to the cold bridging of the through bolts.
There will also be some condensation from bolts but not as bad with grp as metal
Click to expand...
I am not suggesting that you are wrong about GRP & drill bits. I am non commital on that. Only wondering why , having made the assertion, you want to drill even more GRP. Seems counter productive.
Does one have to make the GRP pads separately? If so what a time consuming faff & waste of material. Of course that does not apply if they are obtainable in nice suitable sizes !!!! Is that likely without extensive, dusty, cutting.
The OP suggested channel so I accept that you did not state that.
One drills the aluminium on a pillar drill first. Not rocket science.
However, having a workshop, machining all sorts of metal items, puts me at an advantage. Having used a lot of metal in my joinery works, I expect that my skills are a little bit better than those of some not used to such work with limited tools.

But this is only a discussion with expression of opinion & not an arguement. The OP will make his own decision & one hopes it works Ok. He certainly has a selection of views to consider.
 
Last edited:
Daydream believer said:
I am not suggesting that you are wrong about GRP & drill bits. I am non commital on that. Only wondering why , having made the assertion, you want to drill even more GRP. Seems counter productive.
The OP suggested channel so I accept that you did not state that.
One drills the aluminium on a pillar drill first. Not rocket science.
However, having a workshop, machining all sorts of metal items, puts me at an advantage. Having used a lot of metal in my joinery works, I expect that my skills are a little bit better than those of some not used to such work with limited tools.

But this is only a discussion with expression of opinion & not an arguement. The OP will make his own decision & one hopes it works Ok. He certainly has a selection of views to consider.
Click to expand...
I also have full workshop facilities. Every power tool you can imagine, pillar drill, bench grinder, thickness planers, table saw, spray equipment, etc. I spent the last 12 months working full time on refitting my boat. I don't have to ask on this forum for advice. It the third boat we have refit. You learn the skills if you don't have them. You are not unique
 
geem said:
I also have full workshop facilities. Every power tool you can imagine, pillar drill, bench grinder, thickness planers, table saw, spray equipment, etc. I spent the last 12 months working full time on refitting my boat. I don't have to ask on this forum for advice. It the third boat we have refit. You learn the skills if you don't have them. You are not unique
Click to expand...
Nobody was suggesting that you had to ask for advice. You certainly seem quick to offer it. I was not suggesting that you in particular did not have the skill set. However, one only has to wander round the boat yard or club cruiser storage area to see that many have not had the chance to pick up the skills, or have not had the background that enables them to pick up the skills. Those bought up working with paper have different skills to the man bought up chiselling wood. Some can cross the divide easily. Some find it difficult. Nothing wrong with either though.
 
I wonder what the GRP channel-shaped backing plates are going to look like on the inside of the boat? A bit more intrusive than nuts.
 
Some people will tell you that stanchions should be attached in such a way that they can be ripped off in a collision without tearing great chunks out of the hull.
I vaguely remember reading similar in some code of practice but it was a long time ago and cannot recall the source.
It does make some sense, you wouldn't want a few square feet of deck missing after hitting something.
Most stanchions are fairly lightly attached and work fine in everyday real life use?
 
  • Like
Reactions: pvb
You must log in or register to reply here.

Share this page

Top