Babystay Backing Chainplate size?

[Tim Good]

This is my babystay. I’m replacing the Ubolt with a proper chainplate because one of my other U Bolt chainplates snapped. See my other thread about that.

On this one you can see discolouration around the U bolt on the deck side. It’s also lifting very slightly which you maybe can’t see.


Here is a picture of the backing plate on the underside. I don’t know but it looks very small to me and perhaps why on the top side the U bolt looks like it is lifting slightly?

Does anybody else hear think that this stainless backing plate looks remarkably small?

 

[TernVI]

I would guess that the babystay was originally designed to take a certain load, then later someone decided to set a sail on it?
One some boats the babystay is quite light, it's a control, to stop the mast inverting and prevent 'pumping' over waves.
If you want to use it to set a sail on it a lot of breeze, you need to design it for the job.
It becomes a forestay, and as the sail deflects it into a curve, it will take a lot of the load off the 'real' forestay.
That would include understanding about how the force gets back to the foot of the mast (loosely speaking!)
It's trying to lift the deck off. The load should not be into the deck, it needs a path through bulkheads or other verticals, or a very strong beam across to the hull skin.
You need a shipwright or mechanical design engineer, not a vendor of slightly bigger shinier brackets.

 

[Tim Good]

I would guess that the babystay was originally designed to take a certain load, then later someone decided to set a sail on it?
One some boats the babystay is quite light, it's a control, to stop the mast inverting and prevent 'pumping' over waves.
If you want to use it to set a sail on it a lot of breeze, you need to design it for the job.
It becomes a forestay, and as the sail deflects it into a curve, it will take a lot of the load off the 'real' forestay.
That would include understanding about how the force gets back to the foot of the mast (loosely speaking!)
It's trying to lift the deck off. The load should not be into the deck, it needs a path through bulkheads or other verticals, or a very strong beam across to the hull skin.
You need a shipwright or mechanical design engineer, not a vendor of slightly bigger shinier brackets.

Well you could be right. The designer was Ian Anderson and it was built in Falmouth to a Lloyds certification so I imagine it was well thought through. It doesn’t change my impression of these U bolts however.

I was considering have a detachable babystay since it snags my Twistle Rig when deployed. But I’ve never been brave enough to remove it. You’d think when running downwind under two poles out sails they it wouldn’t be doing much but I still wasn’t man enough to risk removing it.

 

[TernVI]

One of my dinghies has U-bolts for the shrouds.
M6 U-bolt for 3mm shroud.
That is a comfortable ratio.
A boat I used to own had 3mm shrouds on big staple-type things each with 2 M8 bolts.
And these are light rigs not needing much pre-tension.

I'm not familiar with Ian Anderson, unless you're talking a bout a man known for playing the flute while standing on one leg.
If the designer is still around why not get in touch?
I still get hassled about things I designed last century, although thankflly most of it went in a skip years ago....

If the rig was designed to Lloyds with those fittings, it might mean that the lowers and babystay are not meant to be doing much.

 

[Tim Good]

If the rig was designed to Lloyds with those fittings, it might mean that the lowers and babystay are not meant to be doing much

I would tend to agree but I heard of a boat similar to mine with a very similar rig losing its lower aft and it lost the most. I was quite surprised really but that is apparently what happened. So now I’ve heard that I’m beefing things up a tad.

 

[TernVI]

I would tend to agree but I heard of a boat similar to mine with a very similar rig losing its lower aft and it lost the most. I was quite surprised really but that is apparently what happened. So now I’ve heard that I’m beefing things up a tad.

Beefing things up has to be done right.
Thicker wire for the lowers will stretch less, so their chain plates take more load. You strengthen the chain plate, you may need to strengthen that which it is bolted to. Frankly, from what I can see of the structure, the stainless bits are not the most worrying. They don't look to have a big safety factor compared to the wire, but look quite capable of pulling the deck off. Obviously I can't see the whole picture and it's not exactly my field, but I think you need it looking at by a man who understands these things.

I'm not sure what the Lloyds accreditation actually proves. It may just be to assure you it's built to design, not that it was designed as a brick outhouse.

 

[bristoljim]

This is my babystay. I’m replacing the Ubolt with a proper chainplate because one of my other U Bolt chainplates snapped. See my other thread about that.

On this one you can see discolouration around the U bolt on the deck side. It’s also lifting very slightly which you maybe can’t see.

View attachment 101512
Here is a picture of the backing plate on the underside. I don’t know but it looks very small to me and perhaps why on the top side the U bolt looks like it is lifting slightly?

Does anybody else hear think that this stainless backing plate looks remarkably small?

View attachment 101514

This is my babystay. I’m replacing the Ubolt with a proper chainplate because one of my other U Bolt chainplates snapped. See my other thread about that.

On this one you can see discolouration around the U bolt on the deck side. It’s also lifting very slightly which you maybe can’t see.

View attachment 101512
Here is a picture of the backing plate on the underside. I don’t know but it looks very small to me and perhaps why on the top side the U bolt looks like it is lifting slightly?

Does anybody else hear think that this stainless backing plate looks remarkably small?

View attachment 101514

Its crying out for a small deck beam to spread the load - top hat section in carbon ? with 4 bolts through the locally beefed up flanges to the deck fitting - how are your laminating skills
Jim

 

[peter gibbs]

I would guess that the babystay was originally designed to take a certain load, then later someone decided to set a sail on it?
One some boats the babystay is quite light, it's a control, to stop the mast inverting and prevent 'pumping' over waves.
If you want to use it to set a sail on it a lot of breeze, you need to design it for the job.
It becomes a forestay, and as the sail deflects it into a curve, it will take a lot of the load off the 'real' forestay.
That would include understanding about how the force gets back to the foot of the mast (loosely speaking!)
It's trying to lift the deck off. The load should not be into the deck, it needs a path through bulkheads or other verticals, or a very strong beam across to the hull skin.
You need a shipwright or mechanical design engineer, not a vendor of slightly bigger shinier brackets.

When I fitted a baby stay to my Fulmar years ago and researched the stress offsets required, the whole exercise became more of a challenge. Taking the load to the deck alone is wrong and potentially damaging. The U bolt requires to be secured through the deck to a member of such strength and size that the load is actually taken not by the deck but the hull / deck joint. This can be achieved via a piece of steel bedded at its ends, or a serious piece of marine ply shaped and bedded to the hull / deck joint.

Professional opinion is always valuable.but whatever under deck bracing you adopt, you can check its resistance to deflection on the bench in advance of installation.
This arrangement will also deal better with lateral shock stresses as the sail fills and backs than just relying on the deck (often sandwich!)

PWG

 

[doug748]

This is my babystay. I’m replacing the Ubolt with a proper chainplate because one of my other U Bolt chainplates snapped. See my other thread about that.

On this one you can see discolouration around the U bolt on the deck side. It’s also lifting very slightly which you maybe can’t see.

View attachment 101512
Here is a picture of the backing plate on the underside. I don’t know but it looks very small to me and perhaps why on the top side the U bolt looks like it is lifting slightly?

Does anybody else hear think that this stainless backing plate looks remarkably small?

View attachment 101514

My reaction is the same as before really. If there is no cracking or distortion around that backing plate after a quarter of a century then it is unlikely to cause a problem in the next 25 years. Assuming it is used in the same way.
However if it's convenient for you to make it a bit larger then it would certainly do no harm.

Amateurs always tend to overdo things, I am as guilty as anyone but you have to know where to stop.

OTOH that U bolt does look dodgy and I would look for something more robust there.

.

 

[vyv_cox]

A couple of points:
There is nothing wrong with the U-bolt, it just needs bedding in some good mastic sealant. Crevice corrosion is caused by exposure to seawater. Keep it out and all will be well.
The babystay on my Sadler 34 has no plate beneath the single bolt (10 mm I think), just a washer. Perfectly adequate for the past 35 years.

 

[DownWest]

Since you seem to have a bulkhead there(?) Might it be an idea to have a larger backing plate with a tang to carry the load down, even to the hull? If the new fitting is a bit wider, then on this side and have clearance for the nut, or perhaps behind the panel? Bit of peace of mind

 

[Tim Good]

Since you seem to have a bulkhead there(?) Might it be an idea to have a larger backing plate with a tang to carry the load down, even to the hull? If the new fitting is a bit wider, then on this side and have clearance for the nut, or perhaps behind the panel? Bit of peace of mind

Interesting you say that... after thinking that the boat is so well built in many areas it would have been lax not to have done exactly what you said... so I looking forward closely.

You can see a weld which would suggest a downward plate down the bulkhead. Would you concur?

 

[DownWest]

Possibly a weld, but what to? Maybe something that goes down behind the panel, rather than being bolted to it? Any access behind?

 

[TernVI]

TBH, the woodwork and GRP look as if they've seen some trauma, and they don't look ever so 'joined together'.
That dry mat would worry me.

It's not a huge thing to take a step back and think from scratch what structure there should be.
Can you find some other yachts of similar size and rig and form a view of what's normal?
In my view, that babystay needs something like a chainplate through th deck to a beam across to the hull side, or a bulkhead or a tension member down to the keel. Unless of course the deck is actually much thicker than I'm assuming and the necessary 'beam' is within the deck. There are many ways of getting the strength needed.

And/or you need to understand the rig and have an idea of what the tension in the baby stay is. Otherwise you can only think in terms of ensuring that the stays would break long before the hull structure and chainplates.

 

[PetiteFleur]

I had to reinforce the babystay on my Moody33 mk 2 when I bought her 16 yrs ago - picked up by 2 surveyors. It had obviously been leaking where the tang went through the deck( tang not U bolt) The tang was welded to a ss tube which went athwartwise under the deck. The deck joint had obviously been leaking and had damaged the bulkhead. I had to remove the headlining, dismantle the adjacent door frame and repair the bulkhead. This entailed cutting a large vee shaped piece out of the bulkhead and fitting a new piece of ply in an inverted vee. I also added a stainless plate bolted to the tang straddling the 'vee' and the door frame, All joints were covered with teak strips. No evidence of any further leaks and not obviously visible there had been a repair.