Chain plate sizing.

[coopec43]

Originally Posted by Reefmagnet

Yep, laser cut. That's what I did. Got the bolt holes cut slightly undersized too, so just needed to ream the correct size drill bit through them to finish them off.

Cut from mill finish 10mm plate, I linished and polished to a mirror shine in no time.

Easiest way to do it.

Now that the SS jobbers with Laser gear are open hopefully Gil will get some quotes.(He may be surprised!)

The cutting of the bow roller was somewhat expensive but then all the lines were curved and they had to be cut to a pattern.

[coopec43]

Originally Posted by coopec43

Now that the SS jobbers with Laser gear are open hopefully Gil will get some quotes.(He may be surprised!)

The cutting of the bow roller was somewhat expensive but then all the lines were curved and they had to be cut to a pattern.

Here is the work I had done (and it wasn't all that expensive)

[RaymondR]

From a friction viewpoint the thicker and narrower bar would probably be more effective than the thinner bar in that provided the section area is equivalent the section modulus of the thicker bar would be considerably greater. Section modules is what defines the stiffness of a beam and consequently the pressure applied between fastenings would be greater.

Total friction is defined by the product of the friction factor and the force on the sufaces in contact so whilst the area in contact may reduce the force per unit area increases, in this instance for the same bolt tension.

The next thing to check is the section area either side of the pin holes. If it is equal to or more than that of the wider bar both the yield and fatigue life of the material should be the same of less than the wider bar.

My guess is that as long as the toggles will fit over the thicker bar the thinner should be OK and maybe even better.

[MicHughV]

It's not so simple.

Think of it in these terms.

The load from the shroud is transmitted to the lower bolt in the turnbuckle. This in turn is transmitted to the chain plate.
If you look closely at this attachment, only the upper portion of the bolt bears on the chainplate.

So let's take a hypothetical shroud load of 10,000 lbs. This means the entire 10,000 lbs is borne by, say the upper 1/3 perimeter of the bolt which bears against the chain plate.

So let's say, for example, that upper portion of the bolt which is under load is say 3/8" in lenght x the width of the chainplate, say 1/4"...so the contact patch is about 0.09 sq. inches....let's call it 0.10 for simplicity.
Had you used a 3/8" thick plate your contact patch would be around sq.14 sq. inch. a 50% increase.

So, you've got 10,000 lbs working against .10 sq. inches of stainless steel. That load then gets distribute to the tang in a more or less 45 degree angle each side of the bolt.
It's obvious that the greater the distance from the top of the plate to the hole is important. Add in a safety factor of 2 and you've got 20,000 lbs working on 0.1 sq inch.

Stainless steel has a tensile strength of about 84,000 psi, so 20,000 lbs will require about 0. 25 sq inches to resist the 20,000 lbs.

If your plate is 0.25 thick and the hole in the plate has say, 1/2" off cover over it, and assuming a 1/2" dia. hole, then that 20,000 lb load will get distributed to around 0.375 sq. inches of plate, which will have a capacity of about 31,500 lbs or about 3 times the 10,000 lb load.

Fractional increases make a big difference. For instance going to a 3/8" thick plate will make a big difference as RaymondR pointed out above and as noted for the same width, gives you an extra 50% of strength...

The width of the plate is important only in the context of the size of the hole and how much meat is above the hole.
For instance, a plate 5" wide would be superfluous.

You're better off going to a thicker plate.

I've just thrown out some rough numbers as a guideline as I have no idea what your shrouds loads actually are, or if there are more than one shroud going to the chainplate, etc, etc.

[Wotname]

^^ a good analysis of the tensile aspects.
There is still the frictional aspects to consider.

[RaymondR]

And the thicker plate may open up the option of using countersunk bolts which are a lot neater and less likely to foul on jetty edges.

[Wotname]

Originally Posted by RaymondR

From a friction viewpoint the thicker and narrower bar would probably be more effective than the thinner bar in that provided the section area is equivalent the section modulus of the thicker bar would be considerably greater. Section modules is what defines the stiffness of a beam and consequently the pressure applied between fastenings would be greater.

Total friction is defined by the product of the friction factor and the force on the sufaces in contact so whilst the area in contact may reduce the force per unit area increases, in this instance for the same bolt tension.

The next thing to check is the section area either side of the pin holes. If it is equal to or more than that of the wider bar both the yield and fatigue life of the material should be the same of less than the wider bar.

My guess is that as long as the toggles will fit over the thicker bar the thinner should be OK and maybe even better.

Originally Posted by RaymondR

And the thicker plate may open up the option of using countersunk bolts which are a lot neater and less likely to foul on jetty edges.

Both good points.

As other have posted, getting it laser cut from plate by a SS supplier might be a good option. I did that in Perth when making a bow fitting with anchor roller etc and IIRC, it wasn't over the top price wise. Gave them a drawing for about 5 pieces, several with curves and picked up the bits a few days later.

[coopec43]

I don't know whether GiLow is still with us but perhaps he should consider Plasma Cutting as well as it is cheaper than Laser Cutting.

At Acra, we often get asked by our customers “which type of cutting machine should I use to produce my parts – laser or plasma? The answer depends on the specific requirements of your metal cutting project or application. Let’s consider how laser cutting and plasma cutting work and the advantages and disadvantages of each metal fabrication process.

https://www.acra.com.au/laser-cutting-vs-plasma-cutting/

[Reefmagnet]

Originally Posted by coopec43

I don't know whether GiLow is still with us but perhaps he should consider Plasma Cutting as well as it is cheaper than Laser Cutting.

At Acra, we often get asked by our customers “which type of cutting machine should I use to produce my parts – laser or plasma? The answer depends on the specific requirements of your metal cutting project or application. Let’s consider how laser cutting and plasma cutting work and the advantages and disadvantages of each metal fabrication process.

https://www.acra.com.au/laser-cutting-vs-plasma-cutting/

Pay the extra and get laser for this job. And by extra, it won't be that much more. There are both metallurgical and aesthetic benefits to be had from choosing laser.

[coopec43]

Originally Posted by Reefmagnet

Pay the extra and get laser for this job. And by extra, it won't be that much more. There are both metallurgical and aesthetic benefits to be had from choosing laser.

Thanks but I've done all the Laser cutting I will ever do. (Interesting though)

I thought GiLow would be interested but although he's logged in he is obviously not following the thread anymore?

[MicHughV]

As a footnote, it's also important that the upper tang of the chain plate align (bent inwards) with the shroud direction, otherwise the lower turnbuckle bolt will have only one edge of the chainplate working against the load. That contact patch should be...nay..must be.... a flush fitting full contact patch.

Ideally, the entire chain plate location should align with the shroud direction for the lower shrouds, ie, pointed towards the spreaders, but this is rarely the case for the chainplates strapped to the hull, as the they tend to be perpendicular to the sheer line for " looks" purposes.

[team karst]

I am not sure about the friction story.
As the shear load increases on the bolts, there will be some stretch. As soon as the preloaded (in tensile) bolts continue to stretch, (any additional stretch) , contact with the substrate is lost.
When contact is lost, friction is lost.
But I am open to counter-arguments. I’m just a EE [emoji15]

[Bowdrie]

Originally Posted by MicHughV

It's obvious that the greater the distance from the top of the plate to the hole is important.
If your plate is 0.25 thick and the hole in the plate has say, 1/2" off cover over it, and assuming a 1/2" dia. hole, then that 20,000 lb load will get distributed to around 0.375 sq. inches of plate,
The width of the plate is important only in the context of the size of the hole and how much meat is above the hole

Yes, in the book, "Skenes Elements of Yacht Design", there is a fairly detailed description of the calculations.
The height of material above the upper edge of the hole needs to be greater than the pin diameter by a minimum amount, and more is better.
IIRC, once the width is ~4 times or so of the pin diameter additional width accomplishes little, (except more weight).

Originally Posted by team karst

I am not sure about the friction story

Yes, the idea of friction is overblown.
Slippery polished stainless on slippery gelcoat?
And the adhesiveness of the sealant interface is quite subject to elongation under load.
Yes, calculations can be done that will show that a flexible adhesive can carry very high loads in shear, but the area needed is beyond the area of a typical chainplate.
At best, given the surface area, any additional load carrying ability is just a layer of "icing on the cake".
The strength of the bolts is the primary determining factor for carrying the load, (assuming chainplate specs and substrate specs are up to the task).
Perhaps the ideas/concepts of "friction" and "adhesive" sometimes get co-mingled?

[RaymondR]

Originally Posted by Bowdrie

Yes, the idea of friction is overblown.
Slippery polished stainless on slippery gelcoat?
And the adhesiveness of the sealant interface is quite subject to elongation under load.
Yes, calculations can be done that will show that a flexible adhesive can carry very high loads in shear, but the area needed is beyond the area of a typical chainplate.
At best, given the surface area, any additional load carrying ability is just a layer of "icing on the cake".
The strength of the bolts is the primary determining factor for carrying the load, (assuming chainplate specs and substrate specs are up to the task).
Perhaps the ideas/concepts of "friction" and "adhesive" sometimes get co-mingled?

I beg to differ.

If you take the shear on the bolts metal to metal then the load to failure would be the shear strength of the bolts. However one must consider that the opposing material is glass fibre which has a much lower shear strength than the chain plate material and shear failure of the fibre glass will occur far before the shear of the bolt material is likely to occur.

However, it one takes the area entirely along either side of the chain plate and subjects it to shear, the failure load is greatly enhanced. In order to do so the chain plate must be clamped securely to the hull material and a high level of friction be applied over the entire length of the chain plate on both sides. Otherwise one could have only very short chain plates with lots of bolts.

It's distribution of the shear forces into the hull material over a large area which defines the load bearing capability of the chain plates and friction between chain plate and hull material is vital to achieving this. The main purpose of the bolts is achieving the friction.

[MicHughV]

A simple way to think of friction is this.

Place a 100 lb block of concrete on the ground.
Put some wheels under it and pull it horizontally. ...no problem.

Remove the wheels and (try) to pull it horizontally over the ground.

There are various formula's to work this out, but require additional info.