Upper and lower shrouds on one chain plate. How to?

[boatpoker]

Originally Posted by thomm225

If I sail over to the Bahamas, I'll definitely pick a nice week in June or so.

Well the beginning of hurricane season will certainly be a test, you are more adventurous than I

[Chotu]

Originally Posted by soerencarlsen

Does this drawing make sense to you?

This is exactly what was done, with a little bend in it to make up for the differing angles of the different shrouds.

So yes, you are all correct. Everyone.

The piece is being made up now. It grabs the center, it grabs both ends, it has two holes in it, and one of those holes is angled more sharply than the other so that the shrouds are in alignment with the piece.

[Chotu]

Originally Posted by Tupaia

I agree the only way this will work properly is if the forces are mono-planar so the chain plate pin would need to be on a radial axis pointing to the mast and it is not. The two shrouds at different angels will induce a twist into to articulated plate. It may work if it is over engineered just because it big enough to resist the twisting or the shackle pins are loose enough to allow articulation.


You could as Jedi suggests make a split, bend the plate and re-weld it such that the angles are more closely matched.


This a Kurt Hughes design assuming the chain plate anchors are to spec what did he propose for the connections?

A single shroud.

for some reason the used Mast I got has uppers and lowers. And so does my sister ship. I’m not sure why.

But it is what it is. We don’t want to forgo the lowers even though they are not in the plans.

[malbert73]

Originally Posted by s/v Jedi

The idea is that you have three times as much (potential) trouble. It can crack, leak, develop hairline cracks, corrosion etc. in three places instead of just one place.



If you have one big chainplate that is mounted properly, it simply doesn’t fail. If you ever encounter a Sundeer 64, take a close look at those chainplates, the bolts, the bolt pattern etc. Dashew has a chain plate fetish and this is the result

Exactly. 3 separate chainplates is 3x the issue. And each is essential and in rough stuff losing 1 can also lose you the rig. I’m a single chainplate convert

[thomm225]

Originally Posted by boatpoker

Well the beginning of hurricane season will certainly be a test, you are more adventurous than I

The beginning of hurricane season is much better than the end I have found based on my experiences living in Florida for 12 years where we had about 8-9 hurricanes

[thomm225]

Originally Posted by malbert73

Exactly. 3 separate chainplates is 3x the issue. And each is essential and in rough stuff losing 1 can also lose you the rig. I’m a single chainplate convert

I'll go with that any time. (3 separate chain plates)

If I lose a chain plate or two for the shrouds, I don't believe my boat a 1974 Bristol 27 would even notice it.

The mast may lean off a bit but I'm thinking it will still stand and I can sail it in since it only has to support a very small amount of sail area which if the failure did occur I would reduce even more

Sean said at one point off New Zealand I think it was he dealt with 55 knot winds on his $1,000 Bristol 27 and I don't believe he had the money to replace all the rigging and chain plates at that time. He said the hull was flexing I believe but his boat appears to have had the partial secondary bulkhead whereas mine has two full super thick bulkheads in the area of the mast

Some folks simply don't have any understanding of their boats I guess and how strong they are built

[thomm225]

Originally Posted by boatpoker

Well the beginning of hurricane season will certainly be a test, you are more adventurous than I

PS. Most of the hurricanes I have seen close up which number around 10 or so have mostly occurred in late August, September, and October the first being Donna in 1960

I was a little kid but lightning from the storm hit a power pole and it caught fire. Quite dramatic to see as a child

The largest was Cat 5 Ivan which back down to 3/4 before it almost destroyed Pensacola. I hit the deck at my lady friends house several times due to pressure changes.

She was already camped out under the stairwell but I was listening to am radio in the living room on battery power.

This in Pensacola September 2004

[boatpoker]

Originally Posted by thomm225

PS. Most of the hurricanes I have seen close up which number around 10 or so have mostly occurred in late August, September, and October the first being Donna in 1960

I was a little kid but lightning from the storm hit a power pole and it caught fire. Quite dramatic to see as a child

The largest was Cat 5 Ivan which back down to 3/4 before it almost destroyed Pensacola. I hit the deck at my lady friends house several times due to pressure changes.

She was already camped out under the stairwell but I was listening to am radio in the living room on battery power.

This in Pensacola September 2004

Having survived Olive and Matthew at anchor. I'm not sure hiding out in a house is equivalent to what a cruiser experiences or ... his chainplates.

[Tupaia]

Originally Posted by Chotu

A single shroud.

for some reason the used Mast I got has uppers and lowers. And so does my sister ship. I’m not sure why.

But it is what it is. We don’t want to forgo the lowers even though they are not in the plans.

A 6 point rig as compared to 3 point rig is considerably more robust.

Under certain conditions the lowers and baby stay will reduce pumping or shock loading in the absence of running backstays.

Many riggers who are unfamiliar with multihulls will under tighten for fear of distorting the hulls or overtighten when it has to be done right. On a big cat this requires experience as tension gauges do not work on large diameter wire of synthetic shrouds. It is vitally important to tension correctly otherwise they will fight against each other resulting in uncontrollable vibrations and fatigue of the fittings.

Unlike a monohull the shrouds are there simply to hold up the mast the diamonds or the mast structure itself should be designed to maintain it in column.

[thomm225]

Originally Posted by boatpoker

Having survived Olive and Matthew at anchor. I'm not sure hiding out in a house is equivalent to what a cruiser experiences or ... his chainplates.

I don't plan on being at anchor during any hurricane ever cruising or not because I have been through too many of them and know how bad they can be.

Then there sometimes is no power for a couple weeks. No gas, water is usually bad, etc

The worst Hurricane though was Ivan in 2004 (Katrina 2005 but that missed us thankfully) with it's 18' surge. It had been a Cat 5 right up until it hit then came in Pensacola pass close to cat 4 but still pushing all that water and there were lots of tornadoes as well

This hurricane destroyed all the boats except one in the local hurricane hole we used to keep an eye on during our hurricane parties.

It also floated the Navy Marina docks over their pilings. That is what took out most of the anchored boats

The party place, the apartment complex where we watch from, was also basically destroyed with 8' of water inside. It took two years to rebuilt it

Everyone had to move when there was no where to move to as everyone on Pensacola Beach had to find new housing also so that meant a FEMA Trailer court

Not fun.

Also local official wouldn't let any boats out into the local waters afterward

[Chotu]

Originally Posted by Tupaia

A 6 point rig as compared to 3 point rig is considerably more robust.

Under certain conditions the lowers and baby stay will reduce pumping or shock loading in the absence of running backstays.

Many riggers who are unfamiliar with multihulls will under tighten for fear of distorting the hulls or overtighten when it has to be done right. On a big cat this requires experience as tension gauges do not work on large diameter wire of synthetic shrouds. It is vitally important to tension correctly otherwise they will fight against each other resulting in uncontrollable vibrations and fatigue of the fittings.

Unlike a monohull the shrouds are there simply to hold up the mast the diamonds or the mast structure itself should be designed to maintain it in column.

Yes. That’s what I was realizing. The diamonds do everything.

I haven’t looked very closely at the rigging before. For any Catamarans. I had enough going on already.

But upon looking at this, the diamonds hold it in column. Definitely.

And my plans show a three point attachment. We have a five point attachment now with lowers.

There is no baby stay. Just a forestay. Then if you add a bowsprit you can get another something or other up there that is mainly to hold a Furler.

It’s a fractional rig.

That’s good news to hear the lower shrouds will help with any pumping or vibration. That’s excellent. Seems accurate. Because they connect a bit lower than the cap shrouds.

[Tupaia]

Originally Posted by Chotu

Yes. That’s what I was realizing. The diamonds do everything.

I haven’t looked very closely at the rigging before. For any Catamarans. I had enough going on already.

But upon looking at this, the diamonds hold it in column. Definitely.

And my plans show a three point attachment. We have a five point attachment now with lowers.

There is no baby stay. Just a forestay. Then if you add a bowsprit you can get another something or other up there that is mainly to hold a Furler.

It’s a fractional rig.

That’s good news to hear the lower shrouds will help with any pumping or vibration. That’s excellent. Seems accurate. Because they connect a bit lower than the cap shrouds.

Without a baby stay, if you run a masthead foresail, screecher or spinnaker you need to ensure that the forces do not result in the mast inverting as a result of snap through, so you may need runners.

[Chotu]

Originally Posted by Tupaia

Without a baby stay, if you run a masthead foresail, screecher or spinnaker you need to ensure that the forces do not result in the mast inverting as a result of snap through, so you may need runners.

I don’t get it. That’s not in the plans nor is it in the rig that I bought. Why would I need extra things that are not in the plans or the rig?

I’m definitely running an asymmetrical Spinnaker. It shows them in the plans.

Maybe you’re not aware that the stays sweep aft? They are not in column with the mast.

It’s also a fractional rig.

Hmmm. I am definitely confused because neither the design nor the used mast have these.

Are you talking about the very very top of the mast? After all of the shrouds and forestay? The unsupported top?

So if I have a lot of force on there, I could snap that?

[Tupaia]

It must assumed that if a 3 point rig was specified then the mast section and or diamonds would have been designed to resist the top mast forces imposed by a screecher or spinnaker and if there are any size/wind limitations.


The fact that your mast has lowers may indicate that the section and or diamonds requires supplementary restraint. The forces imposed by a large screecher on a bow spit are enormous. Having someone analyse the structural elements of the top mast will help you understand it's limitations if any and if runners are needed.


How does the new mast compare to the designed spec?

[rslifkin]

Originally Posted by Chotu

I don’t get it. That’s not in the plans nor is it in the rig that I bought. Why would I need extra things that are not in the plans or the rig?

I’m definitely running an asymmetrical Spinnaker. It shows them in the plans.

Maybe you’re not aware that the stays sweep aft? They are not in column with the mast.

It’s also a fractional rig.

Hmmm. I am definitely confused because neither the design nor the used mast have these.

Are you talking about the very very top of the mast? After all of the shrouds and forestay? The unsupported top?

So if I have a lot of force on there, I could snap that?

There's always the question of what sails the rig was designed to carry vs what you really want to put on there. And whether that prompts any additional support or not.

A reasonable size asym was likely accounted for based on what you've said. Of course, extra support may enable using a bigger one, or carrying it in higher winds without worrying about hurting the rig.