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

[Chotu]

Originally Posted by 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?

Confusing.

The used mast is beefier than the one in the plans. It’s a thicker wall. It also is slightly larger. It has a slightly larger moment.

I can’t understand why this Mast would need extra things on it when the one in the plans that is thinner with a smaller moment wouldn’t need it.

When the multi hull designer approved this Mast, I would assume he approved it for a downwind sail as well right?

I mean, who doesn’t fly a downwind sail? Wouldn’t that be part of just normal operations?

Why does this forum give me a heart attack every other day? Ha ha ha

I appreciate the concern very much and value your posts greatly, but it sure is stressful. Whew.

I don’t even know what to do with this additional information. I don’t see other boats with these. They’re not in my plans. They’re not on the mast I bought. They are not on the sister ship. Do I really need to worry this much?

[Chotu]

Originally Posted by rslifkin

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.

Yes. The plans show an asymmetrical. The sail plan shows that as one of the sails.

[Tupaia]

Originally Posted by Chotu

Confusing.

The used mast is beefier than the one in the plans. It’s a thicker wall. It also is slightly larger. It has a slightly larger moment.

I can’t understand why this Mast would need extra things on it when the one in the plans that is thinner with a smaller moment wouldn’t need it.

When the multi hull designer approved this Mast, I would assume he approved it for a downwind sail as well right?

I mean, who doesn’t fly a downwind sail? Wouldn’t that be part of just normal operations?

Why does this forum give me a heart attack every other day?

I appreciate the concern, but God it’s stressful.

I don’t even know what to do with this additional information. I don’t see other boats with these. They’re not in my plans. They’re not on the mast I bought. They are not on the sister ship. Do I really need to worry this much?

It looks like you have conferred with the designer, we didn't know that so just pointing out the possible areas of failure when you change things.

All things are linked especially when dealing with engineered structures such as modern multihulls.

You have extended the mast, the spreaders are at different levels and the pre-bend is probably different so lots of things to account for.

From a practical point of view you are currently looking at the connections at deck level. Are the angles on the mast tangs sufficient to cope with changes between the boat the mast was designed for and your boat now?

[Chotu]

Originally Posted by Tupaia

It looks like you have conferred with the designer, we didn't know that so just pointing out the possible areas of failure when you change things.

All things are linked especially when dealing with engineered structures such as modern multihulls.

You have extended the mast, the spreaders are at different levels and the pre-bend is probably different so lots of things to account for.

From a practical point of view you are currently looking at the connections at deck level. Are the angles on the mast tangs sufficient to cope with changes between the boat the mast was designed for and your boat now?

Makes sense. I appreciate the concern.

I’ll have to say I have no idea if the Tangs will support the slight change. It wasn’t much of a change. Very small. I think it was something like a 2° difference.

Unfortunately, all my records are on the boat and I’m not allowed on the boat. So I don’t have them in front of me. But I believe there was approximately a 2° change.

And actually, thinking about it a little bit more, I don’t think the Tangs make a difference? It’s the spreaders right? The Tangs direct the Shroud to the spreader. Then from the spreader they head off to the angle. Right?

Of course that’s different for the lower shrouds. I think those go from some kind of connector that is welded on directly to the mast… to the chain plate without anything else involved.

Whew. Definitely a foggy picture of the rig in my mind when I am describing this. I have never seen it put together.

[s/v Jedi]

Here’s the deepest zoom I can do on our chainplate. The leftmost turnbuckle is for the lower which is clearly going another direction than the two on the right, which are the intermediate and the capshroud, which both go to the lower spreader tip.

The chainplate has two “lips”, one for the lower and the other for the intermediate and capshroud. There is a cut in between and both are bent in the correct direction.

But there is no twist; the toggle for the lower allows the stay to go forward of the chainplate position.

So the chainplates are bent for the inward direction of the attached stays/shrouds but not for the fore/aft direction. You often see chainplates angled for that, these are straight up like Chotu has.

[Chotu]

Exactly, Jedi.

That’s exactly what they are working up. It’s a little bit of a different attachment due to my chain plate design, but it’s the same idea. With the same little bend for the lowers.

[GRIT]

[Quote/ Chotu;3723684]Confusing.

The used mast is beefier than the one in the plans. It’s a thicker wall. It also is slightly larger. It has a slightly larger moment.

I can’t understand why this Mast would need extra things on it when the one in the plans that is thinner with a smaller moment wouldn’t need it.

When the multi hull designer approved this Mast, I would assume he approved it for a downwind sail as well right?

I mean, who doesn’t fly a downwind sail? Wouldn’t that be part of just normal operations?

Why does this forum give me a heart attack every other day? Ha ha ha

I appreciate the concern very much and value your posts greatly, but it sure is stressful. Whew.

I don’t even know what to do with this additional information. I don’t see other boats with these. They’re not in my plans. They’re not on the mast I bought. They are not on the sister ship. Do I really need to worry this much?[/QUOTE]


A little help with the numbers...

We built, own, and cruise aboard Chotu's sistership. I designed the sail areas, and halyard heights, after tons of research, and with help from the designers at Selden. So I have an in-depth understanding of the rig and sails aboard GRIT.

Our mast is 19.7m tall; has the spinnaker halyard at 18m above deck, the code zero with 2:1 halyard at 17m above the deck and the forestay at 16m above the deck. The running backs are at 17.7m and the uppers are at 16.3m. We also have a forestay at 12m, for a heavy weather sail, which will only be deployed in winds above 25 knots, when forereaching. (When beating into 25 knots, that's up to 40 knots of apparent wind, and the jib is nearly useless beating in those winds).

The mainsail is 75m2, the jib 37m2, the code zero 100m2 and the spinnaker will be 155m2. The boat's mass at launch was 7300kg without mast, but with building materials and 600kg in fluids (fuel and water) aboard.

The reason we have upper and lower shrouds is because I didn't want the forward triangles at the spreaders, which would hamper tacking a 100% self tacking jib. I wanted the jib to brush the mast on it's way by. We've since changed the jib to a non-self tacking jib for more area, and to accommodate a mast mounted radar, but will change it back to a mast brushing self tacker in the future. The mast is set up with a vertical jib sheet, for the self tacker, and the halyard and sheet are already installed in the mast.

The lowers obviate the need for triangles. (Someone here knows the right word for those things; please post...) Jumper struts

So there you go, a not-so-short explanation of lowers; and a suggestion that the "probable" proper placement of Chotu's spinnaker halyard is likely a metre above the cap shrouds; or more if he installs runners too.

It should also be noted that Chotu's boat is lighter than GRIT. I'm not sure by how much, but he won't need quite as much sail area as we have, to sail well.

I hope this helps with some of the questions I've seen on this thread.

Cheers.
Paul.

Ps. I've tried to make this photo show vertically, but no matter how I edit it on my computer, it shows up on it's side. There is a bend that's not obvious, but each shroud has a fair lead off the plate.

[OutOfControl]

[JPA Cate]

A number of rude, baiting posts were removed in their entirety from this thread. Sorry the information is lost, but that is the penalty we all pay for others not following the community rules.

JPA Cate

[GRIT]

Thanks "out of control".

That looks better!

Was it easy to do, or does it require in-depth knowledge of forum software?

In other words... how embarrassed should I be?

Cheers.
Paul.

[GRIT]

Originally Posted by JPA Cate

A number of rude, baiting posts were removed in their entirety from this thread. Sorry the information is lost, but that is the penalty we all pay for others not following the community rules.

JPA Cate

Thanks for doing that.

Intentionally nasty, and hateful, posts often make me wonder if this is really a website to which I'd like to contribute. They seem to be increasing in frequency this last year, though it may just happen that I'm reading the wrong threads.

I've used the "ignore" feature several times, but I think my time here is nearing an end.

Thanks again.

Cheers.
Paul.

[JPA Cate]

@ grit, sorry to hear that. We've gone through a rough patch recently. We'll miss your infomative and well reasoned posts if you go.

If you do, your choice and all that, but it helps the people who don't post following the community rules, win. I hope you don't.

If you go, fair winds.

Ann

[Franziska]

Originally Posted by GRIT

Thanks for doing that.



Intentionally nasty, and hateful, posts often make me wonder if this is really a website to which I'd like to contribute. They seem to be increasing in frequency this last year, though it may just happen that I'm reading the wrong threads.



I've used the "ignore" feature several times, but I think my time here is nearing an end.



Thanks again.



Cheers.

Paul.

Hey, don't leave. I'm in line what Ann wrote and appreciate your informative posts.
Just ignore the bad posts (it's hard sometimes!).
While I don't think that I have someone on a blocked list, I just stopped replying to posts from a few guys.

Back to the threads topic now, if there is anything to add.
Happy holidays everyone.

[Chotu]

Whew! Glad I missed the additional posts that were removed. It sure has felt stressful lately being the punching bag on here.

Grit: as always, thank you very much. This certainly does help clear up the questions about the rig. For some reason, I thought this part was going to be pretty straightforward. Should have known better. Ha ha ha.

I also sort of assumed that Riggers would let me know what to do with all this.

So it would appear I need these running backs.

Can anyone explain to me why it is that I need them? The best multihull people on here have said I do. That’s not something to take lightly.

Reading Wikipedia, it says that the swept back spreaders do enough. However, that doesn’t seem to be the consensus here among the people with performance multihulls that know how to sail them.


From Wikipedia…. Notice the last paragraph.


Maintaining forestay tension
Edit

An inherent problem of a fractional rig is its inability to exert as much tension on the forestay as a similar masthead rig. The reason for this is because the attachment point of the forestay is not directly opposite to the backstay. Under certain conditions, the moment arm that results from these offset attachment points can be used to advantage as this is an effective method of inducing bend in the mast which in turn flattens the mainsail. If the distance between the attachment points is too great, a mast of average stiffness will be unable to apply optimum forestay tension, unless one of the following mast-stiffening design features is used:

Jumper stays — These additional stays and their associated jumper struts limit the amount that the upper portion of the mast can bend and thereby enable tension to be effectively transferred from the backstay to the forestay. Jumper stays were common in the first part of the 20th century. Their biggest disadvantage is weight and windage aloft.
Running backstays — These are supplemental temporary backstays (one on each side) that attach opposite of the forestay. They are very effective at generating forestay tension, but make the boat more difficult to tack because one running backstay needs to be released and the other one applied each time the boat tacks.
Swept back spreaders — Swept back spreaders (or rather their associated shrouds, which attach to the deck significantly aft of the mast) provide significant fore-and-aft support to the mast and thereby increase tension in the forestay. The biggest disadvantage of this scheme is that it makes it difficult to deliberately slacken the forestay for the purpose of making the jib fuller in light winds.

[Chotu]

I’m going to have a look at those attachment points for the halyards. Especially that spinnaker halyard. There are a lot of attachment points on this mast externally that I’m not even sure what they are. Even the Rigger wasn’t sure. At first look.

Is it common to have your spinnaker halyard external to the mast?

I think it’s time to study this Mast in more detail with all of this information.

And Grit, what has you changing back to the blade self tacking jib from the one that you are using now? The less changes the better of course. I’ve already done most things two or three times on the boat. So I would like to learn from your experience with the Jibs.

As far as how I will sail the boat, I do see myself mostly doing downwind and reaching work. I tend to be lazy and just wait for a nice weather window. I don’t usually beat into anything. I mean, the boat still needs to be able to do that, but most of my ceiling will be done downwind and reaching.

Of course, this is coming from a slow catamaran and slow monohull point of view. I know the apparent wind will make it seem like I’m always going to windward right? Or at least often?