mast hound angle question

[Judy B]

Also, does the toggle allow the lower mounting point to twist with respect the upper hole ? It doesnt look like it, and if it doesnt, I dont see how it changes the lateral forces on the stay- other than rotate the thimble by 90 degrees....maybe that is the key...

Ive been sailing 10 years without one on my CDI FF2 btw...

Ah.... I understand Catigale's comment (I think). I have been using the wrong term saying it was like a "U joint". A U-joint permits two rigid rotating shafts to have limited angular freedom of motion from each other. Catigale doesn't see any rotation here and he's correct.



It's been a long time since I took intro to mechanics and I don't use the right terms.... my bad....

Lemme try again

Using a toggle at the top of the headstay allows limited freedom in translation (not rotation) in the X, Y, and Z planes between the hounds. I think the correct way to describe that is "three degrees of translational freedom between the forestay and the hounds. "

Using a toggle at the top of the forestay converts any angular misalignment between the forestay and the hounds into lateral and vertical translation which occurs at the pins in the toggle and hound.

The mast is not at all rigid, and the forestay is quite flexible... The forestay and mast are constantly moving relative to each other.... whence cometh the problem of how to link them

With a toggle at the top, the wire rope doesn't flex sharply at the swage or the top of the furler extrusion (which breaks wires over time); instead, the toggle permits the swage to move in translation (absorbing the lateral forces on the forestay wire)

Okay, is that as clear as mud? Have I mangled the terminology again!?!

Judy B

[mike uk]

So here's another (related) question:-

Judy B's picture of a toggle shows one with a split pin as the securing method. Does anyone have a view on the idea of using a snap shackle for this purpose? Are they secure enough for this purpose? They are used in lots of other fairly important locations but are they OK for the purpose of holding the mast up?

I ask the question because we usually detach the forestay at the top of the mast when trailering in order to move the jib along the mast to reduce the overhang at the bow. A split pin would be fairly tedious to remove and replace each time. (At present we have a bolt directly through the tangs and the loop at the top of the forestay).

I think I want to add a toggle but which type would be secure enough and convenient?

Thanks
Mike

[Catigale]

You could use a bolt and nylok nut of course - as it came from the factory on the

If you did use a shackle, I would wire it shut or, even better, and now officially in Chapmans as 'nautical', secure the shackle with a plastic zip tie.

[mastreb]

Hi Mike,

I've had a snap-shackle fail and drop my mast. Bent it. The problem is that when a snap-shackle pin deforms, the pin is not retained inside the shackle and it can pop out. Use a screw shackle, and don't be afraid to use an over-rated one if it will fit. When a screw-pin shackle deforms, the screw remains screwed into the shackle and still can't pop-out.

Matt

So here's another (related) question:-

Judy B's picture of a toggle shows one with a split pin as the securing method. Does anyone have a view on the idea of using a snap shackle for this purpose? Are they secure enough for this purpose? They are used in lots of other fairly important locations but are they OK for the purpose of holding the mast up?

I ask the question because we usually detach the forestay at the top of the mast when trailering in order to move the jib along the mast to reduce the overhang at the bow. A split pin would be fairly tedious to remove and replace each time. (At present we have a bolt directly through the tangs and the loop at the top of the forestay).

I think I want to add a toggle but which type would be secure enough and convenient?

Thanks
Mike

[mike uk]

Thanks Matt - that sounds like excellent advice.
Mike

[vizwhiz]

Thread rehash warning...wasnt there some confusion about whether you needed an upper toggle with the CDI?

Also, does the toggle allow the lower mounting point to twist with respect the upper hole ? It doesnt look like it, and if it doesnt, I dont see how it changes the lateral forces on the stay- other than rotate the thimble by 90 degrees....maybe that is the key...

Ive been sailing 10 years without one on my CDI FF2 btw...

(1) I realize that this thread has turned into a rehash of the one about the forestay failure, which I read (most of) several weeks back...that was not my intention here, although I am VERY grateful to all who have posted and offered their advice. I am not a novice to mechanics, just to sailboats and sailing...which have been around longer than I have...(but maybe not as long as...wait, I'd better not go there...)

(2) After my last reply, (and I am still grateful for your explanations Judy) I started to think about the forces on the top of the forestay at the hound. I don't see how they are any different than a hank-on jib when the sail is flying. With the exception of when you're actually rolling the furler, which might set up a small twisting load, the forces on the forestay/hound from the furler jib flying should be nearly identical to those of a hank-on jib of equal size, and no shackle is required for that set-up...I mean, the sail is pulling along the luff at a particular angle and with a particular force based on the wind - and that has nothing to do with how it is attached at the top. As a matter of fact, the forces from the furler jib should be more equally distributed along the length of the forestay because it uses a bolt-rope arrangement instead of "n" number of individual hanks which create point-loads on the forestay. I would bet it has more to do with someone at the CDI factory selling one to somebody who pretzeled their forestay because the furler twisted it funny than it has to do with the difference in forces at the hound because of the furler. CDI doesn't even want the luff going all the way up to the thimble on the forestay... Maybe I'm missing something...(wouldn't be the first time!).

(3) the idea of a U-joint isn't a bad analogy at all. Because the forestay is under tension, and the hound is essentially a rigid connection also (a hinge joint), the idea of allowing multiple degrees of freedom correlates very well. I do not think it is a bad idea at all to put a toggle up there...I'm just not sure CDI has communicated a valid reason for doing so - they just say to do it. I'll be looking for a toggle in my "spare" time...

[Catigale]

Think we have established

1 toggle is not a ujoint

2 net effect of toggle is to rotate upper swage from eye horizontal to eye vertical

3 this changes how the stay and the thimble are loaded

4 my personal swag on this is that the changes in 3 on these boats that the advantage is minimal

I'm guessing the CDI recommendation is a generic one intended for larger boats with loads going ip as boat size ^2

[vizwhiz]

Okay...so we've changed the orientation of the upper thimble from "hole goes side-to-side" to "hole goes up-and-down".

Original setup has the hole in the thimble going side-to-side with the horizontal bolt from the hound going through it. This would allow the forestay to move in the vertical without hinderance, essentially allowing the mast (at the hound) to flex fore and aft, and the forestay/jib to flex up/down in the vertical, without putting any strain at all on the forestay/hound connection. However, side loading in this arrangement would "cock" the bolt/thimble interface, resisting side-to-side motion of the forestay cable relative to the thimble, thereby putting strain on the cable at the thimble.***

Adding the toggle would rotate the thimble 90-degrees, so that the bolt hole would be in the vertical, and the toggle would join the hound in the horizontal. The toggle then, would take the flexing of the mast fore/aft, and the vertical motion of the forestay/jib, and the thimble connection would allow side loading because the thimble would now be free to angle sideways under the load of the forestay/jib, thus eliminating the strain between the thimble and the forestay cable.

This being the case, I would think it would ALWAYS be a good idea to have a toggle on the top of the forestay, furler or not!

***If the bolt hole through the thimble is significantly larger than the bolt going through it, allowing a lot of "slop" in this connection, then this probably is not as much of an issue, and is probably why your rig has held up so long Cat... Those who have maxed-out forestay tension and up-sized bolts and such may have aggravated the a problem slightly if there is no toggle. I'll be dropping the mast and checking this connection just to see how much flexibility there really is...and I'm still going to look for a toggle...

[Sumner]

No the forestay doesn't rotate so you don't need to use a 'true' U-joint, but I think the concept of a U-joint is easier for some to visualize and even if a U-joint doesn't turn it will not load the connecting point with a bending movement no matter which way the load bends withing limits of course.

A toggle is in no ways constructed like a U-joint, but still it won't allow a bending load on the top of the forestay to occur and that is what CDI doesn't want to happen and no it won't always result in forestay failure, but at least they have protected their butt.

Mike I thing the difference with the hank-on vs. the furler is that with the hank-on the forestay can bend over its entire length into a bend. The foil limits that to some degree as the forestay is captured inside of it and probably more bending would take place in the area at the end of the furler foil and the fitting at the hound, just a couple inches. Now saying that the foil is quite flexible, so this is still minimal.

I think that Cat is right that for CDI it is more of a protection deal and that one is unlikely to have a problem on our boats, but still there have been forestay failures reported here. My feeling is that for something that costs less than $20 and is a one time purchase why not do it.



On the same rant a toggle might cost a little more than a shackle, but I think it looks better

Sum

Our Endeavour 37

Our Trips to Utah, Idaho, Canada, Florida

Our MacGregor S Pages

Mac-Venture Links

[Judy B]

A toggle is in no ways constructed like a U-joint, but still it won't allow a bending load on the top of the forestay to occur and that is what CDI doesn't want to happen and no it won't always result in forestay failure, but at least they have protected their butt.

Mike I thing the difference with the hank-on vs. the furler is that with the hank-on the forestay can bend over its entire length into a bend. The foil limits that to some degree as the forestay is captured inside of it and probably more bending would take place in the area at the end of the furler foil and the fitting at the hound, just a couple inches. Now saying that the foil is quite flexible, so this is still minimal.

Sum

I'm with Sumner on this. I'm an authorized Schaefer dealer, and i have talked with the engineers who support their Schaefer furlers to get answers to questions I have. I'm not an engineer or an expert myself, but I have access to the experts. Using a furler concentrates sideways bending forces where the wires of the forestay enter the swage. That can lead to forestay failure.

By the way, you don't need to have furler for this to happen. Most riggers recommend that the "right" way to attach a shroud or stay to a hound or chain plate is with with a toggle (like the t-bar toggles that come attached to good turnbuckles.) (or there are other special fittings for specific brands of masts)

The CD-500 is for boats under 24 feet LOA, and, according to my discussions with the engineers at Schaefer, it's the right SnapFurl for the 26X and 26M's as well.

The engineers at Schaefer, Harkin and all the other companies recommend a toggle at the top of the forestay and build them into the bottom of the furling units.

Here is a picture from the Schaefer CF-500 Snapfurl installation manual, showing a toggle at the top.



Here's a picture from the Harken MkiV 0 installation manual. It's got a toggle at the top too.



Fair winds,
Judy B

[Catigale]

To sum up, the toggle functions solely to change the orientation of the upper forestay swage from a vertical (eye of the swage faces horizontally, from port to starboard) to a horizontal ( eye of the swage faces up at the angle of the forestay )

I suspect the recommendation is geared to bigger boats with higher loadings than Macs. I would weigh the benefit of this recommendation against the two added failure points on your forestay carefully.

Next time I'm in Homer NY I'll stop by and ask Tom on this.

[Sumner]

To sum up, the toggle functions solely to change the orientation of the upper forestay swage from a vertical (eye of the swage faces horizontally, from port to starboard) to a horizontal ( eye of the swage faces up at the angle of the forestay )....

Not sure if I understand the sentence above or not, but it isn't about the orientation, but that the forestay can move in any direction without a bending moment on the wire at the swage since there are two pivot points that are at 90 deg. to each other.

Maybe we are saying the same thing ,

Sum

Our Endeavour 37

Our Trips to Utah, Idaho, Canada, Florida

Our MacGregor S Pages

Mac-Venture Links

[Catigale]

Sum...no, you have pointed out the toggle allows two degrees of freedom of swage motion where the absence of the toggle only allows one...critical difference.

[vizwhiz]

This being the case, I would think it would ALWAYS be a good idea to have a toggle on the top of the forestay, furler or not!

I think based on everything I've heard so far, I stand by my statement above...I don't think it's only needed when you have a furler, it's probably just that CDI states that you need to have one to be sure you do...perhaps knowledgeable of Roger's thriftiness?

I also still feel that with a "sloppy" enough connection, and relatively low forces, which is not something you'd find on a high-end boat perhaps, this is not as necessary, thus the longevity in the case of most of the Mac mast hound connections...

I'm planning to add a toggle...but it might not be something I do before getting the boat into the water...

[dxg68]

Sum...no, you have pointed out the toggle allows two degrees of freedom of swage motion where the absence of the toggle only allows one...critical difference.

Sorry for reviving this thread and being off-topic, but I am installing CDI FF2 and doing research of whether to use toggle to attach stay to mast. My M came with a shackle on top of the mast to attach stay and upper shrouds. I called CDI tech support and asked them if I need toggle between stay's 'eye' and shackle and the answer was 'probably not'. I was told that they recommend toggle on top to give stay some flexibility to move. But 'eye' with shackle is adequate enough to accomplish that. Thought I would share.